Merge from rust-lang/rust

8 files changed, 235 insertions, 107 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/archive.rs b/compiler/rustc_codegen_ssa/src/back/archive.rs
index 58eb137c068..60af462b6b6 100644
--- a/compiler/rustc_codegen_ssa/src/back/archive.rs
+++ b/compiler/rustc_codegen_ssa/src/back/archive.rs
@@ -414,10 +414,10 @@ impl<'a> ArchiveBuilder for ArArchiveBuilder<'a> {
                     let member_path = archive_path.parent().unwrap().join(Path::new(&file_name));
                     self.entries.push((file_name.into_bytes(), ArchiveEntry::File(member_path)));
                 } else {
-                    self.entries.push((file_name.into_bytes(), ArchiveEntry::FromArchive {
-                        archive_index,
-                        file_range: entry.file_range(),
-                    }));
+                    self.entries.push((
+                        file_name.into_bytes(),
+                        ArchiveEntry::FromArchive { archive_index, file_range: entry.file_range() },
+                    ));
                 }
             }
         }
diff --git a/compiler/rustc_codegen_ssa/src/back/command.rs b/compiler/rustc_codegen_ssa/src/back/command.rs
index b3c5b86ccf4..63023fdba20 100644
--- a/compiler/rustc_codegen_ssa/src/back/command.rs
+++ b/compiler/rustc_codegen_ssa/src/back/command.rs
@@ -13,6 +13,7 @@ pub(crate) struct Command {
     args: Vec<OsString>,
     env: Vec<(OsString, OsString)>,
     env_remove: Vec<OsString>,
+    env_clear: bool,
 }
 
 #[derive(Clone)]
@@ -36,7 +37,13 @@ impl Command {
     }
 
     fn _new(program: Program) -> Command {
-        Command { program, args: Vec::new(), env: Vec::new(), env_remove: Vec::new() }
+        Command {
+            program,
+            args: Vec::new(),
+            env: Vec::new(),
+            env_remove: Vec::new(),
+            env_clear: false,
+        }
     }
 
     pub(crate) fn arg<P: AsRef<OsStr>>(&mut self, arg: P) -> &mut Command {
@@ -79,6 +86,11 @@ impl Command {
         self
     }
 
+    pub(crate) fn env_clear(&mut self) -> &mut Command {
+        self.env_clear = true;
+        self
+    }
+
     fn _env_remove(&mut self, key: &OsStr) {
         self.env_remove.push(key.to_owned());
     }
@@ -106,6 +118,9 @@ impl Command {
         for k in &self.env_remove {
             ret.env_remove(k);
         }
+        if self.env_clear {
+            ret.env_clear();
+        }
         ret
     }
 
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index df35b5e8426..105a4cb81f0 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -15,12 +15,14 @@ use rustc_ast::CRATE_NODE_ID;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::temp_dir::MaybeTempDir;
-use rustc_errors::DiagCtxtHandle;
+use rustc_errors::{DiagCtxtHandle, LintDiagnostic};
 use rustc_fs_util::{fix_windows_verbatim_for_gcc, try_canonicalize};
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
+use rustc_macros::LintDiagnostic;
 use rustc_metadata::fs::{METADATA_FILENAME, copy_to_stdout, emit_wrapper_file};
 use rustc_metadata::{find_native_static_library, walk_native_lib_search_dirs};
 use rustc_middle::bug;
+use rustc_middle::lint::lint_level;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols::SymbolExportKind;
@@ -29,6 +31,7 @@ use rustc_session::config::{
     OutputType, PrintKind, SplitDwarfKind, Strip,
 };
 use rustc_session::cstore::DllImport;
+use rustc_session::lint::builtin::LINKER_MESSAGES;
 use rustc_session::output::{check_file_is_writeable, invalid_output_for_target, out_filename};
 use rustc_session::search_paths::PathKind;
 use rustc_session::utils::NativeLibKind;
@@ -749,6 +752,14 @@ fn link_dwarf_object(sess: &Session, cg_results: &CodegenResults, executable_out
     }
 }
 
