[llvm] [InstCombine] Reassociate commutative binops over select/phi/minmax (PR #187493)

[Yingwei Zheng via llvm-commits]

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@@ -522,6 +522,17 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   /// or commutative.
   bool SimplifyAssociativeOrCommutative(BinaryOperator &I);
 
+  /// If InnerVal1 and OuterVal form a symmetric pair, and "op" is commutative:
+  /// "(InnerVal0 op InnerVal1) op OuterVal" ==> "(X op' Y) op InnerVal0".
+  /// "OuterVal op (InnerVal0 op InnerVal1)" ==> "InnerVal0 op (X op' Y)".
+  /// X and Y are the inputs to the symmetric pair. "op'" indicates that
+  /// InnerOp will have its poison-generating flags dropped. Warning:
+  /// associativity not checked.
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dtcxzyw wrote:

I guess only `InnerOp.isAssociative() && InnerOp.hasOneUse()` should be checked by the callee.

https://github.com/llvm/llvm-project/pull/187493