codegen-llvm: never combine DSOLocal and DllImport

compiler/rustc_codegen_llvm/src/consts.rs

@@ -295,8 +295,18 @@ impl<'ll> CodegenCx<'ll, '_> {
             llvm::set_thread_local_mode(g, self.tls_model);
         }
 
+        let dso_local = unsafe { self.should_assume_dso_local(g, true) };
+        if dso_local {
+            unsafe {
+                llvm::LLVMRustSetDSOLocal(g, true);
+            }
+        }
+
         if !def_id.is_local() {
             let needs_dll_storage_attr = self.use_dll_storage_attrs && !self.tcx.is_foreign_item(def_id) &&
+                // Local definitions can never be imported, so we must not apply
+                // the DLLImport annotation.
+                !dso_local &&
                 // ThinLTO can't handle this workaround in all cases, so we don't
                 // emit the attrs. Instead we make them unnecessary by disallowing
                 // dynamic linking when linker plugin based LTO is enabled.
@@ -340,12 +350,6 @@ impl<'ll> CodegenCx<'ll, '_> {
             }
         }
 
-        unsafe {
-            if self.should_assume_dso_local(g, true) {
-                llvm::LLVMRustSetDSOLocal(g, true);
-            }
-        }
-
         self.instances.borrow_mut().insert(instance, g);
         g
     }

src/test/codegen/auxiliary/extern_decl.rs

@@ -0,0 +1,11 @@
+// Auxiliary crate that exports a function and static. Both always
+// evaluate to `71`. We force mutability on the static to prevent
+// it from being inlined as constant.
+
+#![crate_type = "lib"]
+
+#[no_mangle]
+pub fn extern_fn() -> u8 { unsafe { extern_static } }
+
+#[no_mangle]
+pub static mut extern_static: u8 = 71;

src/test/codegen/static-relocation-model-msvc.rs

@@ -0,0 +1,26 @@
+// Verify linkage of external symbols in the static relocation model on MSVC.
+//
+// compile-flags: -O -C relocation-model=static
+// aux-build: extern_decl.rs
+// only-x86_64-pc-windows-msvc
+
+#![crate_type = "rlib"]
+
+extern crate extern_decl;
+
+// The `extern_decl` definitions are imported from a statically linked rust
+// crate, thus they are expected to be marked `dso_local` without `dllimport`.
+//
+// The `access_extern()` symbol is from this compilation unit, thus we expect
+// it to be marked `dso_local` as well, given the static relocation model.
+//
+// CHECK: @extern_static = external dso_local local_unnamed_addr global i8
+// CHECK: define dso_local i8 @access_extern() {{.*}}
+// CHECK: declare dso_local i8 @extern_fn() {{.*}}
+
+#[no_mangle]
+pub fn access_extern() -> u8 {
+    unsafe {
+        extern_decl::extern_fn() + extern_decl::extern_static
+    }
+}