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[LoopDeletion] NFC: Add debug statements to the optimization 

We have a DEBUG option for loop deletion, but no related debug messages.
Added some debug messages to state why loop deletion failed.

llvm-svn: 307078
This commit is contained in:
Anna Thomas 2017-07-04 14:05:19 +00:00
parent 4d2f976208
commit 90f69abc8b
1 changed files with 24 additions and 13 deletions
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37
llvm/lib/Transforms/Scalar/LoopDeletion.cpp
View File

@ -148,25 +148,27 @@ static bool deleteLoopIfDead(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
LoopInfo &LI, LPMUpdater *Updater = nullptr) {
assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
// We can only remove the loop if there is a preheader that we can
// branch from after removing it.
// We can only remove the loop if there is a preheader that we can branch from
// after removing it. Also, if LoopSimplify form is not available, stay out
// of trouble.
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader)
if (!Preheader || !L->hasDedicatedExits()) {
DEBUG(dbgs()
<< "Deletion requires Loop with preheader and dedicated exits.\n");
return false;
// If LoopSimplify form is not available, stay out of trouble.
if (!L->hasDedicatedExits())
return false;
}
// We can't remove loops that contain subloops. If the subloops were dead,
// they would already have been removed in earlier executions of this pass.
if (L->begin() != L->end())
if (L->begin() != L->end()) {
DEBUG(dbgs() << "Loop contains subloops.\n");
return false;
}
BasicBlock *ExitBlock = L->getUniqueExitBlock();
if (ExitBlock && isLoopNeverExecuted(L)) {
DEBUG(dbgs() << "Loop is proven to never execute, delete it!");
// Set incoming value to undef for phi nodes in the exit block.
BasicBlock::iterator BI = ExitBlock->begin();
while (PHINode *P = dyn_cast<PHINode>(BI)) {
@ -188,20 +190,26 @@ static bool deleteLoopIfDead(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
// be in the situation of needing to be able to solve statically which exit
// block will be branched to, or trying to preserve the branching logic in
// a loop invariant manner.
if (!ExitBlock)
if (!ExitBlock) {
DEBUG(dbgs() << "Deletion requires single exit block\n");
return false;
}
// Finally, we have to check that the loop really is dead.
bool Changed = false;
if (!isLoopDead(L, SE, ExitingBlocks, ExitBlock, Changed, Preheader))
if (!isLoopDead(L, SE, ExitingBlocks, ExitBlock, Changed, Preheader)) {
DEBUG(dbgs() << "Loop is not invariant, cannot delete.\n");
return Changed;
}
// Don't remove loops for which we can't solve the trip count.
// They could be infinite, in which case we'd be changing program behavior.
const SCEV *S = SE.getMaxBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(S))
if (isa<SCEVCouldNotCompute>(S)) {
DEBUG(dbgs() << "Could not compute SCEV MaxBackedgeTakenCount.\n");
return Changed;
}
DEBUG(dbgs() << "Loop is invariant, delete it!");
deleteDeadLoop(L, DT, SE, LI, Updater);
++NumDeleted;
@ -311,6 +319,9 @@ static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &Updater) {
DEBUG(dbgs() << "Analyzing Loop for deletion: ");
DEBUG(L.dump());
if (!deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI, &Updater))
return PreservedAnalyses::all();