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Auto merge of rust-lang#140053 - ChrisDenton:rollup-tt00skl, r=ChrisDenton
Rollup of 7 pull requests Successful merges: - rust-lang#139042 (Do not remove trivial `SwitchInt` in analysis MIR) - rust-lang#139533 (add next_index to Enumerate) - rust-lang#139843 (Setup editor file associations for non-rs extensions) - rust-lang#140000 (skip llvm-config in autodiff check builds, when its unavailable) - rust-lang#140008 (Improve `clean_maybe_renamed_item` function code a bit) - rust-lang#140024 (Remove early exits from JumpThreading.) - rust-lang#140039 (Add option for stable backport poll) r? `@ghost` `@rustbot` modify labels: rollup
2 parents 077cedc + 4c36aed commit 90fd16e

29 files changed

+363
-149
lines changed

compiler/rustc_interface/src/tests.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -818,8 +818,8 @@ fn test_unstable_options_tracking_hash() {
818818
tracked!(min_function_alignment, Some(Align::EIGHT));
819819
tracked!(mir_emit_retag, true);
820820
tracked!(mir_enable_passes, vec![("DestProp".to_string(), false)]);
821-
tracked!(mir_keep_place_mention, true);
822821
tracked!(mir_opt_level, Some(4));
822+
tracked!(mir_preserve_ub, true);
823823
tracked!(move_size_limit, Some(4096));
824824
tracked!(mutable_noalias, false);
825825
tracked!(next_solver, NextSolverConfig { coherence: true, globally: true });

compiler/rustc_mir_transform/src/early_otherwise_branch.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -223,7 +223,7 @@ impl<'tcx> crate::MirPass<'tcx> for EarlyOtherwiseBranch {
223223
// Since this optimization adds new basic blocks and invalidates others,
224224
// clean up the cfg to make it nicer for other passes
225225
if should_cleanup {
226-
simplify_cfg(body);
226+
simplify_cfg(tcx, body);
227227
}
228228
}
229229

compiler/rustc_mir_transform/src/inline.rs

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -63,7 +63,7 @@ impl<'tcx> crate::MirPass<'tcx> for Inline {
6363
let _guard = span.enter();
6464
if inline::<NormalInliner<'tcx>>(tcx, body) {
6565
debug!("running simplify cfg on {:?}", body.source);
66-
simplify_cfg(body);
66+
simplify_cfg(tcx, body);
6767
deref_finder(tcx, body);
6868
}
6969
}
@@ -99,7 +99,7 @@ impl<'tcx> crate::MirPass<'tcx> for ForceInline {
9999
let _guard = span.enter();
100100
if inline::<ForceInliner<'tcx>>(tcx, body) {
101101
debug!("running simplify cfg on {:?}", body.source);
102-
simplify_cfg(body);
102+
simplify_cfg(tcx, body);
103103
deref_finder(tcx, body);
104104
}
105105
}

compiler/rustc_mir_transform/src/jump_threading.rs

Lines changed: 64 additions & 71 deletions
Large diffs are not rendered by default.

compiler/rustc_mir_transform/src/match_branches.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -43,7 +43,7 @@ impl<'tcx> crate::MirPass<'tcx> for MatchBranchSimplification {
4343
}
4444

4545
if should_cleanup {
46-
simplify_cfg(body);
46+
simplify_cfg(tcx, body);
4747
}
4848
}
4949

compiler/rustc_mir_transform/src/remove_place_mention.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ pub(super) struct RemovePlaceMention;
88

99
impl<'tcx> crate::MirPass<'tcx> for RemovePlaceMention {
1010
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
11-
!sess.opts.unstable_opts.mir_keep_place_mention
11+
!sess.opts.unstable_opts.mir_preserve_ub
1212
}
1313

1414
fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

compiler/rustc_mir_transform/src/remove_unneeded_drops.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -35,7 +35,7 @@ impl<'tcx> crate::MirPass<'tcx> for RemoveUnneededDrops {
3535
// if we applied optimizations, we potentially have some cfg to cleanup to
3636
// make it easier for further passes
3737
if should_simplify {
38-
simplify_cfg(body);
38+
simplify_cfg(tcx, body);
3939
}
4040
}
4141

compiler/rustc_mir_transform/src/simplify.rs

Lines changed: 26 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -26,6 +26,13 @@
2626
//! Here the block (`{ return; }`) has the return type `char`, rather than `()`, but the MIR we
2727
//! naively generate still contains the `_a = ()` write in the unreachable block "after" the
2828
//! return.
29+
//!
30+
//! **WARNING**: This is one of the few optimizations that runs on built and analysis MIR, and
31+
//! so its effects may affect the type-checking, borrow-checking, and other analysis of MIR.
32+
//! We must be extremely careful to only apply optimizations that preserve UB and all
33+
//! non-determinism, since changes here can affect which programs compile in an insta-stable way.
34+
//! The normal logic that a program with UB can be changed to do anything does not apply to
35+
//! pre-"runtime" MIR!
2936
3037
use rustc_index::{Idx, IndexSlice, IndexVec};
3138
use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
@@ -66,8 +73,8 @@ impl SimplifyCfg {
6673
}
6774
}
6875

69-
pub(super) fn simplify_cfg(body: &mut Body<'_>) {
70-
CfgSimplifier::new(body).simplify();
76+
pub(super) fn simplify_cfg<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
77+
CfgSimplifier::new(tcx, body).simplify();
7178
remove_dead_blocks(body);
7279

