[llvm] [InstCombine] Fold operation into select, when one operand is zext of select's condition (PR #166816)

[Gábor Spaits via llvm-commits]

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@@ -1758,6 +1758,9 @@ static Value *simplifyOperationIntoSelectOperand(Instruction &I, SelectInst *SI,
                                     m_Specific(Op), m_Value(V))) &&
                isGuaranteedNotToBeUndefOrPoison(V)) {
       // Pass
+    } else if (match(Op, m_ZExt(m_Specific(SI->getCondition())))) {
+      V = IsTrueArm ? ConstantInt::get(Op->getType(), 1)
+                    : ConstantInt::getNullValue(Op->getType());
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spaits wrote:

Shouldn't we add the same for `sext` instruction? I know that we don't have any evidence of any frontend that would generate that pattern, but it may happen and the handling wouldn't mean a significant cost burden.

https://github.com/llvm/llvm-project/pull/166816