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Diffstat (limited to 'contrib/llvm-project/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp')
| -rw-r--r-- | contrib/llvm-project/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp | 2989 |
1 files changed, 2989 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/contrib/llvm-project/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp new file mode 100644 index 000000000000..aeac6f548b32 --- /dev/null +++ b/contrib/llvm-project/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp @@ -0,0 +1,2989 @@ +///===- SimpleLoopUnswitch.cpp - Hoist loop-invariant control flow ---------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/Sequence.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/Twine.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/CodeMetrics.h" +#include "llvm/Analysis/GuardUtils.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LoopAnalysisManager.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopIterator.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/MemorySSA.h" +#include "llvm/Analysis/MemorySSAUpdater.h" +#include "llvm/Analysis/Utils/Local.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/Constant.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/GenericDomTree.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/LoopUtils.h" +#include "llvm/Transforms/Utils/ValueMapper.h" +#include <algorithm> +#include <cassert> +#include <iterator> +#include <numeric> +#include <utility> + +#define DEBUG_TYPE "simple-loop-unswitch" + +using namespace llvm; + +STATISTIC(NumBranches, "Number of branches unswitched"); +STATISTIC(NumSwitches, "Number of switches unswitched"); +STATISTIC(NumGuards, "Number of guards turned into branches for unswitching"); +STATISTIC(NumTrivial, "Number of unswitches that are trivial"); +STATISTIC( + NumCostMultiplierSkipped, + "Number of unswitch candidates that had their cost multiplier skipped"); + +static cl::opt<bool> EnableNonTrivialUnswitch( + "enable-nontrivial-unswitch", cl::init(false), cl::Hidden, + cl::desc("Forcibly enables non-trivial loop unswitching rather than " + "following the configuration passed into the pass.")); + +static cl::opt<int> + UnswitchThreshold("unswitch-threshold", cl::init(50), cl::Hidden, + cl::desc("The cost threshold for unswitching a loop.")); + +static cl::opt<bool> EnableUnswitchCostMultiplier( + "enable-unswitch-cost-multiplier", cl::init(true), cl::Hidden, + cl::desc("Enable unswitch cost multiplier that prohibits exponential " + "explosion in nontrivial unswitch.")); +static cl::opt<int> UnswitchSiblingsToplevelDiv( + "unswitch-siblings-toplevel-div", cl::init(2), cl::Hidden, + cl::desc("Toplevel siblings divisor for cost multiplier.")); +static cl::opt<int> UnswitchNumInitialUnscaledCandidates( + "unswitch-num-initial-unscaled-candidates", cl::init(8), cl::Hidden, + cl::desc("Number of unswitch candidates that are ignored when calculating " + "cost multiplier.")); +static cl::opt<bool> UnswitchGuards( + "simple-loop-unswitch-guards", cl::init(true), cl::Hidden, + cl::desc("If enabled, simple loop unswitching will also consider " + "llvm.experimental.guard intrinsics as unswitch candidates.")); + +/// Collect all of the loop invariant input values transitively used by the +/// homogeneous instruction graph from a given root. +/// +/// This essentially walks from a root recursively through loop variant operands +/// which have the exact same opcode and finds all inputs which are loop +/// invariant. For some operations these can be re-associated and unswitched out +/// of the loop entirely. +static TinyPtrVector<Value *> +collectHomogenousInstGraphLoopInvariants(Loop &L, Instruction &Root, + LoopInfo &LI) { + assert(!L.isLoopInvariant(&Root) && + "Only need to walk the graph if root itself is not invariant."); + TinyPtrVector<Value *> Invariants; + + // Build a worklist and recurse through operators collecting invariants. + SmallVector<Instruction *, 4> Worklist; + SmallPtrSet<Instruction *, 8> Visited; + Worklist.push_back(&Root); + Visited.insert(&Root); + do { + Instruction &I = *Worklist.pop_back_val(); + for (Value *OpV : I.operand_values()) { + // Skip constants as unswitching isn't interesting for them. + if (isa<Constant>(OpV)) + continue; + + // Add it to our result if loop invariant. + if (L.isLoopInvariant(OpV)) { + Invariants.push_back(OpV); + continue; + } + + // If not an instruction with the same opcode, nothing we can do. + Instruction *OpI = dyn_cast<Instruction>(OpV); + if (!OpI || OpI->getOpcode() != Root.getOpcode()) + continue; + + // Visit this operand. + if (Visited.insert(OpI).second) + Worklist.push_back(OpI); + } + } while (!Worklist.empty()); + + return Invariants; +} + +static void replaceLoopInvariantUses(Loop &L, Value *Invariant, + Constant &Replacement) { + assert(!isa<Constant>(Invariant) && "Why are we unswitching on a constant?"); + + // Replace uses of LIC in the loop with the given constant. + for (auto UI = Invariant->use_begin(), UE = Invariant->use_end(); UI != UE;) { + // Grab the use and walk past it so we can clobber it in the use list. + Use *U = &*UI++; + Instruction *UserI = dyn_cast<Instruction>(U->getUser()); + + // Replace this use within the loop body. + if (UserI && L.contains(UserI)) + U->set(&Replacement); + } +} + +/// Check that all the LCSSA PHI nodes in the loop exit block have trivial +/// incoming values along this edge. +static bool areLoopExitPHIsLoopInvariant(Loop &L, BasicBlock &ExitingBB, + BasicBlock &ExitBB) { + for (Instruction &I : ExitBB) { + auto *PN = dyn_cast<PHINode>(&I); + if (!PN) + // No more PHIs to check. + return true; + + // If the incoming value for this edge isn't loop invariant the unswitch + // won't be trivial. + if (!L.isLoopInvariant(PN->getIncomingValueForBlock(&ExitingBB))) + return false; + } + llvm_unreachable("Basic blocks should never be empty!"); +} + +/// Insert code to test a set of loop invariant values, and conditionally branch +/// on them. +static void buildPartialUnswitchConditionalBranch(BasicBlock &BB, + ArrayRef<Value *> Invariants, + bool Direction, + BasicBlock &UnswitchedSucc, + BasicBlock &NormalSucc) { + IRBuilder<> IRB(&BB); + + Value *Cond = Direction ? IRB.CreateOr(Invariants) : + IRB.CreateAnd(Invariants); + IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc, + Direction ? &NormalSucc : &UnswitchedSucc); +} + +/// Rewrite the PHI nodes in an unswitched loop exit basic block. +/// +/// Requires that the loop exit and unswitched basic block are the same, and +/// that the exiting block was a unique predecessor of that block. Rewrites the +/// PHI nodes in that block such that what were LCSSA PHI nodes become trivial +/// PHI nodes from the old preheader that now contains the unswitched +/// terminator. +static void rewritePHINodesForUnswitchedExitBlock(BasicBlock &UnswitchedBB, + BasicBlock &OldExitingBB, + BasicBlock &OldPH) { + for (PHINode &PN : UnswitchedBB.phis()) { + // When the loop exit is directly unswitched we just need to update the + // incoming basic block. We loop to handle weird cases with repeated + // incoming blocks, but expect to typically only have one operand here. + for (auto i : seq<int>(0, PN.getNumOperands())) { + assert(PN.getIncomingBlock(i) == &OldExitingBB && + "Found incoming block different from unique predecessor!"); + PN.setIncomingBlock(i, &OldPH); + } + } +} + +/// Rewrite the PHI nodes in the loop exit basic block and the split off +/// unswitched block. +/// +/// Because the exit block remains an exit from the loop, this rewrites the +/// LCSSA PHI nodes in it to remove the unswitched edge and introduces PHI +/// nodes into the unswitched basic block to select between the value in the +/// old preheader and the loop exit. +static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB, + BasicBlock &UnswitchedBB, + BasicBlock &OldExitingBB, + BasicBlock &OldPH, + bool FullUnswitch) { + assert(&ExitBB != &UnswitchedBB && + "Must have different loop exit and unswitched blocks!"); + Instruction *InsertPt = &*UnswitchedBB.begin(); + for (PHINode &PN : ExitBB.phis()) { + auto *NewPN = PHINode::Create(PN.getType(), /*NumReservedValues*/ 2, + PN.getName() + ".split", InsertPt); + + // Walk backwards over the old PHI node's inputs to minimize the cost of + // removing each one. We have to do this weird loop manually so that we + // create the same number of new incoming edges in the new PHI as we expect + // each case-based edge to be included in the unswitched switch in some + // cases. + // FIXME: This is really, really gross. It would be much cleaner if LLVM + // allowed us to create a single entry for a predecessor block without + // having separate entries for each "edge" even though these edges are + // required to produce identical results. + for (int i = PN.getNumIncomingValues() - 1; i >= 0; --i) { + if (PN.getIncomingBlock(i) != &OldExitingBB) + continue; + + Value *Incoming = PN.getIncomingValue(i); + if (FullUnswitch) + // No more edge from the old exiting block to the exit block. + PN.removeIncomingValue(i); + + NewPN->addIncoming(Incoming, &OldPH); + } + + // Now replace the old PHI with the new one and wire the old one in as an + // input to the new one. + PN.replaceAllUsesWith(NewPN); + NewPN->addIncoming(&PN, &ExitBB); + } +} + +/// Hoist the current loop up to the innermost loop containing a remaining exit. +/// +/// Because we've removed an exit from the loop, we may have changed the set of +/// loops reachable and need to move the current loop up the loop nest or even +/// to an entirely separate nest. +static void hoistLoopToNewParent(Loop &L, BasicBlock &Preheader, + DominatorTree &DT, LoopInfo &LI, + MemorySSAUpdater *MSSAU) { + // If the loop is already at the top level, we can't hoist it anywhere. + Loop *OldParentL = L.getParentLoop(); + if (!OldParentL) + return; + + SmallVector<BasicBlock *, 4> Exits; + L.getExitBlocks(Exits); + Loop *NewParentL = nullptr; + for (auto *ExitBB : Exits) + if (Loop *ExitL = LI.getLoopFor(ExitBB)) + if (!NewParentL || NewParentL->contains(ExitL)) + NewParentL = ExitL; + + if (NewParentL == OldParentL) + return; + + // The new parent loop (if different) should always contain the old one. + if (NewParentL) + assert(NewParentL->contains(OldParentL) && + "Can only hoist this loop up the nest!"); + + // The preheader will need to move with the body of this loop. However, + // because it isn't in this loop we also need to update the primary loop map. + assert(OldParentL == LI.getLoopFor(&Preheader) && + "Parent loop of this loop should contain this loop's preheader!"); + LI.changeLoopFor(&Preheader, NewParentL); + + // Remove this loop from its old parent. + OldParentL->removeChildLoop(&L); + + // Add the loop either to the new parent or as a top-level loop. + if (NewParentL) + NewParentL->addChildLoop(&L); + else + LI.addTopLevelLoop(&L); + + // Remove this loops blocks from the old parent and every other loop up the + // nest until reaching the new parent. Also update all of these + // no-longer-containing loops to reflect the nesting change. + for (Loop *OldContainingL = OldParentL; OldContainingL != NewParentL; + OldContainingL = OldContainingL->getParentLoop()) { + llvm::erase_if(OldContainingL->getBlocksVector(), + [&](const BasicBlock *BB) { + return BB == &Preheader || L.contains(BB); + }); + + OldContainingL->getBlocksSet().erase(&Preheader); + for (BasicBlock *BB : L.blocks()) + OldContainingL->getBlocksSet().erase(BB); + + // Because we just hoisted a loop out of this one, we have essentially + // created new exit paths from it. That means we need to form LCSSA PHI + // nodes for values used in the no-longer-nested loop. + formLCSSA(*OldContainingL, DT, &LI, nullptr); + + // We shouldn't need to form dedicated exits because the exit introduced + // here is the (just split by unswitching) preheader. However, after trivial + // unswitching it is possible to get new non-dedicated exits out of parent + // loop so let's conservatively form dedicated exit blocks and figure out + // if we can optimize later. + formDedicatedExitBlocks(OldContainingL, &DT, &LI, MSSAU, + /*PreserveLCSSA*/ true); + } +} + +/// Unswitch a trivial branch if the condition is loop invariant. +/// +/// This routine should only be called when loop code leading to the branch has +/// been validated as trivial (no side effects). This routine checks if the +/// condition is invariant and one of the successors is a loop exit. This +/// allows us to unswitch without duplicating the loop, making it trivial. +/// +/// If this routine fails to unswitch the branch it returns false. +/// +/// If the branch can be unswitched, this routine splits the preheader and +/// hoists the branch above that split. Preserves loop simplified form +/// (splitting the exit block as necessary). It simplifies the branch within +/// the loop to an unconditional branch but doesn't remove it entirely. Further +/// cleanup can be done with some simplify-cfg like pass. +/// +/// If `SE` is not null, it will be updated based on the potential loop SCEVs +/// invalidated by this. +static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT, + LoopInfo &LI, ScalarEvolution *SE, + MemorySSAUpdater *MSSAU) { + assert(BI.isConditional() && "Can only unswitch a conditional branch!"); + LLVM_DEBUG(dbgs() << " Trying to unswitch branch: " << BI << "\n"); + + // The loop invariant values that we want to unswitch. + TinyPtrVector<Value *> Invariants; + + // When true, we're fully unswitching the branch rather than just unswitching + // some input conditions to the branch. + bool FullUnswitch = false; + + if (L.isLoopInvariant(BI.getCondition())) { + Invariants.push_back(BI.getCondition()); + FullUnswitch = true; + } else { + if (auto *CondInst = dyn_cast<Instruction>(BI.getCondition())) + Invariants = collectHomogenousInstGraphLoopInvariants(L, *CondInst, LI); + if (Invariants.empty()) + // Couldn't find invariant inputs! + return false; + } + + // Check that one of the branch's successors exits, and which one. + bool ExitDirection = true; + int LoopExitSuccIdx = 0; + auto *LoopExitBB = BI.getSuccessor(0); + if (L.contains(LoopExitBB)) { + ExitDirection = false; + LoopExitSuccIdx = 1; + LoopExitBB = BI.getSuccessor(1); + if (L.contains(LoopExitBB)) + return false; + } + auto *ContinueBB = BI.getSuccessor(1 - LoopExitSuccIdx); + auto *ParentBB = BI.getParent(); + if (!areLoopExitPHIsLoopInvariant(L, *ParentBB, *LoopExitBB)) + return false; + + // When unswitching only part of the branch's