From 0dfdb6c3da4698357b9895625dc743f9f2ff8e67 Mon Sep 17 00:00:00 2001
From: Manuel Drehwald <git@manuel.drehwald.info>
Date: Mon, 17 Nov 2025 01:50:10 -0500
Subject: [PATCH] rlib handling

---
 compiler/rustc_codegen_llvm/src/intrinsic.rs       | 14 ++++++++++++--
 .../rustc_mir_transform/src/cross_crate_inline.rs  |  8 ++++++++
 .../rustc_monomorphize/src/collector/autodiff.rs   |  2 ++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index 84fc6ebbc317..029c43e0ba82 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -15,6 +15,7 @@
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, HasTypingEnv, LayoutOf};
 use rustc_middle::ty::{self, GenericArgsRef, Instance, SimdAlign, Ty, TyCtxt, TypingEnv};
 use rustc_middle::{bug, span_bug};
+use rustc_session::config::CrateType;
 use rustc_span::{Span, Symbol, sym};
 use rustc_symbol_mangling::{mangle_internal_symbol, symbol_name_for_instance_in_crate};
 use rustc_target::callconv::PassMode;
@@ -1136,8 +1137,17 @@ fn codegen_autodiff<'ll, 'tcx>(
     if !tcx.sess.opts.unstable_opts.autodiff.contains(&rustc_session::config::AutoDiff::Enable) {
         let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithoutEnable);
     }
-    if tcx.sess.lto() != rustc_session::config::Lto::Fat {
-        let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithoutLto);
+
+    let ct = tcx.crate_types();
+    let lto = tcx.sess.lto();
+    if ct.len() == 1 && ct.contains(&CrateType::Executable) {
+        if lto != rustc_session::config::Lto::Fat {
+            let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithoutLto);
+        }
+    } else {
+        if lto != rustc_session::config::Lto::Fat && !tcx.sess.opts.cg.linker_plugin_lto.enabled() {
+            let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithoutLto);
+        }
     }
 
     let fn_args = instance.args;
diff --git a/compiler/rustc_mir_transform/src/cross_crate_inline.rs b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
index 7fc9fb9cca2d..69248cf91f24 100644
--- a/compiler/rustc_mir_transform/src/cross_crate_inline.rs
+++ b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
@@ -34,6 +34,14 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
         return true;
     }
 
+    // FIXME(autodiff): replace this as per discussion in https://github.com/rust-lang/rust/pull/149033#discussion_r2535465880
+    if tcx.has_attr(def_id, sym::autodiff_forward)
+        || tcx.has_attr(def_id, sym::autodiff_reverse)
+        || tcx.has_attr(def_id, sym::rustc_autodiff)
+    {
+        return true;
+    }
+
     if tcx.has_attr(def_id, sym::rustc_intrinsic) {
         // Intrinsic fallback bodies are always cross-crate inlineable.
         // To ensure that the MIR inliner doesn't cluelessly try to inline fallback
diff --git a/compiler/rustc_monomorphize/src/collector/autodiff.rs b/compiler/rustc_monomorphize/src/collector/autodiff.rs
index 13868cca944a..e3646596e75e 100644
--- a/compiler/rustc_monomorphize/src/collector/autodiff.rs
+++ b/compiler/rustc_monomorphize/src/collector/autodiff.rs
@@ -7,6 +7,8 @@
 // mono so this does not interfere in `autodiff` intrinsics
 // codegen process. If they are unused, LLVM will remove them when
 // compiling with O3.
+// FIXME(autodiff): Remove this whole file, as per discussion in
+// https://github.com/rust-lang/rust/pull/149033#discussion_r2535465880
 pub(crate) fn collect_autodiff_fn<'tcx>(
     tcx: TyCtxt<'tcx>,
     instance: ty::Instance<'tcx>,