Fix Access Violation when using lld & ThinLTO on windows-msvc

compiler/rustc_codegen_llvm/src/consts.rs

@@ -19,6 +19,7 @@ use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_middle::{bug, span_bug};
+use rustc_session::config::Lto;
 use rustc_target::abi::{
     AddressSpace, Align, HasDataLayout, Primitive, Scalar, Size, WrappingRange,
 };
@@ -303,7 +304,8 @@ impl<'ll> CodegenCx<'ll, '_> {
                 // 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.opts.cg.linker_plugin_lto.enabled() &&
+                self.tcx.sess.lto() != Lto::Thin;
 
             // If this assertion triggers, there's something wrong with commandline
             // argument validation.

src/test/codegen/auxiliary/static_dllimport_aux.rs

@@ -0,0 +1,13 @@
+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)()
+    }
+}

src/test/codegen/issue-81408-dllimport-thinlto-windows.rs

@@ -0,0 +1,15 @@
+// compile-flags: -O -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();
+}