[llvm] [InstSimplify] Use multi-op replacement when simplify `select` (PR #121708)

[via llvm-commits]

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@@ -4712,23 +4733,29 @@ static Value *simplifySelectWithICmpCond(Value *CondVal, Value *TrueVal,
     if (match(CmpLHS, m_Or(m_Value(X), m_Value(Y))) &&
         match(CmpRHS, m_Zero())) {
       // (X | Y) == 0 implies X == 0 and Y == 0.
-      if (Value *V = simplifySelectWithEquivalence(X, CmpRHS, TrueVal, FalseVal,
-                                                   Q, MaxRecurse))
+      if (Value *V = simplifySelectWithEquivalence(
+              {{X, CmpRHS}, {Y, CmpRHS}}, TrueVal, FalseVal, Q, MaxRecurse))
+        return V;
+      if (Value *V = simplifySelectWithEquivalence({{X, CmpRHS}}, TrueVal,
+                                                   FalseVal, Q, MaxRecurse))
         return V;
-      if (Value *V = simplifySelectWithEquivalence(Y, CmpRHS, TrueVal, FalseVal,
-                                                   Q, MaxRecurse))
+      if (Value *V = simplifySelectWithEquivalence({{Y, CmpRHS}}, TrueVal,
+                                                   FalseVal, Q, MaxRecurse))
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goldsteinn wrote:

Because our simplification goal is TrueVal == FalseVal, not the complete simplification of either arm independently. If we only do the double replace we can hit some cases where we oversimplify a side and then fail to optimize our the select.

https://github.com/llvm/llvm-project/pull/121708