[llvm] [NVPTX] Remove `NVPTX::IMAD` opcode, and rely on intruction selection only (PR #121724)

[Justin Fargnoli via llvm-commits]

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@@ -4902,8 +4897,10 @@ static SDValue matchMADConstOnePattern(SDValue Add) {
 static SDValue combineMADConstOne(SDValue X, SDValue Add, EVT VT, SDLoc DL,
                                   TargetLowering::DAGCombinerInfo &DCI) {
 
-  if (SDValue Y = matchMADConstOnePattern(Add))
-    return DCI.DAG.getNode(NVPTXISD::IMAD, DL, VT, X, Y, X);
+  if (SDValue Y = matchMADConstOnePattern(Add)) {
+    SDValue Mul = DCI.DAG.getNode(ISD::MUL, DL, VT, X, Y);
+    return DCI.DAG.getNode(ISD::ADD, DL, VT, Mul, X);
+  }
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justinfargnoli wrote:

Ditto. LINK

https://github.com/llvm/llvm-project/pull/121724