diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp | 698 |
1 files changed, 698 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/contrib/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp new file mode 100644 index 000000000000..d3ea1564115b --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp @@ -0,0 +1,698 @@ +//===-- UnrollLoopRuntime.cpp - Runtime Loop unrolling utilities ----------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements some loop unrolling utilities for loops with run-time +// trip counts. See LoopUnroll.cpp for unrolling loops with compile-time +// trip counts. +// +// The functions in this file are used to generate extra code when the +// run-time trip count modulo the unroll factor is not 0. When this is the +// case, we need to generate code to execute these 'left over' iterations. +// +// The current strategy generates an if-then-else sequence prior to the +// unrolled loop to execute the 'left over' iterations before or after the +// unrolled loop. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/UnrollLoop.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/LoopIterator.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include <algorithm> + +using namespace llvm; + +#define DEBUG_TYPE "loop-unroll" + +STATISTIC(NumRuntimeUnrolled, + "Number of loops unrolled with run-time trip counts"); + +/// Connect the unrolling prolog code to the original loop. +/// The unrolling prolog code contains code to execute the +/// 'extra' iterations if the run-time trip count modulo the +/// unroll count is non-zero. +/// +/// This function performs the following: +/// - Create PHI nodes at prolog end block to combine values +/// that exit the prolog code and jump around the prolog. +/// - Add a PHI operand to a PHI node at the loop exit block +/// for values that exit the prolog and go around the loop. +/// - Branch around the original loop if the trip count is less +/// than the unroll factor. +/// +static void ConnectProlog(Loop *L, Value *BECount, unsigned Count, + BasicBlock *PrologExit, BasicBlock *PreHeader, + BasicBlock *NewPreHeader, ValueToValueMapTy &VMap, + DominatorTree *DT, LoopInfo *LI, bool PreserveLCSSA) { + BasicBlock *Latch = L->getLoopLatch(); + assert(Latch && "Loop must have a latch"); + BasicBlock *PrologLatch = cast<BasicBlock>(VMap[Latch]); + + // Create a PHI node for each outgoing value from the original loop + // (which means it is an outgoing value from the prolog code too). + // The new PHI node is inserted in the prolog end basic block. + // The new PHI node value is added as an operand of a PHI node in either + // the loop header or the loop exit block. + for (BasicBlock *Succ : successors(Latch)) { + for (Instruction &BBI : *Succ) { + PHINode *PN = dyn_cast<PHINode>(&BBI); + // Exit when we passed all PHI nodes. + if (!PN) + break; + // Add a new PHI node to the prolog end block and add the + // appropriate incoming values. + PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr", + PrologExit->getFirstNonPHI()); + // Adding a value to the new PHI node from the original loop preheader. + // This is the value that skips all the prolog code. + if (L->contains(PN)) { + NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader), + PreHeader); + } else { + NewPN->addIncoming(UndefValue::get(PN->getType()), PreHeader); + } + + Value *V = PN->getIncomingValueForBlock(Latch); + if (Instruction *I = dyn_cast<Instruction>(V)) { + if (L->contains(I)) { + V = VMap.lookup(I); + } + } + // Adding a value to the new PHI node from the last prolog block + // that was created. + NewPN->addIncoming(V, PrologLatch); + + // Update the existing PHI node operand with the value from the + // new PHI node. How this is done depends on if