[clang] [SystemZ][z/OS] Implement #pragma export (PR #141671)

[Erich Keane via cfe-commits]

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@@ -1327,6 +1327,60 @@ void Sema::AddImplicitMSFunctionNoBuiltinAttr(FunctionDecl *FD) {
     FD->addAttr(NoBuiltinAttr::CreateImplicit(Context, V.data(), V.size()));
 }
 
+NamedDecl *Sema::lookupExternCName(IdentifierInfo *IdentId,
+                                   SourceLocation NameLoc, Scope *curScope) {
+  LookupResult Result(*this, IdentId, NameLoc, LookupOrdinaryName);
+  LookupName(Result, curScope);
+  if (!getLangOpts().CPlusPlus)
+    return Result.getAsSingle<NamedDecl>();
+  for (LookupResult::iterator I = Result.begin(); I != Result.end(); ++I) {
+    NamedDecl *D = (*I)->getUnderlyingDecl();
+    if (auto *FD = dyn_cast<FunctionDecl>(D->getCanonicalDecl()))
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erichkeane wrote:

Don't do `getCanonicalDecl`, else you get the 1st one.  For functions, we always want the 'most recent', as they'll have the most information.  I'd suggest not doing `getCanonicalDecl` at all.

https://github.com/llvm/llvm-project/pull/141671