+#[derive(LintDiagnostic)]
+#[diag(codegen_ssa_linker_output)]
+/// Translating this is kind of useless. We don't pass translation flags to the linker, so we'd just
+/// end up with inconsistent languages within the same diagnostic.
+struct LinkerOutput {
+    inner: String,
+}
+
 /// Create a dynamic library or executable.
 ///
 /// This will invoke the system linker/cc to create the resulting file. This links to all upstream
@@ -981,6 +992,11 @@ fn link_natively(
 
     match prog {
         Ok(prog) => {
+            let is_msvc_link_exe = sess.target.is_like_msvc
+                && flavor == LinkerFlavor::Msvc(Lld::No)
+                // Match exactly "link.exe"
+                && linker_path.to_str() == Some("link.exe");
+
             if !prog.status.success() {
                 let mut output = prog.stderr.clone();
                 output.extend_from_slice(&prog.stdout);
@@ -991,22 +1007,16 @@ fn link_natively(
                     command: cmd,
                     escaped_output,
                     verbose: sess.opts.verbose,
+                    sysroot_dir: sess.sysroot.clone(),
                 };
                 sess.dcx().emit_err(err);
                 // If MSVC's `link.exe` was expected but the return code
                 // is not a Microsoft LNK error then suggest a way to fix or
                 // install the Visual Studio build tools.
                 if let Some(code) = prog.status.code() {
-                    if sess.target.is_like_msvc
-                        && flavor == LinkerFlavor::Msvc(Lld::No)
-                        // Respect the command line override
-                        && sess.opts.cg.linker.is_none()
-                        // Match exactly "link.exe"
-                        && linker_path.to_str() == Some("link.exe")
-                        // All Microsoft `link.exe` linking error codes are
-                        // four digit numbers in the range 1000 to 9999 inclusive
-                        && (code < 1000 || code > 9999)
-                    {
+                    // All Microsoft `link.exe` linking ror codes are
+                    // four digit numbers in the range 1000 to 9999 inclusive
+                    if is_msvc_link_exe && (code < 1000 || code > 9999) {
                         let is_vs_installed = windows_registry::find_vs_version().is_ok();
                         let has_linker =
                             windows_registry::find_tool(&sess.target.arch, "link.exe").is_some();
@@ -1028,8 +1038,49 @@ fn link_natively(
 
                 sess.dcx().abort_if_errors();
             }
-            info!("linker stderr:\n{}", escape_string(&prog.stderr));
-            info!("linker stdout:\n{}", escape_string(&prog.stdout));
+
+            let stderr = escape_string(&prog.stderr);
+            let mut stdout = escape_string(&prog.stdout);
+            info!("linker stderr:\n{}", &stderr);
+            info!("linker stdout:\n{}", &stdout);
+
+            // Hide some progress messages from link.exe that we don't care about.
+            // See https://github.com/chromium/chromium/blob/bfa41e41145ffc85f041384280caf2949bb7bd72/build/toolchain/win/tool_wrapper.py#L144-L146
+            if is_msvc_link_exe {
+                if let Ok(str) = str::from_utf8(&prog.stdout) {
+                    let mut output = String::with_capacity(str.len());
+                    for line in stdout.lines() {
+                        if line.starts_with("   Creating library")
+                            || line.starts_with("Generating code")
+                            || line.starts_with("Finished generating code")
+                        {
+                            continue;
+                        }
+                        output += line;
+                        output += "\r\n"
+                    }
+                    stdout = escape_string(output.trim().as_bytes())
+                }
+            }
+
+            let (level, src) = codegen_results.crate_info.lint_levels.linker_messages;
+            let lint = |msg| {
+                lint_level(sess, LINKER_MESSAGES, level, src, None, |diag| {
+                    LinkerOutput { inner: msg }.decorate_lint(diag)
+                })
+            };
+
+            if !prog.stderr.is_empty() {
+                // We already print `warning:` at the start of the diagnostic. Remove it from the linker output if present.
+                let stderr = stderr
+                    .strip_prefix("warning: ")
+                    .unwrap_or(&stderr)
+                    .replace(": warning: ", ": ");
+                lint(format!("linker stderr: {stderr}"));
+            }
+            if !stdout.is_empty() {
+                lint(format!("linker stdout: {}", stdout))
+            }
         }
         Err(e) => {
             let linker_not_found = e.kind() == io::ErrorKind::NotFound;
diff --git a/compiler/rustc_codegen_ssa/src/back/linker/tests.rs b/compiler/rustc_codegen_ssa/src/back/linker/tests.rs
index bf3e8c90200..143df085dbf 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker/tests.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker/tests.rs
@@ -10,23 +10,22 @@ fn test_rpaths_to_args() {
 #[test]
 fn test_xlinker() {
     let mut cmd = Command::new("foo");
-    convert_link_args_to_cc_args(&mut cmd, &[
-        "arg1",
-        "arg2",
-        "arg3,with,comma",
-        "arg4,with,comma",
-        "arg5",
-        "arg6,with,comma",
-    ]);
+    convert_link_args_to_cc_args(
+        &mut cmd,
+        &["arg1", "arg2", "arg3,with,comma", "arg4,with,comma", "arg5", "arg6,with,comma"],
+    );
 
