Apply dllimport in ThinLTO

compiler/rustc_codegen_llvm/src/consts.rs

@@ -16,7 +16,6 @@ use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::Instance;
 use rustc_middle::ty::layout::{HasTypingEnv, LayoutOf};
 use rustc_middle::{bug, span_bug};
-use rustc_session::config::Lto;
 use tracing::{debug, instrument, trace};
 
 use crate::common::{AsCCharPtr, CodegenCx};
@@ -344,11 +343,11 @@ impl<'ll> CodegenCx<'ll, '_> {
                 // 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.
-                && !self.tcx.sess.opts.cg.linker_plugin_lto.enabled()
-                && self.tcx.sess.lto() != Lto::Thin;
+                // Linker plugin ThinLTO doesn't create the self-dllimport Rust uses for rlibs
+                // as the code generation happens out of process. Instead we assume static linkage
+                // and disallow dynamic linking when linker plugin based LTO is enabled.
+                // Regular in-process ThinLTO doesn't need this workaround.
+                && !self.tcx.sess.opts.cg.linker_plugin_lto.enabled();
 
             // If this assertion triggers, there's something wrong with commandline
             // argument validation.

tests/codegen/issues/auxiliary/static_dllimport_aux.rs

@@ -1,13 +0,0 @@
-use std::sync::atomic::{AtomicPtr, Ordering};
-
-#[inline(always)]
-pub fn memrchr() {
-    fn detect() {}
-
-    static CROSS_CRATE_STATIC_ITEM: AtomicPtr<()> = AtomicPtr::new(detect as *mut ());
-
-    unsafe {
-        let fun = CROSS_CRATE_STATIC_ITEM.load(Ordering::SeqCst);
-        std::mem::transmute::<*mut (), fn()>(fun)()
-    }
-}

tests/codegen/issues/issue-81408-dllimport-thinlto-windows.rs

@@ -1,15 +0,0 @@
-//@ compile-flags: -Copt-level=3 -C lto=thin -C prefer-dynamic=no
-//@ only-windows
-//@ aux-build:static_dllimport_aux.rs
-
-// Test that on Windows, when performing ThinLTO, we do not mark cross-crate static items with
-// dllimport because lld does not fix the symbol names for us.
-
-extern crate static_dllimport_aux;
-
-// CHECK-LABEL: @{{.+}}CROSS_CRATE_STATIC_ITEM{{.+}} =
-// CHECK-SAME: external local_unnamed_addr global %"{{.+}}AtomicPtr
-
-pub fn main() {
-    static_dllimport_aux::memrchr();
-}