[clang] [Clang][Sema] Synthesize a memcpy body for defaulted union assignment (PR #206579)

[Erich Keane via cfe-commits]

================
@@ -15005,6 +15015,14 @@ buildMemcpyForAssignmentOp(Sema &S, SourceLocation Loc, QualType T,
   Expr *CallArgs[] = {
     To, From, IntegerLiteral::Create(S.Context, Size, SizeType, Loc)
   };
+
+  // The synthesized union whole-object copy is a memcpy of a possibly
+  // non-trivially-copyable record, which is correct here; skip the memaccess
+  // warning across just this call rather than casting the arguments to void*.
+  std::optional<llvm::SaveAndRestore<bool>> DisableMemaccessCheck;
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erichkeane wrote:

This is a SUPER odd way to use this... 

Why isn't this whole area just `llvm::SaveAndRestore<boo> DisableMemaccessCheck(S.SuppressMemaccessCheck, SuppressMemaccessWarning)`? 

https://github.com/llvm/llvm-project/pull/206579