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

[Allen zhong via Phabricator via llvm-commits]

Allen marked 2 inline comments as done.
Allen 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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goldstein.w.n wrote:
> 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?
Yes, it is already done, but need swap it max/min values for **negitive value**


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https://reviews.llvm.org/D156845