[PATCH] D102255: [SelectionDAG] Generate scoped AA metadata when lowering memcpy.

[Jeroen Dobbelaere via Phabricator via llvm-commits]

jeroen.dobbelaere added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:6399-6422
+  AAMDNodes DstAAInfo, SrcAAInfo;
+  DstAAInfo = SrcAAInfo = NewAAInfo;
+  // Generate new scoped AA metadata for this memcpy instance if enabled.
+  if (EnableMemCpyScopedNoAlias) {
+    MDBuilder MDB(*DAG.getContext());
+    MDNode *Domain =
+        MDB.createAnonymousAliasScopeDomain("MemcpyLoweringDomain");
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As mentioned in  D102255#2766721, we still would need to use separate scopes for ever load/store pair.
That's the only way to avoid a possible 'noalias' result when the source and destination happen to be identical.
(based on the AA Techcall discussion, such a situation was considered to be not acceptable).


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102255/new/

https://reviews.llvm.org/D102255