// actual pass or policy, but provides a single function to perform loop
// unrolling.
//
-// It works best when loops have been canonicalized by the -indvars pass,
-// allowing it to determine the trip counts of loops easily.
-//
// The process of unrolling can produce extraneous basic blocks linked with
// unconditional branches. This will be corrected in the future.
//
if (It != VMap.end())
I->setOperand(op, It->second);
}
+
+ if (PHINode *PN = dyn_cast<PHINode>(I)) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ ValueToValueMapTy::iterator It = VMap.find(PN->getIncomingBlock(i));
+ if (It != VMap.end())
+ PN->setIncomingBlock(i, cast<BasicBlock>(It->second));
+ }
+ }
}
/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it
/// only has one predecessor, and that predecessor only has one successor.
/// The LoopInfo Analysis that is passed will be kept consistent.
/// Returns the new combined block.
-static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) {
+static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI,
+ LPPassManager *LPM) {
// 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.
// 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);
+ // Move all definitions in the successor to the predecessor...
+ OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
+
std::string OldName = BB->getName();
// Erase basic block from the function...
+
+ // ScalarEvolution holds references to loop exit blocks.
+ if (ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>()) {
+ if (Loop *L = LI->getLoopFor(BB))
+ SE->forgetLoop(L);
+ }
LI->removeBlock(BB);
BB->eraseFromParent();
}
/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true
-/// if unrolling was succesful, or false if the loop was unmodified. Unrolling
+/// if unrolling was successful, or false if the loop was unmodified. Unrolling
/// can only fail when the loop's latch block is not terminated by a conditional
/// branch instruction. However, if the trip count (and multiple) are not known,
/// loop unrolling will mostly produce more code that is no faster.
///
+/// TripCount is generally defined as the number of times the loop header
+/// executes. UnrollLoop relaxes the definition to permit early exits: here
+/// TripCount is the iteration on which control exits LatchBlock if no early
+/// exits were taken. Note that UnrollLoop assumes that the loop counter test
+/// terminates LatchBlock in order to remove unnecesssary instances of the
+/// test. In other words, control may exit the loop prior to TripCount
+/// iterations via an early branch, but control may not exit the loop from the
+/// LatchBlock's terminator prior to TripCount iterations.
+///
+/// Similarly, TripMultiple divides the number of times that the LatchBlock may
+/// execute without exiting the loop.
+///
/// The LoopInfo Analysis that is passed will be kept consistent.
///
/// If a LoopPassManager is passed in, and the loop is fully removed, it will be
/// removed from the LoopPassManager as well. LPM can also be NULL.
-bool llvm::UnrollLoop(Loop *L, unsigned Count, LoopInfo* LI, LPPassManager* LPM) {
+bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
+ unsigned TripMultiple, LoopInfo *LI, LPPassManager *LPM) {
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) {
DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
BasicBlock *Header = L->getHeader();
BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
-
+
if (!BI || BI->isUnconditional()) {
// The loop-rotate pass can be helpful to avoid this in many cases.
DEBUG(dbgs() <<
return false;
}
+ if (Header->hasAddressTaken()) {
+ // The loop-rotate pass can be helpful to avoid this in many cases.
+ DEBUG(dbgs() <<
+ " Won't unroll loop: address of header block is taken.\n");
+ return false;
+ }
+
// Notify ScalarEvolution that the loop will be substantially changed,
// if not outright eliminated.
if (ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>())
SE->forgetLoop(L);
- // Find trip count
- unsigned TripCount = L->getSmallConstantTripCount();
- // Find trip multiple if count is not available
- unsigned TripMultiple = 1;
- if (TripCount == 0)
- TripMultiple = L->getSmallConstantTripMultiple();
-
if (TripCount != 0)
DEBUG(dbgs() << " Trip Count = " << TripCount << "\n");
if (TripMultiple != 1)
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
OrigPHINode.push_back(PN);
- if (Instruction *I =
+ if (Instruction *I =
dyn_cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock)))
if (L->contains(I))
LastValueMap[I] = I;
for (unsigned It = 1; It != Count; ++It) {
std::vector<BasicBlock*> NewBlocks;
-
+
for (std::vector<BasicBlock*>::iterator BB = LoopBlocks.begin(),
E = LoopBlocks.end(); BB != E; ++BB) {
ValueToValueMapTy VMap;
// 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)) {
- PHINode *phi = cast<PHINode>(UseInst);
- Value *Incoming = phi->getIncomingValueForBlock(*BB);
- phi->addIncoming(Incoming, New);
- }
- }
+ for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB); SI != SE;
+ ++SI)
+ if (!L->contains(*SI))
+ for (BasicBlock::iterator BBI = (*SI)->begin();
+ PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
+ 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.
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);
}
-
+
// 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();
+ for (succ_iterator SI = succ_begin(LatchBlock), SE = succ_end(LatchBlock);
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))
- InVal = LastValueMap[InVal];
+ for (BasicBlock::iterator BBI = (*SI)->begin();
+ PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
+ 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))
+ InVal = LastValueMap[InVal];
+ }
+ PN->addIncoming(InVal, LastIterationBB);
}
- PN->addIncoming(InVal, LastIterationBB);
}
}
// Replace the conditional branch with an unconditional one.
BranchInst::Create(Dest, Term);
Term->eraseFromParent();
- // Merge adjacent basic blocks, if possible.
- if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI)) {
+ }
+ }
+
+ // Merge adjacent basic blocks, if possible.
+ for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
+ BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());
+ if (Term->isUnconditional()) {
+ BasicBlock *Dest = Term->getSuccessor(0);
+ if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM))
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.
projects / oota-llvm.git / blobdiff