code-cov: generate dead functions with private/default linkage

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -212,8 +212,8 @@ fn declare_unused_fn(cx: &CodegenCx<'ll, 'tcx>, def_id: &DefId) -> Instance<'tcx
         ),
     );
 
-    llvm::set_linkage(llfn, llvm::Linkage::WeakAnyLinkage);
-    llvm::set_visibility(llfn, llvm::Visibility::Hidden);
+    llvm::set_linkage(llfn, llvm::Linkage::PrivateLinkage);
+    llvm::set_visibility(llfn, llvm::Visibility::Default);
 
     assert!(cx.instances.borrow_mut().insert(instance, llfn).is_none());
 

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.issue-85461.txt

@@ -0,0 +1,36 @@
+../coverage/issue-85461.rs:
+    1|       |// Regression test for #85461: MSVC sometimes fail to link with dead code and #[inline(always)]
+    2|       |
+    3|       |extern crate inline_always_with_dead_code;
+    4|       |
+    5|       |use inline_always_with_dead_code::{bar, baz};
+    6|       |
+    7|      1|fn main() {
+    8|      1|    bar::call_me();
+    9|      1|    baz::call_me();
+   10|      1|}
+
+../coverage/lib/inline_always_with_dead_code.rs:
+    1|       |// compile-flags: -Zinstrument-coverage -Ccodegen-units=4 -Copt-level=0
+    2|       |
+    3|       |#![allow(dead_code)]
+    4|       |
+    5|       |mod foo {
+    6|       |    #[inline(always)]
+    7|      2|    pub fn called() { }
+    8|       |
+    9|      0|    fn uncalled() { }
+   10|       |}
+   11|       |
+   12|       |pub mod bar {
+   13|      1|    pub fn call_me() {
+   14|      1|        super::foo::called();
+   15|      1|    }
+   16|       |}
+   17|       |
+   18|       |pub mod baz {
+   19|      1|    pub fn call_me() {
+   20|      1|        super::foo::called();
+   21|      1|    }
+   22|       |}
+

src/test/run-make-fulldeps/coverage/issue-85461.rs

@@ -0,0 +1,10 @@
+// Regression test for #85461: MSVC sometimes fail to link with dead code and #[inline(always)]
+
+extern crate inline_always_with_dead_code;
+
+use inline_always_with_dead_code::{bar, baz};
+
+fn main() {
+    bar::call_me();
+    baz::call_me();
+}

src/test/run-make-fulldeps/coverage/lib/inline_always_with_dead_code.rs

@@ -0,0 +1,22 @@
+// compile-flags: -Zinstrument-coverage -Ccodegen-units=4 -Copt-level=0
+
+#![allow(dead_code)]
+
+mod foo {
+    #[inline(always)]
+    pub fn called() { }
+
+    fn uncalled() { }
+}
+
+pub mod bar {
+    pub fn call_me() {
+        super::foo::called();
+    }
+}
+
+pub mod baz {
+    pub fn call_me() {
+        super::foo::called();
+    }
+}

src/test/ui/issues/issue-85461.rs

@@ -0,0 +1,27 @@
+// compile-flags: -Zinstrument-coverage -Ccodegen-units=4 --crate-type dylib -Copt-level=0
+// build-pass
+// needs-profiler-support
+
+// Regression test for #85461 where MSVC sometimes fails to link instrument-coverage binaries
+// with dead code and #[inline(always)].
+
+#![allow(dead_code)]
+
+mod foo {
+    #[inline(always)]
+    pub fn called() { }
+
+    fn uncalled() { }
+}
+
+pub mod bar {
+    pub fn call_me() {
+        super::foo::called();
+    }
+}
+
+pub mod baz {
+    pub fn call_me() {
+        super::foo::called();
+    }
+}