[PATCH] D145811: [SystemZ] Don't reuse a sub that can overflow during isel.

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa added inline comments.


================
Comment at: llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:2426
       if (N->getOpcode() == ISD::SUB &&
+          (!N->getFlags().hasNoSignedWrap() && !N->getFlags().hasNoUnsignedWrap()) &&
           ((N->getOperand(0) == C.Op0 && N->getOperand(1) == C.Op1) ||
----------------
nikic wrote:
> It would be better to drop the flags instead -- the general preference is to drop nowrap flags rather than block optimizations due to their presence.
Hmm - I wish I had a better grasp of this.. How is it that we can just drop the nowrap flag and let the program behavior change and print the wrong result?



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  https://reviews.llvm.org/D145811/new/

https://reviews.llvm.org/D145811