[clang] Implement [[msvc::no_unique_address]] (PR #65675)

[Reid Kleckner via cfe-commits]

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@@ -4505,6 +4505,14 @@ bool FieldDecl::isZeroSize(const ASTContext &Ctx) const {
   if (!CXXRD->isEmpty())
     return false;
 
+  // MS ABI: nonzero if class type with class type fields
+  if (Ctx.getTargetInfo().getCXXABI().isMicrosoft() &&
+      llvm::any_of(CXXRD->fields(), [](const FieldDecl *Field) {
+        return Field->getType()->getAs<RecordType>();
+      })) {
+    return false;
+  }
+
   // Otherwise, [...] the circumstances under which the object has zero size
   // are implementation-defined.
   // FIXME: This might be Itanium ABI specific; we don't yet know what the MS
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rnk wrote:

I think you've addressed this FIXME. Perhaps you can early return true if !MS ABI, and then return a result based on the any_of check.

https://github.com/llvm/llvm-project/pull/65675