-    assert_eq!(cmd.get_args(), [
-        OsStr::new("-Wl,arg1,arg2"),
-        OsStr::new("-Xlinker"),
-        OsStr::new("arg3,with,comma"),
-        OsStr::new("-Xlinker"),
-        OsStr::new("arg4,with,comma"),
-        OsStr::new("-Wl,arg5"),
-        OsStr::new("-Xlinker"),
-        OsStr::new("arg6,with,comma"),
-    ]);
+    assert_eq!(
+        cmd.get_args(),
+        [
+            OsStr::new("-Wl,arg1,arg2"),
+            OsStr::new("-Xlinker"),
+            OsStr::new("arg3,with,comma"),
+            OsStr::new("-Xlinker"),
+            OsStr::new("arg4,with,comma"),
+            OsStr::new("-Wl,arg5"),
+            OsStr::new("-Xlinker"),
+            OsStr::new("arg6,with,comma"),
+        ]
+    );
 }
diff --git a/compiler/rustc_codegen_ssa/src/back/lto.rs b/compiler/rustc_codegen_ssa/src/back/lto.rs
index efccf7687a1..9fd984b6419 100644
--- a/compiler/rustc_codegen_ssa/src/back/lto.rs
+++ b/compiler/rustc_codegen_ssa/src/back/lto.rs
@@ -4,7 +4,6 @@ use std::sync::Arc;
 use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_data_structures::memmap::Mmap;
 use rustc_errors::FatalError;
-use rustc_middle::ty::TyCtxt;
 
 use super::write::CodegenContext;
 use crate::ModuleCodegen;
@@ -89,13 +88,12 @@ impl<B: WriteBackendMethods> LtoModuleCodegen<B> {
     pub unsafe fn autodiff(
         self,
         cgcx: &CodegenContext<B>,
-        tcx: TyCtxt<'_>,
         diff_fncs: Vec<AutoDiffItem>,
         config: &ModuleConfig,
     ) -> Result<LtoModuleCodegen<B>, FatalError> {
         match &self {
             LtoModuleCodegen::Fat(module) => {
-                B::autodiff(cgcx, tcx, &module, diff_fncs, config)?;
+                B::autodiff(cgcx, &module, diff_fncs, config)?;
             }
             _ => panic!("autodiff called with non-fat LTO module"),
         }
diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index ba7b53321a8..d70413b8a47 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -704,13 +704,17 @@ pub fn create_metadata_file_for_wasm(sess: &Session, data: &[u8], section_name:
     let mut imports = wasm_encoder::ImportSection::new();
 
     if sess.target.pointer_width == 64 {
-        imports.import("env", "__linear_memory", wasm_encoder::MemoryType {
-            minimum: 0,
-            maximum: None,
-            memory64: true,
-            shared: false,
-            page_size_log2: None,
-        });
+        imports.import(
+            "env",
+            "__linear_memory",
+            wasm_encoder::MemoryType {
+                minimum: 0,
+                maximum: None,
+                memory64: true,
+                shared: false,
+                page_size_log2: None,
+            },
+        );
     }
 
     if imports.len() > 0 {
diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index 60ab2919352..1dbaffaa577 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -140,11 +140,14 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
         .into();
 
     if let Some(id) = tcx.proc_macro_decls_static(()) {
-        reachable_non_generics.insert(id.to_def_id(), SymbolExportInfo {
-            level: SymbolExportLevel::C,
-            kind: SymbolExportKind::Data,
-            used: false,
-        });
+        reachable_non_generics.insert(
+            id.to_def_id(),
+            SymbolExportInfo {
+                level: SymbolExportLevel::C,
+                kind: SymbolExportKind::Data,
+                used: false,
+            },
+        );
     }
 
