zmodem wrote:
I looked at this some more. Here's a slightly reduced version of your test case:
```
template <typename> void foo();
template <typename> void f() {
foo<void>();
}
void g() { f<void>(); }
template <> void __declspec(dllexport) foo<void>() {}
```
What happens (when building with `-fno-delayed-template-parsing`) is something
like:
1. The `f()` template gets parsed. Because the call to `foo` is not
type-dependent, the call gets resolved to a FunctionDecl for `foo<void>`, which
isn't dllexport because that happens later.
2. `g()` calls `f<void>()`, so the latter gets queued up for codegen at the end
of the TU.
3. Codegen for `foo<void>` happens, with dllexport.
4. (End of the TU) Codegen for `f<void>` happens. When generating the call to
`foo<void>`, it uses the FunctionDecl from step 1). We enter
`CodeGenModule::GetOrCreateLLVMFunction`, see that the old `Entry` is dllexport
but the new FunctionDecl isn't, and so the attribute gets dropped.
I think the "surprise" is that the latter call to `GetOrCreateLLVMFunction` is
using an earlier `FunctionDecl`. Because of that, I'm thinking maybe the fix is
to call `getMostRecentDecl` on it, something like:
```
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp
b/clang/lib/CodeGen/CodeGenModule.cpp
index 489c08a4d481..8fe36305e104 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4554,10 +4554,13 @@ llvm::Constant *CodeGenModule::GetOrCreateLLVMFunction(
}
// Handle dropped DLL attributes.
- if (D && !D->hasAttr<DLLImportAttr>() && !D->hasAttr<DLLExportAttr>() &&
- !shouldMapVisibilityToDLLExport(cast_or_null<NamedDecl>(D))) {
- Entry->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
- setDSOLocal(Entry);
+ if (D) {
+ const Decl *MRD = D->getMostRecentDecl();
+ if (!MRD->hasAttr<DLLImportAttr>() && !MRD->hasAttr<DLLExportAttr>() &&
+ !shouldMapVisibilityToDLLExport(cast<NamedDecl>(MRD))) {
+ Entry->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
+ setDSOLocal(Entry);
+ }
}
// If there are two attempts to define the same mangled name, issue an
```
If we're concerned about the extra function call in a common codepath, we could
only do this if there is a dll attribute on the `Entry`.
https://github.com/llvm/llvm-project/pull/93302
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