[PATCH] D158510: [InstCombine] Propagate nsw flag when negating

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp:264
       return BinaryOperator::CreateMul(
           NegOp0, ConstantExpr::getNeg(cast<Constant>(Op1)), I.getName());
 
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goldstein.w.n wrote:
> nikic wrote:
> > goldstein.w.n wrote:
> > > You can have NSW on this mul given that `Op1` is a constant.
> > I don't think you can add nsw on the mul if I got this right: https://alive2.llvm.org/ce/z/lSk99J
> > 
> > Though it looks like passing nsw to the negator would be okay: https://alive2.llvm.org/ce/z/MrwT5K
> You have it right, the idea though is that since `Op1` is a constant we can infer when it would be NSW i.e:
> https://alive2.llvm.org/ce/z/6JPtJR
edit: Actually you can just propagate the NSW flag i.e:
https://alive2.llvm.org/ce/z/Xw992v


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D158510/new/

https://reviews.llvm.org/D158510