[llvm] [InstCombine] Fold `icmp eq/ne (X and C), 0` when partial bits are known (PR #85863)

[via llvm-commits]

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@@ -1771,11 +1771,14 @@ Instruction *InstCombinerImpl::foldICmpAndConstConst(ICmpInst &Cmp,
       return new ICmpInst(NewPred, X, Zero);
     }
 
-    APInt NewC2 = *C2;
     KnownBits Know = computeKnownBits(And->getOperand(0), 0, And);
+    if (Know.One.intersects(*C2))
+      return replaceInstUsesWith(
+          Cmp, ConstantInt::getBool(Cmp.getType(), isICMP_NE));
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goldsteinn wrote:

Is there another place we could hijack an existing knownbits calls?
This could be generalized to `!((Know.One & *C2) & ~C1).isZero()` Maybe put this in `foldICmpUsingKnownBits`?

https://github.com/llvm/llvm-project/pull/85863