the existing + // PHI node is in the original loop block, or the exit block. + if (L->contains(PN)) { + PN->setIncomingValue(PN->getBasicBlockIndex(NewPreHeader), NewPN); + } else { + PN->addIncoming(NewPN, PrologExit); + } + } + } + + // Make sure that created prolog loop is in simplified form + SmallVector<BasicBlock *, 4> PrologExitPreds; + Loop *PrologLoop = LI->getLoopFor(PrologLatch); + if (PrologLoop) { + for (BasicBlock *PredBB : predecessors(PrologExit)) + if (PrologLoop->contains(PredBB)) + PrologExitPreds.push_back(PredBB); + + SplitBlockPredecessors(PrologExit, PrologExitPreds, ".unr-lcssa", DT, LI, + PreserveLCSSA); + } + + // Create a branch around the original loop, which is taken if there are no + // iterations remaining to be executed after running the prologue. + Instruction *InsertPt = PrologExit->getTerminator(); + IRBuilder<> B(InsertPt); + + assert(Count != 0 && "nonsensical Count!"); + + // If BECount <u (Count - 1) then (BECount + 1) % Count == (BECount + 1) + // This means %xtraiter is (BECount + 1) and all of the iterations of this + // loop were executed by the prologue. Note that if BECount <u (Count - 1) + // then (BECount + 1) cannot unsigned-overflow. + Value *BrLoopExit = + B.CreateICmpULT(BECount, ConstantInt::get(BECount->getType(), Count - 1)); + BasicBlock *Exit = L->getUniqueExitBlock(); + assert(Exit && "Loop must have a single exit block only"); + // Split the exit to maintain loop canonicalization guarantees + SmallVector<BasicBlock*, 4> Preds(predecessors(Exit)); + SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", DT, LI, + PreserveLCSSA); + // Add the branch to the exit block (around the unrolled loop) + B.CreateCondBr(BrLoopExit, Exit, NewPreHeader); + InsertPt->eraseFromParent(); +} + +/// Connect the unrolling epilog code to the original loop. +/// The unrolling epilog code contains code to execute the +/// 'extra' iterations if the run-time trip count modulo the +/// unroll count is non-zero. +/// +/// This function performs the following: +/// - Update PHI nodes at the unrolling loop exit and epilog loop exit +/// - Create PHI nodes at the unrolling loop exit to combine +/// values that exit the unrolling loop code and jump around it. +/// - Update PHI operands in the epilog loop by the new PHI nodes +/// - Branch around the epilog loop if extra iters (ModVal) is zero. +/// +static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit, + BasicBlock *Exit, BasicBlock *PreHeader, + BasicBlock *EpilogPreHeader, BasicBlock *NewPreHeader, + ValueToValueMapTy &VMap, DominatorTree *DT, + LoopInfo *LI, bool PreserveLCSSA) { + BasicBlock *Latch = L->getLoopLatch(); + assert(Latch && "Loop must have a latch"); + BasicBlock *EpilogLatch = cast<BasicBlock>(VMap[Latch]); + + // Loop structure should be the following: + // + // PreHeader + // NewPreHeader + // Header + // ... + // Latch + // NewExit (PN) + // EpilogPreHeader + // EpilogHeader + // ... + // EpilogLatch + // Exit (EpilogPN) + + // Update PHI nodes at NewExit and Exit. + for (Instruction &BBI : *NewExit) { + PHINode *PN = dyn_cast<PHINode>(&BBI); + // Exit when we passed all PHI nodes. + if (!PN) + break; + // PN should be used in another PHI located in Exit block as + // Exit was split by SplitBlockPredecessors into Exit and NewExit + // Basicaly it should look like: + // NewExit: + // PN = PHI [I, Latch] + // ... + // Exit: + // EpilogPN = PHI [PN, EpilogPreHeader] + // + // There is EpilogPreHeader incoming block instead of NewExit as + // NewExit was spilt 1 more time to get EpilogPreHeader. + assert(PN->hasOneUse() && "The phi should have 1 use"); + PHINode *EpilogPN = cast<PHINode> (PN->use_begin()->getUser()); + assert(EpilogPN->getParent() == Exit && "EpilogPN should be in Exit