[llvm] [InstCombine] Fix the correctness of missing check reassoc attribute (PR #71277)

[via llvm-commits]

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@@ -177,6 +177,15 @@ void Instruction::setNonNeg(bool b) {
                          (b * PossiblyNonNegInst::NonNeg);
 }
 
+bool Instruction::hasAllowReassocOfAllOperand() const {
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vfdff wrote:

hi @arsenm @jcranmer-intel @nikic 
  would you help to give some input on this?  I'm not sure if this reassoc flag can propagate this logic correctly?
 If it is correct, we should not need to check whether `the FPMathOperator of the instruction` has the reassoc flag when we try this combine.

https://github.com/llvm/llvm-project/pull/71277