     reachable_non_generics
@@ -185,11 +188,14 @@ fn exported_symbols_provider_local(
     if !tcx.sess.target.dll_tls_export {
         symbols.extend(sorted.iter().filter_map(|(&def_id, &info)| {
             tcx.needs_thread_local_shim(def_id).then(|| {
-                (ExportedSymbol::ThreadLocalShim(def_id), SymbolExportInfo {
-                    level: info.level,
-                    kind: SymbolExportKind::Text,
-                    used: info.used,
-                })
+                (
+                    ExportedSymbol::ThreadLocalShim(def_id),
+                    SymbolExportInfo {
+                        level: info.level,
+                        kind: SymbolExportKind::Text,
+                        used: info.used,
+                    },
+                )
             })
         }))
     }
@@ -198,11 +204,14 @@ fn exported_symbols_provider_local(
         let exported_symbol =
             ExportedSymbol::NoDefId(SymbolName::new(tcx, tcx.sess.target.entry_name.as_ref()));
 
-        symbols.push((exported_symbol, SymbolExportInfo {
-            level: SymbolExportLevel::C,
-            kind: SymbolExportKind::Text,
-            used: false,
-        }));
+        symbols.push((
+            exported_symbol,
+            SymbolExportInfo {
+                level: SymbolExportLevel::C,
+                kind: SymbolExportKind::Text,
+                used: false,
+            },
+        ));
     }
 
     // Mark allocator shim symbols as exported only if they were generated.
@@ -214,20 +223,26 @@ fn exported_symbols_provider_local(
         {
             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 
-            symbols.push((exported_symbol, SymbolExportInfo {
-                level: SymbolExportLevel::Rust,
-                kind: SymbolExportKind::Text,
-                used: false,
-            }));
+            symbols.push((
+                exported_symbol,
+                SymbolExportInfo {
+                    level: SymbolExportLevel::Rust,
+                    kind: SymbolExportKind::Text,
+                    used: false,
+                },
+            ));
         }
 
         let exported_symbol =
             ExportedSymbol::NoDefId(SymbolName::new(tcx, NO_ALLOC_SHIM_IS_UNSTABLE));
-        symbols.push((exported_symbol, SymbolExportInfo {
-            level: SymbolExportLevel::Rust,
-            kind: SymbolExportKind::Data,
-            used: false,
-        }))
+        symbols.push((
+            exported_symbol,
+            SymbolExportInfo {
+                level: SymbolExportLevel::Rust,
+                kind: SymbolExportKind::Data,
+                used: false,
+            },
+        ))
     }
 
     if tcx.sess.instrument_coverage() || tcx.sess.opts.cg.profile_generate.enabled() {
@@ -239,11 +254,14 @@ fn exported_symbols_provider_local(
 
         symbols.extend(PROFILER_WEAK_SYMBOLS.iter().map(|sym| {
             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
-            (exported_symbol, SymbolExportInfo {
-                level: SymbolExportLevel::C,
-                kind: SymbolExportKind::Data,
-                used: false,
-            })
+            (
+                exported_symbol,
+                SymbolExportInfo {
+                    level: SymbolExportLevel::C,
+                    kind: SymbolExportKind::Data,
+                    used: false,
+                },
+            )
         }));
     }
 
@@ -261,11 +279,14 @@ fn exported_symbols_provider_local(
 
         symbols.extend(msan_weak_symbols.into_iter().map(|sym| {
             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, sym));
-            (exported_symbol, SymbolExportInfo {
-                level: SymbolExportLevel::C,
-                kind: SymbolExportKind::Data,
-                used: false,
-            })
+            (
+                exported_symbol,
+                SymbolExportInfo {
+                    level: SymbolExportLevel::C,
+                    kind: SymbolExportKind::Data,
+                    used: false,
+                },
+            )
         }));
     }
 
@@ -275,11 +296,14 @@ fn exported_symbols_provider_local(
         let symbol_name = metadata_symbol_name(tcx);
         let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 
-        symbols.push((exported_symbol, SymbolExportInfo {
-            level: SymbolExportLevel::C,
-            kind: SymbolExportKind::Data,
-            used: true,
-        }));
+        symbols.push((
+            exported_symbol,
+            SymbolExportInfo {
+                level: SymbolExportLevel::C,
+                kind: SymbolExportKind::Data,
+                used: true,
+            },
+        ));
     }
 
     if tcx.local_crate_exports_generics() {
@@ -293,7 +317,7 @@ fn exported_symbols_provider_local(
         // external linkage is enough for monomorphization to be linked to.
         let need_visibility = tcx.sess.target.dynamic_linking && !tcx.sess.target.only_cdylib;
 
