[llvm] Update foldFMulReassoc to respect absent fast-math flags (PR #88589)

[Matt Arsenault via llvm-commits]

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@@ -636,26 +636,43 @@ Instruction *InstCombinerImpl::foldFMulReassoc(BinaryOperator &I) {
   // expression.
   if (match(Op1, m_Constant(C)) && C->isFiniteNonZeroFP()) {
     Constant *C1;
-    if (match(Op0, m_OneUse(m_FDiv(m_Constant(C1), m_Value(X))))) {
+    if (match(Op0,
+              m_AllowReassoc(m_OneUse(m_FDiv(m_Constant(C1), m_Value(X)))))) {
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arsenm wrote:

Yes, something like that would be better. It shouldn't be the dissociated matcher it is today 

https://github.com/llvm/llvm-project/pull/88589