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Improve Session/CodegenBackend construction #161432

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2ac1351
Split `build_session`
nnethercote Aug 19, 2026
1225a52
Change `CodegenBackend::init` to take `&mut self`
nnethercote Aug 19, 2026
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42 changes: 20 additions & 22 deletions compiler/rustc_codegen_cranelift/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,6 @@ extern crate rustc_target;
extern crate rustc_driver;

use std::any::Any;
use std::cell::OnceCell;
use std::env;
use std::sync::Arc;

Expand All @@ -43,7 +42,7 @@ use rustc_data_structures::unord::UnordSet;
use rustc_log::tracing::info;
use rustc_middle::dep_graph::WorkProductMap;
use rustc_session::config::{NATIVE_CPU, OutputFilenames};
use rustc_session::{IncrCompSession, Session};
use rustc_session::{CodegenBackendInit, EarlySession, IncrCompSession, Session};
use rustc_span::{Symbol, sym};
use rustc_target::spec::{Arch, CfgAbi, Env, Os};

Expand Down Expand Up @@ -118,40 +117,43 @@ impl<F: Fn() -> String> Drop for PrintOnPanic<F> {
}

pub struct CraneliftCodegenBackend {
pub config: OnceCell<BackendConfig>,
// `None` before `init`, `Some` after.

@bjorn3 bjorn3 Aug 21, 2026 •
edited by rustbot
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Suggested change
// `None` before `init`, `Some` after.
// Set by `init` if not yet set.

and appropriate changes to init. This is intended to allow setting the config when building CraneliftCodegenBackend already.

View changes since the review

pub config: Option<BackendConfig>,
}

impl CodegenBackend for CraneliftCodegenBackend {
fn name(&self) -> &'static str {
"cranelift"
}

fn init(&self, sess: &Session) {
use rustc_session::config::{InstrumentCoverage, Lto};
match sess.lto() {
Lto::No | Lto::ThinLocal => {}
Lto::Thin | Lto::Fat => {
sess.dcx().fatal("LTO is not supported by rustc_codegen_cranelift");
fn init(&mut self, sess: &EarlySession) -> CodegenBackendInit {
use rustc_session::config::{InstrumentCoverage, LtoCli};

match (sess.target.requires_lto, sess.early_lto()) {
(true, _) | (false, LtoCli::Yes | LtoCli::Fat | LtoCli::NoParam | LtoCli::Thin) => {
sess.dcx().fatal("LTO is not supported by rustc_codegen_cranelift")
}
(false, LtoCli::Unspecified | LtoCli::No) => {}
}

if sess.opts.cg.instrument_coverage() != InstrumentCoverage::No {
sess.dcx()
.fatal("`-Cinstrument-coverage` is LLVM specific and not supported by Cranelift");
}

let config = self.config.get_or_init(|| {
BackendConfig::from_opts(&sess.opts.cg.llvm_args)
.unwrap_or_else(|err| sess.dcx().fatal(err))
});
let config = BackendConfig::from_opts(&sess.opts.cg.llvm_args)
.unwrap_or_else(|err| sess.dcx().fatal(err));

if config.jit_mode && !sess.opts.output_types.should_codegen() {
sess.dcx().fatal("JIT mode doesn't work with `cargo check`");
}
}
self.config = Some(config);

fn thin_lto_supported(&self) -> bool {
false
CodegenBackendInit {
replaced_intrinsics: vec![],
fallback_intrinsics: vec![sym::type_id_eq],
thin_lto_supported: false,
}
}

fn target_config(&self, sess: &Session) -> TargetConfig {
Expand Down Expand Up @@ -215,7 +217,7 @@ impl CodegenBackend for CraneliftCodegenBackend {

fn codegen_crate(&self, tcx: TyCtxt<'_>) -> Box<dyn Any> {
info!("codegen crate {}", tcx.crate_name(LOCAL_CRATE));
let config = self.config.get().unwrap();
let config = self.config.as_ref().unwrap();
if config.jit_mode {
#[cfg(feature = "jit")]
driver::jit::run_jit(tcx, self.target_cpu(tcx.sess), config.jit_args.clone());
Expand All @@ -240,10 +242,6 @@ impl CodegenBackend for CraneliftCodegenBackend {
.unwrap()
.join(sess, incr_comp_session, crate_info)
}

