[llvm] [InstCombine] Fold `(add X, (sext/zext (icmp eq X, C)))` (PR #93840)

[via llvm-commits]

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@@ -1694,6 +1694,26 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
     return BinaryOperator::CreateOr(LHS, Zext);
   }
 
+  {
+    Value *Cond, *Ext;
+    Constant *C;
+    // (add X, (sext/zext (icmp eq X, C)))
+    //    -> (select (icmp eq X, C), (add C, (sext/zext 1)), X)
+    auto CondMatcher = m_CombineAnd(
+        m_Value(Cond), m_ICmp(Pred, m_Deferred(A), m_ImmConstant(C)));
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goldsteinn wrote:

That will be flakey if `X` itself is a `sext`/`zext` of another value though no?

https://github.com/llvm/llvm-project/pull/93840