[llvm] [X86] Fold generic ADD/SUB with constants to X86ISD::SUB/ADD (PR #164316)

[Simon Pilgrim via llvm-commits]

================
@@ -57631,8 +57631,25 @@ static SDValue combineX86AddSub(SDNode *N, SelectionDAG &DAG,
       DCI.CombineTo(GenericAddSub, Op);
     }
   };
-  MatchGeneric(LHS, RHS, false);
-  MatchGeneric(RHS, LHS, X86ISD::SUB == N->getOpcode());
+  MatchGeneric(GenericOpc, LHS, RHS, false);
+  MatchGeneric(GenericOpc, RHS, LHS, X86ISD::SUB == N->getOpcode());
+
+  if (ConstantSDNode *Const = dyn_cast<ConstantSDNode>(RHS)) {
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RKSimon wrote:

(style)
```suggestion
  if (auto *Const = dyn_cast<ConstantSDNode>(RHS)) {
```

https://github.com/llvm/llvm-project/pull/164316