-        let (_, cgus) = tcx.collect_and_partition_mono_items(());
+        let cgus = tcx.collect_and_partition_mono_items(()).codegen_units;
 
         // The symbols created in this loop are sorted below it
         #[allow(rustc::potential_query_instability)]
@@ -325,21 +349,27 @@ fn exported_symbols_provider_local(
                 MonoItem::Fn(Instance { def: InstanceKind::Item(def), args }) => {
                     if args.non_erasable_generics().next().is_some() {
                         let symbol = ExportedSymbol::Generic(def, args);
-                        symbols.push((symbol, SymbolExportInfo {
-                            level: SymbolExportLevel::Rust,
-                            kind: SymbolExportKind::Text,
-                            used: false,
-                        }));
+                        symbols.push((
+                            symbol,
+                            SymbolExportInfo {
+                                level: SymbolExportLevel::Rust,
+                                kind: SymbolExportKind::Text,
+                                used: false,
+                            },
+                        ));
                     }
                 }
                 MonoItem::Fn(Instance { def: InstanceKind::DropGlue(_, Some(ty)), args }) => {
                     // A little sanity-check
                     assert_eq!(args.non_erasable_generics().next(), Some(GenericArgKind::Type(ty)));
-                    symbols.push((ExportedSymbol::DropGlue(ty), SymbolExportInfo {
-                        level: SymbolExportLevel::Rust,
-                        kind: SymbolExportKind::Text,
-                        used: false,
-                    }));
+                    symbols.push((
+                        ExportedSymbol::DropGlue(ty),
+                        SymbolExportInfo {
+                            level: SymbolExportLevel::Rust,
+                            kind: SymbolExportKind::Text,
+                            used: false,
+                        },
+                    ));
                 }
                 MonoItem::Fn(Instance {
                     def: InstanceKind::AsyncDropGlueCtorShim(_, Some(ty)),
@@ -347,11 +377,14 @@ fn exported_symbols_provider_local(
                 }) => {
                     // A little sanity-check
                     assert_eq!(args.non_erasable_generics().next(), Some(GenericArgKind::Type(ty)));
-                    symbols.push((ExportedSymbol::AsyncDropGlueCtorShim(ty), SymbolExportInfo {
-                        level: SymbolExportLevel::Rust,
-                        kind: SymbolExportKind::Text,
-                        used: false,
-                    }));
+                    symbols.push((
+                        ExportedSymbol::AsyncDropGlueCtorShim(ty),
+                        SymbolExportInfo {
+                            level: SymbolExportLevel::Rust,
+                            kind: SymbolExportKind::Text,
+                            used: false,
+                        },
+                    ));
                 }
                 _ => {
                     // Any other symbols don't qualify for sharing
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index b40bb4ed5d2..ce2161a07eb 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -7,6 +7,7 @@ use std::sync::mpsc::{Receiver, Sender, channel};
 use std::{fs, io, mem, str, thread};
 
 use rustc_ast::attr;
+use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_data_structures::jobserver::{self, Acquired};
 use rustc_data_structures::memmap::Mmap;
@@ -40,7 +41,7 @@ use tracing::debug;
 use super::link::{self, ensure_removed};
 use super::lto::{self, SerializedModule};
 use super::symbol_export::symbol_name_for_instance_in_crate;
-use crate::errors::ErrorCreatingRemarkDir;
+use crate::errors::{AutodiffWithoutLto, ErrorCreatingRemarkDir};
 use crate::traits::*;
 use crate::{
     CachedModuleCodegen, CodegenResults, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind,
@@ -118,6 +119,7 @@ pub struct ModuleConfig {
     pub merge_functions: bool,
     pub emit_lifetime_markers: bool,
     pub llvm_plugins: Vec<String>,
+    pub autodiff: Vec<config::AutoDiff>,
 }
 
 impl ModuleConfig {
@@ -266,6 +268,7 @@ impl ModuleConfig {
 
             emit_lifetime_markers: sess.emit_lifetime_markers(),
             llvm_plugins: if_regular!(sess.opts.unstable_opts.llvm_plugins.clone(), vec![]),
+            autodiff: if_regular!(sess.opts.unstable_opts.autodiff.clone(), vec![]),
         }
     }
 
