diff options
| -rw-r--r-- | include/llvm/Analysis/LoopInfo.h | 53 | ||||
| -rw-r--r-- | lib/Transforms/Scalar/LoopUnroll.cpp | 393 | ||||
| -rw-r--r-- | lib/Transforms/Utils/UnrollLoop.cpp | 371 |
3 files changed, 438 insertions, 379 deletions
diff --git a/include/llvm/Analysis/LoopInfo.h b/include/llvm/Analysis/LoopInfo.h index 28748b0e54..e3e2cdd32d 100644 --- a/include/llvm/Analysis/LoopInfo.h +++ b/include/llvm/Analysis/LoopInfo.h @@ -418,6 +418,59 @@ public: return 0; } + /// getSmallConstantTripCount - Returns the trip count of this loop as a + /// normal unsigned value, if possible. Returns 0 if the trip count is unknown + /// of not constant. Will also return 0 if the trip count is very large + /// (>= 2^32) + inline unsigned getSmallConstantTripCount() const { + Value* TripCount = this->getTripCount(); + if (TripCount) { + if (ConstantInt *TripCountC = dyn_cast<ConstantInt>(TripCount)) { + // Guard against huge trip counts. + if (TripCountC->getValue().getActiveBits() <= 32) { + return (unsigned)TripCountC->getZExtValue(); + } + } + } + return 0; + } + + /// getSmallConstantTripMultiple - Returns the largest constant divisor of the + /// trip count of this loop as a normal unsigned value, if possible. This + /// means that the actual trip count is always a multiple of the returned + /// value (don't forget the trip count could very well be zero as well!). + /// + /// Returns 1 if the trip count is unknown or not guaranteed to be the + /// multiple of a constant (which is also the case if the trip count is simply + /// constant, use getSmallConstantTripCount for that case), Will also return 1 + /// if the trip count is very large (>= 2^32). + inline unsigned getSmallConstantTripMultiple() const { + Value* TripCount = this->getTripCount(); + // This will hold the ConstantInt result, if any + ConstantInt *Result = NULL; + if (TripCount) { + // See if the trip count is constant itself + Result = dyn_cast<ConstantInt>(TripCount); + // if not, see if it is a multiplication + if (!Result) + if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TripCount)) { + switch (BO->getOpcode()) { + case BinaryOperator::Mul: + Result = dyn_cast<ConstantInt>(BO->getOperand(1)); + break; + default: + break; + } + } + } + // Guard against huge trip counts. + if (Result && Result->getValue().getActiveBits() <= 32) { + return (unsigned)Result->getZExtValue(); + } else { + return 1; + } + } + /// isLCSSAForm - Return true if the Loop is in LCSSA form inline bool isLCSSAForm() const { // Sort the blocks vector so that we can use binary search to do quick diff --git a/lib/Transforms/Scalar/LoopUnroll.cpp b/lib/Transforms/Scalar/LoopUnroll.cpp index d329970204..ad8cfd4eeb 100644 --- a/lib/Transforms/Scalar/LoopUnroll.cpp +++ b/lib/Transforms/Scalar/LoopUnroll.cpp @@ -10,39 +10,19 @@ // 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/IntrinsicInst.h" #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 <algorithm> -#include <climits> -#include <cstdio> -using namespace llvm; +#include "llvm/Transforms/Utils/UnrollLoop.h" -STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled"); -STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)"); +using namespace llvm; static cl::opt<unsigned> UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden, @@ -54,7 +34,6 @@ UnrollCount("unroll-count", cl::init(0), cl::Hidden, namespace { 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) {} @@ -65,8 +44,6 @@ namespace { 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... @@ -121,136 +98,18 @@ static unsigned ApproximateLoopSize(const Loop *L) { return Size; } -// RemapInstruction - Convert the instruction operands from referencing the -// current values into those specified by ValueMap. -// -static inline void RemapInstruction(Instruction *I, - DenseMap<const Value *, Value*> &ValueMap) { - for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { - Value *Op = I->getOperand(op); - DenseMap<const Value *, Value*>::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<PHINode>(&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<LoopInfo>(); - - // 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()); + LoopInfo *LI = &getAnalysis<LoopInfo>(); BasicBlock *Header = L->getHeader(); - BasicBlock *LatchBlock = L->getLoopLatch(); - BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator()); - DOUT << "Loop Unroll: