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+//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the LoopInfo class that is used to identify natural loops
+// and determine the loop depth of various nodes of the CFG. Note that the
+// loops identified may actually be several natural loops that share the same
+// header node... not just a single natural loop.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/ScopeExit.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/Analysis/IVDescriptors.h"
+#include "llvm/Analysis/LoopInfoImpl.h"
+#include "llvm/Analysis/LoopIterator.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Config/llvm-config.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugLoc.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/IRPrintingPasses.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+using namespace llvm;
+
+// Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
+template class llvm::LoopBase<BasicBlock, Loop>;
+template class llvm::LoopInfoBase<BasicBlock, Loop>;
+
+// Always verify loopinfo if expensive checking is enabled.
+#ifdef EXPENSIVE_CHECKS
+bool llvm::VerifyLoopInfo = true;
+#else
+bool llvm::VerifyLoopInfo = false;
+#endif
+static cl::opt<bool, true>
+ VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
+ cl::Hidden, cl::desc("Verify loop info (time consuming)"));
+
+//===----------------------------------------------------------------------===//
+// Loop implementation
+//
+
+bool Loop::isLoopInvariant(const Value *V) const {
+ if (const Instruction *I = dyn_cast<Instruction>(V))
+ return !contains(I);
+ return true; // All non-instructions are loop invariant
+}
+
+bool Loop::hasLoopInvariantOperands(const Instruction *I) const {
+ return all_of(I->operands(), [this](Value *V) { return isLoopInvariant(V); });
+}
+
+bool Loop::makeLoopInvariant(Value *V, bool &Changed, Instruction *InsertPt,
+ MemorySSAUpdater *MSSAU) const {
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ return makeLoopInvariant(I, Changed, InsertPt, MSSAU);
+ return true; // All non-instructions are loop-invariant.
+}
+
+bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
+ Instruction *InsertPt,
+ MemorySSAUpdater *MSSAU) const {
+ // Test if the value is already loop-invariant.
+ if (isLoopInvariant(I))
+ return true;
+ if (!isSafeToSpeculativelyExecute(I))
+ return false;
+ if (I->mayReadFromMemory())
+ return false;
+ // EH block instructions are immobile.
+ if (I->isEHPad())
+ return false;
+ // Determine the insertion point, unless one was given.
+ if (!InsertPt) {
+ BasicBlock *Preheader = getLoopPreheader();
+ // Without a preheader, hoisting is not feasible.
+ if (!Preheader)
+ return false;
+ InsertPt = Preheader->getTerminator();
+ }
+ // Don't hoist instructions with loop-variant operands.
+ for (Value *Operand : I->operands())
+ if (!makeLoopInvariant(Operand, Changed, InsertPt, MSSAU))
+ return false;
+
+ // Hoist.
+ I->moveBefore(InsertPt);
+ if (MSSAU)
+ if (auto *MUD = MSSAU->getMemorySSA()->getMemoryAccess(I))
+ MSSAU->moveToPlace(MUD, InsertPt->getParent(), MemorySSA::End);
+
+ // There is possibility of hoisting this instruction above some arbitrary
+ // condition. Any metadata defined on it can be control dependent on this
+ // condition. Conservatively strip it here so that we don't give any wrong
+ // information to the optimizer.
+ I->dropUnknownNonDebugMetadata();
+
+ Changed = true;
+ return true;
+}
+
+bool Loop::getIncomingAndBackEdge(BasicBlock *&Incoming,
+ BasicBlock *&Backedge) const {
+ BasicBlock *H = getHeader();
+
+ Incoming = nullptr;
+ Backedge = nullptr;
+ pred_iterator PI = pred_begin(H);
+ assert(PI != pred_end(H) && "Loop must have at least one backedge!");
+ Backedge = *PI++;
+ if (PI == pred_end(H))
+ return false; // dead loop
+ Incoming = *PI++;
+ if (PI != pred_end(H))
+ return false; // multiple backedges?
+
+ if (contains(Incoming)) {
+ if (contains(Backedge))
+ return false;
+ std::swap(Incoming, Backedge);
+ } else if (!contains(Backedge))
+ return false;
+
+ assert(Incoming && Backedge && "expected non-null incoming and backedges");
+ return true;
+}
+
+PHINode *Loop::getCanonicalInductionVariable() const {
+ BasicBlock *H = getHeader();
+
+ BasicBlock *Incoming = nullptr, *Backedge = nullptr;
+ if (!getIncomingAndBackEdge(Incoming, Backedge))
+ return nullptr;
+
+ // Loop over all of the PHI nodes, looking for a canonical indvar.
+ for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
+ if (CI->isZero())
+ if (Instruction *Inc =
+ dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
+ if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
+ if (CI->isOne())
+ return PN;
+ }
+ return nullptr;
+}
+
+/// Get the latch condition instruction.
+static ICmpInst *getLatchCmpInst(const Loop &L) {
+ if (BasicBlock *Latch = L.getLoopLatch())
+ if (BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator()))
+ if (BI->isConditional())
+ return dyn_cast<ICmpInst>(BI->getCondition());
+
+ return nullptr;
+}
+
+/// Return the final value of the loop induction variable if found.
