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Only call mir_const_qualif if absolutely necessary #117166

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Merged
merged 1 commit into from
Oct 27, 2023
Merged

Only call mir_const_qualif if absolutely necessary #117166

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26 changes: 23 additions & 3 deletions compiler/rustc_mir_transform/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ extern crate tracing;
#[macro_use]
extern crate rustc_middle;

use hir::ConstContext;
use required_consts::RequiredConstsVisitor;
use rustc_const_eval::util;
use rustc_data_structures::fx::FxIndexSet;
Expand Down Expand Up @@ -251,8 +252,13 @@ fn mir_const_qualif(tcx: TyCtxt<'_>, def: LocalDefId) -> ConstQualifs {
let const_kind = tcx.hir().body_const_context(def);

// No need to const-check a non-const `fn`.
if const_kind.is_none() {
return Default::default();
match const_kind {
Some(ConstContext::Const { .. } | ConstContext::Static(_))
| Some(ConstContext::ConstFn) => {}
None => span_bug!(
tcx.def_span(def),
"`mir_const_qualif` should only be called on const fns and const items"
),
}

// N.B., this `borrow()` is guaranteed to be valid (i.e., the value
Expand Down Expand Up @@ -317,7 +323,21 @@ fn mir_promoted(
// Ensure that we compute the `mir_const_qualif` for constants at
// this point, before we steal the mir-const result.
// Also this means promotion can rely on all const checks having been done.
let const_qualifs = tcx.mir_const_qualif(def);

let const_qualifs = match tcx.def_kind(def) {
DefKind::Fn | DefKind::AssocFn | DefKind::Closure
if tcx.constness(def) == hir::Constness::Const
|| tcx.is_const_default_method(def.to_def_id()) =>
{
tcx.mir_const_qualif(def)
}
DefKind::AssocConst
| DefKind::Const
| DefKind::Static(_)
| DefKind::InlineConst
| DefKind::AnonConst => tcx.mir_const_qualif(def),
_ => ConstQualifs::default(),
};
let mut body = tcx.mir_const(def).steal();
if let Some(error_reported) = const_qualifs.tainted_by_errors {
body.tainted_by_errors = Some(error_reported);
Expand Down