[llvm] [X86] Honor rewrite semantics of `contract` in X86ISel combines (PR #174440)

[Simon Pilgrim via llvm-commits]

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@@ -56639,6 +56602,10 @@ static SDValue combineFMA(SDNode *N, SelectionDAG &DAG,
 // Combine FMSUBADD(A, B, FNEG(C)) -> FMADDSUB(A, B, C)
 static SDValue combineFMADDSUB(SDNode *N, SelectionDAG &DAG,
                                TargetLowering::DAGCombinerInfo &DCI) {
+  // FIXME: We should check for contract to perform this combine; but this
+  // breaks lowering of certain intrinsics that depend on this combine being
+  // perfomed (i.e.llvm.x86.avx512.mask3.vfmsubadd).
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RKSimon wrote:

is this still relevant? its purely about negating the accumulator operand

https://github.com/llvm/llvm-project/pull/174440