From f17a25c88b892d30c2b41ba7ecdfbdfb2b4be9cc Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Wed, 18 Jul 2007 16:29:46 +0000 Subject: It's not necessary to do rounding for alloca operations when the requested alignment is equal to the stack alignment. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40004 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/LoopUnroll.cpp | 500 +++++++++++++++++++++++++++++++++++ 1 file changed, 500 insertions(+) create mode 100644 lib/Transforms/Scalar/LoopUnroll.cpp (limited to 'lib/Transforms/Scalar/LoopUnroll.cpp') diff --git a/lib/Transforms/Scalar/LoopUnroll.cpp b/lib/Transforms/Scalar/LoopUnroll.cpp new file mode 100644 index 0000000..babfc24 --- /dev/null +++ b/lib/Transforms/Scalar/LoopUnroll.cpp @@ -0,0 +1,500 @@ +//===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and is distributed under +// the University of Illinois Open Source License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This pass implements a simple loop unroller. It works best when loops have +// been canonicalized by the -indvars pass, allowing it to determine the trip +// counts of loops easily. +// +// This pass will multi-block loops only if they contain no non-unrolled +// subloops. The process of unrolling can produce extraneous basic blocks +// linked with unconditional branches. This will be corrected in the future. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "loop-unroll" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Constants.h" +#include "llvm/Function.h" +#include "llvm/Instructions.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Support/CFG.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/IntrinsicInst.h" +#include +#include +using namespace llvm; + +STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled"); +STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)"); + +namespace { + cl::opt + UnrollThreshold + ("unroll-threshold", cl::init(100), cl::Hidden, + cl::desc("The cut-off point for automatic loop unrolling")); + + cl::opt + UnrollCount + ("unroll-count", cl::init(0), cl::Hidden, + cl::desc("Use this unroll count for all loops, for testing purposes")); + + class VISIBILITY_HIDDEN LoopUnroll : public LoopPass { + LoopInfo *LI; // The current loop information + public: + static char ID; // Pass ID, replacement for typeid + LoopUnroll() : LoopPass((intptr_t)&ID) {} + + /// A magic value for use with the Threshold parameter to indicate + /// that the loop unroll should be performed regardless of how much + /// code expansion would result. + static const unsigned NoThreshold = UINT_MAX; + + bool runOnLoop(Loop *L, LPPassManager &LPM); + bool unrollLoop(Loop *L, unsigned Count, unsigned Threshold); + BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB); + + /// This transformation requires natural loop information & requires that + /// loop preheaders be inserted into the CFG... + /// + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequiredID(LoopSimplifyID); + AU.addRequiredID(LCSSAID); + AU.addRequired(); + AU.addPreservedID(LCSSAID); + AU.addPreserved(); + } + }; + char LoopUnroll::ID = 0; + RegisterPass X("loop-unroll", "Unroll loops"); +} + +LoopPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); } + +/// ApproximateLoopSize - Approximate the size of the loop. +static unsigned ApproximateLoopSize(const Loop *L) { + unsigned Size = 0; + for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) { + BasicBlock *BB = L->getBlocks()[i]; + Instruction *Term = BB->getTerminator(); + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + if (isa(I) && BB == L->getHeader()) { + // Ignore PHI nodes in the header. + } else if (I->hasOneUse() && I->use_back() == Term) { + // Ignore instructions only used by the loop terminator. + } else if (isa(I)) { + // Ignore debug instructions + } else { + ++Size; + } + + // TODO: Ignore expressions derived from PHI and constants if inval of phi + // is a constant, or if operation is associative. This will get induction + // variables. + } + } + + return Size; +} + +// RemapInstruction - Convert the instruction operands from referencing the +// current values into those specified by ValueMap. +// +static inline void RemapInstruction(Instruction *I, + DenseMap &ValueMap) { + for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { + Value *Op = I->getOperand(op); + DenseMap::iterator It = ValueMap.find(Op); + if (It != ValueMap.end()) Op = It->second; + I->setOperand(op, Op); + } +} + +// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it +// only has one predecessor, and that predecessor only has one successor. +// Returns the new combined block. +BasicBlock *LoopUnroll::FoldBlockIntoPredecessor(BasicBlock *BB) { + // Merge basic blocks into their predecessor if there is only one distinct + // pred, and if there is only one distinct successor of the predecessor, and + // if there are no PHI nodes. + // + BasicBlock *OnlyPred = BB->getSinglePredecessor(); + if (!OnlyPred) return 0; + + if (OnlyPred->getTerminator()->getNumSuccessors() != 1) + return 0; + + DOUT << "Merging: " << *BB << "into: " << *OnlyPred; + + // Resolve any PHI nodes at the start of the block. They are all + // guaranteed to have exactly one entry if they exist, unless there are + // multiple duplicate (but guaranteed to be equal) entries for the + // incoming edges. This occurs when there are multiple edges from + // OnlyPred to OnlySucc. + // + while (PHINode *PN = dyn_cast(&BB->front())) { + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + BB->getInstList().pop_front(); // Delete the phi node... + } + + // Delete the unconditional branch from the predecessor... + OnlyPred->getInstList().pop_back(); + + // Move all definitions in the successor to the predecessor... + OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); + + // Make all PHI nodes that referred to BB now refer to Pred as their + // source... + BB->replaceAllUsesWith(OnlyPred); + + std::string OldName = BB->getName(); + + // Erase basic block from the function... + LI->removeBlock(BB); + BB->eraseFromParent(); + + // Inherit predecessor's name if it exists... + if (!OldName.empty() && !OnlyPred->hasName()) + OnlyPred->setName(OldName); + + return OnlyPred; +} + +bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { + LI = &getAnalysis(); + + // Unroll the loop. + if (!unrollLoop(L, UnrollCount, UnrollThreshold)) + return false; + + // Update the loop information for this loop. + // If we completely unrolled the loop, remove it from the parent. + if (L->getNumBackEdges() == 0) + LPM.deleteLoopFromQueue(L); + + return true; +} + +/// Unroll the given loop by UnrollCount, or by a heuristically-determined +/// value if Count is zero. If Threshold is not NoThreshold, it is a value +/// to limit code size expansion. If the loop size would expand beyond the +/// threshold value, unrolling is suppressed. The return value is true if +/// any transformations are performed. +/// +bool LoopUnroll::unrollLoop(Loop *L, unsigned Count, unsigned Threshold) { + assert(L->isLCSSAForm()); + + BasicBlock *Header = L->getHeader(); + BasicBlock *LatchBlock = L->getLoopLatch(); + BranchInst *BI = dyn_cast(LatchBlock->getTerminator()); + + DOUT << "Loop Unroll: F[" << Header->getParent()->getName() + << "] Loop %" << Header->getName() << "\n"; + + if (!BI || BI->isUnconditional()) { + // The loop-rorate pass can be helpful to avoid this in many cases. + DOUT << " Can't unroll; loop not terminated by a conditional branch.\n"; + return false; + } + + // Determine the trip count and/or trip multiple. A TripCount value of zero + // is used to mean an unknown trip count. The TripMultiple value is the + // greatest known integer multiple of the trip count. + unsigned TripCount = 0; + unsigned TripMultiple = 1; + if (Value *TripCountValue = L->getTripCount()) { + if (ConstantInt *TripCountC = dyn_cast(TripCountValue)) { + // Guard against huge trip counts. This also guards against assertions in + // APInt from the use of getZExtValue, below. + if (TripCountC->getValue().getActiveBits() <= 32) { + TripCount = (unsigned)TripCountC->getZExtValue(); + } + } else if (BinaryOperator *BO = dyn_cast(TripCountValue)) { + switch (BO->getOpcode()) { + case BinaryOperator::Mul: + if (ConstantInt *MultipleC = dyn_cast(BO->getOperand(1))) { + if (MultipleC->getValue().getActiveBits() <= 32) { + TripMultiple = (unsigned)MultipleC->getZExtValue(); + } + } + break; + default: break; + } + } + } + if (TripCount != 0) + DOUT << " Trip Count = " << TripCount << "\n"; + if (TripMultiple != 1) + DOUT << " Trip Multiple = " << TripMultiple << "\n"; + + // Automatically select an unroll count. + if (Count == 0) { + // Conservative heuristic: if we know the trip count, see if we can + // completely unroll (subject to the threshold, checked below); otherwise + // don't unroll. + if (TripCount != 0) { + Count = TripCount; + } else { + return false; + } + } + + // Effectively "DCE" unrolled iterations that are beyond the tripcount + // and will never be executed. + if (TripCount != 0 && Count > TripCount) + Count = TripCount; + + assert(Count > 0); + assert(TripMultiple > 0); + assert(TripCount == 0 || TripCount % TripMultiple == 0); + + // Enforce the threshold. + if (Threshold != NoThreshold) { + unsigned LoopSize = ApproximateLoopSize(L); + DOUT << " Loop Size = " << LoopSize << "\n"; + uint64_t Size = (uint64_t)LoopSize*Count; + if (TripCount != 1 && Size > Threshold) { + DOUT << " TOO LARGE TO UNROLL: " + << Size << ">" << Threshold << "\n"; + return false; + } + } + + // Are we eliminating the loop control altogether? + bool CompletelyUnroll = Count == TripCount; + + // If we know the trip count, we know the multiple... + unsigned BreakoutTrip = 0; + if (TripCount != 0) { + BreakoutTrip = TripCount % Count; + TripMultiple = 0; + } else { + // Figure out what multiple to use. + BreakoutTrip = TripMultiple = + (unsigned)GreatestCommonDivisor64(Count, TripMultiple); + } + + if (CompletelyUnroll) { + DOUT << "COMPLETELY UNROLLING loop %" << Header->getName() + << " with trip count " << TripCount << "!\n"; + } else { + DOUT << "UNROLLING loop %" << Header->getName() + << " by " << Count; + if (TripMultiple == 0 || BreakoutTrip != TripMultiple) { + DOUT << " with a breakout at trip " << BreakoutTrip; + } else if (TripMultiple != 1) { + DOUT << " with " << TripMultiple << " trips per branch"; + } + DOUT << "!\n"; + } + + std::vector LoopBlocks = L->getBlocks(); + + bool ContinueOnTrue = L->contains(BI->getSuccessor(0)); + BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue); + + // For the first iteration of the loop, we should use the precloned values for + // PHI nodes. Insert associations now. + typedef DenseMap ValueMapTy; + ValueMapTy LastValueMap; + std::vector OrigPHINode; + for (BasicBlock::iterator I = Header->begin(); isa(I); ++I) { + PHINode *PN = cast(I); + OrigPHINode.push_back(PN); + if (Instruction *I = + dyn_cast(PN->getIncomingValueForBlock(LatchBlock))) + if (L->contains(I->getParent())) + LastValueMap[I] = I; + } + + std::vector Headers; + std::vector Latches; + Headers.push_back(Header); + Latches.push_back(LatchBlock); + + for (unsigned It = 1; It != Count; ++It) { + char SuffixBuffer[100]; + sprintf(SuffixBuffer, ".%d", It); + + std::vector NewBlocks; + + for (std::vector::iterator BB = LoopBlocks.begin(), + E = LoopBlocks.end(); BB != E; ++BB) { + ValueMapTy ValueMap; + BasicBlock *New = CloneBasicBlock(*BB, ValueMap, SuffixBuffer); + Header->getParent()->getBasicBlockList().push_back(New); + + // Loop over all of the PHI nodes in the block, changing them to use the + // incoming values from the previous block. + if (*BB == Header) + for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { + PHINode *NewPHI = cast(ValueMap[OrigPHINode[i]]); + Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock); + if (Instruction *InValI = dyn_cast(InVal)) + if (It > 1 && L->contains(InValI->getParent())) + InVal = LastValueMap[InValI]; + ValueMap[OrigPHINode[i]] = InVal; + New->getInstList().erase(NewPHI); + } + + // Update our running map of newest clones + LastValueMap[*BB] = New; + for (ValueMapTy::iterator VI = ValueMap.begin(), VE = ValueMap.end(); + VI != VE; ++VI) + LastValueMap[VI->first] = VI->second; + + L->addBasicBlockToLoop(New, *LI); + + // Add phi entries for newly created values to all exit blocks except + // the successor of the latch block. The successor of the exit block will + // be updated specially after unrolling all the way. + if (*BB != LatchBlock) + for (Value::use_iterator UI = (*BB)->use_begin(), UE = (*BB)->use_end(); + UI != UE; ++UI) { + Instruction *UseInst = cast(*UI); + if (isa(UseInst) && !L->contains(UseInst->getParent())) { + PHINode *phi = cast(UseInst); + Value *Incoming = phi->getIncomingValueForBlock(*BB); + if (isa(Incoming)) + Incoming = LastValueMap[Incoming]; + + phi->addIncoming(Incoming, New); + } + } + + // Keep track of new headers and latches as we create them, so that + // we can insert the proper branches later. + if (*BB == Header) + Headers.push_back(New); + if (*BB == LatchBlock) { + Latches.push_back(New); + + // Also, clear out the new latch's back edge so that it doesn't look + // like a new loop, so that it's amenable to being merged with adjacent + // blocks later on. + TerminatorInst *Term = New->getTerminator(); + assert(L->contains(Term->getSuccessor(!ContinueOnTrue))); + assert(Term->getSuccessor(ContinueOnTrue) == LoopExit); + Term->setSuccessor(!ContinueOnTrue, NULL); + } + + NewBlocks.push_back(New); + } + + // Remap all instructions in the most recent iteration + for (unsigned i = 0; i < NewBlocks.size(); ++i) + for (BasicBlock::iterator I = NewBlocks[i]->begin(), + E = NewBlocks[i]->end(); I != E; ++I) + RemapInstruction(I, LastValueMap); + } + + // The latch block exits the loop. If there are any PHI nodes in the + // successor blocks, update them to use the appropriate values computed as the + // last iteration of the loop. + if (Count != 1) { + SmallPtrSet Users; + for (Value::use_iterator UI = LatchBlock->use_begin(), + UE = LatchBlock->use_end(); UI != UE; ++UI) + if (PHINode *phi = dyn_cast(*UI)) + Users.insert(phi); + + BasicBlock *LastIterationBB = cast(LastValueMap[LatchBlock]); + for (SmallPtrSet::iterator SI = Users.begin(), SE = Users.end(); + SI != SE; ++SI) { + PHINode *PN = *SI; + Value *InVal = PN->removeIncomingValue(LatchBlock, false); + // If this value was defined in the loop, take the value defined by the + // last iteration of the loop. + if (Instruction *InValI = dyn_cast(InVal)) { + if (L->contains(InValI->getParent())) + InVal = LastValueMap[InVal]; + } + PN->addIncoming(InVal, LastIterationBB); + } + } + + // Now, if we're doing complete unrolling, loop over the PHI nodes in the + // original block, setting them to their incoming values. + if (CompletelyUnroll) { + BasicBlock *Preheader = L->getLoopPreheader(); + for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { + PHINode *PN = OrigPHINode[i]; + PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader)); + Header->getInstList().erase(PN); + } + } + + // Now that all the basic blocks for the unrolled iterations are in place, + // set up the branches to connect them. + for (unsigned i = 0, e = Latches.size(); i != e; ++i) { + // The original branch was replicated in each unrolled iteration. + BranchInst *Term = cast(Latches[i]->getTerminator()); + + // The branch destination. + unsigned j = (i + 1) % e; + BasicBlock *Dest = Headers[j]; + bool NeedConditional = true; + + // For a complete unroll, make the last iteration end with a branch + // to the exit block. + if (CompletelyUnroll && j == 0) { + Dest = LoopExit; + NeedConditional = false; + } + + // If we know the trip count or a multiple of it, we can safely use an + // unconditional branch for some iterations. + if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) { + NeedConditional = false; + } + + if (NeedConditional) { + // Update the conditional branch's successor for the following + // iteration. + Term->setSuccessor(!ContinueOnTrue, Dest); + } else { + Term->setUnconditionalDest(Dest); + // Merge adjacent basic blocks, if possible. + if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest)) { + std::replace(Latches.begin(), Latches.end(), Dest, Fold); + std::replace(Headers.begin(), Headers.end(), Dest, Fold); + } + } + } + + // At this point, the code is well formed. We now do a quick sweep over the + // inserted code, doing constant propagation and dead code elimination as we + // go. + const std::vector &NewLoopBlocks = L->getBlocks(); + for (std::vector::const_iterator BB = NewLoopBlocks.begin(), + BBE = NewLoopBlocks.end(); BB != BBE; ++BB) + for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ) { + Instruction *Inst = I++; + + if (isInstructionTriviallyDead(Inst)) + (*BB)->getInstList().erase(Inst); + else if (Constant *C = ConstantFoldInstruction(Inst)) { + Inst->replaceAllUsesWith(C); + (*BB)->getInstList().erase(Inst); + } + } + + NumCompletelyUnrolled += CompletelyUnroll; + ++NumUnrolled; + return true; +} -- cgit v1.1