1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
#![allow(rustc::potential_query_instability)]
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
#![feature(box_patterns)]
#![feature(decl_macro)]
#![feature(is_sorted)]
#![feature(let_chains)]
#![feature(map_try_insert)]
#![feature(min_specialization)]
#![feature(never_type)]
#![feature(option_get_or_insert_default)]
#![feature(trusted_step)]
#![feature(try_blocks)]
#![feature(yeet_expr)]
#![feature(if_let_guard)]
#![recursion_limit = "256"]

#[macro_use]
extern crate tracing;
#[macro_use]
extern crate rustc_middle;

use required_consts::RequiredConstsVisitor;
use rustc_const_eval::util;
use rustc_data_structures::fx::FxIndexSet;
use rustc_data_structures::steal::Steal;
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_index::IndexVec;
use rustc_middle::mir::visit::Visitor as _;
use rustc_middle::mir::{
    traversal, AnalysisPhase, Body, CallSource, ClearCrossCrate, ConstOperand, ConstQualifs,
    LocalDecl, MirPass, MirPhase, Operand, Place, ProjectionElem, Promoted, RuntimePhase, Rvalue,
    SourceInfo, Statement, StatementKind, TerminatorKind, START_BLOCK,
};
use rustc_middle::query::Providers;
use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
use rustc_span::sym;
use rustc_trait_selection::traits;

#[macro_use]
mod pass_manager;

use pass_manager::{self as pm, Lint, MirLint, WithMinOptLevel};

mod abort_unwinding_calls;
mod add_call_guards;
mod add_moves_for_packed_drops;
mod add_retag;
mod check_const_item_mutation;
mod check_packed_ref;
pub mod check_unsafety;
mod remove_place_mention;
// This pass is public to allow external drivers to perform MIR cleanup
mod add_subtyping_projections;
pub mod cleanup_post_borrowck;
mod const_debuginfo;
mod const_goto;
mod const_prop;
mod const_prop_lint;
mod copy_prop;
mod coverage;
mod ctfe_limit;
mod dataflow_const_prop;
mod dead_store_elimination;
mod deduce_param_attrs;
mod deduplicate_blocks;
mod deref_separator;
mod dest_prop;
pub mod dump_mir;
mod early_otherwise_branch;
mod elaborate_box_derefs;
mod elaborate_drops;
mod errors;
mod ffi_unwind_calls;
mod function_item_references;
mod generator;
mod gvn;
pub mod inline;
mod instsimplify;
mod large_enums;
mod lower_intrinsics;
mod lower_slice_len;
mod match_branches;
mod multiple_return_terminators;
mod normalize_array_len;
mod nrvo;
mod prettify;
mod ref_prop;
mod remove_noop_landing_pads;
mod remove_storage_markers;
mod remove_uninit_drops;
mod remove_unneeded_drops;
mod remove_zsts;
mod required_consts;
mod reveal_all;
mod separate_const_switch;
mod shim;
mod ssa;
// This pass is public to allow external drivers to perform MIR cleanup
mod check_alignment;
pub mod simplify;
mod simplify_branches;
mod simplify_comparison_integral;
mod sroa;
mod uninhabited_enum_branching;
mod unreachable_prop;

use rustc_const_eval::transform::check_consts::{self, ConstCx};
use rustc_const_eval::transform::promote_consts;
use rustc_const_eval::transform::validate;
use rustc_mir_dataflow::rustc_peek;

use rustc_errors::{DiagnosticMessage, SubdiagnosticMessage};
use rustc_fluent_macro::fluent_messages;

fluent_messages! { "../messages.ftl" }

pub fn provide(providers: &mut Providers) {
    check_unsafety::provide(providers);
    coverage::query::provide(providers);
    ffi_unwind_calls::provide(providers);
    shim::provide(providers);
    *providers = Providers {
        mir_keys,
        mir_const,
        mir_const_qualif,
        mir_promoted,
        mir_drops_elaborated_and_const_checked,
        mir_for_ctfe,
        mir_generator_witnesses: generator::mir_generator_witnesses,
        optimized_mir,
        is_mir_available,
        is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
        mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
        mir_inliner_callees: inline::cycle::mir_inliner_callees,
        promoted_mir,
        deduced_param_attrs: deduce_param_attrs::deduced_param_attrs,
        ..*providers
    };
}

