[llvm] [AMDGPU][DAGCombiner][GlobalISel] Prevent FMA contraction when multiply cannot be eliminated (PR #169735)

[Matt Arsenault via llvm-commits]

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@@ -15495,6 +15461,36 @@ unsigned SITargetLowering::getFusedOpcode(const SelectionDAG &DAG,
   return 0;
 }
 
+// Check if an FADD node should be contracted into a fused operation.
+// Returns true if the FADD has only one use, or if all uses are contractable
+// FADD/FSUB operations that would allow the FADD to be eliminated.
+static bool shouldContractFAdd(SDValue FAdd, SelectionDAG &DAG) {
+  if (FAdd->hasOneUse())
+    return true;
+
+  // Check if all uses are contractable fadd or fsub operations
+  const TargetOptions &Options = DAG.getTarget().Options;
+  for (const auto *User : FAdd->users()) {
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arsenm wrote:

Don't do an uncontrolled user scan 

https://github.com/llvm/llvm-project/pull/169735