+static Value *findFinalIVValue(const Loop &L, const PHINode &IndVar,
+ const Instruction &StepInst) {
+ ICmpInst *LatchCmpInst = getLatchCmpInst(L);
+ if (!LatchCmpInst)
+ return nullptr;
+
+ Value *Op0 = LatchCmpInst->getOperand(0);
+ Value *Op1 = LatchCmpInst->getOperand(1);
+ if (Op0 == &IndVar || Op0 == &StepInst)
+ return Op1;
+
+ if (Op1 == &IndVar || Op1 == &StepInst)
+ return Op0;
+
+ return nullptr;
+}
+
+Optional<Loop::LoopBounds> Loop::LoopBounds::getBounds(const Loop &L,
+ PHINode &IndVar,
+ ScalarEvolution &SE) {
+ InductionDescriptor IndDesc;
+ if (!InductionDescriptor::isInductionPHI(&IndVar, &L, &SE, IndDesc))
+ return None;
+
+ Value *InitialIVValue = IndDesc.getStartValue();
+ Instruction *StepInst = IndDesc.getInductionBinOp();
+ if (!InitialIVValue || !StepInst)
+ return None;
+
+ const SCEV *Step = IndDesc.getStep();
+ Value *StepInstOp1 = StepInst->getOperand(1);
+ Value *StepInstOp0 = StepInst->getOperand(0);
+ Value *StepValue = nullptr;
+ if (SE.getSCEV(StepInstOp1) == Step)
+ StepValue = StepInstOp1;
+ else if (SE.getSCEV(StepInstOp0) == Step)
+ StepValue = StepInstOp0;
+
+ Value *FinalIVValue = findFinalIVValue(L, IndVar, *StepInst);
+ if (!FinalIVValue)
+ return None;
+
+ return LoopBounds(L, *InitialIVValue, *StepInst, StepValue, *FinalIVValue,
+ SE);
+}
+
+using Direction = Loop::LoopBounds::Direction;
+
+ICmpInst::Predicate Loop::LoopBounds::getCanonicalPredicate() const {
+ BasicBlock *Latch = L.getLoopLatch();
+ assert(Latch && "Expecting valid latch");
+
+ BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator());
+ assert(BI && BI->isConditional() && "Expecting conditional latch branch");
+
+ ICmpInst *LatchCmpInst = dyn_cast<ICmpInst>(BI->getCondition());
+ assert(LatchCmpInst &&
+ "Expecting the latch compare instruction to be a CmpInst");
+
+ // Need to inverse the predicate when first successor is not the loop
+ // header
+ ICmpInst::Predicate Pred = (BI->getSuccessor(0) == L.getHeader())
+ ? LatchCmpInst->getPredicate()
+ : LatchCmpInst->getInversePredicate();
+
+ if (LatchCmpInst->getOperand(0) == &getFinalIVValue())
+ Pred = ICmpInst::getSwappedPredicate(Pred);
+
+ // Need to flip strictness of the predicate when the latch compare instruction
+ // is not using StepInst
+ if (LatchCmpInst->getOperand(0) == &getStepInst() ||
+ LatchCmpInst->getOperand(1) == &getStepInst())
+ return Pred;
+
+ // Cannot flip strictness of NE and EQ
+ if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
+ return ICmpInst::getFlippedStrictnessPredicate(Pred);
+
+ Direction D = getDirection();
+ if (D == Direction::Increasing)
+ return ICmpInst::ICMP_SLT;
+
+ if (D == Direction::Decreasing)
+ return ICmpInst::ICMP_SGT;
+
+ // If cannot determine the direction, then unable to find the canonical
+ // predicate
+ return ICmpInst::BAD_ICMP_PREDICATE;
+}
+
+Direction Loop::LoopBounds::getDirection() const {
+ if (const SCEVAddRecExpr *StepAddRecExpr =
+ dyn_cast<SCEVAddRecExpr>(SE.getSCEV(&getStepInst())))
+ if (const SCEV *StepRecur = StepAddRecExpr->getStepRecurrence(SE)) {
+ if (SE.isKnownPositive(StepRecur))
+ return Direction::Increasing;
+ if (SE.isKnownNegative(StepRecur))
+ return Direction::Decreasing;
+ }
+
+ return Direction::Unknown;
+}
+
+Optional<Loop::LoopBounds> Loop::getBounds(ScalarEvolution &SE) const {
+ if (PHINode *IndVar = getInductionVariable(SE))
+ return LoopBounds::getBounds(*this, *IndVar, SE);
+
+ return None;
+}
+
+PHINode *Loop::getInductionVariable(ScalarEvolution &SE) const {
+ if (!isLoopSimplifyForm())
+ return nullptr;
+
+ BasicBlock *Header = getHeader();
+ assert(Header && "Expected a valid loop header");
+ ICmpInst *CmpInst = getLatchCmpInst(*this);
+ if (!CmpInst)
+ return nullptr;
+
+ Instruction *LatchCmpOp0 = dyn_cast<Instruction>(CmpInst->getOperand(0));