fn remap_mir_for_const_eval_select<'tcx>(
    tcx: TyCtxt<'tcx>,
    mut body: Body<'tcx>,
    context: hir::Constness,
) -> Body<'tcx> {
    for bb in body.basic_blocks.as_mut().iter_mut() {
        let terminator = bb.terminator.as_mut().expect("invalid terminator");
        match terminator.kind {
            TerminatorKind::Call {
                func: Operand::Constant(box ConstOperand { ref const_, .. }),
                ref mut args,
                destination,
                target,
                unwind,
                fn_span,
                ..
            } if let ty::FnDef(def_id, _) = *const_.ty().kind()
                && tcx.item_name(def_id) == sym::const_eval_select
                && tcx.is_intrinsic(def_id) =>
            {
                let [tupled_args, called_in_const, called_at_rt]: [_; 3] = std::mem::take(args).try_into().unwrap();
                let ty = tupled_args.ty(&body.local_decls, tcx);
                let fields = ty.tuple_fields();
                let num_args = fields.len();
                let func = if context == hir::Constness::Const { called_in_const } else { called_at_rt };
                let (method, place): (fn(Place<'tcx>) -> Operand<'tcx>, Place<'tcx>) = match tupled_args {
                    Operand::Constant(_) => {
                        // there is no good way of extracting a tuple arg from a constant (const generic stuff)
                        // so we just create a temporary and deconstruct that.
                        let local = body.local_decls.push(LocalDecl::new(ty, fn_span));
                        bb.statements.push(Statement {
                            source_info: SourceInfo::outermost(fn_span),
                            kind: StatementKind::Assign(Box::new((local.into(), Rvalue::Use(tupled_args.clone())))),
                        });
                        (Operand::Move, local.into())
                    }
                    Operand::Move(place) => (Operand::Move, place),
                    Operand::Copy(place) => (Operand::Copy, place),
                };
                let place_elems = place.projection;
                let arguments = (0..num_args).map(|x| {
                    let mut place_elems = place_elems.to_vec();
                    place_elems.push(ProjectionElem::Field(x.into(), fields[x]));
                    let projection = tcx.mk_place_elems(&place_elems);
                    let place = Place {
                        local: place.local,
                        projection,
                    };
                    method(place)
                }).collect();
                terminator.kind = TerminatorKind::Call { func, args: arguments, destination, target, unwind, call_source: CallSource::Misc, fn_span };
            }
            _ => {}
        }
    }
    body
}

fn is_mir_available(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
    tcx.mir_keys(()).contains(&def_id)
}

/// Finds the full set of `DefId`s within the current crate that have
/// MIR associated with them.
fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
    let mut set = FxIndexSet::default();

    // All body-owners have MIR associated with them.
    set.extend(tcx.hir().body_owners());

    // Additionally, tuple struct/variant constructors have MIR, but
    // they don't have a BodyId, so we need to build them separately.
    struct GatherCtors<'a> {
        set: &'a mut FxIndexSet<LocalDefId>,
    }
    impl<'tcx> Visitor<'tcx> for GatherCtors<'_> {
        fn visit_variant_data(&mut self, v: &'tcx hir::VariantData<'tcx>) {
            if let hir::VariantData::Tuple(_, _, def_id) = *v {
                self.set.insert(def_id);
            }
            intravisit::walk_struct_def(self, v)
        }
    }
    tcx.hir().visit_all_item_likes_in_crate(&mut GatherCtors { set: &mut set });

    set
}

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();
    }

    // N.B., this `borrow()` is guaranteed to be valid (i.e., the value
    // cannot yet be stolen), because `mir_promoted()`, which steals
    // from `mir_const()`, forces this query to execute before
    // performing the steal.
    let body = &tcx.mir_const(def).borrow();

    if body.return_ty().references_error() {
        tcx.sess.delay_span_bug(body.span, "mir_const_qualif: MIR had errors");
        return Default::default();
    }

    let ccx = check_consts::ConstCx { body, tcx, const_kind, param_env: tcx.param_env(def) };

    let mut validator = check_consts::check::Checker::new(&ccx);
    validator.check_body();