condition, we need the exit + // block to be reached directly from the partially unswitched input. This can + // be done when the exit block is along the true edge and the branch condition + // is a graph of `or` operations, or the exit block is along the false edge + // and the condition is a graph of `and` operations. + if (!FullUnswitch) { + if (ExitDirection) { + if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::Or) + return false; + } else { + if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::And) + return false; + } + } + + LLVM_DEBUG({ + dbgs() << " unswitching trivial invariant conditions for: " << BI + << "\n"; + for (Value *Invariant : Invariants) { + dbgs() << " " << *Invariant << " == true"; + if (Invariant != Invariants.back()) + dbgs() << " ||"; + dbgs() << "\n"; + } + }); + + // If we have scalar evolutions, we need to invalidate them including this + // loop and the loop containing the exit block. + if (SE) { + if (Loop *ExitL = LI.getLoopFor(LoopExitBB)) + SE->forgetLoop(ExitL); + else + // Forget the entire nest as this exits the entire nest. + SE->forgetTopmostLoop(&L); + } + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // Split the preheader, so that we know that there is a safe place to insert + // the conditional branch. We will change the preheader to have a conditional + // branch on LoopCond. + BasicBlock *OldPH = L.getLoopPreheader(); + BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU); + + // Now that we have a place to insert the conditional branch, create a place + // to branch to: this is the exit block out of the loop that we are + // unswitching. We need to split this if there are other loop predecessors. + // Because the loop is in simplified form, *any* other predecessor is enough. + BasicBlock *UnswitchedBB; + if (FullUnswitch && LoopExitBB->getUniquePredecessor()) { + assert(LoopExitBB->getUniquePredecessor() == BI.getParent() && + "A branch's parent isn't a predecessor!"); + UnswitchedBB = LoopExitBB; + } else { + UnswitchedBB = + SplitBlock(LoopExitBB, &LoopExitBB->front(), &DT, &LI, MSSAU); + } + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // Actually move the invariant uses into the unswitched position. If possible, + // we do this by moving the instructions, but when doing partial unswitching + // we do it by building a new merge of the values in the unswitched position. + OldPH->getTerminator()->eraseFromParent(); + if (FullUnswitch) { + // If fully unswitching, we can use the existing branch instruction. + // Splice it into the old PH to gate reaching the new preheader and re-point + // its successors. + OldPH->getInstList().splice(OldPH->end(), BI.getParent()->getInstList(), + BI); + if (MSSAU) { + // Temporarily clone the terminator, to make MSSA update cheaper by + // separating "insert edge" updates from "remove edge" ones. + ParentBB->getInstList().push_back(BI.clone()); + } else { + // Create a new unconditional branch that will continue the loop as a new + // terminator. + BranchInst::Create(ContinueBB, ParentBB); + } + BI.setSuccessor(LoopExitSuccIdx, UnswitchedBB); + BI.setSuccessor(1 - LoopExitSuccIdx, NewPH); + } else { + // Only unswitching a subset of inputs to the condition, so we will need to + // build a new branch that merges the invariant inputs. + if (ExitDirection) + assert(cast<Instruction>(BI.getCondition())->getOpcode() == + Instruction::Or && + "Must have an `or` of `i1`s for the condition!"); + else + assert(cast<Instruction>(BI.getCondition())->getOpcode() == + Instruction::And && + "Must have an `and` of `i1`s for the condition!"); + buildPartialUnswitchConditionalBranch(*OldPH, Invariants, ExitDirection, + *UnswitchedBB, *NewPH); + } + + // Update the dominator tree with the added edge. + DT.insertEdge(OldPH, UnswitchedBB); + + // After the dominator tree was updated with the added edge, update MemorySSA + // if available. + if (MSSAU) { + SmallVector<CFGUpdate, 1> Updates; + Updates.push_back({cfg::UpdateKind::Insert, OldPH, UnswitchedBB}); + MSSAU->applyInsertUpdates(Updates, DT); + } + + // Finish updating dominator tree and memory ssa for full unswitch. + if (FullUnswitch) { + if (MSSAU) { + // Remove the cloned branch instruction. + ParentBB->getTerminator()->eraseFromParent(); + // Create unconditional branch now. + BranchInst::Create(ContinueBB, ParentBB); + MSSAU->removeEdge(ParentBB, LoopExitBB); + } + DT.deleteEdge(ParentBB, LoopExitBB); + } + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // Rewrite the relevant PHI nodes. + if (UnswitchedBB == LoopExitBB) + rewritePHINodesForUnswitchedExitBlock(*UnswitchedBB, *ParentBB, *OldPH); + else + rewritePHINodesForExitAndUnswitchedBlocks(*LoopExitBB, *UnswitchedBB, + *ParentBB, *OldPH, FullUnswitch); + + // The constant we can replace all of our invariants with inside the loop + // body. If any of the invariants have a value other than this the loop won't + // be entered. + ConstantInt *Replacement = ExitDirection + ? ConstantInt::getFalse(BI.getContext()) + : ConstantInt::getTrue(BI.getContext()); + + // Since this is an i1 condition we can also trivially replace uses of it + // within the loop with a constant. + for (Value *Invariant : Invariants) + replaceLoopInvariantUses(L, Invariant, *Replacement); + + // If this was full unswitching, we may have changed the nesting relationship + // for this loop so hoist it to its correct parent if needed. + if (FullUnswitch) + hoistLoopToNewParent(L, *NewPH, DT, LI, MSSAU); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + LLVM_DEBUG(dbgs() << " done: unswitching trivial branch...\n"); + ++NumTrivial; + ++NumBranches; + return true; +} + +/// Unswitch a trivial switch if the condition is loop invariant. +/// +/// This routine should only be called when loop code leading to the switch has +/// been validated as trivial (no side effects). This routine checks if the +/// condition is invariant and that at least one of the successors is a loop +/// exit. This allows us to unswitch without duplicating the loop, making it +/// trivial. +/// +/// If this routine fails to unswitch the switch it returns false. +/// +/// If the switch can be unswitched, this routine splits the preheader and +/// copies the switch above that split. If the default case is one of the +/// exiting cases, it copies the non-exiting cases and points them at the new +/// preheader. If the default case is not exiting, it copies the exiting cases +/// and points the default at the preheader. It preserves loop simplified form +/// (splitting the exit blocks as necessary). It simplifies the switch within +/// the loop by removing now-dead cases. If the default case is one of those +/// unswitched, it replaces its destination with a new basic block containing +/// only unreachable. Such basic blocks, while technically loop exits, are not +/// considered for unswitching so this is a stable transform and the same +/// switch will not be revisited. If after unswitching there is only a single +/// in-loop successor, the switch is further simplified to an unconditional +/// branch. Still more cleanup can be done with some simplify-cfg like pass. +/// +/// If `SE` is not null, it will be updated based on the potential loop SCEVs +/// invalidated by this. +static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT, + LoopInfo &LI, ScalarEvolution *SE, + MemorySSAUpdater *MSSAU) { + LLVM_DEBUG(dbgs() << " Trying to unswitch switch: " << SI << "\n"); + Value *LoopCond = SI.getCondition(); + + // If this isn't switching on an invariant condition, we can't unswitch it. + if (!L.isLoopInvariant(LoopCond)) + return false; + + auto *ParentBB = SI.getParent(); + + SmallVector<int, 4> ExitCaseIndices; + for (auto Case : SI.cases()) { + auto *SuccBB = Case.getCaseSuccessor(); + if (!L.contains(SuccBB) && + areLoopExitPHIsLoopInvariant(L, *ParentBB, *SuccBB)) + ExitCaseIndices.push_back(Case.getCaseIndex()); + } + BasicBlock *DefaultExitBB = nullptr; + SwitchInstProfUpdateWrapper::CaseWeightOpt DefaultCaseWeight = + SwitchInstProfUpdateWrapper::getSuccessorWeight(SI, 0); + if (!L.contains(SI.getDefaultDest()) && + areLoopExitPHIsLoopInvariant(L, *ParentBB, *SI.getDefaultDest()) && + !isa<UnreachableInst>(SI.getDefaultDest()->getTerminator())) { + DefaultExitBB = SI.getDefaultDest(); + } else if (ExitCaseIndices.empty()) + return false; + + LLVM_DEBUG(dbgs() << " unswitching trivial switch...\n"); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // We may need to invalidate SCEVs for the outermost loop reached by any of + // the exits. + Loop *OuterL = &L; + + if (DefaultExitBB) { + // Clear out the default destination temporarily to allow accurate + // predecessor lists to be examined below. + SI.setDefaultDest(nullptr); + // Check the loop containing this exit. + Loop *ExitL = LI.getLoopFor(DefaultExitBB); + if (!ExitL || ExitL->contains(OuterL)) + OuterL = ExitL; + } + + // Store the exit cases into a separate data structure and remove them from + // the switch. + SmallVector<std::tuple<ConstantInt *, BasicBlock *, + SwitchInstProfUpdateWrapper::CaseWeightOpt>, + 4> ExitCases; + ExitCases.reserve(ExitCaseIndices.size()); + SwitchInstProfUpdateWrapper SIW(SI); + // We walk the case indices backwards so that we remove the last case first + // and don't disrupt the earlier indices. + for (unsigned Index : reverse(ExitCaseIndices)) { + auto CaseI = SI.case_begin() + Index; + // Compute the outer loop from this exit. + Loop *ExitL = LI.getLoopFor(CaseI->getCaseSuccessor()); + if (!ExitL || ExitL->contains(OuterL)) + OuterL = ExitL; + // Save the value of this case. + auto W = SIW.getSuccessorWeight(CaseI->getSuccessorIndex()); + ExitCases.emplace_back(CaseI->getCaseValue(), CaseI->getCaseSuccessor(), W); + // Delete the unswitched cases. + SIW.removeCase(CaseI); + } + + if (SE) { + if (OuterL) + SE->forgetLoop(OuterL); + else + SE->forgetTopmostLoop(&L); + } + + // Check if after this all of the remaining cases point at the same + // successor. + BasicBlock *CommonSuccBB = nullptr; + if (SI.getNumCases() > 0 && + std::all_of(std::next(SI.case_begin()), SI.case_end(), + [&SI](const SwitchInst::CaseHandle &Case) { + return Case.getCaseSuccessor() == + SI.case_begin()->getCaseSuccessor(); + })) + CommonSuccBB = SI.case_begin()->getCaseSuccessor(); + if (!DefaultExitBB) { + // If we're not unswitching the default, we need it to match any cases to + // have a common successor or if we have no cases it is the common + // successor. + if (SI.getNumCases() == 0) + CommonSuccBB = SI.getDefaultDest(); + else if (SI.getDefaultDest() != CommonSuccBB) + CommonSuccBB = nullptr; + } + + // Split the preheader, so that we know that there is a safe place to insert + // the switch. + BasicBlock *OldPH = L.getLoopPreheader(); + BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI, MSSAU); + OldPH->getTerminator()->eraseFromParent(); + + // Now add the unswitched switch. + auto *NewSI = SwitchInst::Create(LoopCond, NewPH, ExitCases.size(), OldPH); + SwitchInstProfUpdateWrapper NewSIW(*NewSI); + + // Rewrite the IR for the unswitched basic blocks. This requires two steps. + // First, we split any exit blocks with remaining in-loop predecessors. Then + // we update the PHIs in one of two ways depending on if there was a split. + // We walk in reverse so that we split in the same order as the cases + // appeared. This is purely for convenience of reading the resulting IR, but + // it doesn't cost anything really. + SmallPtrSet<BasicBlock *, 2> UnswitchedExitBBs; + SmallDenseMap<BasicBlock *, BasicBlock *, 2> SplitExitBBMap; + // Handle the default exit if necessary. + // FIXME: It'd be great if we could merge this with the loop below but LLVM's + // ranges aren't quite powerful enough yet. + if (DefaultExitBB) { + if (pred_empty(DefaultExitBB)) { + UnswitchedExitBBs.insert(DefaultExitBB); + rewritePHINodesForUnswitchedExitBlock(*DefaultExitBB, *ParentBB, *OldPH); + } else { + auto *SplitBB = + SplitBlock(DefaultExitBB, &DefaultExitBB->front(), &DT, &LI, MSSAU); + rewritePHINodesForExitAndUnswitchedBlocks(*DefaultExitBB, *SplitBB, + *ParentBB, *OldPH, + /*FullUnswitch*/ true); + DefaultExitBB = SplitExitBBMap[DefaultExitBB] = SplitBB; + } + } + // Note that we must use a reference in the for loop so that we update the + // container. + for (auto &ExitCase : reverse(ExitCases)) { + // Grab a reference to the exit block in the pair so that we can update it. + BasicBlock *ExitBB = std::get<1>(ExitCase); + + // If this case is the last edge into the exit block, we can simply reuse it + // as it will no longer be a loop exit. No mapping necessary. + if (pred_empty(ExitBB)) { + // Only rewrite once. + if (UnswitchedExitBBs.insert(ExitBB).second) + rewritePHINodesForUnswitchedExitBlock(*ExitBB, *ParentBB, *OldPH); + continue; + } + + // Otherwise we need to split the exit block so that we retain an exit + // block from the loop and a target for the unswitched condition. + BasicBlock *&SplitExitBB = SplitExitBBMap[ExitBB]; + if (!SplitExitBB) { + // If this is the first time we see this, do the split and remember it. + SplitExitBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU); + rewritePHINodesForExitAndUnswitchedBlocks(*ExitBB, *SplitExitBB, + *ParentBB, *OldPH, + /*FullUnswitch*/ true); + } + // Update the case pair to point to the split block. + std::get<1>(ExitCase) = SplitExitBB; + } + + // Now add the unswitched cases. We do this in reverse order as we built them + // in reverse order. + for (auto &ExitCase : reverse(ExitCases)) { + ConstantInt *CaseVal = std::get<0>(ExitCase); + BasicBlock *UnswitchedBB = std::get<1>(ExitCase); + + NewSIW.addCase(CaseVal, UnswitchedBB, std::get<2>(ExitCase)); + } + + // If the default was unswitched, re-point it and add explicit cases for + // entering the loop. + if (DefaultExitBB) { + NewSIW->setDefaultDest(DefaultExitBB); + NewSIW.setSuccessorWeight(0, DefaultCaseWeight); + + // We removed all the exit cases, so we just copy the cases to the + // unswitched switch. + for (const auto &Case : SI.cases()) + NewSIW.addCase(Case.getCaseValue(), NewPH, + SIW.getSuccessorWeight(Case.getSuccessorIndex())); + } else if (DefaultCaseWeight) { + // We have to set branch weight of the default case. + uint64_t SW = *DefaultCaseWeight; + for (const auto &Case : SI.cases()) { + auto W = SIW.getSuccessorWeight(Case.getSuccessorIndex()); + assert(W && + "case weight must be defined as default case weight is defined"); + SW += *W; + } + NewSIW.setSuccessorWeight(0, SW); + } + + // If we ended up with a common successor for