fn fallback_intrinsics(&self) -> Vec<Symbol> {
vec![sym::type_id_eq]
}
}

/// Determine if the Cranelift ir verifier should run.
Expand Down Expand Up @@ -375,5 +373,5 @@ fn build_isa(sess: &Session, jit: bool) -> Arc<dyn TargetIsa + 'static> {
/// This is the entrypoint for a hot plugged rustc_codegen_cranelift
#[unsafe(no_mangle)]
pub fn __rustc_codegen_backend() -> Box<dyn CodegenBackend> {
Box::new(CraneliftCodegenBackend { config: OnceCell::new() })
Box::new(CraneliftCodegenBackend { config: None })
}
8 changes: 4 additions & 4 deletions compiler/rustc_codegen_gcc/src/base.rs
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Expand Up @@ -21,7 +21,7 @@ use rustc_target::spec::{Arch, RelocModel};

use crate::builder::Builder;
use crate::context::CodegenCx;
use crate::{GccContext, LockedTargetInfo, LtoMode, SyncContext, gcc_util, new_context};
use crate::{GccContext, LtoMode, SharedTargetInfo, SyncContext, gcc_util, new_context};

#[cfg(feature = "master")]
pub fn visibility_to_gcc(visibility: Visibility) -> gccjit::Visibility {
Expand Down Expand Up @@ -73,7 +73,7 @@ pub fn linkage_to_gcc(linkage: Linkage) -> FunctionType {
pub fn compile_codegen_unit(
tcx: TyCtxt<'_>,
cgu_name: Symbol,
target_info: LockedTargetInfo,
target_info: SharedTargetInfo,
lto_supported: bool,
) -> (ModuleCodegen<GccContext>, u64) {
let prof_timer = tcx.prof.generic_activity("codegen_module");
Expand All @@ -96,7 +96,7 @@ pub fn compile_codegen_unit(
fn module_codegen(
tcx: TyCtxt<'_>,
cgu_name: Symbol,
target_info: LockedTargetInfo,
target_info: SharedTargetInfo,
lto_supported: bool,
) -> ModuleCodegen<GccContext> {
let cgu = tcx.codegen_unit(cgu_name);
Expand Down Expand Up @@ -162,7 +162,7 @@ pub fn compile_codegen_unit(

add_pic_option(&context, tcx.sess.relocation_model());

let target_cpu = gcc_util::target_cpu(tcx.sess);
let target_cpu = gcc_util::target_cpu(&tcx.sess.opts, &tcx.sess.target);
if target_cpu != "generic" {
context.add_command_line_option(format!("-march={}", target_cpu));
}
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_codegen_gcc/src/context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -451,7 +451,7 @@ impl<'gcc, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
}
let tcx = self.tcx;
let func = match tcx.lang_items().eh_personality() {
Some(def_id) if !wants_msvc_seh(self.sess()) => {
Some(def_id) if !wants_msvc_seh(&self.sess().target) => {
let instance = ty::Instance::expect_resolve(
tcx,
self.typing_env(),
Expand All @@ -466,7 +466,7 @@ impl<'gcc, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
self.declare_fn(symbol_name, fn_abi)
}
_ => {
let name = if wants_msvc_seh(self.sess()) {
let name = if wants_msvc_seh(&self.sess().target) {
"__CxxFrameHandler3"
} else {
"rust_eh_personality"
Expand Down
10 changes: 5 additions & 5 deletions compiler/rustc_codegen_gcc/src/gcc_util.rs
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Expand Up @@ -3,8 +3,8 @@ use gccjit::Context;
use rustc_codegen_ssa::target_features;
use rustc_data_structures::smallvec::{SmallVec, smallvec};
use rustc_session::Session;
use rustc_session::config::NATIVE_CPU;
use rustc_target::spec::Arch;
use rustc_session::config::{NATIVE_CPU, Options};
use rustc_target::spec::{Arch, Target};

fn gcc_features_by_flags(sess: &Session, features: &mut Vec<String>) {
target_features::retpoline_features_by_flags(sess, features);
Expand Down Expand Up @@ -130,9 +130,9 @@ fn handle_native(name: &str) -> &str {
unimplemented!();
}

pub fn target_cpu(sess: &Session) -> &str {
match sess.opts.cg.target_cpu {
pub fn target_cpu<'a>(sopts: &'a Options, target: &'a Target) -> &'a str {
match sopts.cg.target_cpu {
Some(ref name) => handle_native(name),
None => handle_native(sess.target.cpu.as_ref()),
None => handle_native(target.cpu.as_ref()),
}
}
2 changes: 1 addition & 1 deletion compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
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Expand Up @@ -1353,7 +1353,7 @@ fn try_intrinsic<'a, 'b, 'gcc, 'tcx>(
// we can never unwind.
OperandValue::Immediate(bx.const_bool(false)).store(bx, dest);
} else {
if wants_msvc_seh(bx.sess()) {
if wants_msvc_seh(&bx.sess().target) {
unimplemented!();
}
#[cfg(feature = "master")]
Expand Down
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