    // We return the qualifs in the return place for every MIR body, even though it is only used
    // when deciding to promote a reference to a `const` for now.
    validator.qualifs_in_return_place()
}

/// Make MIR ready for const evaluation. This is run on all MIR, not just on consts!
/// FIXME(oli-obk): it's unclear whether we still need this phase (and its corresponding query).
/// We used to have this for pre-miri MIR based const eval.
fn mir_const(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
    // Unsafety check uses the raw mir, so make sure it is run.
    if !tcx.sess.opts.unstable_opts.thir_unsafeck {
        tcx.ensure_with_value().unsafety_check_result(def);
    }

    // has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
    tcx.ensure_with_value().has_ffi_unwind_calls(def);

    let mut body = tcx.mir_built(def).steal();

    pass_manager::dump_mir_for_phase_change(tcx, &body);

    pm::run_passes(
        tcx,
        &mut body,
        &[
            // MIR-level lints.
            &Lint(check_packed_ref::CheckPackedRef),
            &Lint(check_const_item_mutation::CheckConstItemMutation),
            &Lint(function_item_references::FunctionItemReferences),
            // What we need to do constant evaluation.
            &simplify::SimplifyCfg::Initial,
            &rustc_peek::SanityCheck, // Just a lint
        ],
        None,
    );
    tcx.alloc_steal_mir(body)
}

/// Compute the main MIR body and the list of MIR bodies of the promoteds.
fn mir_promoted(
    tcx: TyCtxt<'_>,
    def: LocalDefId,
) -> (&Steal<Body<'_>>, &Steal<IndexVec<Promoted, Body<'_>>>) {
    // 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 mut body = tcx.mir_const(def).steal();
    if let Some(error_reported) = const_qualifs.tainted_by_errors {
        body.tainted_by_errors = Some(error_reported);
    }

    let mut required_consts = Vec::new();
    let mut required_consts_visitor = RequiredConstsVisitor::new(&mut required_consts);
    for (bb, bb_data) in traversal::reverse_postorder(&body) {
        required_consts_visitor.visit_basic_block_data(bb, bb_data);
    }
    body.required_consts = required_consts;

    // What we need to run borrowck etc.
    let promote_pass = promote_consts::PromoteTemps::default();
    pm::run_passes(
        tcx,
        &mut body,
        &[&promote_pass, &simplify::SimplifyCfg::PromoteConsts, &coverage::InstrumentCoverage],
        Some(MirPhase::Analysis(AnalysisPhase::Initial)),
    );

    let promoted = promote_pass.promoted_fragments.into_inner();
    (tcx.alloc_steal_mir(body), tcx.alloc_steal_promoted(promoted))
}

/// Compute the MIR that is used during CTFE (and thus has no optimizations run on it)
fn mir_for_ctfe(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &Body<'_> {
    tcx.arena.alloc(inner_mir_for_ctfe(tcx, def_id))
}

fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: LocalDefId) -> Body<'_> {
    // FIXME: don't duplicate this between the optimized_mir/mir_for_ctfe queries
    if tcx.is_constructor(def.to_def_id()) {
        // There's no reason to run all of the MIR passes on constructors when
        // we can just output the MIR we want directly. This also saves const
        // qualification and borrow checking the trouble of special casing
        // constructors.
        return shim::build_adt_ctor(tcx, def.to_def_id());
    }

