//===-- 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 file 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 is currently extremely limited. It only currently only unrolls
-// single basic block loops that execute a constant number of times.
-//
//===----------------------------------------------------------------------===//
#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/LoopInfo.h"
-#include "llvm/Transforms/Utils/Cloning.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "Support/CommandLine.h"
-#include "Support/Debug.h"
-#include "Support/Statistic.h"
-#include <cstdio>
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/UnrollLoop.h"
+#include <climits>
+
using namespace llvm;
-namespace {
- Statistic<> NumUnrolled("loop-unroll", "Number of loops completely unrolled");
+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>
- UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden,
- cl::desc("The cut-off point for loop unrolling"));
+static cl::opt<unsigned>
+UnrollCount("unroll-count", cl::init(0), cl::Hidden,
+ cl::desc("Use this unroll count for all loops, for testing purposes"));
- class LoopUnroll : public FunctionPass {
- LoopInfo *LI; // The current loop information
+namespace {
+ class VISIBILITY_HIDDEN LoopUnroll : public LoopPass {
public:
- virtual bool runOnFunction(Function &F);
- bool visitLoop(Loop *L);
+ 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);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG...
///
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesCFG();
AU.addRequiredID(LoopSimplifyID);
+ AU.addRequiredID(LCSSAID);
AU.addRequired<LoopInfo>();
+ AU.addPreservedID(LCSSAID);
+ AU.addPreserved<LoopInfo>();
}
};
- RegisterOpt<LoopUnroll> X("loop-unroll", "Unroll loops");
}
-FunctionPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
+char LoopUnroll::ID = 0;
+static RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
-bool LoopUnroll::runOnFunction(Function &F) {
- bool Changed = false;
- LI = &getAnalysis<LoopInfo>();
+LoopPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
- for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
- Changed |= visitLoop(*I);
-
- return Changed;
-}
-
-/// ApproximateLoopSize - Approximate the size of the loop after it has been
-/// unrolled.
+/// 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) {
// 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<DbgInfoIntrinsic>(I)) {
+ // Ignore debug instructions
+ } else if (isa<CallInst>(I)) {
+ // Estimate size overhead introduced by call instructions which
+ // is higher than other instructions. Here 3 and 10 are magic
+ // numbers that help one isolated test case from PR2067 without
+ // negatively impacting measured benchmarks.
+ if (isa<IntrinsicInst>(I))
+ Size = Size + 3;
+ else
+ Size = Size + 10;
} else {
++Size;
}
return Size;
}
-// RemapInstruction - Convert the instruction operands from referencing the
-// current values into those specified by ValueMap.
-//
-static inline void RemapInstruction(Instruction *I,
- std::map<const Value *, Value*> &ValueMap) {
- for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
- Value *Op = I->getOperand(op);
- std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
- if (It != ValueMap.end()) Op = It->second;
- I->setOperand(op, Op);
- }
-}
-
-
-bool LoopUnroll::visitLoop(Loop *L) {
- bool Changed = false;
-
- // Recurse through all subloops before we process this loop. Copy the loop
- // list so that the child can update the loop tree if it needs to delete the
- // loop.
- std::vector<Loop*> SubLoops(L->begin(), L->end());
- for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
- Changed |= visitLoop(SubLoops[i]);
+bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
+ assert(L->isLCSSAForm());
+ LoopInfo *LI = &getAnalysis<LoopInfo>();
- // We only handle single basic block loops right now.
- if (L->getBlocks().size() != 1)
- return Changed;
+ BasicBlock *Header = L->getHeader();
+ DOUT << "Loop Unroll: F[" << Header->getParent()->getName()
+ << "] Loop %" << Header->getName() << "\n";
- BasicBlock *BB = L->getHeader();
- BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
- if (BI == 0) return Changed; // Must end in a conditional branch
-
- ConstantInt *TripCountC = dyn_cast_or_null<ConstantInt>(L->getTripCount());
- if (!TripCountC) return Changed; // Must have constant trip count!
-
- unsigned TripCount = TripCountC->getRawValue();
- if (TripCount != TripCountC->getRawValue())
- return Changed; // More than 2^32 iterations???
