[PATCH] D117365: [InstCombine] optimize icmp-ugt-ashr

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp:2253
       APInt ShiftedC = (C + 1).shl(ShAmtVal) - 1;
-      if (!C.isMaxSignedValue() && !(C + 1).shl(ShAmtVal).isMinSignedValue() &&
-          (ShiftedC + 1).ashr(ShAmtVal) == (C + 1))
+      if (!C.isMaxSignedValue() && (ShiftedC + 1).ashr(ShAmtVal) == (C + 1))
+        return new ICmpInst(Pred, X, ConstantInt::get(ShrTy, ShiftedC));
----------------
I think the `!(C + 1).shl(ShAmtVal).isMinSignedValue()` term is required for the signed case isn't it? It's the commented out code in my alive proof.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117365/new/

https://reviews.llvm.org/D117365