+ Instruction *LatchCmpOp1 = dyn_cast<Instruction>(CmpInst->getOperand(1));
+
+ for (PHINode &IndVar : Header->phis()) {
+ InductionDescriptor IndDesc;
+ if (!InductionDescriptor::isInductionPHI(&IndVar, this, &SE, IndDesc))
+ continue;
+
+ Instruction *StepInst = IndDesc.getInductionBinOp();
+
+ // case 1:
+ // IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]
+ // StepInst = IndVar + step
+ // cmp = StepInst < FinalValue
+ if (StepInst == LatchCmpOp0 || StepInst == LatchCmpOp1)
+ return &IndVar;
+
+ // case 2:
+ // IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]
+ // StepInst = IndVar + step
+ // cmp = IndVar < FinalValue
+ if (&IndVar == LatchCmpOp0 || &IndVar == LatchCmpOp1)
+ return &IndVar;
+ }
+
+ return nullptr;
+}
+
+bool Loop::getInductionDescriptor(ScalarEvolution &SE,
+ InductionDescriptor &IndDesc) const {
+ if (PHINode *IndVar = getInductionVariable(SE))
+ return InductionDescriptor::isInductionPHI(IndVar, this, &SE, IndDesc);
+
+ return false;
+}
+
+bool Loop::isAuxiliaryInductionVariable(PHINode &AuxIndVar,
+ ScalarEvolution &SE) const {
+ // Located in the loop header
+ BasicBlock *Header = getHeader();
+ if (AuxIndVar.getParent() != Header)
+ return false;
+
+ // No uses outside of the loop
+ for (User *U : AuxIndVar.users())
+ if (const Instruction *I = dyn_cast<Instruction>(U))
+ if (!contains(I))
+ return false;
+
+ InductionDescriptor IndDesc;
+ if (!InductionDescriptor::isInductionPHI(&AuxIndVar, this, &SE, IndDesc))
+ return false;
+
+ // The step instruction opcode should be add or sub.
+ if (IndDesc.getInductionOpcode() != Instruction::Add &&
+ IndDesc.getInductionOpcode() != Instruction::Sub)
+ return false;
+
+ // Incremented by a loop invariant step for each loop iteration
+ return SE.isLoopInvariant(IndDesc.getStep(), this);
+}
+
+BranchInst *Loop::getLoopGuardBranch() const {
+ if (!isLoopSimplifyForm())
+ return nullptr;
+
+ BasicBlock *Preheader = getLoopPreheader();
+ BasicBlock *Latch = getLoopLatch();
+ assert(Preheader && Latch &&
+ "Expecting a loop with valid preheader and latch");
+
+ // Loop should be in rotate form.
+ if (!isLoopExiting(Latch))
+ return nullptr;
+
+ // Disallow loops with more than one unique exit block, as we do not verify
+ // that GuardOtherSucc post dominates all exit blocks.
+ BasicBlock *ExitFromLatch = getUniqueExitBlock();
+ if (!ExitFromLatch)
+ return nullptr;
+
+ BasicBlock *ExitFromLatchSucc = ExitFromLatch->getUniqueSuccessor();
+ if (!ExitFromLatchSucc)
+ return nullptr;
+
+ BasicBlock *GuardBB = Preheader->getUniquePredecessor();
+ if (!GuardBB)
+ return nullptr;
+
+ assert(GuardBB->getTerminator() && "Expecting valid guard terminator");
+
+ BranchInst *GuardBI = dyn_cast<BranchInst>(GuardBB->getTerminator());
+ if (!GuardBI || GuardBI->isUnconditional())
+ return nullptr;
+
+ BasicBlock *GuardOtherSucc = (GuardBI->getSuccessor(0) == Preheader)
+ ? GuardBI->getSuccessor(1)
+ : GuardBI->getSuccessor(0);
+ return (GuardOtherSucc == ExitFromLatchSucc) ? GuardBI : nullptr;
+}
+
+bool Loop::isCanonical(ScalarEvolution &SE) const {
+ InductionDescriptor IndDesc;
+ if (!getInductionDescriptor(SE, IndDesc))
+ return false;
+
+ ConstantInt *Init = dyn_cast_or_null<ConstantInt>(IndDesc.getStartValue());
+ if (!Init || !Init->isZero())
+ return false;
+
+ if (IndDesc.getInductionOpcode() != Instruction::Add)
+ return false;
+
+ ConstantInt *Step = IndDesc.getConstIntStepValue();
+ if (!Step || !Step->isOne())
+ return false;
+
+ return true;
+}
+
+// Check that 'BB' doesn't have any uses outside of the 'L'
+static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
+ DominatorTree &DT) {
+ for (const Instruction &I : BB) {
+ // Tokens can't be used in PHI nodes and live-out tokens prevent loop
+ // optimizations, so for the purposes of considered LCSSA form, we
+ // can ignore them.