-
- unsigned LoopSize = ApproximateLoopSize(L);
- DEBUG(std::cerr << "Loop Unroll: F[" << BB->getParent()->getName()
- << "] Loop %" << BB->getName() << " Loop Size = " << LoopSize
- << " Trip Count = " << TripCount << " - ");
- if (LoopSize*TripCount > UnrollThreshold) {
- DEBUG(std::cerr << "TOO LARGE: " << LoopSize*TripCount << ">"
- << UnrollThreshold << "\n");
- return Changed;
- }
- DEBUG(std::cerr << "UNROLLING!\n");
-
- assert(L->getExitBlocks().size() == 1 && "Must have exactly one exit block!");
- BasicBlock *LoopExit = L->getExitBlocks()[0];
-
- // Create a new basic block to temporarily hold all of the cloned code.
- BasicBlock *NewBlock = new BasicBlock();
-
- // For the first iteration of the loop, we should use the precloned values for
- // PHI nodes. Insert associations now.
- std::map<const Value*, Value*> LastValueMap;
- std::vector<PHINode*> OrigPHINode;
- for (BasicBlock::iterator I = BB->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
- OrigPHINode.push_back(PN);
- if (Instruction *I =dyn_cast<Instruction>(PN->getIncomingValueForBlock(BB)))
- if (I->getParent() == BB)
- LastValueMap[I] = I;
- }
-
- // Remove the exit branch from the loop
- BB->getInstList().erase(BI);
-
- assert(TripCount != 0 && "Trip count of 0 is impossible!");
- for (unsigned It = 1; It != TripCount; ++It) {
- char SuffixBuffer[100];
- sprintf(SuffixBuffer, ".%d", It);
- std::map<const Value*, Value*> ValueMap;
- BasicBlock *New = CloneBasicBlock(BB, ValueMap, SuffixBuffer);
-
- // Loop over all of the PHI nodes in the block, changing them to use the
- // incoming values from the previous block.
- for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
- PHINode *NewPHI = cast<PHINode>(ValueMap[OrigPHINode[i]]);
- Value *InVal = NewPHI->getIncomingValueForBlock(BB);
- if (Instruction *InValI = dyn_cast<Instruction>(InVal))
- if (InValI->getParent() == BB)
- InVal = LastValueMap[InValI];
- ValueMap[OrigPHINode[i]] = InVal;
- New->getInstList().erase(NewPHI);
+ // 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
+ // completely unroll (subject to the threshold, checked below); otherwise
+ // don't unroll.
+ if (TripCount != 0) {
+ Count = TripCount;
+ } else {
+ return false;
}
-
- for (BasicBlock::iterator I = New->begin(), E = New->end(); I != E; ++I)
- RemapInstruction(I, ValueMap);
-
- // Now that all of the instructions are remapped, splice them into the end
- // of the NewBlock.
- NewBlock->getInstList().splice(NewBlock->end(), New->getInstList());
- delete New;
-
- // LastValue map now contains values from this iteration.
- std::swap(LastValueMap, ValueMap);
}
- // If there was more than one iteration, replace any uses of values computed
- // in the loop with values computed during last iteration of the loop.
- if (TripCount != 1)
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
- std::vector<User*> Users(I->use_begin(), I->use_end());
- for (unsigned i = 0, e = Users.size(); i != e; ++i) {
- Instruction *UI = cast<Instruction>(Users[i]);
- if (UI->getParent() != BB && UI->getParent() != NewBlock)
- UI->replaceUsesOfWith(I, LastValueMap[I]);
- }
- }
-
- // Now that we cloned the block as many times as we needed, stitch the new
- // code into the original block and delete the temporary block.
- BB->getInstList().splice(BB->end(), NewBlock->getInstList());
- delete NewBlock;
-
- // Now loop over the PHI nodes in the original block, setting them to their
- // incoming values.
- BasicBlock *Preheader = L->getLoopPreheader();
- for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
- PHINode *PN = OrigPHINode[i];
- PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
- BB->getInstList().erase(PN);
- }
-
- // Finally, add an unconditional branch to the block to continue into the exit
- // block.
- new BranchInst(LoopExit, BB);
-
- // 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.
- 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);
+ // Enforce the threshold.
+ if (UnrollThreshold != NoThreshold) {
+ unsigned LoopSize = ApproximateLoopSize(L);
+ DOUT << " Loop Size = " << LoopSize << "\n";
+ uint64_t Size = (uint64_t)LoopSize*Count;
+ if (TripCount != 1 && Size > UnrollThreshold) {
+ DOUT << " TOO LARGE TO UNROLL: "
+ << Size << ">" << UnrollThreshold << "\n";
+ return false;
}
}
- // FIXME: Should update analyses
-
- // FIXME: Should fold into preheader and exit block
+ // Unroll the loop.
+ if (!UnrollLoop(L, Count, LI, &LPM))
+ return false;
- ++NumUnrolled;
return true;
}
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