every path through the switch + // after unswitching, rewrite it to an unconditional branch to make it easy + // to recognize. Otherwise we potentially have to recognize the default case + // pointing at unreachable and other complexity. + if (CommonSuccBB) { + BasicBlock *BB = SI.getParent(); + // We may have had multiple edges to this common successor block, so remove + // them as predecessors. We skip the first one, either the default or the + // actual first case. + bool SkippedFirst = DefaultExitBB == nullptr; + for (auto Case : SI.cases()) { + assert(Case.getCaseSuccessor() == CommonSuccBB && + "Non-common successor!"); + (void)Case; + if (!SkippedFirst) { + SkippedFirst = true; + continue; + } + CommonSuccBB->removePredecessor(BB, + /*KeepOneInputPHIs*/ true); + } + // Now nuke the switch and replace it with a direct branch. + SIW.eraseFromParent(); + BranchInst::Create(CommonSuccBB, BB); + } else if (DefaultExitBB) { + assert(SI.getNumCases() > 0 && + "If we had no cases we'd have a common successor!"); + // Move the last case to the default successor. This is valid as if the + // default got unswitched it cannot be reached. This has the advantage of + // being simple and keeping the number of edges from this switch to + // successors the same, and avoiding any PHI update complexity. + auto LastCaseI = std::prev(SI.case_end()); + + SI.setDefaultDest(LastCaseI->getCaseSuccessor()); + SIW.setSuccessorWeight( + 0, SIW.getSuccessorWeight(LastCaseI->getSuccessorIndex())); + SIW.removeCase(LastCaseI); + } + + // Walk the unswitched exit blocks and the unswitched split blocks and update + // the dominator tree based on the CFG edits. While we are walking unordered + // containers here, the API for applyUpdates takes an unordered list of + // updates and requires them to not contain duplicates. + SmallVector<DominatorTree::UpdateType, 4> DTUpdates; + for (auto *UnswitchedExitBB : UnswitchedExitBBs) { + DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedExitBB}); + DTUpdates.push_back({DT.Insert, OldPH, UnswitchedExitBB}); + } + for (auto SplitUnswitchedPair : SplitExitBBMap) { + DTUpdates.push_back({DT.Delete, ParentBB, SplitUnswitchedPair.first}); + DTUpdates.push_back({DT.Insert, OldPH, SplitUnswitchedPair.second}); + } + DT.applyUpdates(DTUpdates); + + if (MSSAU) { + MSSAU->applyUpdates(DTUpdates, DT); + if (VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + } + + assert(DT.verify(DominatorTree::VerificationLevel::Fast)); + + // We may have changed the nesting relationship for this loop so hoist it to + // its correct parent if needed. + hoistLoopToNewParent(L, *NewPH, DT, LI, MSSAU); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + ++NumTrivial; + ++NumSwitches; + LLVM_DEBUG(dbgs() << " done: unswitching trivial switch...\n"); + return true; +} + +/// This routine scans the loop to find a branch or switch which occurs before +/// any side effects occur. These can potentially be unswitched without +/// duplicating the loop. If a branch or switch is successfully unswitched the +/// scanning continues to see if subsequent branches or switches have become +/// trivial. Once all trivial candidates have been unswitched, this routine +/// returns. +/// +/// The return value indicates whether anything was unswitched (and therefore +/// changed). +/// +/// If `SE` is not null, it will be updated based on the potential loop SCEVs +/// invalidated by this. +static bool unswitchAllTrivialConditions(Loop &L, DominatorTree &DT, + LoopInfo &LI, ScalarEvolution *SE, + MemorySSAUpdater *MSSAU) { + bool Changed = false; + + // If loop header has only one reachable successor we should keep looking for + // trivial condition candidates in the successor as well. An alternative is + // to constant fold conditions and merge successors into loop header (then we + // only need to check header's terminator). The reason for not doing this in + // LoopUnswitch pass is that it could potentially break LoopPassManager's + // invariants. Folding dead branches could either eliminate the current loop + // or make other loops unreachable. LCSSA form might also not be preserved + // after deleting branches. The following code keeps traversing loop header's + // successors until it finds the trivial condition candidate (condition that + // is not a constant). Since unswitching generates branches with constant + // conditions, this scenario could be very common in practice. + BasicBlock *CurrentBB = L.getHeader(); + SmallPtrSet<BasicBlock *, 8> Visited; + Visited.insert(CurrentBB); + do { + // Check if there are any side-effecting instructions (e.g. stores, calls, + // volatile loads) in the part of the loop that the code *would* execute + // without unswitching. + if (MSSAU) // Possible early exit with MSSA + if (auto *Defs = MSSAU->getMemorySSA()->getBlockDefs(CurrentBB)) + if (!isa<MemoryPhi>(*Defs->begin()) || (++Defs->begin() != Defs->end())) + return Changed; + if (llvm::any_of(*CurrentBB, + [](Instruction &I) { return I.mayHaveSideEffects(); })) + return Changed; + + Instruction *CurrentTerm = CurrentBB->getTerminator(); + + if (auto *SI = dyn_cast<SwitchInst>(CurrentTerm)) { + // Don't bother trying to unswitch past a switch with a constant + // condition. This should be removed prior to running this pass by + // simplify-cfg. + if (isa<Constant>(SI->getCondition())) + return Changed; + + if (!unswitchTrivialSwitch(L, *SI, DT, LI, SE, MSSAU)) + // Couldn't unswitch this one so we're done. + return Changed; + + // Mark that we managed to unswitch something. + Changed = true; + + // If unswitching turned the terminator into an unconditional branch then + // we can continue. The unswitching logic specifically works to fold any + // cases it can into an unconditional branch to make it easier to + // recognize here. + auto *BI = dyn_cast<BranchInst>(CurrentBB->getTerminator()); + if (!BI || BI->isConditional()) + return Changed; + + CurrentBB = BI->getSuccessor(0); + continue; + } + + auto *BI = dyn_cast<BranchInst>(CurrentTerm); + if (!BI) + // We do not understand other terminator instructions. + return Changed; + + // Don't bother trying to unswitch past an unconditional branch or a branch + // with a constant value. These should be removed by simplify-cfg prior to + // running this pass. + if (!BI->isConditional() || isa<Constant>(BI->getCondition())) + return Changed; + + // Found a trivial condition candidate: non-foldable conditional branch. If + // we fail to unswitch this, we can't do anything else that is trivial. + if (!unswitchTrivialBranch(L, *BI, DT, LI, SE, MSSAU)) + return Changed; + + // Mark that we managed to unswitch something. + Changed = true; + + // If we only unswitched some of the conditions feeding the branch, we won't + // have collapsed it to a single successor. + BI = cast<BranchInst>(CurrentBB->getTerminator()); + if (BI->isConditional()) + return Changed; + + // Follow the newly unconditional branch into its successor. + CurrentBB = BI->getSuccessor(0); + + // When continuing, if we exit the loop or reach a previous visited block, + // then we can not reach any trivial condition candidates (unfoldable + // branch instructions or switch instructions) and no unswitch can happen. + } while (L.contains(CurrentBB) && Visited.insert(CurrentBB).second); + + return Changed; +} + +/// Build the cloned blocks for an unswitched copy of the given loop. +/// +/// The cloned blocks are inserted before the loop preheader (`LoopPH`) and +/// after the split block (`SplitBB`) that will be used to select between the +/// cloned and original loop. +/// +/// This routine handles cloning all of the necessary loop blocks and exit +/// blocks including rewriting their instructions and the relevant PHI nodes. +/// Any loop blocks or exit blocks which are dominated by a different successor +/// than the one for this clone of the loop blocks can be trivially skipped. We +/// use the `DominatingSucc` map to determine whether a block satisfies that +/// property with a simple map lookup. +/// +/// It also correctly creates the unconditional branch in the cloned +/// unswitched parent block to only point at the unswitched successor. +/// +/// This does not handle most of the necessary updates to `LoopInfo`. Only exit +/// block splitting is correctly reflected in `LoopInfo`, essentially all of +/// the cloned blocks (and their loops) are left without full `LoopInfo` +/// updates. This also doesn't fully update `DominatorTree`. It adds the cloned +/// blocks to them but doesn't create the cloned `DominatorTree` structure and +/// instead the caller must recompute an accurate DT. It *does* correctly +/// update the `AssumptionCache` provided in `AC`. +static BasicBlock *buildClonedLoopBlocks( + Loop &L, BasicBlock *LoopPH, BasicBlock *SplitBB, + ArrayRef<BasicBlock *> ExitBlocks, BasicBlock *ParentBB, + BasicBlock *UnswitchedSuccBB, BasicBlock *ContinueSuccBB, + const SmallDenseMap<BasicBlock *, BasicBlock *, 16> &DominatingSucc, + ValueToValueMapTy &VMap, + SmallVectorImpl<DominatorTree::UpdateType> &DTUpdates, AssumptionCache &AC, + DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) { + SmallVector<BasicBlock *, 4> NewBlocks; + NewBlocks.reserve(L.getNumBlocks() + ExitBlocks.size()); + + // We will need to clone a bunch of blocks, wrap up the clone operation in + // a helper. + auto CloneBlock = [&](BasicBlock *OldBB) { + // Clone the basic block and insert it before the new preheader. + BasicBlock *NewBB = CloneBasicBlock(OldBB, VMap, ".us", OldBB->getParent()); + NewBB->moveBefore(LoopPH); + + // Record this block and the mapping. + NewBlocks.push_back(NewBB); + VMap[OldBB] = NewBB; + + return NewBB; + }; + + // We skip cloning blocks when they have a dominating succ that is not the + // succ we are cloning for. + auto SkipBlock = [&](BasicBlock *BB) { + auto It = DominatingSucc.find(BB); + return It != DominatingSucc.end() && It->second != UnswitchedSuccBB; + }; + + // First, clone the preheader. + auto *ClonedPH = CloneBlock(LoopPH); + + // Then clone all the loop blocks, skipping the ones that aren't necessary. + for (auto *LoopBB : L.blocks()) + if (!SkipBlock(LoopBB)) + CloneBlock(LoopBB); + + // Split all the loop exit edges so that when we clone the exit blocks, if + // any of the exit blocks are *also* a preheader for some other loop, we + // don't create multiple predecessors entering the loop header. + for (auto *ExitBB : ExitBlocks) { + if (SkipBlock(ExitBB)) + continue; + + // When we are going to clone an exit, we don't need to clone all the + // instructions in the exit block and we want to ensure we have an easy + // place to merge the CFG, so split the exit first. This is always safe to + // do because there cannot be any non-loop predecessors of a loop exit in + // loop simplified form. + auto *MergeBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU); + + // Rearrange the names to make it easier to write test cases by having the + // exit block carry the suffix rather than the merge block carrying the + // suffix. + MergeBB->takeName(ExitBB); + ExitBB->setName(Twine(MergeBB->getName()) + ".split"); + + // Now clone the original exit block. + auto *ClonedExitBB = CloneBlock(ExitBB); + assert(ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && + "Exit block should have been split to have one successor!"); + assert(ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && + "Cloned exit block has the wrong successor!"); + + // Remap any cloned instructions and create a merge phi node for them. + for (auto ZippedInsts : llvm::zip_first( + llvm::make_range(ExitBB->begin(), std::prev(ExitBB->end())), + llvm::make_range(ClonedExitBB->begin(), + std::prev(ClonedExitBB->end())))) { + Instruction &I = std::get<0>(ZippedInsts); + Instruction &ClonedI = std::get<1>(ZippedInsts); + + // The only instructions in the exit block should be PHI nodes and + // potentially a landing pad. + assert( + (isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && + "Bad instruction in exit block!"); + // We should have a value map between the instruction and its clone. + assert(VMap.lookup(&I) == &ClonedI && "Mismatch in the value map!"); + + auto *MergePN = + PHINode::Create(I.getType(), /*NumReservedValues*/ 2, ".us-phi", + &*MergeBB->getFirstInsertionPt()); + I.replaceAllUsesWith(MergePN); + MergePN->addIncoming(&I, ExitBB); + MergePN->addIncoming(&ClonedI, ClonedExitBB); + } + } + + // Rewrite the instructions in the cloned blocks to refer to the instructions + // in the cloned blocks. We have to do this as a second pass so that we have + // everything available. Also, we have inserted new instructions which may + // include assume intrinsics, so we update the assumption cache while + // processing this. + for (auto *ClonedBB : NewBlocks) + for (Instruction &I : *ClonedBB) { + RemapInstruction(&I, VMap, + RF_NoModuleLevelChanges | RF_IgnoreMissingLocals); + if (auto *II = dyn_cast<IntrinsicInst>(&I)) + if (II->getIntrinsicID() == Intrinsic::assume) + AC.registerAssumption(II); + } + + // Update any PHI nodes in the cloned successors of the skipped blocks to not + // have spurious incoming values. + for (auto *LoopBB : L.blocks()) + if (SkipBlock(LoopBB)) + for (auto *SuccBB : successors(LoopBB)) + if (auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB))) + for (PHINode &PN : ClonedSuccBB->phis()) + PN.removeIncomingValue(LoopBB, /*DeletePHIIfEmpty*/ false); + + // Remove the cloned parent as a predecessor of any successor we ended up + // cloning other than the unswitched one. + auto *ClonedParentBB = cast<BasicBlock>(VMap.lookup(ParentBB)); + for (auto *SuccBB : successors(ParentBB)) { + if (SuccBB == UnswitchedSuccBB) + continue; + + auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB)); + if (!ClonedSuccBB) + continue; + + ClonedSuccBB->removePredecessor(ClonedParentBB, + /*KeepOneInputPHIs*/ true); + } + + // Replace the cloned branch with an unconditional branch to the cloned + // unswitched successor. + auto *ClonedSuccBB = cast<BasicBlock>(VMap.lookup(UnswitchedSuccBB)); + ClonedParentBB->getTerminator()->eraseFromParent(); + BranchInst::Create(ClonedSuccBB, ClonedParentBB); + + // If there are duplicate entries in the PHI nodes because of multiple edges + // to the unswitched successor, we need to nuke all but one as we replaced it + // with a direct branch. + for (PHINode &PN : ClonedSuccBB->phis()) { + bool Found = false; + // Loop over the incoming operands backwards so we can easily delete as we + // go without invalidating the index. + for (int i = PN.getNumOperands() - 