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Elide superfluous storage markers #99946

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Aug 25, 2022
Merged

Elide superfluous storage markers #99946

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943a380
Elide storage markers when elaborating box derefs
tmiasko Jul 30, 2022
162bd16
Elide storage markers when elaborating deref projections
tmiasko Jul 30, 2022
625af2c
Elide storage markers for internal locals when inlining
tmiasko Jul 30, 2022
c2b74f9
Remove support for adding statement to all successors
tmiasko Jul 30, 2022
f8ca6aa
./x.py test --bless
tmiasko Aug 23, 2022
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26 changes: 6 additions & 20 deletions compiler/rustc_middle/src/mir/patch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -68,22 +68,25 @@ impl<'tcx> MirPatch<'tcx> {
Location { block: bb, statement_index: offset }
}

pub fn new_local_with_info(
pub fn new_internal_with_info(
&mut self,
ty: Ty<'tcx>,
span: Span,
local_info: Option<Box<LocalInfo<'tcx>>>,
) -> Local {
let index = self.next_local;
self.next_local += 1;
let mut new_decl = LocalDecl::new(ty, span);
let mut new_decl = LocalDecl::new(ty, span).internal();
new_decl.local_info = local_info;
self.new_locals.push(new_decl);
Local::new(index as usize)
}

pub fn new_temp(&mut self, ty: Ty<'tcx>, span: Span) -> Local {
self.new_local_with_info(ty, span, None)
let index = self.next_local;
self.next_local += 1;
self.new_locals.push(LocalDecl::new(ty, span));
Local::new(index as usize)
}

pub fn new_internal(&mut self, ty: Ty<'tcx>, span: Span) -> Local {
Expand Down Expand Up @@ -147,7 +150,6 @@ impl<'tcx> MirPatch<'tcx> {

let mut delta = 0;
let mut last_bb = START_BLOCK;
let mut stmts_and_targets: Vec<(Statement<'_>, BasicBlock)> = Vec::new();
for (mut loc, stmt) in new_statements {
if loc.block != last_bb {
delta = 0;
Expand All @@ -156,27 +158,11 @@ impl<'tcx> MirPatch<'tcx> {
debug!("MirPatch: adding statement {:?} at loc {:?}+{}", stmt, loc, delta);
loc.statement_index += delta;
let source_info = Self::source_info_for_index(&body[loc.block], loc);

// For mir-opt `Derefer` to work in all cases we need to
// get terminator's targets and apply the statement to all of them.
if loc.statement_index > body[loc.block].statements.len() {
let term = body[loc.block].terminator();
for i in term.successors() {
stmts_and_targets.push((Statement { source_info, kind: stmt.clone() }, i));
}
delta += 1;
continue;
}

body[loc.block]
.statements
.insert(loc.statement_index, Statement { source_info, kind: stmt });
delta += 1;
}

for (stmt, target) in stmts_and_targets.into_iter().rev() {
body[target].statements.insert(0, stmt);
}
}

pub fn source_info_for_index(data: &BasicBlockData<'_>, loc: Location) -> SourceInfo {
Expand Down
20 changes: 1 addition & 19 deletions compiler/rustc_mir_transform/src/deref_separator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,8 +28,6 @@ impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
let mut last_len = 0;
let mut last_deref_idx = 0;

let mut prev_temp: Option<Local> = None;

for (idx, elem) in place.projection[0..].iter().enumerate() {
if *elem == ProjectionElem::Deref {
last_deref_idx = idx;
Expand All @@ -39,14 +37,12 @@ impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
for (idx, (p_ref, p_elem)) in place.iter_projections().enumerate() {
if !p_ref.projection.is_empty() && p_elem == ProjectionElem::Deref {
let ty = p_ref.ty(&self.local_decls, self.tcx).ty;
let temp = self.patcher.new_local_with_info(
let temp = self.patcher.new_internal_with_info(
ty,
self.local_decls[p_ref.local].source_info.span,
Some(Box::new(LocalInfo::DerefTemp)),
);

self.patcher.add_statement(loc, StatementKind::StorageLive(temp));

// We are adding current p_ref's projections to our
// temp value, excluding projections we already covered.
let deref_place = Place::from(place_local)
Expand All @@ -66,22 +62,8 @@ impl<'tcx> MutVisitor<'tcx> for DerefChecker<'tcx> {
Place::from(temp).project_deeper(&place.projection[idx..], self.tcx);
*place = temp_place;
}

