//===-- 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 is currently extremely limited. It only currently only unrolls
-// single basic block loops that execute a constant number of times.
+// 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.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include <cstdio>
#include <set>
#include <algorithm>
-
using namespace llvm;
namespace {
- Statistic<> NumUnrolled("loop-unroll", "Number of loops completely unrolled");
+ Statistic NumUnrolled("loop-unroll", "Number of loops completely unrolled");
cl::opt<unsigned>
UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden,
public:
virtual bool runOnFunction(Function &F);
bool visitLoop(Loop *L);
+ 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<LoopInfo>();
+ AU.addPreservedID(LCSSAID);
AU.addPreserved<LoopInfo>();
}
};
- RegisterOpt<LoopUnroll> X("loop-unroll", "Unroll loops");
+ RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops");
}
FunctionPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
// 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)) {
- // Ignore debug instructions
+ } else if (isa<DbgInfoIntrinsic>(I)) {
+ // Ignore debug instructions
} else {
++Size;
}
return Size;
}
-// RemapInstruction - Convert the instruction operands from referencing the
+// RemapInstruction - Convert the instruction operands from referencing the
// current values into those specified by ValueMap.
//
-static inline void RemapInstruction(Instruction *I,
+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);
}
}
+// 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 predecessors name if it exists...
+ if (!OldName.empty() && !OnlyPred->hasName())
+ OnlyPred->setName(OldName);
+
+ return OnlyPred;
+}
+
bool LoopUnroll::visitLoop(Loop *L) {
bool Changed = false;
for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
Changed |= visitLoop(SubLoops[i]);
- // We only handle single basic block loops right now.
- if (L->getBlocks().size() != 1)
- return Changed;
+ BasicBlock* Header = L->getHeader();
+ BasicBlock* LatchBlock = L->getLoopLatch();
- BasicBlock *BB = L->getHeader();
- BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
+ BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->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!
- uint64_t TripCountFull = TripCountC->getRawValue();
- if (TripCountFull != TripCountC->getRawValue() || TripCountFull == 0)
+ 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[" << BB->getParent()->getName()
- << "] Loop %" << BB->getName() << " Loop Size = " << LoopSize
- << " Trip Count = " << TripCountFull << " - ");
+ DOUT << "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");
+ DOUT << "TOO LARGE: " << Size << ">" << UnrollThreshold << "\n";
return Changed;
}
- DEBUG(std::cerr << "UNROLLING!\n");
-
- unsigned TripCount = (unsigned)TripCountFull;
+ DOUT << "UNROLLING!\n";
- BasicBlock *LoopExit = BI->getSuccessor(L->contains(BI->getSuccessor(0)));
+ std::vector<BasicBlock*> LoopBlocks = L->getBlocks();
- // Create a new basic block to temporarily hold all of the cloned code.
- BasicBlock *NewBlock = new BasicBlock();
+ 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 =
BB->begin(); isa<PHINode>(I); ++I) {
+ 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(BB)))
- if (I->getParent() == BB)
+ if (Instruction *I =
+ dyn_cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock)))
+ if (L->contains(I->getParent()))
LastValueMap[I] = I;
}
// Remove the exit branch from the loop
- BB->getInstList().erase(BI);
+ 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::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);
+
+ 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);
}
-
- 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);
+
+ // 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);
}
- // If there was more than one iteration, replace any uses of values computed
- // in the loop with values computed during the last iteration of the loop.
- if (TripCount != 1) {
- std::set<User*> Users;
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
- Users.insert(I->use_begin(), I->use_end());
-
- // We don't want to reprocess entries with PHI nodes in them. For this
- // reason, we look at each operand of each user exactly once, performing the
- // stubstitution exactly once.
- for (std::set<User*>::iterator UI = Users.begin(), E = Users.end(); UI != E;
- ++UI) {
- Instruction *I = cast<Instruction>(*UI);
- if (I->getParent() != BB && I->getParent() != NewBlock)
- RemapInstruction(I, LastValueMap);
+
+
+ // 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 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);
+ 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);
+ }
+ }
+
// Finally, add an unconditional branch to the block to continue into the exit
// block.
- new BranchInst(LoopExit, BB);
-
+ 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.
- 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);
+ 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);
+ }
}
- }
// Update the loop information for this loop.
Loop *Parent = L->getParentLoop();
// Move all of the basic blocks in the loop into the parent loop.
- LI->changeLoopFor(BB, Parent);
+ 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)
else
delete LI->removeLoop(std::find(LI->begin(), LI->end(), L));
-
- // FIXME: Should update dominator analyses
-
-
- // Now that everything is up-to-date that will be, we fold the loop block into
- // the preheader and exit block, updating our analyses as we go.
- LoopExit->getInstList().splice(LoopExit->begin(), BB->getInstList(),
- BB->getInstList().begin(),
- prior(BB->getInstList().end()));
- LoopExit->getInstList().splice(LoopExit->begin(), Preheader->getInstList(),
- Preheader->getInstList().begin(),
- prior(Preheader->getInstList().end()));
-
- // Make all other blocks in the program branch to LoopExit now instead of
- // Preheader.
- Preheader->replaceAllUsesWith(LoopExit);
-
- // Remove BB and LoopExit from our analyses.
- LI->removeBlock(Preheader);
- LI->removeBlock(BB);
-
- // If the preheader was the entry block of this function, move the exit block
- // to be the new entry of the loop.
- Function *F = LoopExit->getParent();
- if (Preheader == &F->front())
- F->getBasicBlockList().splice(F->begin(), F->getBasicBlockList(), LoopExit);
-
- // Actually delete the blocks now.
- F->getBasicBlockList().erase(Preheader);
- F->getBasicBlockList().erase(BB);
-
++NumUnrolled;
return true;
}
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