1; i >= 0; --i) { + if (PN.getIncomingBlock(i) != ClonedParentBB) + continue; + if (!Found) { + Found = true; + continue; + } + PN.removeIncomingValue(i, /*DeletePHIIfEmpty*/ false); + } + } + + // Record the domtree updates for the new blocks. + SmallPtrSet<BasicBlock *, 4> SuccSet; + for (auto *ClonedBB : NewBlocks) { + for (auto *SuccBB : successors(ClonedBB)) + if (SuccSet.insert(SuccBB).second) + DTUpdates.push_back({DominatorTree::Insert, ClonedBB, SuccBB}); + SuccSet.clear(); + } + + return ClonedPH; +} + +/// Recursively clone the specified loop and all of its children. +/// +/// The target parent loop for the clone should be provided, or can be null if +/// the clone is a top-level loop. While cloning, all the blocks are mapped +/// with the provided value map. The entire original loop must be present in +/// the value map. The cloned loop is returned. +static Loop *cloneLoopNest(Loop &OrigRootL, Loop *RootParentL, + const ValueToValueMapTy &VMap, LoopInfo &LI) { + auto AddClonedBlocksToLoop = [&](Loop &OrigL, Loop &ClonedL) { + assert(ClonedL.getBlocks().empty() && "Must start with an empty loop!"); + ClonedL.reserveBlocks(OrigL.getNumBlocks()); + for (auto *BB : OrigL.blocks()) { + auto *ClonedBB = cast<BasicBlock>(VMap.lookup(BB)); + ClonedL.addBlockEntry(ClonedBB); + if (LI.getLoopFor(BB) == &OrigL) + LI.changeLoopFor(ClonedBB, &ClonedL); + } + }; + + // We specially handle the first loop because it may get cloned into + // a different parent and because we most commonly are cloning leaf loops. + Loop *ClonedRootL = LI.AllocateLoop(); + if (RootParentL) + RootParentL->addChildLoop(ClonedRootL); + else + LI.addTopLevelLoop(ClonedRootL); + AddClonedBlocksToLoop(OrigRootL, *ClonedRootL); + + if (OrigRootL.empty()) + return ClonedRootL; + + // If we have a nest, we can quickly clone the entire loop nest using an + // iterative approach because it is a tree. We keep the cloned parent in the + // data structure to avoid repeatedly querying through a map to find it. + SmallVector<std::pair<Loop *, Loop *>, 16> LoopsToClone; + // Build up the loops to clone in reverse order as we'll clone them from the + // back. + for (Loop *ChildL : llvm::reverse(OrigRootL)) + LoopsToClone.push_back({ClonedRootL, ChildL}); + do { + Loop *ClonedParentL, *L; + std::tie(ClonedParentL, L) = LoopsToClone.pop_back_val(); + Loop *ClonedL = LI.AllocateLoop(); + ClonedParentL->addChildLoop(ClonedL); + AddClonedBlocksToLoop(*L, *ClonedL); + for (Loop *ChildL : llvm::reverse(*L)) + LoopsToClone.push_back({ClonedL, ChildL}); + } while (!LoopsToClone.empty()); + + return ClonedRootL; +} + +/// Build the cloned loops of an original loop from unswitching. +/// +/// Because unswitching simplifies the CFG of the loop, this isn't a trivial +/// operation. We need to re-verify that there even is a loop (as the backedge +/// may not have been cloned), and even if there are remaining backedges the +/// backedge set may be different. However, we know that each child loop is +/// undisturbed, we only need to find where to place each child loop within +/// either any parent loop or within a cloned version of the original loop. +/// +/// Because child loops may end up cloned outside of any cloned version of the +/// original loop, multiple cloned sibling loops may be created. All of them +/// are returned so that the newly introduced loop nest roots can be +/// identified. +static void buildClonedLoops(Loop &OrigL, ArrayRef<BasicBlock *> ExitBlocks, + const ValueToValueMapTy &VMap, LoopInfo &LI, + SmallVectorImpl<Loop *> &NonChildClonedLoops) { + Loop *ClonedL = nullptr; + + auto *OrigPH = OrigL.getLoopPreheader(); + auto *OrigHeader = OrigL.getHeader(); + + auto *ClonedPH = cast<BasicBlock>(VMap.lookup(OrigPH)); + auto *ClonedHeader = cast<BasicBlock>(VMap.lookup(OrigHeader)); + + // We need to know the loops of the cloned exit blocks to even compute the + // accurate parent loop. If we only clone exits to some parent of the + // original parent, we want to clone into that outer loop. We also keep track + // of the loops that our cloned exit blocks participate in. + Loop *ParentL = nullptr; + SmallVector<BasicBlock *, 4> ClonedExitsInLoops; + SmallDenseMap<BasicBlock *, Loop *, 16> ExitLoopMap; + ClonedExitsInLoops.reserve(ExitBlocks.size()); + for (auto *ExitBB : ExitBlocks) + if (auto *ClonedExitBB = cast_or_null<BasicBlock>(VMap.lookup(ExitBB))) + if (Loop *ExitL = LI.getLoopFor(ExitBB)) { + ExitLoopMap[ClonedExitBB] = ExitL; + ClonedExitsInLoops.push_back(ClonedExitBB); + if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL))) + ParentL = ExitL; + } + assert((!ParentL || ParentL == OrigL.getParentLoop() || + ParentL->contains(OrigL.getParentLoop())) && + "The computed parent loop should always contain (or be) the parent of " + "the original loop."); + + // We build the set of blocks dominated by the cloned header from the set of + // cloned blocks out of the original loop. While not all of these will + // necessarily be in the cloned loop, it is enough to establish that they + // aren't in unreachable cycles, etc. + SmallSetVector<BasicBlock *, 16> ClonedLoopBlocks; + for (auto *BB : OrigL.blocks()) + if (auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB))) + ClonedLoopBlocks.insert(ClonedBB); + + // Rebuild the set of blocks that will end up in the cloned loop. We may have + // skipped cloning some region of this loop which can in turn skip some of + // the backedges so we have to rebuild the blocks in the loop based on the + // backedges that remain after cloning. + SmallVector<BasicBlock *, 16> Worklist; + SmallPtrSet<BasicBlock *, 16> BlocksInClonedLoop; + for (auto *Pred : predecessors(ClonedHeader)) { + // The only possible non-loop header predecessor is the preheader because + // we know we cloned the loop in simplified form. + if (Pred == ClonedPH) + continue; + + // Because the loop was in simplified form, the only non-loop predecessor + // should be the preheader. + assert(ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop " + "header other than the preheader " + "that is not part of the loop!"); + + // Insert this block into the loop set and on the first visit (and if it + // isn't the header we're currently walking) put it into the worklist to + // recurse through. + if (BlocksInClonedLoop.insert(Pred).second && Pred != ClonedHeader) + Worklist.push_back(Pred); + } + + // If we had any backedges then there *is* a cloned loop. Put the header into + // the loop set and then walk the worklist backwards to find all the blocks + // that remain within the loop after cloning. + if (!BlocksInClonedLoop.empty()) { + BlocksInClonedLoop.insert(ClonedHeader); + + while (!Worklist.empty()) { + BasicBlock *BB = Worklist.pop_back_val(); + assert(BlocksInClonedLoop.count(BB) && + "Didn't put block into the loop set!"); + + // Insert any predecessors that are in the possible set into the cloned + // set, and if the insert is successful, add them to the worklist. Note + // that we filter on the blocks that are definitely reachable via the + // backedge to the loop header so we may prune out dead code within the + // cloned loop. + for (auto *Pred : predecessors(BB)) + if (ClonedLoopBlocks.count(Pred) && + BlocksInClonedLoop.insert(Pred).second) + Worklist.push_back(Pred); + } + + ClonedL = LI.AllocateLoop(); + if (ParentL) { + ParentL->addBasicBlockToLoop(ClonedPH, LI); + ParentL->addChildLoop(ClonedL); + } else { + LI.addTopLevelLoop(ClonedL); + } + NonChildClonedLoops.push_back(ClonedL); + + ClonedL->reserveBlocks(BlocksInClonedLoop.size()); + // We don't want to just add the cloned loop blocks based on how we + // discovered them. The original order of blocks was carefully built in + // a way that doesn't rely on predecessor ordering. Rather than re-invent + // that logic, we just re-walk the original blocks (and those of the child + // loops) and filter them as we add them into the cloned loop. + for (auto *BB : OrigL.blocks()) { + auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB)); + if (!ClonedBB || !BlocksInClonedLoop.count(ClonedBB)) + continue; + + // Directly add the blocks that are only in this loop. + if (LI.getLoopFor(BB) == &OrigL) { + ClonedL->addBasicBlockToLoop(ClonedBB, LI); + continue; + } + + // We want to manually add it to this loop and parents. + // Registering it with LoopInfo will happen when we clone the top + // loop for this block. + for (Loop *PL = ClonedL; PL; PL = PL->getParentLoop()) + PL->addBlockEntry(ClonedBB); + } + + // Now add each child loop whose header remains within the cloned loop. All + // of the blocks within the loop must satisfy the same constraints as the + // header so once we pass the header checks we can just clone the entire + // child loop nest. + for (Loop *ChildL : OrigL) { + auto *ClonedChildHeader = + cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader())); + if (!ClonedChildHeader || !BlocksInClonedLoop.count(ClonedChildHeader)) + continue; + +#ifndef NDEBUG + // We should never have a cloned child loop header but fail to have + // all of the blocks for that child loop. + for (auto *ChildLoopBB : ChildL->blocks()) + assert(BlocksInClonedLoop.count( + cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && + "Child cloned loop has a header within the cloned outer " + "loop but not all of its blocks!"); +#endif + + cloneLoopNest(*ChildL, ClonedL, VMap, LI); + } + } + + // Now that we've handled all the components of the original loop that were + // cloned into a new loop, we still need to handle anything from the original + // loop that wasn't in a cloned loop. + + // Figure out what blocks are left to place within any loop nest containing + // the unswitched loop. If we never formed a loop, the cloned PH is one of + // them. + SmallPtrSet<BasicBlock *, 16> UnloopedBlockSet; + if (BlocksInClonedLoop.empty()) + UnloopedBlockSet.insert(ClonedPH); + for (auto *ClonedBB : ClonedLoopBlocks) + if (!BlocksInClonedLoop.count(ClonedBB)) + UnloopedBlockSet.insert(ClonedBB); + + // Copy the cloned exits and sort them in ascending loop depth, we'll work + // backwards across these to process them inside out. The order shouldn't + // matter as we're just trying to build up the map from inside-out; we use + // the map in a more stably ordered way below. + auto OrderedClonedExitsInLoops = ClonedExitsInLoops; + llvm::sort(OrderedClonedExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) { + return ExitLoopMap.lookup(LHS)->getLoopDepth() < + ExitLoopMap.lookup(RHS)->getLoopDepth(); + }); + + // Populate the existing ExitLoopMap with everything reachable from each + // exit, starting from the inner most exit. + while (!UnloopedBlockSet.empty() && !OrderedClonedExitsInLoops.empty()) { + assert(Worklist.empty() && "Didn't clear worklist!"); + + BasicBlock *ExitBB = OrderedClonedExitsInLoops.pop_back_val(); + Loop *ExitL = ExitLoopMap.lookup(ExitBB); + + // Walk the CFG back until we hit the cloned PH adding everything reachable + // and in the unlooped set to this exit block's loop. + Worklist.push_back(ExitBB); + do { + BasicBlock *BB = Worklist.pop_back_val(); + // We can stop recursing at the cloned preheader (if we get there). + if (BB == ClonedPH) + continue; + + for (BasicBlock *PredBB : predecessors(BB)) { + // If this pred has already been moved to our set or is part of some + // (inner) loop, no update needed. + if (!UnloopedBlockSet.erase(PredBB)) { + assert( + (BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && + "Predecessor not mapped to a loop!"); + continue; + } + + // We just insert into the loop set here. We'll add these blocks to the + // exit loop after we build up the set in an order that doesn't rely on + // predecessor order (which in turn relies on use list order). + bool Inserted = ExitLoopMap.insert({PredBB, ExitL}).second; + (void)Inserted; + assert(Inserted && "Should only visit an unlooped block once!"); + + // And recurse through to its predecessors. + Worklist.push_back(PredBB); + } + } while (!Worklist.empty()); + } + + // Now that the ExitLoopMap gives as mapping for all the non-looping cloned + // blocks to their outer loops, walk the cloned blocks and the cloned exits + // in their original order adding them to the correct loop. + + // We need a stable insertion order. We use the order of the original loop + // order and map into the correct parent loop. + for (auto *BB : llvm::concat<BasicBlock *const>( + makeArrayRef(ClonedPH), ClonedLoopBlocks, ClonedExitsInLoops)) + if (Loop *OuterL = ExitLoopMap.lookup(BB)) + OuterL->addBasicBlockToLoop(BB, LI); + +#ifndef NDEBUG + for (auto &BBAndL : ExitLoopMap) { + auto *BB = BBAndL.first; + auto *OuterL = BBAndL.second; + assert(LI.getLoopFor(BB) == OuterL && + "Failed to put all blocks into outer loops!"); + } +#endif + + // Now that all the blocks are placed into the correct containing loop in the + // absence of child loops, find all the potentially cloned child loops and + // clone them into whatever outer loop we placed their header into. + for (Loop *ChildL : OrigL) { + auto *ClonedChildHeader = + cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader())); + if (!ClonedChildHeader || BlocksInClonedLoop.count(ClonedChildHeader)) + continue; + +#ifndef NDEBUG + for (auto *ChildLoopBB : ChildL->blocks()) + assert(VMap.count(ChildLoopBB) && + "Cloned a child loop header but not all of that loops blocks!"); +#endif + + NonChildClonedLoops.push_back(cloneLoopNest( + *ChildL, ExitLoopMap.lookup(ClonedChildHeader), VMap, LI)); + } +} + +static void +deleteDeadClonedBlocks(Loop &L, ArrayRef<BasicBlock *> ExitBlocks, + ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps, + DominatorTree &DT, MemorySSAUpdater *MSSAU) { + // Find all the dead clones, and remove them from their successors. + SmallVector<BasicBlock *, 16> DeadBlocks; + for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks)) + for (auto &VMap : VMaps) + if (BasicBlock *ClonedBB = cast_or_null<BasicBlock>(VMap->lookup(BB))) + if (!DT.isReachableFromEntry(ClonedBB)) { + for (BasicBlock *SuccBB : successors(ClonedBB)) + SuccBB->removePredecessor(ClonedBB); + DeadBlocks.push_back(ClonedBB); + } + + // Remove all MemorySSA in the dead blocks + if (MSSAU) { + SmallSetVector<BasicBlock *, 8> DeadBlockSet(DeadBlocks.begin(), + DeadBlocks.end()); + MSSAU->removeBlocks(DeadBlockSet); + } + + // Drop any remaining references to break cycles. + for (BasicBlock *BB : DeadBlocks) + BB->dropAllReferences(); + // Erase them from the IR. + for (BasicBlock *BB : DeadBlocks) + BB->eraseFromParent(); +} + +static