[PATCH] D126591: [InstCombine] Optimise shift+and+boolean conversion pattern to simple comparison

Mon Jun 20 05:12:08 PDT 2022

bcl5980 added a comment.

In D126591#3596021 <https://reviews.llvm.org/D126591#3596021>, @spatel wrote:

> I added a similar fold here:
> 0399473de886 <https://reviews.llvm.org/rG0399473de886595d8ce3346f2cc99c94267496e5>
>
> It seems like we might be missing some generalization for power-of-2 values, but this patch seems fine. Please add alive2 links to the patch summary (these are in issue #56124?).

alive2 link should already in the summary.

================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp:5568-5569
+        if (C1->isOne() && C2.isPowerOf2()) {
           // ((1 << X) & 8) == 0 -> X != 3
           // ((1 << X) & 8) != 0 -> X == 3
+          auto *CmpC = ConstantInt::get(XTy, C2.countTrailingZeros());
----------------
spatel wrote:
> Is this just a special-case of the next pattern? If so, I think it is better to reduce the patch. We might have slightly less efficiency at run-time, but there's less code to maintain here.
I think it is not. But we can remove that after rGbfde861.
And we can also remove line 5590's transform after rGa0c3c607.
Do we need to remvoe these on this patch?

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