[clang] Fix memcpy-operator= generation with restrict parameters. (PR #194906)

[Aaron Ballman via cfe-commits]

================
@@ -14928,6 +14928,23 @@ buildMemcpyForAssignmentOp(Sema &S, SourceLocation Loc, QualType T,
       S.Context, To, UO_AddrOf, S.Context.getPointerType(To->getType()),
       VK_PRValue, OK_Ordinary, Loc, false, S.CurFPFeatureOverrides());
 
+  // If this is restrict qualified, the call to memcpy will fail as this ends up
+  // being an illegal pointer cast (as it has non-local qualifiers in
+  // difference). Sema rules prevent us from calling this with anything other
+  // than the restrict qualifiers as far as I can tell(fields cant have an AS,
+  // copy is deleted if it is const, OBJC can't get here, pointer-auth can't be
+  // applied to any problematic things). In order to avoid that problem, we can
+  // just insert a cast directly to const void * / void *.
----------------
AaronBallman wrote:

```suggestion
  // If this is restrict-qualified, the call to memcpy will fail as this ends up
  // being an invalid pointer cast (as it has non-local qualifiers in
  // difference). Sema rules prevent us from calling this with anything other
  // than the restrict qualifiers as far as I can tell (fields can't have an address space,
  // copy is deleted if it is const, Objective-C can't get here, pointer-auth can't be
  // applied to any problematic things). In order to avoid that problem, we can
  // just insert a cast directly to const void * / void *.
```

https://github.com/llvm/llvm-project/pull/194906