[clang] Enable unique-object-duplication warning for windows (PR #143537)

[Hans Wennborg via cfe-commits]

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@@ -13518,8 +13518,29 @@ bool Sema::GloballyUniqueObjectMightBeAccidentallyDuplicated(
 
   // If the object isn't hidden, the dynamic linker will prevent duplication.
   clang::LinkageInfo Lnk = Target->getLinkageAndVisibility();
-  if (Lnk.getVisibility() != HiddenVisibility)
+
+  // The target is "hidden" (from the dynamic linker) if:
+  // 1. On posix, it has hidden visibility, or
+  // 2. On windows, it has no import/export annotation
+  if (Context.getTargetInfo().shouldDLLImportComdatSymbols()) {
+    if (Target->hasAttr<DLLExportAttr>() || Target->hasAttr<DLLImportAttr>())
+      return false;
+
+    // If the variable isn't directly annotated, check to see if it's a member
+    // of an annotated class.
+    const VarDecl *VD = dyn_cast_if_present<VarDecl>(Target);
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zmodem wrote:

I think `hasAttr` should pick up the inherited attribute, but it's possible that this diagnostic is running before the "inheriting" has taken place, which happens in `Sema::checkClassLevelDLLAttribute`. Maybe it's possible to run the warning logic after that has run?

https://github.com/llvm/llvm-project/pull/143537