+ if (I.getType()->isTokenTy())
+ continue;
+
+ for (const Use &U : I.uses()) {
+ const Instruction *UI = cast<Instruction>(U.getUser());
+ const BasicBlock *UserBB = UI->getParent();
+ if (const PHINode *P = dyn_cast<PHINode>(UI))
+ UserBB = P->getIncomingBlock(U);
+
+ // Check the current block, as a fast-path, before checking whether
+ // the use is anywhere in the loop. Most values are used in the same
+ // block they are defined in. Also, blocks not reachable from the
+ // entry are special; uses in them don't need to go through PHIs.
+ if (UserBB != &BB && !L.contains(UserBB) &&
+ DT.isReachableFromEntry(UserBB))
+ return false;
+ }
+ }
+ return true;
+}
+
+bool Loop::isLCSSAForm(DominatorTree &DT) const {
+ // For each block we check that it doesn't have any uses outside of this loop.
+ return all_of(this->blocks(), [&](const BasicBlock *BB) {
+ return isBlockInLCSSAForm(*this, *BB, DT);
+ });
+}
+
+bool Loop::isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const {
+ // For each block we check that it doesn't have any uses outside of its
+ // innermost loop. This process will transitively guarantee that the current
+ // loop and all of the nested loops are in LCSSA form.
+ return all_of(this->blocks(), [&](const BasicBlock *BB) {
+ return isBlockInLCSSAForm(*LI.getLoopFor(BB), *BB, DT);
+ });
+}
+
+bool Loop::isLoopSimplifyForm() const {
+ // Normal-form loops have a preheader, a single backedge, and all of their
+ // exits have all their predecessors inside the loop.
+ return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
+}
+
+// Routines that reform the loop CFG and split edges often fail on indirectbr.
+bool Loop::isSafeToClone() const {
+ // Return false if any loop blocks contain indirectbrs, or there are any calls
+ // to noduplicate functions.
+ // FIXME: it should be ok to clone CallBrInst's if we correctly update the
+ // operand list to reflect the newly cloned labels.
+ for (BasicBlock *BB : this->blocks()) {
+ if (isa<IndirectBrInst>(BB->getTerminator()) ||
+ isa<CallBrInst>(BB->getTerminator()))
+ return false;
+
+ for (Instruction &I : *BB)
+ if (auto CS = CallSite(&I))
+ if (CS.cannotDuplicate())
+ return false;
+ }
+ return true;
+}
+
+MDNode *Loop::getLoopID() const {
+ MDNode *LoopID = nullptr;
+
+ // Go through the latch blocks and check the terminator for the metadata.
+ SmallVector<BasicBlock *, 4> LatchesBlocks;
+ getLoopLatches(LatchesBlocks);
+ for (BasicBlock *BB : LatchesBlocks) {
+ Instruction *TI = BB->getTerminator();
+ MDNode *MD = TI->getMetadata(LLVMContext::MD_loop);
+
+ if (!MD)
+ return nullptr;
+
+ if (!LoopID)
+ LoopID = MD;
+ else if (MD != LoopID)
+ return nullptr;
+ }
+ if (!LoopID || LoopID->getNumOperands() == 0 ||
+ LoopID->getOperand(0) != LoopID)
+ return nullptr;
+ return LoopID;
+}
+
+void Loop::setLoopID(MDNode *LoopID) const {
+ assert((!LoopID || LoopID->getNumOperands() > 0) &&
+ "Loop ID needs at least one operand");
+ assert((!LoopID || LoopID->getOperand(0) == LoopID) &&
+ "Loop ID should refer to itself");
+
+ SmallVector<BasicBlock *, 4> LoopLatches;
+ getLoopLatches(LoopLatches);
+ for (BasicBlock *BB : LoopLatches)
+ BB->getTerminator()->setMetadata(LLVMContext::MD_loop, LoopID);
+}
+
+void Loop::setLoopAlreadyUnrolled() {
+ LLVMContext &Context = getHeader()->getContext();
+
+ MDNode *DisableUnrollMD =
+ MDNode::get(Context, MDString::get(Context, "llvm.loop.unroll.disable"));
+ MDNode *LoopID = getLoopID();
+ MDNode *NewLoopID = makePostTransformationMetadata(
+ Context, LoopID, {"llvm.loop.unroll."}, {DisableUnrollMD});
+ setLoopID(NewLoopID);
+}
+
+bool Loop::isAnnotatedParallel() const {
+ MDNode *DesiredLoopIdMetadata = getLoopID();
+
+ if (!DesiredLoopIdMetadata)
+ return false;
+
+ MDNode *ParallelAccesses =
+ findOptionMDForLoop(this, "llvm.loop.parallel_accesses");
+ SmallPtrSet<MDNode *, 4>
+ ParallelAccessGroups; // For scalable 'contains' check.