@@ -389,6 +392,7 @@ impl<B: WriteBackendMethods> CodegenContext<B> {
 
 fn generate_lto_work<B: ExtraBackendMethods>(
     cgcx: &CodegenContext<B>,
+    autodiff: Vec<AutoDiffItem>,
     needs_fat_lto: Vec<FatLtoInput<B>>,
     needs_thin_lto: Vec<(String, B::ThinBuffer)>,
     import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
@@ -397,11 +401,19 @@ fn generate_lto_work<B: ExtraBackendMethods>(
 
     if !needs_fat_lto.is_empty() {
         assert!(needs_thin_lto.is_empty());
-        let module =
+        let mut module =
             B::run_fat_lto(cgcx, needs_fat_lto, import_only_modules).unwrap_or_else(|e| e.raise());
+        if cgcx.lto == Lto::Fat && !autodiff.is_empty() {
+            let config = cgcx.config(ModuleKind::Regular);
+            module = unsafe { module.autodiff(cgcx, autodiff, config).unwrap() };
+        }
         // We are adding a single work item, so the cost doesn't matter.
         vec![(WorkItem::LTO(module), 0)]
     } else {
+        if !autodiff.is_empty() {
+            let dcx = cgcx.create_dcx();
+            dcx.handle().emit_fatal(AutodiffWithoutLto {});
+        }
         assert!(needs_fat_lto.is_empty());
         let (lto_modules, copy_jobs) = B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules)
             .unwrap_or_else(|e| e.raise());
@@ -1021,6 +1033,9 @@ pub(crate) enum Message<B: WriteBackendMethods> {
     /// Sent from a backend worker thread.
     WorkItem { result: Result<WorkItemResult<B>, Option<WorkerFatalError>>, worker_id: usize },
 
+    /// A vector containing all the AutoDiff tasks that we have to pass to Enzyme.
+    AddAutoDiffItems(Vec<AutoDiffItem>),
+
     /// The frontend has finished generating something (backend IR or a
     /// post-LTO artifact) for a codegen unit, and it should be passed to the
     /// backend. Sent from the main thread.
@@ -1348,6 +1363,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
 
         // This is where we collect codegen units that have gone all the way
         // through codegen and LLVM.
+        let mut autodiff_items = Vec::new();
         let mut compiled_modules = vec![];
         let mut compiled_allocator_module = None;
         let mut needs_link = Vec::new();
@@ -1459,9 +1475,13 @@ fn start_executing_work<B: ExtraBackendMethods>(
                     let needs_thin_lto = mem::take(&mut needs_thin_lto);
                     let import_only_modules = mem::take(&mut lto_import_only_modules);
 
-                    for (work, cost) in
-                        generate_lto_work(&cgcx, needs_fat_lto, needs_thin_lto, import_only_modules)
-                    {
+                    for (work, cost) in generate_lto_work(
+                        &cgcx,
+                        autodiff_items.clone(),
+                        needs_fat_lto,
+                        needs_thin_lto,
+                        import_only_modules,
+                    ) {
                         let insertion_index = work_items
                             .binary_search_by_key(&cost, |&(_, cost)| cost)
                             .unwrap_or_else(|e| e);
@@ -1596,6 +1616,10 @@ fn start_executing_work<B: ExtraBackendMethods>(
                     main_thread_state = MainThreadState::Idle;
                 }
 
+                Message::AddAutoDiffItems(mut items) => {
+                    autodiff_items.append(&mut items);
+                }
+
                 Message::CodegenComplete => {
                     if codegen_state != Aborted {
                         codegen_state = Completed;
@@ -2070,6 +2094,10 @@ impl<B: ExtraBackendMethods> OngoingCodegen<B> {
         drop(self.coordinator.sender.send(Box::new(Message::CodegenComplete::<B>)));
     }
 
+    pub(crate) fn submit_autodiff_items(&self, items: Vec<AutoDiffItem>) {
+        drop(self.coordinator.sender.send(Box::new(Message::<B>::AddAutoDiffItems(items))));
+    }
+
     pub(crate) fn check_for_errors(&self, sess: &Session) {
         self.shared_emitter_main.check(sess, false);
     }