//
// 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 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/LoopInfo.h"
-#include "llvm/Transforms/Utils/Cloning.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Support/CFG.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Support/Compiler.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/IntrinsicInst.h"
-#include <cstdio>
-#include <set>
-#include <algorithm>
-#include <iostream>
+#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
+static cl::opt<bool>
+UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
+ cl::desc("Allows loops to be partially unrolled until "
+ "-unroll-threshold loop size is reached."));
+
+namespace {
+ class VISIBILITY_HIDDEN LoopUnroll : public LoopPass {
public:
- virtual bool runOnFunction(Function &F);
- bool visitLoop(Loop *L);
- BasicBlock* FoldBlockIntoPredecessor(BasicBlock* BB);
+ static char ID; // Pass ID, replacement for typeid
+ LoopUnroll() : LoopPass(&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...
AU.addRequired<LoopInfo>();
AU.addPreservedID(LCSSAID);
AU.addPreserved<LoopInfo>();
+ // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info.
+ // If loop unroll does not preserve dom info then LCSSA pass on next
+ // loop will receive invalid dom info.
+ // For now, recreate dom info, if loop is unrolled.
+ AU.addPreserved<DominatorTree>();
+ AU.addPreserved<DominanceFrontier>();
}
};
- RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
}
-FunctionPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
-
-bool LoopUnroll::runOnFunction(Function &F) {
- bool Changed = false;
- LI = &getAnalysis<LoopInfo>();
-
- // Transform all the top-level loops. Copy the loop list so that the child
- // can update the loop tree if it needs to delete the loop.
- std::vector<Loop*> SubLoops(LI->begin(), LI->end());
- for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
- Changed |= visitLoop(SubLoops[i]);
+char LoopUnroll::ID = 0;
+static RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
- return Changed;
-}
+Pass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
-/// 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) {
- BasicBlock *BB = L->getBlocks()[i];
+ for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+ I != E; ++I) {
+ BasicBlock *BB = *I;
Instruction *Term = BB->getTerminator();
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
if (isa<PHINode>(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 (DbgInfoIntrinsic *DbgI = dyn_cast<DbgInfoIntrinsic>(I)) {
+ } else if (isa<DbgInfoIntrinsic>(I)) {
// Ignore debug instructions
+ } else if (isa<GetElementPtrInst>(I) && I->hasOneUse()) {
+ // Ignore GEP as they generally are subsumed into a load or store.
+ } 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);
- }
-}
-
-// 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;
-
- DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred);
- TerminatorInst *Term = OnlyPred->getTerminator();
-
- // 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 predecessors name if it exists...
- if (!OldName.empty() && !OnlyPred->hasName())
- OnlyPred->setName(OldName);
-
- return OnlyPred;
-}
-
-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]);
-
- BasicBlock* Header = L->getHeader();
- BasicBlock* LatchBlock = L->getLoopLatch();
+bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
+ assert(L->isLCSSAForm());
+ LoopInfo *LI = &getAnalysis<LoopInfo>();
- BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
- if (BI == 0) return Changed; // Must end in a conditional branch
+ BasicBlock *Header = L->getHeader();
+ DOUT << "Loop Unroll: F[" << Header->getParent()->getName()
+ << "] Loop %" << Header->getName() << "\n";
- ConstantInt *TripCountC = dyn_cast_or_null<ConstantInt>(L->getTripCount());
- if (!TripCountC) return Changed; // Must have constant trip count!
-
- uint64_t TripCountFull = TripCountC->getZExtValue();
- if (TripCountFull != TripCountC->getZExtValue() || TripCountFull == 0)
- return Changed; // More than 2^32 iterations???