void deleteDeadBlocksFromLoop(Loop &L, + SmallVectorImpl<BasicBlock *> &ExitBlocks, + DominatorTree &DT, LoopInfo &LI, + MemorySSAUpdater *MSSAU) { + // Find all the dead blocks tied to this loop, and remove them from their + // successors. + SmallSetVector<BasicBlock *, 8> DeadBlockSet; + + // Start with loop/exit blocks and get a transitive closure of reachable dead + // blocks. + SmallVector<BasicBlock *, 16> DeathCandidates(ExitBlocks.begin(), + ExitBlocks.end()); + DeathCandidates.append(L.blocks().begin(), L.blocks().end()); + while (!DeathCandidates.empty()) { + auto *BB = DeathCandidates.pop_back_val(); + if (!DeadBlockSet.count(BB) && !DT.isReachableFromEntry(BB)) { + for (BasicBlock *SuccBB : successors(BB)) { + SuccBB->removePredecessor(BB); + DeathCandidates.push_back(SuccBB); + } + DeadBlockSet.insert(BB); + } + } + + // Remove all MemorySSA in the dead blocks + if (MSSAU) + MSSAU->removeBlocks(DeadBlockSet); + + // Filter out the dead blocks from the exit blocks list so that it can be + // used in the caller. + llvm::erase_if(ExitBlocks, + [&](BasicBlock *BB) { return DeadBlockSet.count(BB); }); + + // Walk from this loop up through its parents removing all of the dead blocks. + for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop()) { + for (auto *BB : DeadBlockSet) + ParentL->getBlocksSet().erase(BB); + llvm::erase_if(ParentL->getBlocksVector(), + [&](BasicBlock *BB) { return DeadBlockSet.count(BB); }); + } + + // Now delete the dead child loops. This raw delete will clear them + // recursively. + llvm::erase_if(L.getSubLoopsVector(), [&](Loop *ChildL) { + if (!DeadBlockSet.count(ChildL->getHeader())) + return false; + + assert(llvm::all_of(ChildL->blocks(), + [&](BasicBlock *ChildBB) { + return DeadBlockSet.count(ChildBB); + }) && + "If the child loop header is dead all blocks in the child loop must " + "be dead as well!"); + LI.destroy(ChildL); + return true; + }); + + // Remove the loop mappings for the dead blocks and drop all the references + // from these blocks to others to handle cyclic references as we start + // deleting the blocks themselves. + for (auto *BB : DeadBlockSet) { + // Check that the dominator tree has already been updated. + assert(!DT.getNode(BB) && "Should already have cleared domtree!"); + LI.changeLoopFor(BB, nullptr); + BB->dropAllReferences(); + } + + // Actually delete the blocks now that they've been fully unhooked from the + // IR. + for (auto *BB : DeadBlockSet) + BB->eraseFromParent(); +} + +/// Recompute the set of blocks in a loop after unswitching. +/// +/// This walks from the original headers predecessors to rebuild the loop. We +/// take advantage of the fact that new blocks can't have been added, and so we +/// filter by the original loop's blocks. This also handles potentially +/// unreachable code that we don't want to explore but might be found examining +/// the predecessors of the header. +/// +/// If the original loop is no longer a loop, this will return an empty set. If +/// it remains a loop, all the blocks within it will be added to the set +/// (including those blocks in inner loops). +static SmallPtrSet<const BasicBlock *, 16> recomputeLoopBlockSet(Loop &L, + LoopInfo &LI) { + SmallPtrSet<const BasicBlock *, 16> LoopBlockSet; + + auto *PH = L.getLoopPreheader(); + auto *Header = L.getHeader(); + + // A worklist to use while walking backwards from the header. + SmallVector<BasicBlock *, 16> Worklist; + + // First walk the predecessors of the header to find the backedges. This will + // form the basis of our walk. + for (auto *Pred : predecessors(Header)) { + // Skip the preheader. + if (Pred == PH) + continue; + + // Because the loop was in simplified form, the only non-loop predecessor + // is the preheader. + assert(L.contains(Pred) && "Found a predecessor of the loop header other " + "than the preheader that is not part of the " + "loop!"); + + // Insert this block into the loop set and on the first visit and, if it + // isn't the header we're currently walking, put it into the worklist to + // recurse through. + if (LoopBlockSet.insert(Pred).second && Pred != Header) + Worklist.push_back(Pred); + } + + // If no backedges were found, we're done. + if (LoopBlockSet.empty()) + return LoopBlockSet; + + // We found backedges, recurse through them to identify the loop blocks. + while (!Worklist.empty()) { + BasicBlock *BB = Worklist.pop_back_val(); + assert(LoopBlockSet.count(BB) && "Didn't put block into the loop set!"); + + // No need to walk past the header. + if (BB == Header) + continue; + + // Because we know the inner loop structure remains valid we can use the + // loop structure to jump immediately across the entire nested loop. + // Further, because it is in loop simplified form, we can directly jump + // to its preheader afterward. + if (Loop *InnerL = LI.getLoopFor(BB)) + if (InnerL != &L) { + assert(L.contains(InnerL) && + "Should not reach a loop *outside* this loop!"); + // The preheader is the only possible predecessor of the loop so + // insert it into the set and check whether it was already handled. + auto *InnerPH = InnerL->getLoopPreheader(); + assert(L.contains(InnerPH) && "Cannot contain an inner loop block " + "but not contain the inner loop " + "preheader!"); + if (!LoopBlockSet.insert(InnerPH).second) + // The only way to reach the preheader is through the loop body + // itself so if it has been visited the loop is already handled. + continue; + + // Insert all of the blocks (other than those already present) into + // the loop set. We expect at least the block that led us to find the + // inner loop to be in the block set, but we may also have other loop + // blocks if they were already enqueued as predecessors of some other + // outer loop block. + for (auto *InnerBB : InnerL->blocks()) { + if (InnerBB == BB) { + assert(LoopBlockSet.count(InnerBB) && + "Block should already be in the set!"); + continue; + } + + LoopBlockSet.insert(InnerBB); + } + + // Add the preheader to the worklist so we will continue past the + // loop body. + Worklist.push_back(InnerPH); + continue; + } + + // Insert any predecessors that were in the original loop into the new + // set, and if the insert is successful, add them to the worklist. + for (auto *Pred : predecessors(BB)) + if (L.contains(Pred) && LoopBlockSet.insert(Pred).second) + Worklist.push_back(Pred); + } + + assert(LoopBlockSet.count(Header) && "Cannot fail to add the header!"); + + // We've found all the blocks participating in the loop, return our completed + // set. + return LoopBlockSet; +} + +/// Rebuild a loop after unswitching removes some subset of blocks and edges. +/// +/// The removal may have removed some child loops entirely but cannot have +/// disturbed any remaining child loops. However, they may need to be hoisted +/// to the parent loop (or to be top-level loops). The original loop may be +/// completely removed. +/// +/// The sibling loops resulting from this update are returned. If the original +/// loop remains a valid loop, it will be the first entry in this list with all +/// of the newly sibling loops following it. +/// +/// Returns true if the loop remains a loop after unswitching, and false if it +/// is no longer a loop after unswitching (and should not continue to be +/// referenced). +static bool rebuildLoopAfterUnswitch(Loop &L, ArrayRef<BasicBlock *> ExitBlocks, + LoopInfo &LI, + SmallVectorImpl<Loop *> &HoistedLoops) { + auto *PH = L.getLoopPreheader(); + + // Compute the actual parent loop from the exit blocks. Because we may have + // pruned some exits the loop may be different from the original parent. + Loop *ParentL = nullptr; + SmallVector<Loop *, 4> ExitLoops; + SmallVector<BasicBlock *, 4> ExitsInLoops; + ExitsInLoops.reserve(ExitBlocks.size()); + for (auto *ExitBB : ExitBlocks) + if (Loop *ExitL = LI.getLoopFor(ExitBB)) { + ExitLoops.push_back(ExitL); + ExitsInLoops.push_back(ExitBB); + if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL))) + ParentL = ExitL; + } + + // Recompute the blocks participating in this loop. This may be empty if it + // is no longer a loop. + auto LoopBlockSet = recomputeLoopBlockSet(L, LI); + + // If we still have a loop, we need to re-set the loop's parent as the exit + // block set changing may have moved it within the loop nest. Note that this + // can only happen when this loop has a parent as it can only hoist the loop + // *up* the nest. + if (!LoopBlockSet.empty() && L.getParentLoop() != ParentL) { + // Remove this loop's (original) blocks from all of the intervening loops. + for (Loop *IL = L.getParentLoop(); IL != ParentL; + IL = IL->getParentLoop()) { + IL->getBlocksSet().erase(PH); + for (auto *BB : L.blocks()) + IL->getBlocksSet().erase(BB); + llvm::erase_if(IL->getBlocksVector(), [&](BasicBlock *BB) { + return BB == PH || L.contains(BB); + }); + } + + LI.changeLoopFor(PH, ParentL); + L.getParentLoop()->removeChildLoop(&L); + if (ParentL) + ParentL->addChildLoop(&L); + else + LI.addTopLevelLoop(&L); + } + + // Now we update all the blocks which are no longer within the loop. + auto &Blocks = L.getBlocksVector(); + auto BlocksSplitI = + LoopBlockSet.empty() + ? Blocks.begin() + : std::stable_partition( + Blocks.begin(), Blocks.end(), + [&](BasicBlock *BB) { return LoopBlockSet.count(BB); }); + + // Before we erase the list of unlooped blocks, build a set of them. + SmallPtrSet<BasicBlock *, 16> UnloopedBlocks(BlocksSplitI, Blocks.end()); + if (LoopBlockSet.empty()) + UnloopedBlocks.insert(PH); + + // Now erase these blocks from the loop. + for (auto *BB : make_range(BlocksSplitI, Blocks.end())) + L.getBlocksSet().erase(BB); + Blocks.erase(BlocksSplitI, Blocks.end()); + + // Sort the exits in ascending loop depth, we'll work backwards across these + // to process them inside out. + llvm::stable_sort(ExitsInLoops, [&](BasicBlock *LHS, BasicBlock *RHS) { + return LI.getLoopDepth(LHS) < LI.getLoopDepth(RHS); + }); + + // We'll build up a set for each exit loop. + SmallPtrSet<BasicBlock *, 16> NewExitLoopBlocks; + Loop *PrevExitL = L.getParentLoop(); // The deepest possible exit loop. + + auto RemoveUnloopedBlocksFromLoop = + [](Loop &L, SmallPtrSetImpl<BasicBlock *> &UnloopedBlocks) { + for (auto *BB : UnloopedBlocks) + L.getBlocksSet().erase(BB); + llvm::erase_if(L.getBlocksVector(), [&](BasicBlock *BB) { + return UnloopedBlocks.count(BB); + }); + }; + + SmallVector<BasicBlock *, 16> Worklist; + while (!UnloopedBlocks.empty() && !ExitsInLoops.empty()) { + assert(Worklist.empty() && "Didn't clear worklist!"); + assert(NewExitLoopBlocks.empty() && "Didn't clear loop set!"); + + // Grab the next exit block, in decreasing loop depth order. + BasicBlock *ExitBB = ExitsInLoops.pop_back_val(); + Loop &ExitL = *LI.getLoopFor(ExitBB); + assert(ExitL.contains(&L) && "Exit loop must contain the inner loop!"); + + // Erase all of the unlooped blocks from the loops between the previous + // exit loop and this exit loop. This works because the ExitInLoops list is + // sorted in increasing order of loop depth and thus we visit loops in + // decreasing order of loop depth. + for (; PrevExitL != &ExitL; PrevExitL = PrevExitL->getParentLoop()) + RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks); + + // Walk the CFG back until we hit the cloned PH adding everything reachable + // and in the unlooped set to this exit block's loop. + Worklist.push_back(ExitBB); + do { + BasicBlock *BB = Worklist.pop_back_val(); + // We can stop recursing at the cloned preheader (if we get there). + if (BB == PH) + continue; + + for (BasicBlock *PredBB : predecessors(BB)) { + // If this pred has already been moved to our set or is part of some + // (inner) loop, no update needed. + if (!UnloopedBlocks.erase(PredBB)) { + assert((NewExitLoopBlocks.count(PredBB) || + ExitL.contains(LI.getLoopFor(PredBB))) && + "Predecessor not in a nested loop (or already visited)!"); + continue; + } + + // We just insert into the loop set here. We'll add these blocks to the + // exit loop after we build up the set in a deterministic order rather + // than the predecessor-influenced visit order. + bool Inserted = NewExitLoopBlocks.insert(PredBB).second; + (void)Inserted; + assert(Inserted && "Should only visit an unlooped block once!"); + + // And recurse through to its predecessors. + Worklist.push_back(PredBB); + } + } while (!Worklist.empty()); + + // If blocks in this exit loop were directly part of the original loop (as + // opposed to a child loop) update the map to point to this exit loop. This + // just updates a map and so the fact that the order is unstable is fine. + for (auto *BB : NewExitLoopBlocks) + if (Loop *BBL = LI.getLoopFor(BB)) + if (BBL == &L || !L.contains(BBL)) + LI.changeLoopFor(BB, &ExitL); + + // We will remove the remaining unlooped blocks from this loop in the next + // iteration or below. + NewExitLoopBlocks.clear(); + } + + // Any remaining unlooped blocks are no longer part of any loop unless they + // are part of some child loop. + for (; PrevExitL; PrevExitL = PrevExitL->getParentLoop()) + RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks); + for (auto *BB : UnloopedBlocks) + if (Loop *BBL = LI.getLoopFor(BB)) + if (BBL == &L || !L.contains(BBL)) + LI.changeLoopFor(BB, nullptr); + + // Sink all the child loops whose headers are no longer in the loop set to + // the parent (or to be top level loops). We reach into the loop and directly + // update its subloop vector to make this batch update efficient. + auto &SubLoops = L.getSubLoopsVector(); + auto SubLoopsSplitI = + LoopBlockSet.empty() + ? SubLoops.begin() + : std::stable_partition( + SubLoops.begin(), SubLoops.end(), [&](Loop *SubL) { + return LoopBlockSet.count(SubL->getHeader()); + }); + for (auto *HoistedL : make_range(SubLoopsSplitI, SubLoops.end())) { + HoistedLoops.push_back(HoistedL); + HoistedL->setParentLoop(nullptr); + + // To compute the new parent of this hoisted loop we look at where we + // placed the preheader above. We can't lookup the header itself because we + // retained the mapping from the header to the hoisted loop. But the + // preheader and header should have the exact same new parent computed + // based on the set of exit blocks from the original loop as the preheader + // is a predecessor of the header and so reached in the reverse walk. And + // because the loops were all in simplified form the preheader of the + // hoisted loop can't be part of some *other* loop. + if (auto *NewParentL = LI.getLoopFor(HoistedL->getLoopPreheader())) + NewParentL->addChildLoop(HoistedL); + else + LI.addTopLevelLoop(HoistedL); + } + SubLoops.erase(SubLoopsSplitI, SubLoops.end()); + + // Actually delete the loop if nothing remained within it. + if (Blocks.empty()) { + assert(SubLoops.empty() && + "Failed to remove all subloops from the original loop!"); + if (Loop *ParentL = L.getParentLoop()) + ParentL->removeChildLoop(llvm::find(*ParentL, &L)); + else + LI.removeLoop(llvm::find(LI, &L)); + LI.destroy(&L); + return false; + } + + return true; +} + +/// Helper to visit a dominator subtree, invoking a callable on each node. +/// +/// Returning false at any point will stop walking past that node of the tree. +template <typename CallableT> +void visitDomSubTree(DominatorTree &DT, BasicBlock *BB, CallableT Callable) { + SmallVector<DomTreeNode *, 4> DomWorklist; + DomWorklist.push_back(DT[BB]); +#ifndef NDEBUG + SmallPtrSet<DomTreeNode *, 4> Visited; + Visited.insert(DT[BB]); +#endif + do { + DomTreeNode *N = DomWorklist.pop_back_val(); + + // Visit this node. + if (!Callable(N->getBlock())) + continue; + + // Accumulate the child nodes. + for (DomTreeNode *ChildN : *N) { + assert(Visited.insert(ChildN).second && + "Cannot visit a node twice when walking a tree!"); + DomWorklist.push_back(ChildN); + } + } while (!DomWorklist.empty()); +} + +static void unswitchNontrivialInvariants( + Loop &L, Instruction &TI, ArrayRef<Value *> Invariants, + SmallVectorImpl<BasicBlock *> &ExitBlocks, DominatorTree &DT, LoopInfo &LI, + AssumptionCache &AC, function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB, + ScalarEvolution *SE, MemorySSAUpdater *MSSAU) { + auto *ParentBB = TI.getParent(); + BranchInst *BI = dyn_cast<BranchInst>(&TI); + SwitchInst *SI = BI ? nullptr : cast<SwitchInst>(&TI); + + // We can only unswitch switches, conditional branches with an invariant + // condition, or combining invariant conditions with an instruction. + assert((SI || BI->isConditional()) && + "Can only unswitch switches and conditional branch!"); + bool FullUnswitch = SI || BI->getCondition() == Invariants[0]; + if (FullUnswitch) + assert(Invariants.size() == 1 && + "Cannot have other invariants with full unswitching!"); + else + assert(isa<Instruction>(BI->getCondition()) && + "Partial unswitching requires an instruction as the condition!"); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // Constant and BBs tracking the cloned and continuing successor. When we are + // unswitching the entire condition, this can just be trivially chosen to + // unswitch towards `true`. However, when we are unswitching a set of + // invariants combined with `and` or `or`, the combining operation determines + // the best direction to unswitch: we want to unswitch the direction that will + // collapse the branch. + bool Direction = true; + int ClonedSucc = 0; + if (!FullUnswitch) { + if (cast<Instruction>(BI->getCondition())->getOpcode() != Instruction::Or) { + assert(cast<Instruction>(BI->getCondition())->getOpcode() == + Instruction::And && + "Only `or` and `and` instructions can combine invariants being " + "unswitched."); + Direction = false; + ClonedSucc = 1; + } + } + + BasicBlock *RetainedSuccBB = + BI ? BI->getSuccessor(1 - ClonedSucc) : SI->getDefaultDest(); + SmallSetVector<BasicBlock *, 4> UnswitchedSuccBBs; + if (BI) + UnswitchedSuccBBs.insert(BI->getSuccessor(ClonedSucc)); + else + for (auto Case : SI->cases()) + if (Case.getCaseSuccessor() != RetainedSuccBB) + UnswitchedSuccBBs.insert(Case.getCaseSuccessor()); + + assert(!UnswitchedSuccBBs.count(RetainedSuccBB) && + "Should not unswitch the same successor we are retaining!"); + + // The branch should be in this exact loop. Any inner loop's invariant branch + // should be handled by unswitching that inner loop. The caller of this + // routine should filter out any candidates that remain (but were skipped for + // whatever reason). + assert(LI.getLoopFor(ParentBB) == &L && "Branch in an inner loop!"); + + // Compute the parent loop now before we start hacking on things. + Loop *ParentL = L.getParentLoop(); + // Get blocks in RPO order for MSSA update, before changing the CFG. + LoopBlocksRPO LBRPO(&L); + if (MSSAU) + LBRPO.perform(&LI); + + // Compute the outer-most loop containing one of our exit blocks. This is the + // furthest up our loopnest which can be mutated, which we will use below to + // update things. + Loop *OuterExitL = &L; + for (auto *ExitBB : ExitBlocks) { + Loop *NewOuterExitL = LI.getLoopFor(ExitBB); + if (!NewOuterExitL) { + // We exited the entire nest with this block, so we're done. + OuterExitL = nullptr; + break; + } + if (NewOuterExitL != OuterExitL && NewOuterExitL->contains(OuterExitL)) + OuterExitL = NewOuterExitL; + } + + // At this point, we're definitely going to unswitch something so invalidate + // any cached information in ScalarEvolution for the outer most loop + // containing an exit block and all nested loops. + if (SE) { + if (OuterExitL) + SE->forgetLoop(OuterExitL); + else + SE->forgetTopmostLoop(&L); + } + + // If the edge from this terminator to a successor dominates that successor, + // store a map from each block in its dominator subtree to it. This lets us + // tell when cloning for a particular successor if a block is dominated by + // some *other* successor with a single data structure. We use this to + // significantly reduce cloning. + SmallDenseMap<BasicBlock *, BasicBlock *, 16> DominatingSucc; + for (auto *SuccBB : llvm::concat<BasicBlock *const>( + makeArrayRef(RetainedSuccBB), UnswitchedSuccBBs)) + if (SuccBB->getUniquePredecessor() || + llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) { + return PredBB == ParentBB || DT.dominates(SuccBB, PredBB); + })) + visitDomSubTree(DT, SuccBB, [&](BasicBlock *BB) { + DominatingSucc[BB] = SuccBB; + return true; + }); + + // Split the preheader, so that we know that there is a safe place to insert + // the conditional branch. We will change the preheader to have a conditional + // branch on LoopCond. The original preheader will become the split point + // between the unswitched versions, and we will have a new preheader for the + // original loop. + BasicBlock *SplitBB = L.getLoopPreheader(); + BasicBlock *LoopPH = SplitEdge(SplitBB, L.getHeader(), &DT, &LI, MSSAU); + + // Keep track of the dominator tree updates needed. + SmallVector<DominatorTree::UpdateType, 4> DTUpdates; + + // Clone the loop for each unswitched successor. + SmallVector<std::unique_ptr<ValueToValueMapTy>, 4> VMaps; + VMaps.reserve(UnswitchedSuccBBs.size()); + SmallDenseMap<BasicBlock *, BasicBlock *, 4> ClonedPHs; + for (auto *SuccBB : UnswitchedSuccBBs) { + VMaps.emplace_back(new ValueToValueMapTy()); + ClonedPHs[SuccBB] = buildClonedLoopBlocks( + L, LoopPH, SplitBB, ExitBlocks, ParentBB, SuccBB, RetainedSuccBB, + DominatingSucc, *VMaps.back(), DTUpdates, AC, DT, LI, MSSAU); + } + + // The stitching of the branched code back together depends on whether we're + // doing full unswitching or not with the exception that we always want to + // nuke the initial terminator placed in the split block. + SplitBB->getTerminator()->eraseFromParent(); + if (FullUnswitch) { + // Splice the terminator from the original loop and rewrite its + // successors. + SplitBB->getInstList().splice(SplitBB->end(), ParentBB->getInstList(), TI); + + // Keep a clone of the terminator for MSSA updates. + Instruction *NewTI = TI.clone(); + ParentBB->getInstList().push_back(NewTI); + + // First wire up the moved terminator to the preheaders. + if (BI) { + BasicBlock *ClonedPH = ClonedPHs.begin()->second; + BI->setSuccessor(ClonedSucc, ClonedPH); + BI->setSuccessor(1 - ClonedSucc, LoopPH); + DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH}); + } else { + assert(SI && "Must either be a branch or switch!"); + + // Walk the cases and directly update their successors. + assert(SI->getDefaultDest() == RetainedSuccBB && + "Not retaining default successor!"); + SI->setDefaultDest(LoopPH); + for (auto &Case : SI->cases()) + if (Case.getCaseSuccessor() == RetainedSuccBB) + Case.setSuccessor(LoopPH); + else + Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second); + + // We need to use the set to populate domtree updates as even when there + // are multiple cases pointing at the same successor we only want to + // remove and insert one edge in the domtree. + for (BasicBlock *SuccBB : UnswitchedSuccBBs) + DTUpdates.push_back( + {DominatorTree::Insert, SplitBB, ClonedPHs.find(SuccBB)->second}); + } + + if (MSSAU) { + DT.applyUpdates(DTUpdates); + DTUpdates.clear(); + + // Remove all but one edge to the retained block and all unswitched + // blocks. This is to avoid having duplicate entries in the cloned Phis, + // when we know we only keep a single edge for each case. + MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, RetainedSuccBB); + for (BasicBlock *SuccBB : UnswitchedSuccBBs) + MSSAU->removeDuplicatePhiEdgesBetween(ParentBB, SuccBB); + + for (auto &VMap : VMaps) + MSSAU->updateForClonedLoop(LBRPO, ExitBlocks, *VMap, + /*IgnoreIncomingWithNoClones=*/true); + MSSAU->updateExitBlocksForClonedLoop(ExitBlocks, VMaps, DT); + + // Remove all edges to unswitched blocks. + for (BasicBlock *SuccBB : UnswitchedSuccBBs) + MSSAU->removeEdge(ParentBB, SuccBB); + } + + // Now unhook the successor relationship as we'll be replacing + // the terminator with a direct branch. This is much simpler for branches + // than switches so we handle those first. + if (BI) { + // Remove the parent as a predecessor of the unswitched successor. + assert(UnswitchedSuccBBs.size() == 1 && + "Only one possible unswitched block for a branch!"); + BasicBlock *UnswitchedSuccBB = *UnswitchedSuccBBs.begin(); + UnswitchedSuccBB->removePredecessor(ParentBB, + /*KeepOneInputPHIs*/ true); + DTUpdates.push_back({DominatorTree::Delete, ParentBB, UnswitchedSuccBB}); + } else { + // Note that we actually want to remove the parent block as a predecessor + // of *every* case successor. The case successor is either unswitched, + // completely eliminating an edge from the parent to that successor, or it + // is a duplicate edge to the retained successor as the retained successor + // is always the default successor and as we'll replace this with a direct + // branch we no longer need the duplicate entries in the PHI nodes. + SwitchInst *NewSI = cast<SwitchInst>(NewTI); + assert(NewSI->getDefaultDest() == RetainedSuccBB && + "Not retaining default successor!"); + for (auto &Case : NewSI->cases()) + Case.getCaseSuccessor()->removePredecessor( + ParentBB, + /*KeepOneInputPHIs*/ true); + + // We need to use the set to populate domtree updates as even when there + // are multiple cases pointing at the same successor we only want to + // remove and insert one edge in the domtree. + for (BasicBlock *SuccBB : UnswitchedSuccBBs) + DTUpdates.push_back({DominatorTree::Delete, ParentBB, SuccBB}); + } + + // After MSSAU update, remove the cloned terminator instruction NewTI. + ParentBB->getTerminator()->eraseFromParent(); + + // Create a new unconditional branch to the continuing block (as opposed to + // the one cloned). + BranchInst::Create(RetainedSuccBB, ParentBB); + } else { + assert(BI && "Only branches have partial unswitching."); + assert(UnswitchedSuccBBs.size() == 1 && + "Only one possible unswitched block for a branch!"); + BasicBlock *ClonedPH = ClonedPHs.begin()->second; + // When doing a partial unswitch, we have to do a bit more work to build up + // the branch in the split block. + buildPartialUnswitchConditionalBranch(*SplitBB, Invariants, Direction, + *ClonedPH, *LoopPH); + DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH}); + } + + // Apply the updates accumulated above to get an up-to-date dominator tree. + DT.applyUpdates(DTUpdates); + if (!FullUnswitch && MSSAU) { + // Update MSSA for partial unswitch, after DT update. + SmallVector<CFGUpdate, 1> Updates; + Updates.push_back( + {cfg::UpdateKind::Insert, SplitBB, ClonedPHs.begin()->second}); + MSSAU->applyInsertUpdates(Updates, DT); + } + + // Now that we have an accurate dominator tree, first delete the dead cloned + // blocks so that we can accurately build any cloned loops. It is important to + // not delete the blocks from the original loop yet because we still want to + // reference the original loop to understand the cloned loop's structure. + deleteDeadClonedBlocks(L, ExitBlocks, VMaps, DT, MSSAU); + + // Build the cloned loop structure itself. This may be substantially + // different from the original structure due to the simplified CFG. This also + // handles inserting all the cloned blocks into the correct loops. + SmallVector<Loop *, 4> NonChildClonedLoops; + for (std::unique_ptr<ValueToValueMapTy> &VMap : VMaps) + buildClonedLoops(L, ExitBlocks, *VMap, LI, NonChildClonedLoops); + + // Now that our cloned loops have been built, we can update the original loop. + // First we delete the dead blocks from it and then we rebuild the loop + // structure taking these deletions into account. + deleteDeadBlocksFromLoop(L, ExitBlocks, DT, LI, MSSAU); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + SmallVector<Loop *, 4> HoistedLoops; + bool IsStillLoop = rebuildLoopAfterUnswitch(L, ExitBlocks, LI, HoistedLoops); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // This transformation has a high risk of corrupting the dominator tree, and + // the below steps to rebuild loop structures will result in hard to debug + // errors in that case so verify that the dominator tree is sane first. + // FIXME: Remove this when the bugs stop showing up and rely on existing + // verification steps. + assert(DT.verify(DominatorTree::VerificationLevel::Fast)); + + if (BI) { + // If we unswitched a branch which collapses the condition to a known + // constant we want to replace all the uses of the invariants within both + // the original and cloned blocks. We do this here so that we can use the + // now updated dominator tree to identify which side the users are on. + assert(UnswitchedSuccBBs.size() == 1 && + "Only one possible unswitched block for a branch!"); + BasicBlock *ClonedPH = ClonedPHs.begin()->second; + + // When considering multiple partially-unswitched invariants + // we cant just go replace them with constants in both branches. + // + // For 'AND' we infer that true branch ("continue") means true + // for each invariant operand. + // For 'OR' we can infer that false branch ("continue") means false + // for each invariant operand. + // So it happens that for multiple-partial case we dont replace + // in the unswitched branch. + bool ReplaceUnswitched = FullUnswitch || (Invariants.size() == 