    let body = tcx.mir_drops_elaborated_and_const_checked(def);
    let body = match tcx.hir().body_const_context(def) {
        // consts and statics do not have `optimized_mir`, so we can steal the body instead of
        // cloning it.
        Some(hir::ConstContext::Const { .. } | hir::ConstContext::Static(_)) => body.steal(),
        Some(hir::ConstContext::ConstFn) => body.borrow().clone(),
        None => bug!("`mir_for_ctfe` called on non-const {def:?}"),
    };

    let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::Const);
    pm::run_passes(tcx, &mut body, &[&ctfe_limit::CtfeLimit], None);

    body
}

/// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
/// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
/// end up missing the source MIR due to stealing happening.
fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
    if let DefKind::Generator = tcx.def_kind(def) {
        tcx.ensure_with_value().mir_generator_witnesses(def);
    }
    let mir_borrowck = tcx.mir_borrowck(def);

    let is_fn_like = tcx.def_kind(def).is_fn_like();
    if is_fn_like {
        // Do not compute the mir call graph without said call graph actually being used.
        if inline::Inline.is_enabled(&tcx.sess) {
            tcx.ensure_with_value().mir_inliner_callees(ty::InstanceDef::Item(def.to_def_id()));
        }
    }

    let (body, _) = tcx.mir_promoted(def);
    let mut body = body.steal();
    if let Some(error_reported) = mir_borrowck.tainted_by_errors {
        body.tainted_by_errors = Some(error_reported);
    }

    // Check if it's even possible to satisfy the 'where' clauses
    // for this item.
    //
    // This branch will never be taken for any normal function.
    // However, it's possible to `#!feature(trivial_bounds)]` to write
    // a function with impossible to satisfy clauses, e.g.:
    // `fn foo() where String: Copy {}`
    //
    // We don't usually need to worry about this kind of case,
    // since we would get a compilation error if the user tried
    // to call it. However, since we optimize even without any
    // calls to the function, we need to make sure that it even
    // makes sense to try to evaluate the body.
    //
    // If there are unsatisfiable where clauses, then all bets are
    // off, and we just give up.
    //
    // We manually filter the predicates, skipping anything that's not
    // "global". We are in a potentially generic context
    // (e.g. we are evaluating a function without substituting generic
    // parameters, so this filtering serves two purposes:
    //
    // 1. We skip evaluating any predicates that we would
    // never be able prove are unsatisfiable (e.g. `<T as Foo>`
    // 2. We avoid trying to normalize predicates involving generic
    // parameters (e.g. `<T as Foo>::MyItem`). This can confuse
    // the normalization code (leading to cycle errors), since
    // it's usually never invoked in this way.
    let predicates = tcx
        .predicates_of(body.source.def_id())
        .predicates
        .iter()
        .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
    if traits::impossible_predicates(tcx, traits::elaborate(tcx, predicates).collect()) {
        trace!("found unsatisfiable predicates for {:?}", body.source);
        // Clear the body to only contain a single `unreachable` statement.
        let bbs = body.basic_blocks.as_mut();
        bbs.raw.truncate(1);
        bbs[START_BLOCK].statements.clear();
        bbs[START_BLOCK].terminator_mut().kind = TerminatorKind::Unreachable;
        body.var_debug_info.clear();
        body.local_decls.raw.truncate(body.arg_count + 1);
    }

    run_analysis_to_runtime_passes(tcx, &mut body);

    // Now that drop elaboration has been performed, we can check for
    // unconditional drop recursion.
    rustc_mir_build::lints::check_drop_recursion(tcx, &body);

    tcx.alloc_steal_mir(body)
}

// Made public such that `mir_drops_elaborated_and_const_checked` can be overridden
// by custom rustc drivers, running all the steps by themselves.
pub fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
    assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
    let did = body.source.def_id();

    debug!("analysis_mir_cleanup({:?})", did);
    run_analysis_cleanup_passes(tcx, body);
    assert!(body.phase == MirPhase::Analysis(AnalysisPhase::PostCleanup));

    // Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
    if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
        pm::run_passes(
            tcx,
            body,
            &[&remove_uninit_drops::RemoveUninitDrops, &simplify::SimplifyCfg::RemoveFalseEdges],
            None,
        );
        check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
    }

    debug!("runtime_mir_lowering({:?})", did);
    run_runtime_lowering_passes(tcx, body);
    assert!(body.phase == MirPhase::Runtime(RuntimePhase::Initial));

    debug!("runtime_mir_cleanup({:?})", did);
    run_runtime_cleanup_passes(tcx, body);
    assert!(body.phase == MirPhase::Runtime(RuntimePhase::PostCleanup));
}

// FIXME(JakobDegen): Can we make these lists of passes consts?