F[" << Header->getParent()->getName() << "] Loop %" << Header->getName() << "\n"; - if (!BI || BI->isUnconditional()) { - // The loop-rotate 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<ConstantInt>(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<BinaryOperator>(TripCountValue)) { - switch (BO->getOpcode()) { - case BinaryOperator::Mul: - if (ConstantInt *MultipleC = dyn_cast<ConstantInt>(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"; - + // Find trip count + unsigned TripCount = L->getSmallConstantTripCount(); + unsigned Count = UnrollCount; + // Automatically select an unroll count. if (Count == 0) { // Conservative heuristic: if we know the trip count, see if we can @@ -263,245 +122,21 @@ bool LoopUnroll::unrollLoop(Loop *L, unsigned Count, unsigned Threshold) { } } - // 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) { + if (UnrollThreshold != NoThreshold) { unsigned LoopSize = ApproximateLoopSize(L); DOUT << " Loop Size = " << LoopSize << "\n"; uint64_t Size = (uint64_t)LoopSize*Count; - if (TripCount != 1 && Size > Threshold) { + if (TripCount != 1 && Size > UnrollThreshold) { DOUT << " TOO LARGE TO UNROLL: " - << Size << ">" << Threshold << "\n"; + << Size << ">" << UnrollThreshold << "\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<BasicBlock*> 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<const Value*, Value*> ValueMapTy; - ValueMapTy LastValueMap; - std::vector<PHINode*> OrigPHINode; - for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { - PHINode *PN = cast<PHINode>(I); - OrigPHINode.push_back(PN); - if (Instruction *I = - dyn_cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock))) - if (L->contains(I->getParent())) - LastValueMap[I] = I; - } - - std::vector<BasicBlock*> Headers; - std::vector<BasicBlock*> 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<BasicBlock*> NewBlocks; - - for (std::vector<BasicBlock*>::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<PHINode>(ValueMap[OrigPHINode[i]]); - Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock); - if (Instruction *InValI = dyn_cast<Instruction>(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->getBase()); - - // 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;) { - Instruction *UseInst = cast<Instruction>(*UI); - ++UI; - if (isa<PHINode>(UseInst) && !L->contains(UseInst->getParent())) { - PHINode *phi = cast<PHINode>(UseInst); - Value *Incoming = phi->getIncomingValueForBlock(*BB); - 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<PHINode*, 8> Users; - for (Value::use_iterator UI = LatchBlock->use_begin(), - UE = LatchBlock->use_end(); UI != UE; ++UI) - if (PHINode *phi = dyn_cast<PHINode>(*UI)) - Users.insert(phi); - - BasicBlock *LastIterationBB = cast<BasicBlock>(LastValueMap[LatchBlock]); - for (SmallPtrSet<PHINode*,8>::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<Instruction>(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<BranchInst>(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<BasicBlock*> &NewLoopBlocks = L->getBlocks(); - for (std::vector<BasicBlock*>::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); - } - } + // Unroll the loop. + if (!UnrollLoop(L, Count, LI, &LPM)) + return false; - NumCompletelyUnrolled += CompletelyUnroll; - ++NumUnrolled; return true; } diff --git a/lib/Transforms/Utils/UnrollLoop.cpp b/lib/Transforms/Utils/UnrollLoop.cpp new file mode 100644 index 0000000000..a86306c9e4 --- /dev/null +++ b/lib/Transforms/Utils/UnrollLoop.cpp @@ -0,0 +1,371 @@ +//===-- UnrollLoop.cpp - 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. It does not define any +// actual pass or policy, but provides a single function to perform loop +// unrolling. +// +// It works best when loops have been canonicalized by the -indvars pass, +// allowing it to determine the trip counts of loops easily. +// +// 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/Utils/UnrollLoop.h" +#include "llvm/BasicBlock.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Support/Debug.