[PATCH] D148413: [InstCombine] Remove requirement on `trunc` in `slt/sgt` case in `foldSelectICmpAndOr`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:676
     C1Log = CmpLHS->getType()->getScalarSizeInBits() - 1;
     NeedAnd = true;
   }
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nikic wrote:
> Unless I'm missing something, we're missing an assignment to the `V` variable in this branch now? Also, do we still need the `NeedAnd`?
> 
> We should really just be using decomposeBitTestICmp() and a pow2 check I think, but this code is doing some very weird things I don't fully get.
> Unless I'm missing something, we're missing an assignment to the `V` variable in this branch now? 

Good catch not sure how that didn't get caught in the tests.

>Also, do we still need the `NeedAnd`?

Yes. `x >= 0` == `x & SignBit == 0` but we don't have the actual `x & SignBit` expression.

> 
> We should really just be using decomposeBitTestICmp() and a pow2 check I think, but this code is doing some very weird things I don't fully get.

I think that works. Will make it a follow up patch to this.


Repository:
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  https://reviews.llvm.org/D148413/new/

https://reviews.llvm.org/D148413