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Auto merge of #63994 - Centril:refactor-qualify-consts, r=spastorino,oli-obk
Refactor the `MirPass for QualifyAndPromoteConstants` This is an accumulation of drive-by commits while working on `Vec::new` as a stable `const fn`. The PR is probably easiest read commit-by-commit. r? @oli-obk cc @eddyb @ecstatic-morse -- your two PRs https://github.com/rust-lang/rust/pull/63812 and https://github.com/rust-lang/rust/pull/63860 respectively will conflict with this a tiny bit but it should be trivial to reintegrate your changes atop of this.
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2b8116dced
@ -25,11 +25,13 @@ use syntax::feature_gate::{emit_feature_err, GateIssue};
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use syntax::symbol::sym;
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use syntax_pos::{Span, DUMMY_SP};
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use std::borrow::Cow;
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use std::cell::Cell;
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use std::fmt;
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use std::ops::{Deref, Index, IndexMut};
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use std::usize;
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use rustc::hir::HirId;
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use crate::transform::{MirPass, MirSource};
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use super::promote_consts::{self, Candidate, TempState};
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@ -1596,51 +1598,24 @@ impl<'tcx> MirPass<'tcx> for QualifyAndPromoteConstants<'tcx> {
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}
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let def_id = src.def_id();
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let id = tcx.hir().as_local_hir_id(def_id).unwrap();
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let mut const_promoted_temps = None;
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let mode = match tcx.hir().body_owner_kind(id) {
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hir::BodyOwnerKind::Closure => Mode::NonConstFn,
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hir::BodyOwnerKind::Fn => {
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if tcx.is_const_fn(def_id) {
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Mode::ConstFn
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} else {
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Mode::NonConstFn
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}
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}
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hir::BodyOwnerKind::Const => {
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const_promoted_temps = Some(tcx.mir_const_qualif(def_id).1);
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Mode::Const
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}
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hir::BodyOwnerKind::Static(hir::MutImmutable) => Mode::Static,
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hir::BodyOwnerKind::Static(hir::MutMutable) => Mode::StaticMut,
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};
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let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
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let mode = determine_mode(tcx, hir_id, def_id);
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debug!("run_pass: mode={:?}", mode);
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if mode == Mode::NonConstFn || mode == Mode::ConstFn {
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if let Mode::NonConstFn | Mode::ConstFn = mode {
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// This is ugly because Checker holds onto mir,
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// which can't be mutated until its scope ends.
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let (temps, candidates) = {
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let mut checker = Checker::new(tcx, def_id, body, mode);
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if mode == Mode::ConstFn {
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if let Mode::ConstFn = mode {
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if tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
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checker.check_const();
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} else if tcx.is_min_const_fn(def_id) {
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// enforce `min_const_fn` for stable const fns
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// Enforce `min_const_fn` for stable `const fn`s.
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use super::qualify_min_const_fn::is_min_const_fn;
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if let Err((span, err)) = is_min_const_fn(tcx, def_id, body) {
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let mut diag = struct_span_err!(
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tcx.sess,
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span,
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E0723,
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"{}",
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err,
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);
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diag.note("for more information, see issue \
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https://github.com/rust-lang/rust/issues/57563");
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diag.help(
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"add `#![feature(const_fn)]` to the crate attributes to enable",
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);
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diag.emit();
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error_min_const_fn_violation(tcx, span, err);
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} else {
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// this should not produce any errors, but better safe than sorry
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// FIXME(#53819)
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@ -1664,107 +1639,119 @@ impl<'tcx> MirPass<'tcx> for QualifyAndPromoteConstants<'tcx> {
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promote_consts::promote_candidates(def_id, body, tcx, temps, candidates)
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);
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} else {
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if !body.control_flow_destroyed.is_empty() {
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let mut locals = body.vars_iter();
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if let Some(local) = locals.next() {
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let span = body.local_decls[local].source_info.span;
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let mut error = tcx.sess.struct_span_err(
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span,
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&format!(
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"new features like let bindings are not permitted in {}s \
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which also use short circuiting operators",
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mode,
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),
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);
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for (span, kind) in body.control_flow_destroyed.iter() {
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error.span_note(
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*span,
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&format!("use of {} here does not actually short circuit due to \
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the const evaluator presently not being able to do control flow. \
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See https://github.com/rust-lang/rust/issues/49146 for more \
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information.", kind),
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);
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}
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for local in locals {
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let span = body.local_decls[local].source_info.span;
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error.span_note(
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span,
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"more locals defined here",
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);
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}
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error.emit();
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}
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}
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let promoted_temps = if mode == Mode::Const {
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// Already computed by `mir_const_qualif`.
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const_promoted_temps.unwrap()
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} else {
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Checker::new(tcx, def_id, body, mode).check_const().1
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};
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check_short_circuiting_in_const_local(tcx, body, mode);
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// In `const` and `static` everything without `StorageDead`
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// is `'static`, we don't have to create promoted MIR fragments,
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// just remove `Drop` and `StorageDead` on "promoted" locals.
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debug!("run_pass: promoted_temps={:?}", promoted_temps);
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for block in body.basic_blocks_mut() {
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block.statements.retain(|statement| {
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match statement.kind {
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StatementKind::StorageDead(index) => {
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!promoted_temps.contains(index)
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}
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_ => true
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}
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});
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let terminator = block.terminator_mut();
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match terminator.kind {
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TerminatorKind::Drop {
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location: Place {
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base: PlaceBase::Local(index),
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projection: None,
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},
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target,
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..
