[llvm] [InstCombine] fold (Binop phi(a, b) phi(b, a)) -> (Binop a, b) while Binop is commutative. (PR #75765)

[Nikita Popov via llvm-commits]

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@@ -278,6 +278,16 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
                                               IntrinsicInst &Tramp);
   Instruction *foldCommutativeIntrinsicOverSelects(IntrinsicInst &II);
 
+  // match a pair of Phi Nodes like
+  // phi [a, BB0], [b, BB1] & phi [b, BB0], [a, BB1]
+  // return the matched two operands
+  std::optional<std::pair<Value *, Value *>>
+  matchSymmetricPhiNodesPair(PHINode *LHS, PHINode *RHS);
+
+  // Tries to fold (op phi(a, b) phi(b, a)) -> (op a, b)
+  // while op is a commutative intrinsic call
----------------
nikic wrote:

```suggestion
  // while op is a commutative intrinsic call.
```

https://github.com/llvm/llvm-project/pull/75765