[llvm] [X86] Lower i512 ADD/SUB using Kogge-Stone on AVX512 (PR #174761)

[Simon Pilgrim via llvm-commits]

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@@ -54568,6 +54631,10 @@ static SDValue combineStore(SDNode *N, SelectionDAG &DAG,
   // vector type or the operation is likely to expand to a vector type
   // (legalization can scalarize back if it the op failed).
   if (VT == MVT::i256 || VT == MVT::i512) {
+    // Issue : 173996 , PRs : [174761,179503] : when add/sub lowered on avx512
+    // we hit   a regression issue. my approach is to allow the combine only
+    // when the operation is done by our custome handling.
+    // X86TargetLowering::ReplaceNodeResults (ADD/SUB) cases.
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RKSimon wrote:

remove this

https://github.com/llvm/llvm-project/pull/174761