[PATCH] D156845: [ConstantRange] Calculate precise range for shl by -1

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


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Comment at: llvm/lib/IR/ConstantRange.cpp:1501
+    Max = -Max;
+    return ConstantRange::getNonEmpty(std::move(Max), std::move(Min) + 1);
+  }
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Allen wrote:
> goldstein.w.n wrote:
> > Why are you inverting min/max here?
> because this is a negative value. For example
> -1 << x.min > -1 << x.max, so its range [-1 << x.max, -1 << x.min +1]
I'm probably missing something (haven't really worked on ConstantRanges much), but since you are re-negating min/max isn't that already doing it?


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  https://reviews.llvm.org/D156845/new/

https://reviews.llvm.org/D156845