/// After this series of passes, no lifetime analysis based on borrowing can be done.
fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
    let passes: &[&dyn MirPass<'tcx>] = &[
        &cleanup_post_borrowck::CleanupPostBorrowck,
        &remove_noop_landing_pads::RemoveNoopLandingPads,
        &simplify::SimplifyCfg::EarlyOpt,
        &deref_separator::Derefer,
    ];

    pm::run_passes(tcx, body, passes, Some(MirPhase::Analysis(AnalysisPhase::PostCleanup)));
}

/// Returns the sequence of passes that lowers analysis to runtime MIR.
fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
    let passes: &[&dyn MirPass<'tcx>] = &[
        // These next passes must be executed together
        &add_call_guards::CriticalCallEdges,
        &reveal_all::RevealAll, // has to be done before drop elaboration, since we need to drop opaque types, too.
        &add_subtyping_projections::Subtyper, // calling this after reveal_all ensures that we don't deal with opaque types
        &elaborate_drops::ElaborateDrops,
        // This will remove extraneous landing pads which are no longer
        // necessary as well as well as forcing any call in a non-unwinding
        // function calling a possibly-unwinding function to abort the process.
        &abort_unwinding_calls::AbortUnwindingCalls,
        // AddMovesForPackedDrops needs to run after drop
        // elaboration.
        &add_moves_for_packed_drops::AddMovesForPackedDrops,
        // `AddRetag` needs to run after `ElaborateDrops`. Otherwise it should run fairly late,
        // but before optimizations begin.
        &elaborate_box_derefs::ElaborateBoxDerefs,
        &generator::StateTransform,
        &add_retag::AddRetag,
        &Lint(const_prop_lint::ConstProp),
    ];
    pm::run_passes_no_validate(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::Initial)));
}

/// Returns the sequence of passes that do the initial cleanup of runtime MIR.
fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
    let passes: &[&dyn MirPass<'tcx>] = &[
        &lower_intrinsics::LowerIntrinsics,
        &remove_place_mention::RemovePlaceMention,
        &simplify::SimplifyCfg::ElaborateDrops,
    ];

    pm::run_passes(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::PostCleanup)));

    // Clear this by anticipation. Optimizations and runtime MIR have no reason to look
    // into this information, which is meant for borrowck diagnostics.
    for decl in &mut body.local_decls {
        decl.local_info = ClearCrossCrate::Clear;
    }
}

fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
    fn o1<T>(x: T) -> WithMinOptLevel<T> {
        WithMinOptLevel(1, x)
    }

