[llvm] [InstCombine] Fold `(X==Z || Y==Z) ? (X==Z && Y==Z) : X==Y --> X==Y` (PR #108619)

[Marina Taylor via llvm-commits]

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@@ -1406,6 +1406,46 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
   return nullptr;
 }
 
+/// Fold the following code sequence:
+/// \code
+///   %XEq = icmp eq i64 %X, %Z
+///   %YEq = icmp eq i64 %Y, %Z
+///   %either = select i1 %XEq, i1 true, i1 %YEq
+///   %both = select i1 %XEq, i1 %YEq, i1 false
+///   %cmp = icmp eq i64 %X, %Y
+///   %equal = select i1 %either, i1 %both, i1 %cmp
+/// \code
+///
+/// into:
+///   %equal = icmp eq i64 %X, %Y
+///
+/// Equivalently:
+///   (X==Z || Y==Z) ? (X==Z && Y==Z) : X==Y --> X==Y
+Instruction *InstCombinerImpl::foldSelectEqualityTest(SelectInst &Sel) {
+  Value *X, *Y, *Z, *XEq, *YEq;
+  Value *Either = Sel.getCondition(), *Both = Sel.getTrueValue(),
+        *Cmp = Sel.getFalseValue();
+
+  if (!match(Either, m_Select(m_Value(XEq), m_One(), m_Value(YEq))))
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citymarina wrote:

Thanks, I didn't know about these.

https://github.com/llvm/llvm-project/pull/108619