[PartialInlining] Reduce outlining overhead by removing unneeded live-out(s)
Differential Revision: http://reviews.llvm.org/D33694
llvm-svn: 304375
diff --git a/llvm/lib/Transforms/IPO/PartialInlining.cpp b/llvm/lib/Transforms/IPO/PartialInlining.cpp
index 4c417f1..bc09674 100644
--- a/llvm/lib/Transforms/IPO/PartialInlining.cpp
+++ b/llvm/lib/Transforms/IPO/PartialInlining.cpp
@@ -652,12 +652,21 @@
// only split block when necessary:
PHINode *FirstPhi = getFirstPHI(PreReturn);
unsigned NumPredsFromEntries = OI->ReturnBlockPreds.size();
+ auto IsTrivialPhi = [](PHINode *PN) -> Value * {
+ Value *CommonValue = PN->getIncomingValue(0);
+ if (all_of(PN->incoming_values(),
+ [&](Value *V) { return V == CommonValue; }))
+ return CommonValue;
+ return nullptr;
+ };
+
if (FirstPhi && FirstPhi->getNumIncomingValues() > NumPredsFromEntries + 1) {
NewReturnBlock = NewReturnBlock->splitBasicBlock(
NewReturnBlock->getFirstNonPHI()->getIterator());
BasicBlock::iterator I = PreReturn->begin();
Instruction *Ins = &NewReturnBlock->front();
+ SmallVector<Instruction *, 4> DeadPhis;
while (I != PreReturn->end()) {
PHINode *OldPhi = dyn_cast<PHINode>(I);
if (!OldPhi)
@@ -674,8 +683,22 @@
RetPhi->addIncoming(OldPhi->getIncomingValueForBlock(NewE), NewE);
OldPhi->removeIncomingValue(NewE);
}
+
+ // After incoming values splitting, the old phi may become trivial.
+ // Keeping the trivial phi can introduce definition inside the outline
+ // region which is live-out, causing necessary overhead (load, store
+ // arg passing etc).
+ if (auto *OldPhiVal = IsTrivialPhi(OldPhi)) {
+ OldPhi->replaceAllUsesWith(OldPhiVal);
+ DeadPhis.push_back(OldPhi);
+ }
+
++I;
}
+
+ for (auto *DP : DeadPhis)
+ DP->eraseFromParent();
+
for (auto E : OI->ReturnBlockPreds) {
BasicBlock *NewE = cast<BasicBlock>(VMap[E]);
NewE->getTerminator()->replaceUsesOfWith(PreReturn, NewReturnBlock);