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Implement unrolling of multiblock loops. This significantly improves the 

utility of the LoopUnroll pass.

Also, add a testcase for multiblock-loop unrolling.

llvm-svn: 29859
This commit is contained in:
Owen Anderson 2006-08-24 21:28:19 +00:00
parent b5d6b8f26d
commit e001d811ba
2 changed files with 142 additions and 126 deletions
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250
llvm/lib/Transforms/Scalar/LoopUnroll.cpp
View File

@ -11,8 +11,9 @@
// 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.
//
//===----------------------------------------------------------------------===//
@ -53,7 +54,9 @@ namespace {
///
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addRequired<LoopInfo>();
AU.addPreservedID(LCSSAID);
AU.addPreserved<LoopInfo>();
}
};
@ -125,12 +128,10 @@ bool LoopUnroll::visitLoop(Loop *L) {
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());
@ -141,9 +142,9 @@ bool LoopUnroll::visitLoop(Loop *L) {
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 << " - ");
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");
@ -151,81 +152,126 @@ bool LoopUnroll::visitLoop(Loop *L) {
}
DEBUG(std::cerr << "UNROLLING!\n");
std::vector<BasicBlock*> LoopBlocks = L->getBlocks();
unsigned TripCount = (unsigned)TripCountFull;
BasicBlock *LoopExit = BI->getSuccessor(L->contains(BI->getSuccessor(0)));
// Create a new basic block to temporarily hold all of the cloned code.
BasicBlock *NewBlock = new BasicBlock();
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);
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.
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);
// 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);
}
// 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
// substitution 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)
// 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);
}
}
// 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;
// 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]);
// Finally, add an unconditional branch to the block to continue into the exit
// block.
new BranchInst(LoopExit, Latches[Latches.size()-1]);
// 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);
(*SI)->addIncoming(InVal, cast<BasicBlock>(LastValueMap[LatchBlock]));
}
}
// Now loop over the PHI nodes in the original block, setting them to their
// incoming values.
@ -233,32 +279,33 @@ bool LoopUnroll::visitLoop(Loop *L) {
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);
Header->getInstList().erase(PN);
}
// 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++;
const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks();
for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(),
E = NewLoopBlocks.end(); BB != E; ++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);
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)
@ -266,55 +313,6 @@ bool LoopUnroll::visitLoop(Loop *L) {
else
delete LI->removeLoop(std::find(LI->begin(), LI->end(), L));
// Remove single-entry Phis from the exit block.
for (BasicBlock::iterator ExitInstr = LoopExit->begin();
PHINode* PN = dyn_cast<PHINode>(ExitInstr); ++ExitInstr) {
assert(PN->getNumIncomingValues() == 1
&& "Block should only have one pred, so Phi's must be single entry");
PN->replaceAllUsesWith(PN->getOperand(0));
PN->eraseFromParent();
}
// 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);
Function *F = LoopExit->getParent();
if (Parent) {
// Otherwise, if this is a sub-loop, and the preheader was the loop header
// of the parent loop, move the exit block to be the new parent loop header.
if (Parent->getHeader() == Preheader) {
assert(Parent->contains(LoopExit) &&
"Exit block isn't contained in parent?");
Parent->moveToHeader(LoopExit);
}
} else {
// If the preheader was the entry block of this function, move the exit
// block to be the new entry of the function.
if (Preheader == &F->front())
F->getBasicBlockList().splice(F->begin(),
F->getBasicBlockList(), LoopExit);
}
// Remove BB and LoopExit from our analyses.
LI->removeBlock(Preheader);
LI->removeBlock(BB);
// Actually delete the blocks now.
F->getBasicBlockList().erase(Preheader);
F->getBasicBlockList().erase(BB);
++NumUnrolled;
return true;
}

18
llvm/test/Regression/Transforms/LoopUnroll/2006-08-24-MultiBlockLoop.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llvm-as < %s | opt -loop-unroll | llvm-dis | grep "bb72.2"
void %vorbis_encode_noisebias_setup() {
entry:
br label %cond_true.outer
cond_true.outer:
%indvar1.ph = phi uint [ 0, %entry ], [ %indvar.next2, %bb72 ]
br label %bb72
bb72:
%indvar.next2 = add uint %indvar1.ph, 1
%exitcond3 = seteq uint %indvar.next2, 3
br bool %exitcond3, label %cond_true138, label %cond_true.outer
cond_true138:
ret void
}