[clang] [CIR] Add support for global linkage and visibility (PR #141973)

[Bruno Cardoso Lopes via cfe-commits]

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@@ -1075,6 +1089,135 @@ void CIRGenModule::emitTentativeDefinition(const VarDecl *d) {
   emitGlobalVarDefinition(d);
 }
 
+static bool shouldAssumeDSOLocal(const CIRGenModule &cgm,
+                                 cir::CIRGlobalValueInterface gv) {
+  if (gv.hasLocalLinkage())
+    return true;
+
+  if (!gv.hasDefaultVisibility() && !gv.hasExternalWeakLinkage())
+    return true;
+
+  // DLLImport explicitly marks the GV as external.
+  // so it shouldn't be dso_local
+  // But we don't have the info set now
+  assert(!cir::MissingFeatures::opGlobalDLLImportExport());
+
+  const llvm::Triple &tt = cgm.getTriple();
+  const auto &cgOpts = cgm.getCodeGenOpts();
+  if (tt.isWindowsGNUEnvironment()) {
+    // In MinGW, variables without DLLImport can still be automatically
+    // imported from a DLL by the linker; don't mark variables that
+    // potentially could come from another DLL as DSO local.
+
+    // With EmulatedTLS, TLS variables can be autoimported from other DLLs
+    // (and this actually happens in the public interface of libstdc++), so
+    // such variables can't be marked as DSO local. (Native TLS variables
+    // can't be dllimported at all, though.)
+    cgm.errorNYI("shouldAssumeDSOLocal: MinGW");
+  }
+
+  // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
+  // remain unresolved in the link, they can be resolved to zero, which is
+  // outside the current DSO.
+  if (tt.isOSBinFormatCOFF() && gv.hasExternalWeakLinkage())
+    return false;
+
+  // Every other GV is local on COFF.
+  // Make an exception for windows OS in the triple: Some firmware builds use
+  // *-win32-macho triples. This (accidentally?) produced windows relocations
+  // without GOT tables in older clang versions; Keep this behaviour.
+  // FIXME: even thread local variables?
+  if (tt.isOSBinFormatCOFF() || (tt.isOSWindows() && tt.isOSBinFormatMachO()))
+    return true;
+
+  // Only handle COFF and ELF for now.
+  if (!tt.isOSBinFormatELF())
+    return false;
+
+  llvm::Reloc::Model rm = cgOpts.RelocationModel;
+  const auto &lOpts = cgm.getLangOpts();
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bcardosolopes wrote:

and here.

https://github.com/llvm/llvm-project/pull/141973