+ if (ParallelAccesses) {
+ for (const MDOperand &MD : drop_begin(ParallelAccesses->operands(), 1)) {
+ MDNode *AccGroup = cast<MDNode>(MD.get());
+ assert(isValidAsAccessGroup(AccGroup) &&
+ "List item must be an access group");
+ ParallelAccessGroups.insert(AccGroup);
+ }
+ }
+
+ // The loop branch contains the parallel loop metadata. In order to ensure
+ // that any parallel-loop-unaware optimization pass hasn't added loop-carried
+ // dependencies (thus converted the loop back to a sequential loop), check
+ // that all the memory instructions in the loop belong to an access group that
+ // is parallel to this loop.
+ for (BasicBlock *BB : this->blocks()) {
+ for (Instruction &I : *BB) {
+ if (!I.mayReadOrWriteMemory())
+ continue;
+
+ if (MDNode *AccessGroup = I.getMetadata(LLVMContext::MD_access_group)) {
+ auto ContainsAccessGroup = [&ParallelAccessGroups](MDNode *AG) -> bool {
+ if (AG->getNumOperands() == 0) {
+ assert(isValidAsAccessGroup(AG) && "Item must be an access group");
+ return ParallelAccessGroups.count(AG);
+ }
+
+ for (const MDOperand &AccessListItem : AG->operands()) {
+ MDNode *AccGroup = cast<MDNode>(AccessListItem.get());
+ assert(isValidAsAccessGroup(AccGroup) &&
+ "List item must be an access group");
+ if (ParallelAccessGroups.count(AccGroup))
+ return true;
+ }
+ return false;
+ };
+
+ if (ContainsAccessGroup(AccessGroup))
+ continue;
+ }
+
+ // The memory instruction can refer to the loop identifier metadata
+ // directly or indirectly through another list metadata (in case of
+ // nested parallel loops). The loop identifier metadata refers to
+ // itself so we can check both cases with the same routine.
+ MDNode *LoopIdMD =
+ I.getMetadata(LLVMContext::MD_mem_parallel_loop_access);
+
+ if (!LoopIdMD)
+ return false;
+
+ bool LoopIdMDFound = false;
+ for (const MDOperand &MDOp : LoopIdMD->operands()) {
+ if (MDOp == DesiredLoopIdMetadata) {
+ LoopIdMDFound = true;
+ break;
+ }
+ }
+
+ if (!LoopIdMDFound)
+ return false;
+ }
+ }
+ return true;
+}
+
+DebugLoc Loop::getStartLoc() const { return getLocRange().getStart(); }
+
+Loop::LocRange Loop::getLocRange() const {
+ // If we have a debug location in the loop ID, then use it.
+ if (MDNode *LoopID = getLoopID()) {
+ DebugLoc Start;
+ // We use the first DebugLoc in the header as the start location of the loop
+ // and if there is a second DebugLoc in the header we use it as end location
+ // of the loop.
+ for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
+ if (DILocation *L = dyn_cast<DILocation>(LoopID->getOperand(i))) {
+ if (!Start)
+ Start = DebugLoc(L);
+ else
+ return LocRange(Start, DebugLoc(L));
+ }
+ }
+
+ if (Start)
+ return LocRange(Start);
+ }
+
+ // Try the pre-header first.
+ if (BasicBlock *PHeadBB = getLoopPreheader())
+ if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
+ return LocRange(DL);
+
+ // If we have no pre-header or there are no instructions with debug
+ // info in it, try the header.
+ if (BasicBlock *HeadBB = getHeader())
+ return LocRange(HeadBB->getTerminator()->getDebugLoc());
+
+ return LocRange();
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+LLVM_DUMP_METHOD void Loop::dump() const { print(dbgs()); }
+
+LLVM_DUMP_METHOD void Loop::dumpVerbose() const {
+ print(dbgs(), /*Depth=*/0, /*Verbose=*/true);
+}
+#endif
+
+//===----------------------------------------------------------------------===//
+// UnloopUpdater implementation
+//
+
+namespace {
+/// Find the new parent loop for all blocks within the "unloop" whose last
+/// backedges has just been removed.
+class UnloopUpdater {
+ Loop &Unloop;
+ LoopInfo *LI;
+
+ LoopBlocksDFS DFS;
+
+ // Map unloop's immediate subloops to their nearest reachable parents. Nested
+ // loops within these subloops will not change parents. However, an immediate
+ // subloop's new parent will be the nearest loop reachable from either its own
+ // exits *or* any of its nested loop's exits.
+ DenseMap<Loop *, Loop *> SubloopParents;
+
+ // Flag the presence of an irreducible backedge whose destination is a block
+ // directly contained by the original unloop.
+ bool FoundIB;
+
+public:
+ UnloopUpdater(Loop *UL, LoopInfo *LInfo)
+ : Unloop(*UL), LI(LInfo), DFS(UL), FoundIB(false) {}
+
+ void updateBlockParents();
+
+ void removeBlocksFromAncestors();
+
+ void updateSubloopParents();
+
+protected:
+ Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop);
+};
+} // end anonymous namespace
+
+/// Update the parent loop for all blocks that are directly contained within the
+/// original "unloop".
+void UnloopUpdater::updateBlockParents() {
+ if (Unloop.getNumBlocks()) {
+ // Perform a post order CFG traversal of all blocks within this loop,
+ // propagating the nearest loop from successors to predecessors.
