[PATCH] D157762: [WIP] Implement [[msvc::no_unique_address]]

[David Blaikie via Phabricator via cfe-commits]

dblaikie added inline comments.


================
Comment at: clang/lib/AST/Decl.cpp:4523-4524
 bool FieldDecl::isPotentiallyOverlapping() const {
-  return hasAttr<NoUniqueAddressAttr>() && getType()->getAsCXXRecordDecl();
+  return (hasAttr<NoUniqueAddressAttr>() ||
+          hasAttr<NoUniqueAddressMSVCAttr>()) &&
+         getType()->getAsCXXRecordDecl();
----------------
akhuang wrote:
> aaron.ballman wrote:
> > akhuang wrote:
> > > aaron.ballman wrote:
> > > > dblaikie wrote:
> > > > > Having to check both of these in several places seems problematic - can we wrap that up somewhere? (or, maybe ideally, is there a way for `msvc::no_unique_address` to map to the actual NoUniqueAddressAttr as a different spelling of the same thing?)
> > > > This was why I was hoping we could merge the two in Attr.td, but I'm not certain that will be easy.
> > > What does merging the two in Attr.td mean? Could we just put the two spellings in one attribute, or would that make it impossible for clang-cl to ignore the [[no_unique_address]] spelling
> > We can have multiple syntactic spellings for the same semantic attribute (e.g., `__attribute__((foo))` and `__attribute__((bar))` can both map to a single `FooBarAttr` AST node), and we have "accessors" on the AST node that let you tell which spelling was used: https://github.com/llvm/llvm-project/blob/90ecadde62f30275c35fdf7928e3477a41691d21/clang/include/clang/Basic/Attr.td#L4095
> > 
> > The suggestion Erich and I are thinking of is:
> > 
> > 1) Add the additional spelling to `NoUniqueAddress`.
> > 2) Add accessors to differentiate the spellings.
> > 3) Remove the `TargetSpecificAttr` from `NoUniqueAddress`, manually implement those checks in an attribute handler in SemaDeclAttr.cpp.
> > 
> > Then, anywhere you care about the attribute in general, you can look for `isa<NoUniqueAddress>`, and anywhere you care about which spelling, you can use `cast<NoUniqueAddress>(A)->isMSVC()` (or whatever you name the accessors).
> Thanks! This patch should implement this, and so far, I don't think there are any places outside of SemaDeclAttr where we have to differentiate the two.
(awesome - glad to see this was so tidy to do/that the generic attribute handling stuff mostly covers it)


================
Comment at: clang/lib/AST/Decl.cpp:4510
+  if (Ctx.getTargetInfo().getCXXABI().isMicrosoft() &&
+      llvm::any_of(CXXRD->fields(), [&](const FieldDecl *Field) {
+        return Field->getType()->getAs<RecordType>();
----------------



================
Comment at: clang/lib/AST/RecordLayoutBuilder.cpp:3096-3098
+  if (!IsOverlappingEmptyField) {
+    DataSize = std::max(DataSize, FieldOffset + Info.Size);
+  }
----------------



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