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} => {
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if promoted_temps.contains(index) {
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terminator.kind = TerminatorKind::Goto {
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target,
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};
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}
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}
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_ => {}
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}
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}
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let promoted_temps = match mode {
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Mode::Const => tcx.mir_const_qualif(def_id).1,
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_ => Checker::new(tcx, def_id, body, mode).check_const().1,
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};
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remove_drop_and_storage_dead_on_promoted_locals(body, promoted_temps);
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}
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// Statics must be Sync.
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if mode == Mode::Static {
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// `#[thread_local]` statics don't have to be `Sync`.
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for attr in &tcx.get_attrs(def_id)[..] {
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if attr.check_name(sym::thread_local) {
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return;
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}
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}
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let ty = body.return_ty();
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tcx.infer_ctxt().enter(|infcx| {
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let param_env = ty::ParamEnv::empty();
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let cause = traits::ObligationCause::new(body.span, id, traits::SharedStatic);
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let mut fulfillment_cx = traits::FulfillmentContext::new();
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fulfillment_cx.register_bound(&infcx,
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param_env,
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ty,
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tcx.require_lang_item(
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lang_items::SyncTraitLangItem,
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Some(body.span)
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),
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cause);
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if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
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infcx.report_fulfillment_errors(&err, None, false);
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}
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});
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if mode == Mode::Static && !tcx.has_attr(def_id, sym::thread_local) {
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// `static`s (not `static mut`s) which are not `#[thread_local]` must be `Sync`.
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check_static_is_sync(tcx, body, hir_id);
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}
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}
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}
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fn determine_mode(tcx: TyCtxt<'_>, hir_id: HirId, def_id: DefId) -> Mode {
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match tcx.hir().body_owner_kind(hir_id) {
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hir::BodyOwnerKind::Closure => Mode::NonConstFn,
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hir::BodyOwnerKind::Fn if tcx.is_const_fn(def_id) => Mode::ConstFn,
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hir::BodyOwnerKind::Fn => Mode::NonConstFn,
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hir::BodyOwnerKind::Const => Mode::Const,
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hir::BodyOwnerKind::Static(hir::MutImmutable) => Mode::Static,
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hir::BodyOwnerKind::Static(hir::MutMutable) => Mode::StaticMut,
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}
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}
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fn error_min_const_fn_violation(tcx: TyCtxt<'_>, span: Span, msg: Cow<'_, str>) {
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struct_span_err!(tcx.sess, span, E0723, "{}", msg)
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.note("for more information, see issue https://github.com/rust-lang/rust/issues/57563")
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.help("add `#![feature(const_fn)]` to the crate attributes to enable")
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.emit();
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}
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fn check_short_circuiting_in_const_local(tcx: TyCtxt<'_>, body: &mut Body<'tcx>, mode: Mode) {
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if body.control_flow_destroyed.is_empty() {
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return;
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}
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let mut locals = body.vars_iter();
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if let Some(local) = locals.next() {
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let span = body.local_decls[local].source_info.span;
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let mut error = tcx.sess.struct_span_err(
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span,
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&format!(
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"new features like let bindings are not permitted in {}s \
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which also use short circuiting operators",
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mode,
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),
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);
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for (span, kind) in body.control_flow_destroyed.iter() {
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error.span_note(
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*span,
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&format!("use of {} here does not actually short circuit due to \
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the const evaluator presently not being able to do control flow. \
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See https://github.com/rust-lang/rust/issues/49146 for more \
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information.", kind),
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);
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}
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for local in locals {
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let span = body.local_decls[local].source_info.span;
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error.span_note(span, "more locals defined here");
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}
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error.emit();
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}
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}
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/// In `const` and `static` everything without `StorageDead`
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/// is `'static`, we don't have to create promoted MIR fragments,
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/// just remove `Drop` and `StorageDead` on "promoted" locals.
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fn remove_drop_and_storage_dead_on_promoted_locals(
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body: &mut Body<'tcx>,
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promoted_temps: &BitSet<Local>,
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) {
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debug!("run_pass: promoted_temps={:?}", promoted_temps);
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for block in body.basic_blocks_mut() {
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block.statements.retain(|statement| {
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match statement.kind {
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StatementKind::StorageDead(index) => !promoted_temps.contains(index),
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_ => true
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}
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});
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let terminator = block.terminator_mut();
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match terminator.kind {
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TerminatorKind::Drop {
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location: Place {
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base: PlaceBase::Local(index),
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projection: None,
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},
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target,
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..
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} if promoted_temps.contains(index) => {
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terminator.kind = TerminatorKind::Goto { target };
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}
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_ => {}
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}
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}
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}
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fn check_static_is_sync(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, hir_id: HirId) {
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let ty = body.return_ty();
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tcx.infer_ctxt().enter(|infcx| {
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let cause = traits::ObligationCause::new(body.span, hir_id, traits::SharedStatic);
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let mut fulfillment_cx = traits::FulfillmentContext::new();
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let sync_def_id = tcx.require_lang_item(lang_items::SyncTraitLangItem, Some(body.span));
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fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), ty, sync_def_id, cause);
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if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
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infcx.report_fulfillment_errors(&err, None, false);
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}
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});
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}
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fn args_required_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<FxHashSet<usize>> {
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let attrs = tcx.get_attrs(def_id);
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let attr = attrs.iter().find(|a| a.check_name(sym::rustc_args_required_const))?;
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