[PATCH] D87149: [InstCombine] erase instructions leading up to unreachable

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp:2806
+  Instruction *Prev = I.getPrevNonDebugInstruction();
+  if (Prev && Prev->use_empty() && !Prev->isEHPad() &&
+      isGuaranteedToTransferExecutionToSuccessor(Prev)) {
----------------
nikic wrote:
> lebedev.ri wrote:
> > Is there any testcase with non-empty use list?
> > I'd think we could RAUW it with `undef`.
> I don't see how the last instruction can have a non-empty use-list if followed by unreachable and not part of a properly unreachable block (which is ensured by instcombine early). I think it can be an assert.
Yes, I'm not seeing a way to get bogus IR (eg, that references itself) into here unless it's truly in a block that can't be reached from entry. I'll remove the check - the assert already exists in eraseInstFromFunction().


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87149/new/

https://reviews.llvm.org/D87149