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/Local.h" + +using namespace llvm; + +/* TODO: Should these be here or in LoopUnroll? */ +STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled"); +STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)"); + +/// RemapInstruction - Convert the instruction operands from referencing the +/// current values into those specified by ValueMap. +static inline void RemapInstruction(Instruction *I, + DenseMap<const Value *, Value*> &ValueMap) { + for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { + Value *Op = I->getOperand(op); + DenseMap<const Value *, Value*>::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. +/// The LoopInfo Analysis that is passed will be kept consistent. +/// Returns the new combined block. +static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) { + // 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<PHINode>(&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; +} + +/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true +/// if unrolling was succesful, or false if the loop was unmodified. Unrolling +/// can only fail when the loop's latch block is not terminated by a conditional +/// branch instruction. However, if the trip count (and multiple) are not known, +/// loop unrolling will mostly produce more code that is no faster. +/// +/// The LoopInfo Analysis that is passed will be kept consistent. +/// +/// If a LoopPassManager is passed in, and the loop is fully removed, it will be +/// removed from the LoopPassManager as well. LPM can also be NULL. +bool llvm::UnrollLoop(Loop *L, unsigned Count, LoopInfo* LI, LPPassManager* LPM) { + assert(L->isLCSSAForm()); + + BasicBlock *Header = L->getHeader(); + BasicBlock *LatchBlock = L->getLoopLatch(); + BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator()); + + if (!BI || BI->isUnconditional()) { + // The loop-rotate pass can be helpful to avoid this in many cases. + DOUT << " Can't unroll; loop not terminated by a conditional branch.\n"; + return false; + } + + // Find trip count + unsigned TripCount = L->getSmallConstantTripCount(); + // Find trip multiple if count is not available + unsigned TripMultiple = 1; + if (TripCount == 0) + TripMultiple = L->getSmallConstantTripMultiple(); + + if (TripCount != 0) + DOUT << " Trip Count = " << TripCount << "\n"; + if (TripMultiple != 1) + DOUT << " Trip Multiple = " << TripMultiple << "\n"; + + // 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); + + // 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<BasicBlock*> 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<const Value*, Value*> ValueMapTy; + ValueMapTy LastValueMap; + std::vector<PHINode*> OrigPHINode; + for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(I); + OrigPHINode.push_back(PN); + if (Instruction *I = + dyn_cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock))) + if (L->contains(I->getParent())) + LastValueMap[I] = I; + } + + std::vector<BasicBlock*> Headers; + std::vector<BasicBlock*> 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<BasicBlock*> NewBlocks; + + for (std::vector<BasicBlock*>::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<PHINode>(ValueMap[OrigPHINode[i]]); + Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock); + if (Instruction *InValI = dyn_cast<Instruction>(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->getBase()); + + // 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;) { + Instruction *UseInst = cast<Instruction>(*UI); + ++UI; + if (isa<PHINode>(UseInst) && !L->contains(UseInst->getParent())) { + PHINode *phi = cast<PHINode>(UseInst); + Value *Incoming = phi->getIncomingValueForBlock(*BB); + 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<PHINode*, 8> Users; + for (Value::use_iterator UI = LatchBlock->use_begin(), + UE = LatchBlock->use_end(); UI != UE; ++UI) + if (PHINode *phi = dyn_cast<PHINode>(*UI)) + Users.insert(phi); + + BasicBlock *LastIterationBB = cast<BasicBlock>(LastValueMap[LatchBlock]); + for (SmallPtrSet<PHINode*,8>::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<Instruction>(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<BranchInst>(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, LI)) { + 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<BasicBlock*> &NewLoopBlocks = L->getBlocks(); + for (std::vector<BasicBlock*>::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; + // Remove the loop from the LoopPassManager if it's completely removed. + if (CompletelyUnroll && LPM != NULL) + LPM->deleteLoopFromQueue(L); + + // If we didn't completely unroll the loop, it should still be in LCSSA form. + if (!CompletelyUnroll) + assert(L->isLCSSAForm()); + + return true; +} |