[clang] [clang] Keep explicit visibility on a #pragma weak alias (PR #225354)

[Evgenii Kudriashov via cfe-commits]

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@@ -8805,6 +8805,16 @@ void Sema::DeclApplyPragmaWeak(Scope *S, NamedDecl *ND, const WeakInfo &W) {
   if (W.getAlias()) { // clone decl, impersonate __attribute(weak,alias(...))
     IdentifierInfo *NDId = ND->getIdentifier();
     NamedDecl *NewD = DeclClonePragmaWeak(ND, W.getAlias(), W.getLocation());
+    // The clone is not a redeclaration of any existing declaration of the weak
+    // name, so it does not inherit attributes written on one. Carry over an
+    // explicit visibility, which would otherwise be lost and replaced by the
+    // -fvisibility default. GCC uses the visibility of the weak name's own
+    // declaration here, not that of the aliasee. This lookup has to happen
+    // before the PushOnScopeChains() below, which would make it find NewD.
+    if (NamedDecl *WeakND = LookupSingleName(S, W.getAlias(), W.getLocation(),
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e-kud wrote:

`ND` is a target that we clone for an alias. But we need to take visibility of the previously declared alias.

https://github.com/llvm/llvm-project/pull/225354