block"); + + // Add incoming PreHeader from branch around the Loop + PN->addIncoming(UndefValue::get(PN->getType()), PreHeader); + + Value *V = PN->getIncomingValueForBlock(Latch); + Instruction *I = dyn_cast<Instruction>(V); + if (I && L->contains(I)) + // If value comes from an instruction in the loop add VMap value. + V = VMap.lookup(I); + // For the instruction out of the loop, constant or undefined value + // insert value itself. + EpilogPN->addIncoming(V, EpilogLatch); + + assert(EpilogPN->getBasicBlockIndex(EpilogPreHeader) >= 0 && + "EpilogPN should have EpilogPreHeader incoming block"); + // Change EpilogPreHeader incoming block to NewExit. + EpilogPN->setIncomingBlock(EpilogPN->getBasicBlockIndex(EpilogPreHeader), + NewExit); + // Now PHIs should look like: + // NewExit: + // PN = PHI [I, Latch], [undef, PreHeader] + // ... + // Exit: + // EpilogPN = PHI [PN, NewExit], [VMap[I], EpilogLatch] + } + + // Create PHI nodes at NewExit (from the unrolling loop Latch and PreHeader). + // Update corresponding PHI nodes in epilog loop. + for (BasicBlock *Succ : successors(Latch)) { + // Skip this as we already updated phis in exit blocks. + if (!L->contains(Succ)) + continue; + for (Instruction &BBI : *Succ) { + PHINode *PN = dyn_cast<PHINode>(&BBI); + // Exit when we passed all PHI nodes. + if (!PN) + break; + // Add new PHI nodes to the loop exit block and update epilog + // PHIs with the new PHI values. + PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr", + NewExit->getFirstNonPHI()); + // Adding a value to the new PHI node from the unrolling loop preheader. + NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader), PreHeader); + // Adding a value to the new PHI node from the unrolling loop latch. + NewPN->addIncoming(PN->getIncomingValueForBlock(Latch), Latch); + + // Update the existing PHI node operand with the value from the new PHI + // node. Corresponding instruction in epilog loop should be PHI. + PHINode *VPN = cast<PHINode>(VMap[&BBI]); + VPN->setIncomingValue(VPN->getBasicBlockIndex(EpilogPreHeader), NewPN); + } + } + + Instruction *InsertPt = NewExit->getTerminator(); + IRBuilder<> B(InsertPt); + Value *BrLoopExit = B.CreateIsNotNull(ModVal, "lcmp.mod"); + assert(Exit && "Loop must have a single exit block only"); + // Split the exit to maintain loop canonicalization guarantees + SmallVector<BasicBlock*, 4> Preds(predecessors(Exit)); + SplitBlockPredecessors(Exit, Preds, ".epilog-lcssa", DT, LI, + PreserveLCSSA); + // Add the branch to the exit block (around the unrolling loop) + B.CreateCondBr(BrLoopExit, EpilogPreHeader, Exit); + InsertPt->eraseFromParent(); +} + +/// Create a clone of the blocks in a loop and connect them together. +/// If CreateRemainderLoop is false, loop structure will not be cloned, +/// otherwise a new loop will be created including all cloned blocks, and the +/// iterator of it switches to count NewIter down to 0. +/// The cloned blocks should be inserted between InsertTop and InsertBot. +/// If loop structure is cloned InsertTop should be new preheader, InsertBot +/// new loop exit. +/// +static void CloneLoopBlocks(Loop *L, Value *NewIter, + const bool CreateRemainderLoop, + const bool UseEpilogRemainder, + BasicBlock *InsertTop, BasicBlock *InsertBot, + BasicBlock *Preheader, + std::vector<BasicBlock *> &NewBlocks, + LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap, + LoopInfo *LI) { + StringRef suffix = UseEpilogRemainder ? "epil" : "prol"; + BasicBlock *Header = L->getHeader(); + BasicBlock *Latch = L->getLoopLatch(); + Function *F = Header->getParent(); + LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO(); + LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO(); + Loop *NewLoop = nullptr; + Loop *ParentLoop = L->getParentLoop(); + if (CreateRemainderLoop) { + NewLoop = new Loop(); + if (ParentLoop) + ParentLoop->addChildLoop(NewLoop); + else + LI->addTopLevelLoop(NewLoop); + } + + NewLoopsMap NewLoops; + if (NewLoop) + NewLoops[L] = NewLoop; + else if (ParentLoop) + NewLoops[L] = ParentLoop; + + // For each block in the original loop, create a new copy, + // and update the value map with the newly created values. + for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) { + BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, "." + suffix, F); + NewBlocks.push_back(NewBB); + + // If we're unrolling the outermost loop, there's no remainder loop, + // and this block isn't in a nested loop, then the new block is not + // in any loop. Otherwise, add it to loopinfo. + if (CreateRemainderLoop || LI->getLoopFor(*BB) != L || ParentLoop) + addClonedBlockToLoopInfo(*BB, NewBB, LI, NewLoops); + + VMap[*BB] = NewBB; + if (Header == *BB) { + // For the first block, add a CFG connection to this newly + // created block. + InsertTop->getTerminator()->setSuccessor(0, NewBB); + } + + if (Latch == *BB) { + // For the last block, if CreateRemainderLoop is false, create a direct + // jump to InsertBot. If not, create a loop back to cloned head. + VMap.erase((*BB)->getTerminator()); + BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]); + BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator()); + IRBuilder<> Builder(LatchBR); + if (!CreateRemainderLoop) { + Builder.CreateBr(InsertBot); + } else { + PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2, + suffix + ".iter", + FirstLoopBB->getFirstNonPHI()); + Value *IdxSub = + Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1), + NewIdx->getName() + ".sub"); + Value *IdxCmp = + Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp"); + Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot); + NewIdx->addIncoming(NewIter, InsertTop); + NewIdx->addIncoming(IdxSub, NewBB); + } + LatchBR->eraseFromParent(); + } + } + + // Change the incoming values to the ones defined in the preheader or + // cloned loop. + for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { + PHINode *NewPHI = cast<PHINode>(VMap[&*I]); + if (!CreateRemainderLoop) { + if (UseEpilogRemainder) { + unsigned idx = NewPHI->getBasicBlockIndex(Preheader); + NewPHI->setIncomingBlock(idx, InsertTop); + NewPHI->removeIncomingValue(Latch, false); + } else { + VMap[&*I] = NewPHI->getIncomingValueForBlock(Preheader); + cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI); + } + } else { + unsigned idx = NewPHI->getBasicBlockIndex(Preheader); + NewPHI->setIncomingBlock(idx, InsertTop); + BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]); + idx = NewPHI->getBasicBlockIndex(Latch); + Value *InVal = NewPHI->getIncomingValue(idx); + NewPHI->setIncomingBlock(idx, NewLatch); + if (Value *V = VMap.lookup(InVal)) + NewPHI->setIncomingValue(idx, V); + } + } + if (NewLoop) { + // Add unroll disable metadata to disable future unrolling for this loop. + SmallVector<Metadata *, 4> MDs; + // Reserve first location for self reference to the LoopID metadata node. + MDs.push_back(nullptr); + MDNode *LoopID = NewLoop->getLoopID(); + if (LoopID) { + // First remove any existing loop unrolling metadata. + for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) { + bool IsUnrollMetadata = false; + MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); + if (MD) { + const MDString *S = dyn_cast<MDString>(MD->getOperand(0)); + IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll."); + } + if (!IsUnrollMetadata) + MDs.push_back(LoopID->getOperand(i)); + } + } + + LLVMContext &Context = NewLoop->getHeader()->getContext(); + SmallVector<Metadata *, 1> DisableOperands; + DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable")); + MDNode *DisableNode = MDNode::get(Context, DisableOperands); + MDs.push_back(DisableNode); + + MDNode *NewLoopID = MDNode::get(Context, MDs); + // Set operand 0 to refer to the loop id itself. + NewLoopID->replaceOperandWith(0, NewLoopID); + NewLoop->setLoopID(NewLoopID); + } +} + +/// Insert code in the prolog/epilog code when unrolling a loop with a +/// run-time trip-count. +/// +/// This method assumes that the loop unroll factor is total number +/// of loop bodies in the loop after unrolling. (Some folks refer +/// to the unroll factor as the number of *extra* copies added). +/// We assume also that the loop unroll factor is a power-of-two. So, after +/// unrolling the loop, the number of loop bodies executed is 2, +/// 4, 8, etc. Note - LLVM converts the if-then-sequence to a switch +/// instruction in SimplifyCFG.cpp. Then, the backend decides how code for +/// the switch instruction is generated. +/// +/// ***Prolog case*** +/// extraiters = tripcount % loopfactor +/// if (extraiters == 0) jump Loop: +/// else jump Prol: +/// Prol: LoopBody; +/// extraiters -= 1 // Omitted if unroll factor is 2. +/// if (extraiters != 0) jump Prol: // Omitted if unroll factor is 2. +/// if (tripcount < loopfactor) jump End: +/// Loop: +/// ... +/// End: +/// +/// ***Epilog case*** +/// extraiters = tripcount % loopfactor +/// if (tripcount < loopfactor) jump LoopExit: +/// unroll_iters = tripcount - extraiters +/// Loop: LoopBody; (executes unroll_iter times); +/// unroll_iter -= 1 +/// if (unroll_iter != 0) jump Loop: +/// LoopExit: +/// if (extraiters == 0) jump EpilExit: +/// Epil: LoopBody; (executes extraiters times) +/// extraiters -= 1 // Omitted if unroll factor is 2. +/// if (extraiters != 0) jump Epil: // Omitted if unroll factor is 2. +/// EpilExit: + +bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count, + bool AllowExpensiveTripCount, + bool UseEpilogRemainder, + LoopInfo *LI, ScalarEvolution *SE, + DominatorTree *DT, bool PreserveLCSSA) { + // for now, only unroll loops that contain a single exit + if (!L->getExitingBlock()) + return false; + + // Make sure the loop is in canonical form, and there is a single + // exit block only. + if (!L->isLoopSimplifyForm()) + return false; + BasicBlock *Exit = L->getUniqueExitBlock(); // successor out of loop + if (!Exit) + return false; + + // Use Scalar Evolution to compute the trip count. This allows more loops to + // be unrolled than relying on induction var simplification. + if (!SE) + return false; + + // Only unroll loops with a computable trip count, and the trip count needs + // to be an int value (allowing a pointer type is a TODO item). + const SCEV *BECountSC = SE->getBackedgeTakenCount(L); + if (isa<SCEVCouldNotCompute>(BECountSC) || + !BECountSC->getType()->isIntegerTy()) + return false; + + unsigned BEWidth = cast<IntegerType>(BECountSC->getType())->getBitWidth(); + + // Add 1 since the backedge count doesn't include the first loop iteration. + const SCEV *TripCountSC = + SE->getAddExpr(BECountSC, SE->getConstant(BECountSC->getType(), 1)); + if (isa<SCEVCouldNotCompute>(TripCountSC)) + return false; + + BasicBlock *Header = L->getHeader(); + BasicBlock *PreHeader = L->getLoopPreheader(); + BranchInst *PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator()); + const DataLayout &DL = Header->getModule()->getDataLayout(); + SCEVExpander Expander(*SE, DL, "loop-unroll"); + if (!AllowExpensiveTripCount && + Expander.isHighCostExpansion(TripCountSC, L, PreHeaderBR)) + return false; + + // This constraint lets us deal with an overflowing trip count easily; see the + // comment on ModVal below. + if (Log2_32(Count) > BEWidth) + return false; + + BasicBlock *Latch = L->getLoopLatch(); + + // Loop