[llvm] [InstCombine] Prefer to keep power-of-2 constants when combining ashr exact and slt/ult of a constant (PR #86111)

[via llvm-commits]

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@@ -2482,10 +2482,21 @@ Instruction *InstCombinerImpl::foldICmpShrConstant(ICmpInst &Cmp,
   // those conditions rather than checking them. This is difficult because of
   // undef/poison (PR34838).
   if (IsAShr && Shr->hasOneUse()) {
+    if (IsExact && (Pred == CmpInst::ICMP_SLT || Pred == CmpInst::ICMP_ULT) &&
+        !C.isMinSignedValue() && (C - 1).isPowerOf2()) {
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goldsteinn wrote:

Doesn't `(C - 1).isPowerOf2()` preclude `C.isMinSignedValue()`?

https://github.com/llvm/llvm-project/pull/86111