Error if an autodiff user does not set lto=fat

[ZuseZ4]

Based on your feedback, I started to provide a nice error message for a lack of lto=fat, instead of us forcing it.

In a next step, we should replace RUSTFLAGS="-Zautodiff=Enable" with another Cargo.toml setting, as discussed here: #147487 (comment)

As another improvement, we should also figure out why rlib builds do not properly obey the fat=lto setting.

@bjorn3

[rustbot]

r? @madsmtm

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[ZuseZ4]

r? @bjorn3

[rustbot]

Failed to set assignee to bjorn: invalid assignee

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[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[bjorn3]

The first two commits LGTM.

[rustbot]

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[TIMING:end] tool::ToolBuild { build_compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu, tool: "tidy", path: "src/tools/tidy", mode: ToolBootstrap, source_type: InTree, extra_features: [], allow_features: "", cargo_args: [], artifact_kind: Binary } -- 11.798
[TIMING:end] tool::Tidy { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000
fmt check
Diff in /checkout/compiler/rustc_codegen_llvm/src/intrinsic.rs:15:
 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;
Diff in /checkout/compiler/rustc_codegen_llvm/src/intrinsic.rs:21:
 use rustc_target::spec::Os;
 use tracing::debug;
 
-use rustc_session::config::CrateType;
-
 use crate::abi::FnAbiLlvmExt;
 use crate::builder::Builder;
 use crate::builder::autodiff::{adjust_activity_to_abi, generate_enzyme_call};
Diff in /checkout/compiler/rustc_codegen_llvm/src/intrinsic.rs:1148:
     if !tcx.sess.opts.unstable_opts.autodiff.contains(&rustc_session::config::AutoDiff::Enable) {
         let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithoutEnable);
     }
-//pub enum CrateType {
-//    Executable,
-//    Dylib,
-//    Rlib,
-//    Staticlib,
-//    Cdylib,
-//    ProcMacro,
-//    Sdylib,
-//}
+    //pub enum CrateType {
+    //    Executable,
+    //    Dylib,
+    //    Rlib,
+    //    Staticlib,
+    //    Cdylib,
+    //    ProcMacro,
+    //    Sdylib,
+    //}
     let ct = tcx.crate_types();
     let lto = tcx.sess.lto();
     if ct.len() == 1 && ct.contains(&CrateType::Executable) {
Diff in /checkout/compiler/rustc_codegen_llvm/src/intrinsic.rs:1164:
             //let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithIncompatibleCrateType);
         }
     } else {
-        ;
-        if lto != rustc_session::config::Lto::Fat && !tcx.sess.opts.cg.linker_plugin_lto.enabled(){
+        if lto != rustc_session::config::Lto::Fat && !tcx.sess.opts.cg.linker_plugin_lto.enabled() {
             //let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithIncompatibleCrateType);
         }
     }
Diff in /checkout/compiler/rustc_mir_transform/src/cross_crate_inline.rs:34:
         return true;
     }
 
-    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) {
+    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;
     }
 
fmt: checked 6547 files