7380
// FIXME: Should probably be moved into some kind of pass manager
@@ -79,9 +86,9 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyCfg {
7986
self.name()
8087
}
8188

82-
fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
89+
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
8390
debug!("SimplifyCfg({:?}) - simplifying {:?}", self.name(), body.source);
84-
simplify_cfg(body);
91+
simplify_cfg(tcx, body);
8592
}
8693

8794
fn is_required(&self) -> bool {
@@ -90,12 +97,13 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyCfg {
9097
}
9198

9299
struct CfgSimplifier<'a, 'tcx> {
100+
preserve_switch_reads: bool,
93101
basic_blocks: &'a mut IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
94102
pred_count: IndexVec<BasicBlock, u32>,
95103
}
96104

97105
impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
98-
fn new(body: &'a mut Body<'tcx>) -> Self {
106+
fn new(tcx: TyCtxt<'tcx>, body: &'a mut Body<'tcx>) -> Self {
99107
let mut pred_count = IndexVec::from_elem(0u32, &body.basic_blocks);
100108

101109
// we can't use mir.predecessors() here because that counts
@@ -110,9 +118,12 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
110118
}
111119
}
112120

121+
// Preserve `SwitchInt` reads on built and analysis MIR, or if `-Zmir-preserve-ub`.
122+
let preserve_switch_reads = matches!(body.phase, MirPhase::Built | MirPhase::Analysis(_))
123+
|| tcx.sess.opts.unstable_opts.mir_preserve_ub;
113124
let basic_blocks = body.basic_blocks_mut();
114125

115-
CfgSimplifier { basic_blocks, pred_count }
126+
CfgSimplifier { preserve_switch_reads, basic_blocks, pred_count }
116127
}
117128

118129
fn simplify(mut self) {
@@ -253,9 +264,15 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
253264

254265
// turn a branch with all successors identical to a goto
255266
fn simplify_branch(&mut self, terminator: &mut Terminator<'tcx>) -> bool {
256-
match terminator.kind {
257-
TerminatorKind::SwitchInt { .. } => {}
258-
_ => return false,
267+
// Removing a `SwitchInt` terminator may remove reads that result in UB,
268+
// so we must not apply this optimization before borrowck or when
269+
// `-Zmir-preserve-ub` is set.
270+
if self.preserve_switch_reads {
271+
return false;
272+
}
273+
274+
let TerminatorKind::SwitchInt { .. } = terminator.kind else {
275+
return false;
259276
};
260277

261278
let first_succ = {

compiler/rustc_session/src/options.rs

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2322,12 +2322,12 @@ options! {
23222322
mir_include_spans: MirIncludeSpans = (MirIncludeSpans::default(), parse_mir_include_spans, [UNTRACKED],
23232323
"include extra comments in mir pretty printing, like line numbers and statement indices, \
23242324
details about types, etc. (boolean for all passes, 'nll' to enable in NLL MIR only, default: 'nll')"),
2325-
mir_keep_place_mention: bool = (false, parse_bool, [TRACKED],
2326-
"keep place mention MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \
2327-
(default: no)"),
23282325
#[rustc_lint_opt_deny_field_access("use `Session::mir_opt_level` instead of this field")]
23292326
mir_opt_level: Option<usize> = (None, parse_opt_number, [TRACKED],
23302327
"MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),
2328+
mir_preserve_ub: bool = (false, parse_bool, [TRACKED],
2329+
"keep place mention statements and reads in trivial SwitchInt terminators, which are interpreted \
2330+
e.g., by miri; implies -Zmir-opt-level=0 (default: no)"),
23312331
mir_strip_debuginfo: MirStripDebugInfo = (MirStripDebugInfo::None, parse_mir_strip_debuginfo, [TRACKED],
23322332
"Whether to remove some of the MIR debug info from methods. Default: None"),
23332333
move_size_limit: Option<usize> = (None, parse_opt_number, [TRACKED],

library/core/src/iter/adapters/enumerate.rs

Lines changed: 33 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,39 @@ impl<I> Enumerate<I> {
2323
pub(in crate::iter) fn new(iter: I) -> Enumerate<I> {
2424
Enumerate { iter, count: 0 }
2525
}
26+
27+
/// Retrieve the current position of the iterator.
28+
///
29+
/// If the iterator has not advanced, the position returned will be 0.
30+
///
31+
/// The position may also exceed the bounds of the iterator to allow for calculating
32+
/// the displacement of the iterator from following calls to [`Iterator::next`].
33+
///
34+
/// # Examples
35+
///
36+
/// ```
37+
/// #![feature(next_index)]
38+
///
39+
/// let arr = ['a', 'b'];
40+
///
41+
/// let mut iter = arr.iter().enumerate();
42+
///
43+
/// assert_eq!(iter.next_index(), 0);
44+
/// assert_eq!(iter.next(), Some((0, &'a')));
45+
///
46+
/// assert_eq!(iter.next_index(), 1);
47+
/// assert_eq!(iter.next_index(), 1);
48+
/// assert_eq!(iter.next(), Some((1, &'b')));
49+
///
50+
/// assert_eq!(iter.next_index(), 2);
51+
/// assert_eq!(iter.next(), None);
52+
/// assert_eq!(iter.next_index(), 2);
53+
/// ```
54+
#[inline]
55+
#[unstable(feature = "next_index", issue = "130711")]
56+
pub fn next_index(&self) -> usize {
57+
self.count
58+
}
2659
}
2760

2861
#[stable(feature = "rust1", since = "1.0.0")]

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