1); + + ConstantInt *UnswitchedReplacement = + Direction ? ConstantInt::getTrue(BI->getContext()) + : ConstantInt::getFalse(BI->getContext()); + ConstantInt *ContinueReplacement = + Direction ? ConstantInt::getFalse(BI->getContext()) + : ConstantInt::getTrue(BI->getContext()); + for (Value *Invariant : Invariants) + for (auto UI = Invariant->use_begin(), UE = Invariant->use_end(); + UI != UE;) { + // Grab the use and walk past it so we can clobber it in the use list. + Use *U = &*UI++; + Instruction *UserI = dyn_cast<Instruction>(U->getUser()); + if (!UserI) + continue; + + // Replace it with the 'continue' side if in the main loop body, and the + // unswitched if in the cloned blocks. + if (DT.dominates(LoopPH, UserI->getParent())) + U->set(ContinueReplacement); + else if (ReplaceUnswitched && + DT.dominates(ClonedPH, UserI->getParent())) + U->set(UnswitchedReplacement); + } + } + + // We can change which blocks are exit blocks of all the cloned sibling + // loops, the current loop, and any parent loops which shared exit blocks + // with the current loop. As a consequence, we need to re-form LCSSA for + // them. But we shouldn't need to re-form LCSSA for any child loops. + // FIXME: This could be made more efficient by tracking which exit blocks are + // new, and focusing on them, but that isn't likely to be necessary. + // + // In order to reasonably rebuild LCSSA we need to walk inside-out across the + // loop nest and update every loop that could have had its exits changed. We + // also need to cover any intervening loops. We add all of these loops to + // a list and sort them by loop depth to achieve this without updating + // unnecessary loops. + auto UpdateLoop = [&](Loop &UpdateL) { +#ifndef NDEBUG + UpdateL.verifyLoop(); + for (Loop *ChildL : UpdateL) { + ChildL->verifyLoop(); + assert(ChildL->isRecursivelyLCSSAForm(DT, LI) && + "Perturbed a child loop's LCSSA form!"); + } +#endif + // First build LCSSA for this loop so that we can preserve it when + // forming dedicated exits. We don't want to perturb some other loop's + // LCSSA while doing that CFG edit. + formLCSSA(UpdateL, DT, &LI, nullptr); + + // For loops reached by this loop's original exit blocks we may + // introduced new, non-dedicated exits. At least try to re-form dedicated + // exits for these loops. This may fail if they couldn't have dedicated + // exits to start with. + formDedicatedExitBlocks(&UpdateL, &DT, &LI, MSSAU, /*PreserveLCSSA*/ true); + }; + + // For non-child cloned loops and hoisted loops, we just need to update LCSSA + // and we can do it in any order as they don't nest relative to each other. + // + // Also check if any of the loops we have updated have become top-level loops + // as that will necessitate widening the outer loop scope. + for (Loop *UpdatedL : + llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) { + UpdateLoop(*UpdatedL); + if (!UpdatedL->getParentLoop()) + OuterExitL = nullptr; + } + if (IsStillLoop) { + UpdateLoop(L); + if (!L.getParentLoop()) + OuterExitL = nullptr; + } + + // If the original loop had exit blocks, walk up through the outer most loop + // of those exit blocks to update LCSSA and form updated dedicated exits. + if (OuterExitL != &L) + for (Loop *OuterL = ParentL; OuterL != OuterExitL; + OuterL = OuterL->getParentLoop()) + UpdateLoop(*OuterL); + +#ifndef NDEBUG + // Verify the entire loop structure to catch any incorrect updates before we + // progress in the pass pipeline. + LI.verify(DT); +#endif + + // Now that we've unswitched something, make callbacks to report the changes. + // For that we need to merge together the updated loops and the cloned loops + // and check whether the original loop survived. + SmallVector<Loop *, 4> SibLoops; + for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) + if (UpdatedL->getParentLoop() == ParentL) + SibLoops.push_back(UpdatedL); + UnswitchCB(IsStillLoop, SibLoops); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + if (BI) + ++NumBranches; + else + ++NumSwitches; +} + +/// Recursively compute the cost of a dominator subtree based on the per-block +/// cost map provided. +/// +/// The recursive computation is memozied into the provided DT-indexed cost map +/// to allow querying it for most nodes in the domtree without it becoming +/// quadratic. +static int +computeDomSubtreeCost(DomTreeNode &N, + const SmallDenseMap<BasicBlock *, int, 4> &BBCostMap, + SmallDenseMap<DomTreeNode *, int, 4> &DTCostMap) { + // Don't accumulate cost (or recurse through) blocks not in our block cost + // map and thus not part of the duplication cost being considered. + auto BBCostIt = BBCostMap.find(N.getBlock()); + if (BBCostIt == BBCostMap.end()) + return 0; + + // Lookup this node to see if we already computed its cost. + auto DTCostIt = DTCostMap.find(&N); + if (DTCostIt != DTCostMap.end()) + return DTCostIt->second; + + // If not, we have to compute it. We can't use insert above and update + // because computing the cost may insert more things into the map. + int Cost = std::accumulate( + N.begin(), N.end(), BBCostIt->second, [&](int Sum, DomTreeNode *ChildN) { + return Sum + computeDomSubtreeCost(*ChildN, BBCostMap, DTCostMap); + }); + bool Inserted = DTCostMap.insert({&N, Cost}).second; + (void)Inserted; + assert(Inserted && "Should not insert a node while visiting children!"); + return Cost; +} + +/// Turns a llvm.experimental.guard intrinsic into implicit control flow branch, +/// making the following replacement: +/// +/// --code before guard-- +/// call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ] +/// --code after guard-- +/// +/// into +/// +/// --code before guard-- +/// br i1 %cond, label %guarded, label %deopt +/// +/// guarded: +/// --code after guard-- +/// +/// deopt: +/// call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ] +/// unreachable +/// +/// It also makes all relevant DT and LI updates, so that all structures are in +/// valid state after this transform. +static BranchInst * +turnGuardIntoBranch(IntrinsicInst *GI, Loop &L, + SmallVectorImpl<BasicBlock *> &ExitBlocks, + DominatorTree &DT, LoopInfo &LI, MemorySSAUpdater *MSSAU) { + SmallVector<DominatorTree::UpdateType, 4> DTUpdates; + LLVM_DEBUG(dbgs() << "Turning " << *GI << " into a branch.\n"); + BasicBlock *CheckBB = GI->getParent(); + + if (MSSAU && VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + + // Remove all CheckBB's successors from DomTree. A block can be seen among + // successors more than once, but for DomTree it should be added only once. + SmallPtrSet<BasicBlock *, 4> Successors; + for (auto *Succ : successors(CheckBB)) + if (Successors.insert(Succ).second) + DTUpdates.push_back({DominatorTree::Delete, CheckBB, Succ}); + + Instruction *DeoptBlockTerm = + SplitBlockAndInsertIfThen(GI->getArgOperand(0), GI, true); + BranchInst *CheckBI = cast<BranchInst>(CheckBB->getTerminator()); + // SplitBlockAndInsertIfThen inserts control flow that branches to + // DeoptBlockTerm if the condition is true. We want the opposite. + CheckBI->swapSuccessors(); + + BasicBlock *GuardedBlock = CheckBI->getSuccessor(0); + GuardedBlock->setName("guarded"); + CheckBI->getSuccessor(1)->setName("deopt"); + BasicBlock *DeoptBlock = CheckBI->getSuccessor(1); + + // We now have a new exit block. + ExitBlocks.push_back(CheckBI->getSuccessor(1)); + + if (MSSAU) + MSSAU->moveAllAfterSpliceBlocks(CheckBB, GuardedBlock, GI); + + GI->moveBefore(DeoptBlockTerm); + GI->setArgOperand(0, ConstantInt::getFalse(GI->getContext())); + + // Add new successors of CheckBB into DomTree. + for (auto *Succ : successors(CheckBB)) + DTUpdates.push_back({DominatorTree::Insert, CheckBB, Succ}); + + // Now the blocks that used to be CheckBB's successors are GuardedBlock's + // successors. + for (auto *Succ : Successors) + DTUpdates.push_back({DominatorTree::Insert, GuardedBlock, Succ}); + + // Make proper changes to DT. + DT.applyUpdates(DTUpdates); + // Inform LI of a new loop block. + L.addBasicBlockToLoop(GuardedBlock, LI); + + if (MSSAU) { + MemoryDef *MD = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(GI)); + MSSAU->moveToPlace(MD, DeoptBlock, MemorySSA::End); + if (VerifyMemorySSA) + MSSAU->getMemorySSA()->verifyMemorySSA(); + } + + ++NumGuards; + return CheckBI; +} + +/// Cost multiplier is a way to limit potentially exponential behavior +/// of loop-unswitch. Cost is multipied in proportion of 2^number of unswitch +/// candidates available. Also accounting for the number of "sibling" loops with +/// the idea to account for previous unswitches that already happened on this +/// cluster of loops. There was an attempt to keep this formula simple, +/// just enough to limit the worst case behavior. Even if it is not that simple +/// now it is still not an attempt to provide a detailed heuristic size +/// prediction. +/// +/// TODO: Make a proper accounting of "explosion" effect for all kinds of +/// unswitch candidates, making adequate predictions instead of wild guesses. +/// That requires knowing not just the number of "remaining" candidates but +/// also costs of unswitching for each of these candidates. +static int calculateUnswitchCostMultiplier( + Instruction &TI, Loop &L, LoopInfo &LI, DominatorTree &DT, + ArrayRef<std::pair<Instruction *, TinyPtrVector<Value *>>> + UnswitchCandidates) { + + // Guards and other exiting conditions do not contribute to exponential + // explosion as soon as they dominate the latch (otherwise there might be + // another path to the latch remaining that does not allow to eliminate the + // loop copy on unswitch). + BasicBlock *Latch = L.getLoopLatch(); + BasicBlock *CondBlock = TI.getParent(); + if (DT.dominates(CondBlock, Latch) && + (isGuard(&TI) || + llvm::count_if(successors(&TI), [&L](BasicBlock *SuccBB) { + return L.contains(SuccBB); + }) <= 1)) { + NumCostMultiplierSkipped++; + return 1; + } + + auto *ParentL = L.getParentLoop(); + int SiblingsCount = (ParentL ? ParentL->getSubLoopsVector().size() + : std::distance(LI.begin(), LI.end())); + // Count amount of clones that all the candidates might cause during + // unswitching. Branch/guard counts as 1, switch counts as log2 of its cases. + int UnswitchedClones = 0; + for (auto Candidate : UnswitchCandidates) { + Instruction *CI = Candidate.first; + BasicBlock *CondBlock = CI->getParent(); + bool SkipExitingSuccessors = DT.dominates(CondBlock, Latch); + if (isGuard(CI)) { + if (!SkipExitingSuccessors) + UnswitchedClones++; + continue; + } + int NonExitingSuccessors = llvm::count_if( + successors(CondBlock), [SkipExitingSuccessors, &L](BasicBlock *SuccBB) { + return !SkipExitingSuccessors || L.contains(SuccBB); + }); + UnswitchedClones += Log2_32(NonExitingSuccessors); + } + + // Ignore up to the "unscaled candidates" number of unswitch candidates + // when calculating the power-of-two scaling of the cost. The main idea + // with this control is to allow a small number of unswitches to happen + // and rely more on siblings multiplier (see below) when the number + // of candidates is small. + unsigned ClonesPower = + std::max(UnswitchedClones - (int)UnswitchNumInitialUnscaledCandidates, 0); + + // Allowing top-level loops to spread a bit more than nested ones. + int SiblingsMultiplier = + std::max((ParentL ? SiblingsCount + : SiblingsCount / (int)UnswitchSiblingsToplevelDiv), + 1); + // Compute the cost multiplier in a way that won't overflow by saturating + // at an upper bound. + int CostMultiplier; + if (ClonesPower > Log2_32(UnswitchThreshold) || + SiblingsMultiplier > UnswitchThreshold) + CostMultiplier = UnswitchThreshold; + else + CostMultiplier = std::min(SiblingsMultiplier * (1 << ClonesPower), + (int)UnswitchThreshold); + + LLVM_DEBUG(dbgs() << " Computed multiplier " << CostMultiplier + << " (siblings " << SiblingsMultiplier << " * clones " + << (1 << ClonesPower) << ")" + << " for unswitch candidate: " << TI << "\n"); + return CostMultiplier; +} + +static bool +unswitchBestCondition(Loop &L, DominatorTree &DT, LoopInfo &LI, + AssumptionCache &AC, TargetTransformInfo &TTI, + function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB, + ScalarEvolution *SE, MemorySSAUpdater *MSSAU) { + // Collect all invariant conditions within this loop (as opposed to an inner + // loop which would be handled when visiting that inner loop). + SmallVector<std::pair<Instruction *, TinyPtrVector<Value *>>, 4> + UnswitchCandidates; + + // Whether or not we should also collect guards in the loop. + bool CollectGuards = false; + if (UnswitchGuards) { + auto *GuardDecl = L.getHeader()->getParent()->getParent()->getFunction( + Intrinsic::getName(Intrinsic::experimental_guard)); + if (GuardDecl && !GuardDecl->use_empty()) + CollectGuards = true; + } + + for (auto *BB : L.blocks()) { + if (LI.getLoopFor(BB) != &L) + continue; + + if (CollectGuards) + for (auto &I : *BB) + if (isGuard(&I)) { + auto *Cond = cast<IntrinsicInst>(&I)->getArgOperand(0); + // TODO: Support AND, OR conditions and partial unswitching. + if (!isa<Constant>(Cond) && L.isLoopInvariant(Cond)) + UnswitchCandidates.push_back({&I, {Cond}}); + } + + if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { + // We can only consider fully loop-invariant switch conditions as we need + // to completely eliminate the switch after unswitching. + if (!isa<Constant>(SI->getCondition()) && + L.isLoopInvariant(SI->getCondition()) && !BB->getUniqueSuccessor()) + UnswitchCandidates.push_back({SI, {SI->getCondition()}}); + continue; + } + + auto *BI = dyn_cast<BranchInst>(BB->getTerminator()); + if (!BI || !BI->isConditional() || isa<Constant>(BI->getCondition()) || + BI->getSuccessor(0) == BI->getSuccessor(1)) + continue; + + if (L.isLoopInvariant(BI->getCondition())) { + UnswitchCandidates.push_back({BI, {BI->getCondition()}}); + continue; + } + + Instruction &CondI = *cast<Instruction>(BI->getCondition()); + if (CondI.getOpcode() != Instruction::And && + CondI.getOpcode() != Instruction::Or) + continue; + + TinyPtrVector<Value *> Invariants = + collectHomogenousInstGraphLoopInvariants(L, CondI, LI); + if (Invariants.empty()) + continue; + + UnswitchCandidates.push_back({BI, std::move(Invariants)}); + } + + // If we didn't find any candidates, we're done. + if (UnswitchCandidates.empty()) + return false; + + // Check if there are irreducible CFG cycles in this loop. If so, we cannot + // easily unswitch non-trivial edges out of the loop. Doing so might turn the + // irreducible control flow into reducible control flow and introduce new + // loops "out of thin air". If we ever discover important use cases for doing + // this, we can add support to loop unswitch, but it is a lot of complexity + // for what seems little or no real world benefit. + LoopBlocksRPO RPOT(&L); + RPOT.perform(&LI); + if (containsIrreducibleCFG<const BasicBlock *>(RPOT, LI)) + return false; + + SmallVector<BasicBlock *, 4> ExitBlocks; + L.getUniqueExitBlocks(ExitBlocks); + + // We cannot unswitch if exit blocks contain a cleanuppad instruction as we + // don't know how to split those exit blocks. + // FIXME: We should teach SplitBlock to handle this and remove this + // restriction. + for (auto *ExitBB : ExitBlocks) + if (isa<CleanupPadInst>(ExitBB->getFirstNonPHI())) { + dbgs() << "Cannot unswitch because of cleanuppad in exit block\n"; + return false; + } + + LLVM_DEBUG( + dbgs() << "Considering " << UnswitchCandidates.size() + << " non-trivial loop invariant conditions for unswitching.