// 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 "llvm/Transforms/Utils/UnrollLoop.h"
#include <climits>
-#include <cstdio>
-using namespace llvm;
-STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled");
-STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)");
+using namespace llvm;
-namespace {
- cl::opt<unsigned>
- UnrollThreshold
- ("unroll-threshold", cl::init(100), cl::Hidden,
- cl::desc("The cut-off point for automatic loop unrolling"));
+static cl::opt<unsigned>
+UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden,
+ cl::desc("The cut-off point for automatic loop unrolling"));
- cl::opt<unsigned>
- UnrollCount
- ("unroll-count", cl::init(0), cl::Hidden,
- cl::desc("Use this unroll count for all loops, for testing purposes"));
+static cl::opt<unsigned>
+UnrollCount("unroll-count", cl::init(0), cl::Hidden,
+ cl::desc("Use this unroll count for all loops, for testing purposes"));
+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) {}
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...
AU.addPreserved<LoopInfo>();
}
};
- char LoopUnroll::ID = 0;
- RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
}
+char LoopUnroll::ID = 0;
+static RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
+
LoopPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
/// ApproximateLoopSize - Approximate the size of the loop.
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
}
}
- // 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) {
- BasicBlock *NB = NewBlocks[i];
- if (BasicBlock *UnwindDest = NB->getUnwindDest())
- NB->setUnwindDest(cast<BasicBlock>(LastValueMap[UnwindDest]));
-
- for (BasicBlock::iterator I = NB->begin(), E = NB->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;
}
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