+ LoopBlocksTraversal Traversal(DFS, LI);
+ for (BasicBlock *POI : Traversal) {
+
+ Loop *L = LI->getLoopFor(POI);
+ Loop *NL = getNearestLoop(POI, L);
+
+ if (NL != L) {
+ // For reducible loops, NL is now an ancestor of Unloop.
+ assert((NL != &Unloop && (!NL || NL->contains(&Unloop))) &&
+ "uninitialized successor");
+ LI->changeLoopFor(POI, NL);
+ } else {
+ // Or the current block is part of a subloop, in which case its parent
+ // is unchanged.
+ assert((FoundIB || Unloop.contains(L)) && "uninitialized successor");
+ }
+ }
+ }
+ // Each irreducible loop within the unloop induces a round of iteration using
+ // the DFS result cached by Traversal.
+ bool Changed = FoundIB;
+ for (unsigned NIters = 0; Changed; ++NIters) {
+ assert(NIters < Unloop.getNumBlocks() && "runaway iterative algorithm");
+
+ // Iterate over the postorder list of blocks, propagating the nearest loop
+ // from successors to predecessors as before.
+ Changed = false;
+ for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
+ POE = DFS.endPostorder();
+ POI != POE; ++POI) {
+
+ Loop *L = LI->getLoopFor(*POI);
+ Loop *NL = getNearestLoop(*POI, L);
+ if (NL != L) {
+ assert(NL != &Unloop && (!NL || NL->contains(&Unloop)) &&
+ "uninitialized successor");
+ LI->changeLoopFor(*POI, NL);
+ Changed = true;
+ }
+ }
+ }
+}
+
+/// Remove unloop's blocks from all ancestors below their new parents.
+void UnloopUpdater::removeBlocksFromAncestors() {
+ // Remove all unloop's blocks (including those in nested subloops) from
+ // ancestors below the new parent loop.
+ for (Loop::block_iterator BI = Unloop.block_begin(), BE = Unloop.block_end();
+ BI != BE; ++BI) {
+ Loop *OuterParent = LI->getLoopFor(*BI);
+ if (Unloop.contains(OuterParent)) {
+ while (OuterParent->getParentLoop() != &Unloop)
+ OuterParent = OuterParent->getParentLoop();
+ OuterParent = SubloopParents[OuterParent];
+ }
+ // Remove blocks from former Ancestors except Unloop itself which will be
+ // deleted.
+ for (Loop *OldParent = Unloop.getParentLoop(); OldParent != OuterParent;
+ OldParent = OldParent->getParentLoop()) {
+ assert(OldParent && "new loop is not an ancestor of the original");
+ OldParent->removeBlockFromLoop(*BI);
+ }
+ }
+}
+
+/// Update the parent loop for all subloops directly nested within unloop.
+void UnloopUpdater::updateSubloopParents() {
+ while (!Unloop.empty()) {
+ Loop *Subloop = *std::prev(Unloop.end());
+ Unloop.removeChildLoop(std::prev(Unloop.end()));
+
+ assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
+ if (Loop *Parent = SubloopParents[Subloop])
+ Parent->addChildLoop(Subloop);
+ else
+ LI->addTopLevelLoop(Subloop);
+ }
+}
+
+/// Return the nearest parent loop among this block's successors. If a successor
+/// is a subloop header, consider its parent to be the nearest parent of the
+/// subloop's exits.
+///
+/// For subloop blocks, simply update SubloopParents and return NULL.
+Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
+
+ // Initially for blocks directly contained by Unloop, NearLoop == Unloop and
+ // is considered uninitialized.
+ Loop *NearLoop = BBLoop;
+
+ Loop *Subloop = nullptr;
+ if (NearLoop != &Unloop && Unloop.contains(NearLoop)) {
+ Subloop = NearLoop;
+ // Find the subloop ancestor that is directly contained within Unloop.
+ while (Subloop->getParentLoop() != &Unloop) {
+ Subloop = Subloop->getParentLoop();
+ assert(Subloop && "subloop is not an ancestor of the original loop");
+ }
+ // Get the current nearest parent of the Subloop exits, initially Unloop.
+ NearLoop = SubloopParents.insert({Subloop, &Unloop}).first->second;
+ }
+
+ succ_iterator I = succ_begin(BB), E = succ_end(BB);
+ if (I == E) {
+ assert(!Subloop && "subloop blocks must have a successor");
+ NearLoop = nullptr; // unloop blocks may now exit the function.
+ }
+ for (; I != E; ++I) {
+ if (*I == BB)
+ continue; // self loops are uninteresting
+
+ Loop *L = LI->getLoopFor(*I);
+ if (L == &Unloop) {
+ // This successor has not been processed. This path must lead to an
+ // irreducible backedge.
+ assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB");
+ FoundIB = true;
+ }
+ if (L != &Unloop && Unloop.contains(L)) {
+ // Successor is in a subloop.
+ if (Subloop)
+ continue; // Branching within subloops. Ignore it.
+
+ // BB branches from the original into a subloop header.
