[clang] [CIR] Upstream global variable linkage types (PR #129072)

[Henrich Lauko via cfe-commits]

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@@ -210,6 +223,193 @@ void CIRGenModule::emitGlobalDefinition(clang::GlobalDecl gd,
   llvm_unreachable("Invalid argument to CIRGenModule::emitGlobalDefinition");
 }
 
+static bool shouldBeInCOMDAT(CIRGenModule &cgm, const Decl &d) {
+  assert(!cir::MissingFeatures::supportComdat());
+
+  if (d.hasAttr<SelectAnyAttr>())
+    return true;
+
+  GVALinkage linkage;
+  if (auto *vd = dyn_cast<VarDecl>(&d))
+    linkage = cgm.getASTContext().GetGVALinkageForVariable(vd);
+  else
+    linkage =
+        cgm.getASTContext().GetGVALinkageForFunction(cast<FunctionDecl>(&d));
+
+  switch (linkage) {
+  case clang::GVA_Internal:
+  case clang::GVA_AvailableExternally:
+  case clang::GVA_StrongExternal:
+    return false;
+  case clang::GVA_DiscardableODR:
+  case clang::GVA_StrongODR:
+    return true;
+  }
+  llvm_unreachable("No such linkage");
+}
+
+// TODO(CIR): this could be a common method between LLVM codegen.
+static bool isVarDeclStrongDefinition(const ASTContext &astContext,
----------------
xlauko wrote:

This is a copy-paste from `clang/lib/CodeGen/CodeGenModule.h` without an actual dependency on CIR.

`CIRGenModule` is only used to obtain `ASTContext` and check `cgm.supportsCOMDAT()`, both of which can be passed as direct arguments. In fact, `ASTContext` already is; it just needs to be forwarded to `shouldBeInCOMDAT`.

Would it be better to expose this function from Clang CodeGen and adjust the interface for use here? What do you think, @erichkeane?

https://github.com/llvm/llvm-project/pull/129072