if (C->isNullValue() || isa<UndefValue>(C)) {
// Only look at the first use, avoid hurting compile time with long uselists
- User *Use = *I->user_begin();
+ auto *Use = cast<Instruction>(*I->user_begin());
+ // Bail out if Use is not in the same BB as I or Use == I or Use comes
+ // before I in the block. The latter two can be the case if Use is a PHI
+ // node.
+ if (Use->getParent() != I->getParent() || Use == I || Use->comesBefore(I))
+ return false;
// Now make sure that there are no instructions in between that can alter
// control flow (eg. calls)
- for (BasicBlock::iterator
- i = ++BasicBlock::iterator(I),
- UI = BasicBlock::iterator(dyn_cast<Instruction>(Use));
- i != UI; ++i) {
- if (i == I->getParent()->end())
- return false;
- if (!isGuaranteedToTransferExecutionToSuccessor(&*i))
- return false;
- }
+ auto InstrRange =
+ make_range(std::next(I->getIterator()), Use->getIterator());
+ if (any_of(InstrRange, [](Instruction &I) {
+ return !isGuaranteedToTransferExecutionToSuccessor(&I);
+ }))
+ return false;
// Look through GEPs. A load from a GEP derived from NULL is still undefined
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))