-
- unsigned LoopSize = ApproximateLoopSize(L);
- DEBUG(std::cerr << "Loop Unroll: F[" << Header->getParent()->getName()
- << "] Loop %" << Header->getName() << " Loop Size = "
- << LoopSize << " Trip Count = " << TripCountFull << " - ");
- uint64_t Size = (uint64_t)LoopSize*TripCountFull;
- if (Size > UnrollThreshold) {
- DEBUG(std::cerr << "TOO LARGE: " << Size << ">" << UnrollThreshold << "\n");
- return Changed;
- }
- DEBUG(std::cerr << "UNROLLING!\n");
-
- std::vector<BasicBlock*> LoopBlocks = L->getBlocks();
-
- unsigned TripCount = (unsigned)TripCountFull;
-
- BasicBlock *LoopExit = BI->getSuccessor(L->contains(BI->getSuccessor(0)));
-
- // 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 = 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;
- }
-
- // Remove the exit branch from the loop
- LatchBlock->getInstList().erase(BI);
-
- std::vector<BasicBlock*> Headers;
- std::vector<BasicBlock*> Latches;
- Headers.push_back(Header);
- Latches.push_back(LatchBlock);
-
- assert(TripCount != 0 && "Trip count of 0 is impossible!");
- for (unsigned It = 1; It != TripCount; ++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) {
- std::map<const Value*, Value*> 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 (std::map<const Value*, Value*>::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<Instruction>(*UI);
- if (isa<PHINode>(UseInst) && !L->contains(UseInst->getParent())) {
- PHINode* phi = cast<PHINode>(UseInst);
- Value* Incoming = phi->getIncomingValueForBlock(*BB);
- if (isa<Instruction>(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);
-
- 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);
- }
-
-
+ // Find trip count
+ unsigned TripCount = L->getSmallConstantTripCount();
+ unsigned Count = UnrollCount;
- // Update PHI nodes that reference the final latch block
- if (TripCount > 1) {
- std::set<PHINode*> 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);
-
- for (std::set<PHINode*>::iterator SI = Users.begin(), SE = Users.end();
- SI != SE; ++SI) {
- Value* InVal = (*SI)->getIncomingValueForBlock(LatchBlock);
- if (isa<Instruction>(InVal))
- InVal = LastValueMap[InVal];
- (*SI)->removeIncomingValue(LatchBlock, false);
- if (InVal)
- (*SI)->addIncoming(InVal, cast<BasicBlock>(LastValueMap[LatchBlock]));
- }
- }
-
- // 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));
- Header->getInstList().erase(PN);
- }
-
- // Insert the branches that link the different iterations together
- for (unsigned i = 0; i < Latches.size()-1; ++i) {
- new BranchInst(Headers[i+1], Latches[i]);
- if(BasicBlock* Fold = FoldBlockIntoPredecessor(Headers[i+1])) {
- std::replace(Latches.begin(), Latches.end(), Headers[i+1], Fold);
- std::replace(Headers.begin(), Headers.end(), Headers[i+1], Fold);
+ // 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
+ // try to find greatest modulo of the trip count which is still under
+ // threshold value.
+ if (TripCount != 0) {
+ Count = TripCount;
+ } else {
+ return false;
}
}
-
- // Finally, add an unconditional branch to the block to continue into the exit
- // block.
- new BranchInst(LoopExit, Latches[Latches.size()-1]);
- FoldBlockIntoPredecessor(LoopExit);
-
- // 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);
+ // 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 fully unroll with count: " << Count
+ << " because size: " << Size << ">" << UnrollThreshold << "\n";
+ if (UnrollAllowPartial) {
+ // Reduce unroll count to be modulo of TripCount for partial unrolling
+ Count = UnrollThreshold / LoopSize;
+ while (Count != 0 && TripCount%Count != 0) {
+ Count--;
+ }
+ if (Count < 2) {
+ DOUT << " could not unroll partially\n";
+ return false;
+ } else {
+ DOUT << " partially unrolling with count: " << Count << "\n";
+ }
+ } else {
+ DOUT << " will not try to unroll partially because "
+ << "-unroll-allow-partial not given\n";
+ return false;
}
}
+ }
- // Update the loop information for this loop.
- Loop *Parent = L->getParentLoop();
-
- // Move all of the basic blocks in the loop into the parent loop.
- for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(),
- E = NewLoopBlocks.end(); BB != E; ++BB)
- LI->changeLoopFor(*BB, Parent);
-
- // Remove the loop from the parent.
- if (Parent)
- delete Parent->removeChildLoop(std::find(Parent->begin(), Parent->end(),L));
- else
- delete LI->removeLoop(std::find(LI->begin(), LI->end(), L));
-
- ++NumUnrolled;
+ // Unroll the loop.
+ Function *F = L->getHeader()->getParent();
+ if (!UnrollLoop(L, Count, LI, &LPM))
+ return false;
+
+ // FIXME: Reconstruct dom info, because it is not preserved properly.
+ DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
+ if (DT) {
+ DT->runOnFunction(*F);
+ DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
+ if (DF)
+ DF->runOnFunction(*F);
+ }
return true;
}
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