+ assert(L->getParentLoop() == &Unloop && "cannot skip into nested loops");
+
+ // Get the current nearest parent of the Subloop's exits.
+ L = SubloopParents[L];
+ // L could be Unloop if the only exit was an irreducible backedge.
+ }
+ if (L == &Unloop) {
+ continue;
+ }
+ // Handle critical edges from Unloop into a sibling loop.
+ if (L && !L->contains(&Unloop)) {
+ L = L->getParentLoop();
+ }
+ // Remember the nearest parent loop among successors or subloop exits.
+ if (NearLoop == &Unloop || !NearLoop || NearLoop->contains(L))
+ NearLoop = L;
+ }
+ if (Subloop) {
+ SubloopParents[Subloop] = NearLoop;
+ return BBLoop;
+ }
+ return NearLoop;
+}
+
+LoopInfo::LoopInfo(const DomTreeBase<BasicBlock> &DomTree) { analyze(DomTree); }
+
+bool LoopInfo::invalidate(Function &F, const PreservedAnalyses &PA,
+ FunctionAnalysisManager::Invalidator &) {
+ // Check whether the analysis, all analyses on functions, or the function's
+ // CFG have been preserved.
+ auto PAC = PA.getChecker<LoopAnalysis>();
+ return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
+ PAC.preservedSet<CFGAnalyses>());
+}
+
+void LoopInfo::erase(Loop *Unloop) {
+ assert(!Unloop->isInvalid() && "Loop has already been erased!");
+
+ auto InvalidateOnExit = make_scope_exit([&]() { destroy(Unloop); });
+
+ // First handle the special case of no parent loop to simplify the algorithm.
+ if (!Unloop->getParentLoop()) {
+ // Since BBLoop had no parent, Unloop blocks are no longer in a loop.
+ for (Loop::block_iterator I = Unloop->block_begin(),
+ E = Unloop->block_end();
+ I != E; ++I) {
+
+ // Don't reparent blocks in subloops.
+ if (getLoopFor(*I) != Unloop)
+ continue;
+
+ // Blocks no longer have a parent but are still referenced by Unloop until
+ // the Unloop object is deleted.
+ changeLoopFor(*I, nullptr);
+ }
+
+ // Remove the loop from the top-level LoopInfo object.
+ for (iterator I = begin();; ++I) {
+ assert(I != end() && "Couldn't find loop");
+ if (*I == Unloop) {
+ removeLoop(I);
+ break;
+ }
+ }
+
+ // Move all of the subloops to the top-level.
+ while (!Unloop->empty())
+ addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end())));
+
+ return;
+ }
+
+ // Update the parent loop for all blocks within the loop. Blocks within
+ // subloops will not change parents.
+ UnloopUpdater Updater(Unloop, this);
+ Updater.updateBlockParents();
+
+ // Remove blocks from former ancestor loops.
+ Updater.removeBlocksFromAncestors();
+
+ // Add direct subloops as children in their new parent loop.
+ Updater.updateSubloopParents();
+
+ // Remove unloop from its parent loop.
+ Loop *ParentLoop = Unloop->getParentLoop();
+ for (Loop::iterator I = ParentLoop->begin();; ++I) {
+ assert(I != ParentLoop->end() && "Couldn't find loop");
+ if (*I == Unloop) {
+ ParentLoop->removeChildLoop(I);
+ break;
+ }
+ }
+}
+
+AnalysisKey LoopAnalysis::Key;
+
+LoopInfo LoopAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
+ // FIXME: Currently we create a LoopInfo from scratch for every function.
+ // This may prove to be too wasteful due to deallocating and re-allocating
+ // memory each time for the underlying map and vector datastructures. At some
+ // point it may prove worthwhile to use a freelist and recycle LoopInfo
+ // objects. I don't want to add that kind of complexity until the scope of
+ // the problem is better understood.
+ LoopInfo LI;
+ LI.analyze(AM.getResult<DominatorTreeAnalysis>(F));
+ return LI;
+}
+
+PreservedAnalyses LoopPrinterPass::run(Function &F,
+ FunctionAnalysisManager &AM) {
+ AM.getResult<LoopAnalysis>(F).print(OS);
+ return PreservedAnalyses::all();
+}
+
+void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
+
+ if (forcePrintModuleIR()) {
+ // handling -print-module-scope
+ OS << Banner << " (loop: ";
+ L.getHeader()->printAsOperand(OS, false);
+ OS << ")\n";
+
+ // printing whole module
+ OS << *L.getHeader()->getModule();
+ return;
+ }
+
+ OS << Banner;
+
+ auto *PreHeader = L.getLoopPreheader();
+ if (PreHeader) {
+ OS << "\n; Preheader:";
+ PreHeader->print(OS);
+ OS << "\n; Loop:";
+ }
+
+ for (auto *Block : L.blocks())
+ if (Block)
+ Block->print(OS);
+ else
+ OS << "Printing <null> block";
+
+ SmallVector<BasicBlock *, 8> ExitBlocks;
+ L.getExitBlocks(ExitBlocks);
+ if (!ExitBlocks.empty()) {
+ OS << "\n; Exit blocks";
+ for (auto *Block : ExitBlocks)
+ if (Block)
+ Block->print(OS);
+ else
+ OS << "Printing <null> block";
+ }
+}
+
+MDNode *llvm::findOptionMDForLoopID(MDNode *LoopID, StringRef Name) {
+ // No loop metadata node, no loop properties.
