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Make intrinsic fallback bodies cross-crate inlineable

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This change was prompted by the stage1 compiler spending 4% of its time
when compiling the polymorphic-recursion MIR opt test in `unlikely`.

Intrinsic fallback bodies like `unlikely` should always be inlined, it's
very silly if they are not. To do this, we enable the fallback bodies to
be cross-crate inlineable. Not that this matters for our workloads since
the compiler never actually _uses_ the "fallback bodies", it just uses
whatever was cfg(bootstrap)ped, so I've also added `#[inline]` to those.
This commit is contained in:
Nilstrieb 2024-02-19 18:57:27 +01:00
parent e29a1530f6
commit 0f4925e436
4 changed files with 25 additions and 0 deletions
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9
compiler/rustc_mir_transform/src/cross_crate_inline.rs
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@ -9,6 +9,7 @@ use rustc_middle::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::InliningThreshold;
use rustc_session::config::OptLevel;
use rustc_span::sym;
pub fn provide(providers: &mut Providers) {
providers.cross_crate_inlinable = cross_crate_inlinable;
@ -34,6 +35,14 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
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
// bodies even when the backend would implement something better, we stop
// the MIR inliner from ever inlining an intrinsic.
return true;
}
// Obey source annotations first; this is important because it means we can use
// #[inline(never)] to force code generation.
match codegen_fn_attrs.inline {