    // The main optimizations that we do on MIR.
    pm::run_passes(
        tcx,
        body,
        &[
            &check_alignment::CheckAlignment,
            &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
            &unreachable_prop::UnreachablePropagation,
            &uninhabited_enum_branching::UninhabitedEnumBranching,
            &o1(simplify::SimplifyCfg::AfterUninhabitedEnumBranching),
            &inline::Inline,
            &remove_storage_markers::RemoveStorageMarkers,
            &remove_zsts::RemoveZsts,
            &normalize_array_len::NormalizeArrayLen, // has to run after `slice::len` lowering
            &const_goto::ConstGoto,
            &remove_unneeded_drops::RemoveUnneededDrops,
            &ref_prop::ReferencePropagation,
            &sroa::ScalarReplacementOfAggregates,
            &match_branches::MatchBranchSimplification,
            // inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
            &multiple_return_terminators::MultipleReturnTerminators,
            &instsimplify::InstSimplify,
            &simplify::SimplifyLocals::BeforeConstProp,
            &copy_prop::CopyProp,
            // Perform `SeparateConstSwitch` after SSA-based analyses, as cloning blocks may
            // destroy the SSA property. It should still happen before const-propagation, so the
            // latter pass will leverage the created opportunities.
            &separate_const_switch::SeparateConstSwitch,
            &const_prop::ConstProp,
            &gvn::GVN,
            &dataflow_const_prop::DataflowConstProp,
            //
            // Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
            &const_debuginfo::ConstDebugInfo,
            &o1(simplify_branches::SimplifyConstCondition::AfterConstProp),
            &early_otherwise_branch::EarlyOtherwiseBranch,
            &simplify_comparison_integral::SimplifyComparisonIntegral,
            &dead_store_elimination::DeadStoreElimination,
            &dest_prop::DestinationPropagation,
            &o1(simplify_branches::SimplifyConstCondition::Final),
            &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
            &o1(simplify::SimplifyCfg::Final),
            &nrvo::RenameReturnPlace,
            &simplify::SimplifyLocals::Final,
            &multiple_return_terminators::MultipleReturnTerminators,
            &deduplicate_blocks::DeduplicateBlocks,
            &large_enums::EnumSizeOpt { discrepancy: 128 },
            // Some cleanup necessary at least for LLVM and potentially other codegen backends.
            &add_call_guards::CriticalCallEdges,
            // Cleanup for human readability, off by default.
            &prettify::ReorderBasicBlocks,
            &prettify::ReorderLocals,
            // Dump the end result for testing and debugging purposes.
            &dump_mir::Marker("PreCodegen"),
        ],
        Some(MirPhase::Runtime(RuntimePhase::Optimized)),
    );
}

/// Optimize the MIR and prepare it for codegen.
fn optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> &Body<'_> {
    tcx.arena.alloc(inner_optimized_mir(tcx, did))
}

fn inner_optimized_mir(tcx: TyCtxt<'_>, did: LocalDefId) -> Body<'_> {
    if tcx.is_constructor(did.to_def_id()) {
        // There's no reason to run all of the MIR passes on constructors when
        // we can just output the MIR we want directly. This also saves const
        // qualification and borrow checking the trouble of special casing
        // constructors.
        return shim::build_adt_ctor(tcx, did.to_def_id());
    }

    match tcx.hir().body_const_context(did) {
        // Run the `mir_for_ctfe` query, which depends on `mir_drops_elaborated_and_const_checked`
        // which we are going to steal below. Thus we need to run `mir_for_ctfe` first, so it
        // computes and caches its result.
        Some(hir::ConstContext::ConstFn) => tcx.ensure_with_value().mir_for_ctfe(did),
        None => {}
        Some(other) => panic!("do not use `optimized_mir` for constants: {other:?}"),
    }
    debug!("about to call mir_drops_elaborated...");
    let body = tcx.mir_drops_elaborated_and_const_checked(did).steal();
    let mut body = remap_mir_for_const_eval_select(tcx, body, hir::Constness::NotConst);
    debug!("body: {:#?}", body);

    if body.tainted_by_errors.is_some() {
        return body;
    }

    run_optimization_passes(tcx, &mut body);

    body
}

/// Fetch all the promoteds of an item and prepare their MIR bodies to be ready for
/// constant evaluation once all substitutions become known.
fn promoted_mir(tcx: TyCtxt<'_>, def: LocalDefId) -> &IndexVec<Promoted, Body<'_>> {
    if tcx.is_constructor(def.to_def_id()) {
        return tcx.arena.alloc(IndexVec::new());
    }

    tcx.ensure_with_value().mir_borrowck(def);
    let mut promoted = tcx.mir_promoted(def).1.steal();

    for body in &mut promoted {
        run_analysis_to_runtime_passes(tcx, body);
    }

    tcx.arena.alloc(promoted)
}