\n"); + + // Given that unswitching these terminators will require duplicating parts of + // the loop, so we need to be able to model that cost. Compute the ephemeral + // values and set up a data structure to hold per-BB costs. We cache each + // block's cost so that we don't recompute this when considering different + // subsets of the loop for duplication during unswitching. + SmallPtrSet<const Value *, 4> EphValues; + CodeMetrics::collectEphemeralValues(&L, &AC, EphValues); + SmallDenseMap<BasicBlock *, int, 4> BBCostMap; + + // Compute the cost of each block, as well as the total loop cost. Also, bail + // out if we see instructions which are incompatible with loop unswitching + // (convergent, noduplicate, or cross-basic-block tokens). + // FIXME: We might be able to safely handle some of these in non-duplicated + // regions. + int LoopCost = 0; + for (auto *BB : L.blocks()) { + int Cost = 0; + for (auto &I : *BB) { + if (EphValues.count(&I)) + continue; + + if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB)) + return false; + if (auto CS = CallSite(&I)) + if (CS.isConvergent() || CS.cannotDuplicate()) + return false; + + Cost += TTI.getUserCost(&I); + } + assert(Cost >= 0 && "Must not have negative costs!"); + LoopCost += Cost; + assert(LoopCost >= 0 && "Must not have negative loop costs!"); + BBCostMap[BB] = Cost; + } + LLVM_DEBUG(dbgs() << " Total loop cost: " << LoopCost << "\n"); + + // Now we find the best candidate by searching for the one with the following + // properties in order: + // + // 1) An unswitching cost below the threshold + // 2) The smallest number of duplicated unswitch candidates (to avoid + // creating redundant subsequent unswitching) + // 3) The smallest cost after unswitching. + // + // We prioritize reducing fanout of unswitch candidates provided the cost + // remains below the threshold because this has a multiplicative effect. + // + // This requires memoizing each dominator subtree to avoid redundant work. + // + // FIXME: Need to actually do the number of candidates part above. + SmallDenseMap<DomTreeNode *, int, 4> DTCostMap; + // Given a terminator which might be unswitched, computes the non-duplicated + // cost for that terminator. + auto ComputeUnswitchedCost = [&](Instruction &TI, bool FullUnswitch) { + BasicBlock &BB = *TI.getParent(); + SmallPtrSet<BasicBlock *, 4> Visited; + + int Cost = LoopCost; + for (BasicBlock *SuccBB : successors(&BB)) { + // Don't count successors more than once. + if (!Visited.insert(SuccBB).second) + continue; + + // If this is a partial unswitch candidate, then it must be a conditional + // branch with a condition of either `or` or `and`. In that case, one of + // the successors is necessarily duplicated, so don't even try to remove + // its cost. + if (!FullUnswitch) { + auto &BI = cast<BranchInst>(TI); + if (cast<Instruction>(BI.getCondition())->getOpcode() == + Instruction::And) { + if (SuccBB == BI.getSuccessor(1)) + continue; + } else { + assert(cast<Instruction>(BI.getCondition())->getOpcode() == + Instruction::Or && + "Only `and` and `or` conditions can result in a partial " + "unswitch!"); + if (SuccBB == BI.getSuccessor(0)) + continue; + } + } + + // This successor's domtree will not need to be duplicated after + // unswitching if the edge to the successor dominates it (and thus the + // entire tree). This essentially means there is no other path into this + // subtree and so it will end up live in only one clone of the loop. + if (SuccBB->getUniquePredecessor() || + llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) { + return PredBB == &BB || DT.dominates(SuccBB, PredBB); + })) { + Cost -= computeDomSubtreeCost(*DT[SuccBB], BBCostMap, DTCostMap); + assert(Cost >= 0 && + "Non-duplicated cost should never exceed total loop cost!"); + } + } + + // Now scale the cost by the number of unique successors minus one. We + // subtract one because there is already at least one copy of the entire + // loop. This is computing the new cost of unswitching a condition. + // Note that guards always have 2 unique successors that are implicit and + // will be materialized if we decide to unswitch it. + int SuccessorsCount = isGuard(&TI) ? 2 : Visited.size(); + assert(SuccessorsCount > 1 && + "Cannot unswitch a condition without multiple distinct successors!"); + return Cost * (SuccessorsCount - 1); + }; + Instruction *BestUnswitchTI = nullptr; + int BestUnswitchCost; + ArrayRef<Value *> BestUnswitchInvariants; + for (auto &TerminatorAndInvariants : UnswitchCandidates) { + Instruction &TI = *TerminatorAndInvariants.first; + ArrayRef<Value *> Invariants = TerminatorAndInvariants.second; + BranchInst *BI = dyn_cast<BranchInst>(&TI); + int CandidateCost = ComputeUnswitchedCost( + TI, /*FullUnswitch*/ !BI || (Invariants.size() == 1 && + Invariants[0] == BI->getCondition())); + // Calculate cost multiplier which is a tool to limit potentially + // exponential behavior of loop-unswitch. + if (EnableUnswitchCostMultiplier) { + int CostMultiplier = + calculateUnswitchCostMultiplier(TI, L, LI, DT, UnswitchCandidates); + assert( + (CostMultiplier > 0 && CostMultiplier <= UnswitchThreshold) && + "cost multiplier needs to be in the range of 1..UnswitchThreshold"); + CandidateCost *= CostMultiplier; + LLVM_DEBUG(dbgs() << " Computed cost of " << CandidateCost + << " (multiplier: " << CostMultiplier << ")" + << " for unswitch candidate: " << TI << "\n"); + } else { + LLVM_DEBUG(dbgs() << " Computed cost of " << CandidateCost + << " for unswitch candidate: " << TI << "\n"); + } + + if (!BestUnswitchTI || CandidateCost < BestUnswitchCost) { + BestUnswitchTI = &TI; + BestUnswitchCost = CandidateCost; + BestUnswitchInvariants = Invariants; + } + } + + if (BestUnswitchCost >= UnswitchThreshold) { + LLVM_DEBUG(dbgs() << "Cannot unswitch, lowest cost found: " + << BestUnswitchCost << "\n"); + return false; + } + + // If the best candidate is a guard, turn it into a branch. + if (isGuard(BestUnswitchTI)) + BestUnswitchTI = turnGuardIntoBranch(cast<IntrinsicInst>(BestUnswitchTI), L, + ExitBlocks, DT, LI, MSSAU); + + LLVM_DEBUG(dbgs() << " Unswitching non-trivial (cost = " + << BestUnswitchCost << ") terminator: " << *BestUnswitchTI + << "\n"); + unswitchNontrivialInvariants(L, *BestUnswitchTI, BestUnswitchInvariants, + ExitBlocks, DT, LI, AC, UnswitchCB, SE, MSSAU); + return true; +} + +/// Unswitch control flow predicated on loop invariant conditions. +/// +/// This first hoists all branches or switches which are trivial (IE, do not +/// require duplicating any part of the loop) out of the loop body. It then +/// looks at other loop invariant control flows and tries to unswitch those as +/// well by cloning the loop if the result is small enough. +/// +/// The `DT`, `LI`, `AC`, `TTI` parameters are required analyses that are also +/// updated based on the unswitch. +/// The `MSSA` analysis is also updated if valid (i.e. its use is enabled). +/// +/// If either `NonTrivial` is true or the flag `EnableNonTrivialUnswitch` is +/// true, we will attempt to do non-trivial unswitching as well as trivial +/// unswitching. +/// +/// The `UnswitchCB` callback provided will be run after unswitching is +/// complete, with the first parameter set to `true` if the provided loop +/// remains a loop, and a list of new sibling loops created. +/// +/// If `SE` is non-null, we will update that analysis based on the unswitching +/// done. +static bool unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI, + AssumptionCache &AC, TargetTransformInfo &TTI, + bool NonTrivial, + function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB, + ScalarEvolution *SE, MemorySSAUpdater *MSSAU) { + assert(L.isRecursivelyLCSSAForm(DT, LI) && + "Loops must be in LCSSA form before unswitching."); + bool Changed = false; + + // Must be in loop simplified form: we need a preheader and dedicated exits. + if (!L.isLoopSimplifyForm()) + return false; + + // Try trivial unswitch first before loop over other basic blocks in the loop. + if (unswitchAllTrivialConditions(L, DT, LI, SE, MSSAU)) { + // If we unswitched successfully we will want to clean up the loop before + // processing it further so just mark it as unswitched and return. + UnswitchCB(/*CurrentLoopValid*/ true, {}); + return true; + } + + // If we're not doing non-trivial unswitching, we're done. We both accept + // a parameter but also check a local flag that can be used for testing + // a debugging. + if (!NonTrivial && !EnableNonTrivialUnswitch) + return false; + + // For non-trivial unswitching, because it often creates new loops, we rely on + // the pass manager to iterate on the loops rather than trying to immediately + // reach a fixed point. There is no substantial advantage to iterating + // internally, and if any of the new loops are simplified enough to contain + // trivial unswitching we want to prefer those. + + // Try to unswitch the best invariant condition. We prefer this full unswitch to + // a partial unswitch when possible below the threshold. + if (unswitchBestCondition(L, DT, LI, AC, TTI, UnswitchCB, SE, MSSAU)) + return true; + + // No other opportunities to unswitch. + return Changed; +} + +PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM, + LoopStandardAnalysisResults &AR, + LPMUpdater &U) { + Function &F = *L.getHeader()->getParent(); + (void)F; + + LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << L + << "\n"); + + // Save the current loop name in a variable so that we can report it even + // after it has been deleted. + std::string LoopName = L.getName(); + + auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid, + ArrayRef<Loop *> NewLoops) { + // If we did a non-trivial unswitch, we have added new (cloned) loops. + if (!NewLoops.empty()) + U.addSiblingLoops(NewLoops); + + // If the current loop remains valid, we should revisit it to catch any + // other unswitch opportunities. Otherwise, we need to mark it as deleted. + if (CurrentLoopValid) + U.revisitCurrentLoop(); + else + U.markLoopAsDeleted(L, LoopName); + }; + + Optional<MemorySSAUpdater> MSSAU; + if (AR.MSSA) { + MSSAU = MemorySSAUpdater(AR.MSSA); + if (VerifyMemorySSA) + AR.MSSA->verifyMemorySSA(); + } + if (!unswitchLoop(L, AR.DT, AR.LI, AR.AC, AR.TTI, NonTrivial, UnswitchCB, + &AR.SE, MSSAU.hasValue() ? MSSAU.getPointer() : nullptr)) + return PreservedAnalyses::all(); + + if (AR.MSSA && VerifyMemorySSA) + AR.MSSA->verifyMemorySSA(); + + // Historically this pass has had issues with the dominator tree so verify it + // in asserts builds. + assert(AR.DT.verify(DominatorTree::VerificationLevel::Fast)); + + auto PA = getLoopPassPreservedAnalyses(); + if (EnableMSSALoopDependency) + PA.preserve<MemorySSAAnalysis>(); + return PA; +} + +namespace { + +class SimpleLoopUnswitchLegacyPass : public LoopPass { + bool NonTrivial; + +public: + static char ID; // Pass ID, replacement for typeid + + explicit SimpleLoopUnswitchLegacyPass(bool NonTrivial = false) + : LoopPass(ID), NonTrivial(NonTrivial) { + initializeSimpleLoopUnswitchLegacyPassPass( + *PassRegistry::getPassRegistry()); + } + + bool runOnLoop(Loop *L, LPPassManager &LPM) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<TargetTransformInfoWrapperPass>(); + if (EnableMSSALoopDependency) { + AU.addRequired<MemorySSAWrapperPass>(); + AU.addPreserved<MemorySSAWrapperPass>(); + } + getLoopAnalysisUsage(AU); + } +}; + +} // end anonymous namespace + +bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) { + if (skipLoop(L)) + return false; + + Function &F = *L->getHeader()->getParent(); + + LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << *L + << "\n"); + + auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); + auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); + auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); + MemorySSA *MSSA = nullptr; + Optional<MemorySSAUpdater> MSSAU; + if (EnableMSSALoopDependency) { + MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA(); + MSSAU = MemorySSAUpdater(MSSA); + } + + auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>(); + auto *SE = SEWP ? &SEWP->getSE() : nullptr; + + auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid, + ArrayRef<Loop *> NewLoops) { + // If we did a non-trivial unswitch, we have added new (cloned) loops. + for (auto *NewL : NewLoops) + LPM.addLoop(*NewL); + + // If the current loop remains valid, re-add it to the queue. This is + // a little wasteful as we'll finish processing the current loop as well, + // but it is the best we can do in the old PM. + if (CurrentLoopValid) + LPM.addLoop(*L); + else + LPM.markLoopAsDeleted(*L); + }; + + if (MSSA && VerifyMemorySSA) + MSSA->verifyMemorySSA(); + + bool Changed = unswitchLoop(*L, DT, LI, AC, TTI, NonTrivial, UnswitchCB, SE, + MSSAU.hasValue() ? MSSAU.getPointer() : nullptr); + + if (MSSA && VerifyMemorySSA) + MSSA->verifyMemorySSA(); + + // If anything was unswitched, also clear any cached information about this + // loop. + LPM.deleteSimpleAnalysisLoop(L); + + // Historically this pass has had issues with the dominator tree so verify it + // in asserts builds. + assert(DT.verify(DominatorTree::VerificationLevel::Fast)); + + return Changed; +} + +char SimpleLoopUnswitchLegacyPass::ID = 0; +INITIALIZE_PASS_BEGIN(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch", + "Simple unswitch loops", false, false) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(LoopPass) +INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) +INITIALIZE_PASS_END(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch", + "Simple unswitch loops", false, false) + +Pass *llvm::createSimpleLoopUnswitchLegacyPass(bool NonTrivial) { + return new SimpleLoopUnswitchLegacyPass(NonTrivial); +} |