structure is the following: + // + // PreHeader + // Header + // ... + // Latch + // Exit + + BasicBlock *NewPreHeader; + BasicBlock *NewExit = nullptr; + BasicBlock *PrologExit = nullptr; + BasicBlock *EpilogPreHeader = nullptr; + BasicBlock *PrologPreHeader = nullptr; + + if (UseEpilogRemainder) { + // If epilog remainder + // Split PreHeader to insert a branch around loop for unrolling. + NewPreHeader = SplitBlock(PreHeader, PreHeader->getTerminator(), DT, LI); + NewPreHeader->setName(PreHeader->getName() + ".new"); + // Split Exit to create phi nodes from branch above. + SmallVector<BasicBlock*, 4> Preds(predecessors(Exit)); + NewExit = SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", + DT, LI, PreserveLCSSA); + // Split NewExit to insert epilog remainder loop. + EpilogPreHeader = SplitBlock(NewExit, NewExit->getTerminator(), DT, LI); + EpilogPreHeader->setName(Header->getName() + ".epil.preheader"); + } else { + // If prolog remainder + // Split the original preheader twice to insert prolog remainder loop + PrologPreHeader = SplitEdge(PreHeader, Header, DT, LI); + PrologPreHeader->setName(Header->getName() + ".prol.preheader"); + PrologExit = SplitBlock(PrologPreHeader, PrologPreHeader->getTerminator(), + DT, LI); + PrologExit->setName(Header->getName() + ".prol.loopexit"); + // Split PrologExit to get NewPreHeader. + NewPreHeader = SplitBlock(PrologExit, PrologExit->getTerminator(), DT, LI); + NewPreHeader->setName(PreHeader->getName() + ".new"); + } + // Loop structure should be the following: + // Epilog Prolog + // + // PreHeader PreHeader + // *NewPreHeader *PrologPreHeader + // Header *PrologExit + // ... *NewPreHeader + // Latch Header + // *NewExit ... + // *EpilogPreHeader Latch + // Exit Exit + + // Calculate conditions for branch around loop for unrolling + // in epilog case and around prolog remainder loop in prolog case. + // Compute the number of extra iterations required, which is: + // extra iterations = run-time trip count % loop unroll factor + PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator()); + Value *TripCount = Expander.expandCodeFor(TripCountSC, TripCountSC->getType(), + PreHeaderBR); + Value *BECount = Expander.expandCodeFor(BECountSC, BECountSC->getType(), + PreHeaderBR); + IRBuilder<> B(PreHeaderBR); + Value *ModVal; + // Calculate ModVal = (BECount + 1) % Count. + // Note that TripCount is BECount + 1. + if (isPowerOf2_32(Count)) { + // When Count is power of 2 we don't BECount for epilog case, however we'll + // need it for a branch around unrolling loop for prolog case. + ModVal = B.CreateAnd(TripCount, Count - 1, "xtraiter"); + // 1. There are no iterations to be run in the prolog/epilog loop. + // OR + // 2. The addition computing TripCount overflowed. + // + // If (2) is true, we know that TripCount really is (1 << BEWidth) and so + // the number of iterations that remain to be run in the original loop is a + // multiple Count == (1 << Log2(Count)) because Log2(Count) <= BEWidth (we + // explicitly check this above). + } else { + // As (BECount + 1) can potentially unsigned overflow we count + // (BECount % Count) + 1 which is overflow safe as BECount % Count < Count. + Value *ModValTmp = B.CreateURem(BECount, + ConstantInt::get(BECount->getType(), + Count)); + Value *ModValAdd = B.CreateAdd(ModValTmp, + ConstantInt::get(ModValTmp->getType(), 1)); + // At that point (BECount % Count) + 1 could be equal to Count. + // To handle this case we need to take mod by Count one more time. + ModVal = B.CreateURem(ModValAdd, + ConstantInt::get(BECount->getType(), Count), + "xtraiter"); + } + Value *BranchVal = + UseEpilogRemainder ? B.CreateICmpULT(BECount, + ConstantInt::get(BECount->getType(), + Count - 1)) : + B.CreateIsNotNull(ModVal, "lcmp.mod"); + BasicBlock *RemainderLoop = UseEpilogRemainder ? NewExit : PrologPreHeader; + BasicBlock *UnrollingLoop = UseEpilogRemainder ? NewPreHeader : PrologExit; + // Branch to either remainder (extra iterations) loop or unrolling loop. + B.CreateCondBr(BranchVal, RemainderLoop, UnrollingLoop); + PreHeaderBR->eraseFromParent(); + Function *F = Header->getParent(); + // Get an ordered list of blocks in the loop to help with the ordering of the + // cloned blocks in the prolog/epilog code + LoopBlocksDFS LoopBlocks(L); + LoopBlocks.perform(LI); + + // + // For each extra loop iteration, create a copy of the loop's basic blocks + // and generate a condition that branches to the copy depending on the + // number of 'left over' iterations. + // + std::vector<BasicBlock *> NewBlocks; + ValueToValueMapTy VMap; + + // For unroll factor 2 remainder loop will have 1 iterations. + // Do not create 1 iteration loop. + bool CreateRemainderLoop = (Count != 2); + + // Clone all the basic blocks in the loop. If Count is 2, we don't clone + // the loop, otherwise we create a cloned loop to execute the extra + // iterations. This function adds the appropriate CFG connections. + BasicBlock *InsertBot = UseEpilogRemainder ? Exit : PrologExit; + BasicBlock *InsertTop = UseEpilogRemainder ? EpilogPreHeader : PrologPreHeader; + CloneLoopBlocks(L, ModVal, CreateRemainderLoop, UseEpilogRemainder, InsertTop, + InsertBot, NewPreHeader, NewBlocks, LoopBlocks, VMap, LI); + + // Insert the cloned blocks into the function. + F->getBasicBlockList().splice(InsertBot->getIterator(), + F->getBasicBlockList(), + NewBlocks[0]->getIterator(), + F->end()); + + // Loop structure should be the following: + // Epilog Prolog + // + // PreHeader PreHeader + // NewPreHeader PrologPreHeader + // Header PrologHeader + // ... ... + // Latch PrologLatch + // NewExit PrologExit + // EpilogPreHeader NewPreHeader + // EpilogHeader Header + // ... ... + // EpilogLatch Latch + // Exit Exit + + // Rewrite the cloned instruction operands to use the values created when the + // clone is created. + for (BasicBlock *BB : NewBlocks) { + for (Instruction &I : *BB) { + RemapInstruction(&I, VMap, + RF_NoModuleLevelChanges | RF_IgnoreMissingLocals); + } + } + + if (UseEpilogRemainder) { + // Connect the epilog code to the original loop and update the + // PHI functions. + ConnectEpilog(L, ModVal, NewExit, Exit, PreHeader, + EpilogPreHeader, NewPreHeader, VMap, DT, LI, + PreserveLCSSA); + + // Update counter in loop for unrolling. + // I should be multiply of Count. + IRBuilder<> B2(NewPreHeader->getTerminator()); + Value *TestVal = B2.CreateSub(TripCount, ModVal, "unroll_iter"); + BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator()); + B2.SetInsertPoint(LatchBR); + PHINode *NewIdx = PHINode::Create(TestVal->getType(), 2, "niter", + Header->getFirstNonPHI()); + Value *IdxSub = + B2.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1), + NewIdx->getName() + ".nsub"); + Value *IdxCmp; + if (LatchBR->getSuccessor(0) == Header) + IdxCmp = B2.CreateIsNotNull(IdxSub, NewIdx->getName() + ".ncmp"); + else + IdxCmp = B2.CreateIsNull(IdxSub, NewIdx->getName() + ".ncmp"); + NewIdx->addIncoming(TestVal, NewPreHeader); + NewIdx->addIncoming(IdxSub, Latch); + LatchBR->setCondition(IdxCmp); + } else { + // Connect the prolog code to the original loop and update the + // PHI functions. + ConnectProlog(L, BECount, Count, PrologExit, PreHeader, NewPreHeader, + VMap, DT, LI, PreserveLCSSA); + } + + // If this loop is nested, then the loop unroller changes the code in the + // parent loop, so the Scalar Evolution pass needs to be run again. + if (Loop *ParentLoop = L->getParentLoop()) + SE->forgetLoop(ParentLoop); + + NumRuntimeUnrolled++; + return true; +} |