+ if (!LoopID)
+ return nullptr;
+
+ // First operand should refer to the metadata node itself, for legacy reasons.
+ assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
+ assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
+
+ // Iterate over the metdata node operands and look for MDString metadata.
+ for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
+ MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
+ if (!MD || MD->getNumOperands() < 1)
+ continue;
+ MDString *S = dyn_cast<MDString>(MD->getOperand(0));
+ if (!S)
+ continue;
+ // Return the operand node if MDString holds expected metadata.
+ if (Name.equals(S->getString()))
+ return MD;
+ }
+
+ // Loop property not found.
+ return nullptr;
+}
+
+MDNode *llvm::findOptionMDForLoop(const Loop *TheLoop, StringRef Name) {
+ return findOptionMDForLoopID(TheLoop->getLoopID(), Name);
+}
+
+bool llvm::isValidAsAccessGroup(MDNode *Node) {
+ return Node->getNumOperands() == 0 && Node->isDistinct();
+}
+
+MDNode *llvm::makePostTransformationMetadata(LLVMContext &Context,
+ MDNode *OrigLoopID,
+ ArrayRef<StringRef> RemovePrefixes,
+ ArrayRef<MDNode *> AddAttrs) {
+ // First remove any existing loop metadata related to this transformation.
+ SmallVector<Metadata *, 4> MDs;
+
+ // Reserve first location for self reference to the LoopID metadata node.
+ TempMDTuple TempNode = MDNode::getTemporary(Context, None);
+ MDs.push_back(TempNode.get());
+
+ // Remove metadata for the transformation that has been applied or that became
+ // outdated.
+ if (OrigLoopID) {
+ for (unsigned i = 1, ie = OrigLoopID->getNumOperands(); i < ie; ++i) {
+ bool IsVectorMetadata = false;
+ Metadata *Op = OrigLoopID->getOperand(i);
+ if (MDNode *MD = dyn_cast<MDNode>(Op)) {
+ const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
+ if (S)
+ IsVectorMetadata =
+ llvm::any_of(RemovePrefixes, [S](StringRef Prefix) -> bool {
+ return S->getString().startswith(Prefix);
+ });
+ }
+ if (!IsVectorMetadata)
+ MDs.push_back(Op);
+ }
+ }
+
+ // Add metadata to avoid reapplying a transformation, such as
+ // llvm.loop.unroll.disable and llvm.loop.isvectorized.
+ MDs.append(AddAttrs.begin(), AddAttrs.end());
+
+ MDNode *NewLoopID = MDNode::getDistinct(Context, MDs);
+ // Replace the temporary node with a self-reference.
+ NewLoopID->replaceOperandWith(0, NewLoopID);
+ return NewLoopID;
+}
+
+//===----------------------------------------------------------------------===//
+// LoopInfo implementation
+//
+
+char LoopInfoWrapperPass::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopInfoWrapperPass, "loops", "Natural Loop Information",
+ true, true)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_END(LoopInfoWrapperPass, "loops", "Natural Loop Information",
+ true, true)
+
+bool LoopInfoWrapperPass::runOnFunction(Function &) {
+ releaseMemory();
+ LI.analyze(getAnalysis<DominatorTreeWrapperPass>().getDomTree());
+ return false;
+}
+
+void LoopInfoWrapperPass::verifyAnalysis() const {
+ // LoopInfoWrapperPass is a FunctionPass, but verifying every loop in the
+ // function each time verifyAnalysis is called is very expensive. The
+ // -verify-loop-info option can enable this. In order to perform some
+ // checking by default, LoopPass has been taught to call verifyLoop manually
+ // during loop pass sequences.
+ if (VerifyLoopInfo) {
+ auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ LI.verify(DT);
+ }
+}
+
+void LoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesAll();
+ AU.addRequiredTransitive<DominatorTreeWrapperPass>();
+}
+
+void LoopInfoWrapperPass::print(raw_ostream &OS, const Module *) const {
+ LI.print(OS);
+}
+
+PreservedAnalyses LoopVerifierPass::run(Function &F,
+ FunctionAnalysisManager &AM) {
+ LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
+ auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
+ LI.verify(DT);
+ return PreservedAnalyses::all();
+}
+
+//===----------------------------------------------------------------------===//
+// LoopBlocksDFS implementation
+//
+
+/// Traverse the loop blocks and store the DFS result.
+/// Useful for clients that just want the final DFS result and don't need to
+/// visit blocks during the initial traversal.
+void LoopBlocksDFS::perform(LoopInfo *LI) {
+ LoopBlocksTraversal Traversal(*this, LI);
+ for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
+ POE = Traversal.end();
+ POI != POE; ++POI)
+ ;
+}
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