// We are destroying the previous temp since it's no longer used.
if let Some(prev_temp) = prev_temp {
self.patcher.add_statement(loc, StatementKind::StorageDead(prev_temp));
}
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prev_temp = Some(temp);
}
}

// Since we won't be able to reach final temp, we destroy it outside the loop.
if let Some(prev_temp) = prev_temp {
let last_loc =
Location { block: loc.block, statement_index: loc.statement_index + 1 };
self.patcher.add_statement(last_loc, StatementKind::StorageDead(prev_temp));
}
}
}
}
Expand Down
9 changes: 1 addition & 8 deletions compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,9 +69,7 @@ impl<'tcx, 'a> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'tcx, 'a> {
let (unique_ty, nonnull_ty, ptr_ty) =
build_ptr_tys(tcx, base_ty.boxed_ty(), self.unique_did, self.nonnull_did);

let ptr_local = self.patch.new_temp(ptr_ty, source_info.span);

self.patch.add_statement(location, StatementKind::StorageLive(ptr_local));
let ptr_local = self.patch.new_internal(ptr_ty, source_info.span);

self.patch.add_assign(
location,
Expand All @@ -83,11 +81,6 @@ impl<'tcx, 'a> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'tcx, 'a> {
);

place.local = ptr_local;

self.patch.add_statement(
Location { block: location.block, statement_index: location.statement_index + 1 },
StatementKind::StorageDead(ptr_local),
);
}

self.super_place(place, context, location);
Expand Down
8 changes: 6 additions & 2 deletions compiler/rustc_mir_transform/src/inline.rs
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Expand Up @@ -616,7 +616,9 @@ impl<'tcx> Inliner<'tcx> {
// If there are any locals without storage markers, give them storage only for the
// duration of the call.
for local in callee_body.vars_and_temps_iter() {
if integrator.always_live_locals.contains(local) {
if !callee_body.local_decls[local].internal
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cc @rust-lang/wg-const-eval I think we could do something similar for internal locals without storage markers in const eval. Basically not eagerly initialize them and also not error when writing to them without marking them as live first.

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Sounds like you are suggesting a change to the operational semantics of MIR? I don't quite understand what change you are suggesting, though.

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Somewhat. We'd need to change MIR validation to make sure that internal locals are only referenced after being assigned to first. If that is guaranteed, then it's just an evaluator optimization to lazily initialize internal locals

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We'd also have to make sure that syntactically they are never accessed after the StorageDead, and that they never have their address taken. Otherwise we could miss UB.

&& integrator.always_live_locals.contains(local)
{
let new_local = integrator.map_local(local);
caller_body[callsite.block].statements.push(Statement {
source_info: callsite.source_info,
Expand All @@ -629,7 +631,9 @@ impl<'tcx> Inliner<'tcx> {
// the slice once.
let mut n = 0;
for local in callee_body.vars_and_temps_iter().rev() {
if integrator.always_live_locals.contains(local) {
if !callee_body.local_decls[local].internal
&& integrator.always_live_locals.contains(local)
{
let new_local = integrator.map_local(local);
caller_body[block].statements.push(Statement {
source_info: callsite.source_info,
Expand Down
4 changes: 0 additions & 4 deletions src/test/mir-opt/const_prop/boxes.main.ConstProp.diff
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Expand Up @@ -35,16 +35,12 @@
bb1: {
StorageLive(_7); // scope 0 at $DIR/boxes.rs:+1:14: +1:22
_7 = ShallowInitBox(move _6, i32); // scope 0 at $DIR/boxes.rs:+1:14: +1:22
StorageLive(_8); // scope 0 at $DIR/boxes.rs:+1:19: +1:21
_8 = (((_7.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32); // scope 0 at $DIR/boxes.rs:+1:19: +1:21
(*_8) = const 42_i32; // scope 0 at $DIR/boxes.rs:+1:19: +1:21
StorageDead(_8); // scope 0 at $DIR/boxes.rs:+1:14: +1:22
_3 = move _7; // scope 0 at $DIR/boxes.rs:+1:14: +1:22
StorageDead(_7); // scope 0 at $DIR/boxes.rs:+1:21: +1:22
StorageLive(_9); // scope 0 at $DIR/boxes.rs:+1:13: +1:22
_9 = (((_3.0: std::ptr::Unique<i32>).0: std::ptr::NonNull<i32>).0: *const i32); // scope 0 at $DIR/boxes.rs:+1:13: +1:22
_2 = (*_9); // scope 0 at $DIR/boxes.rs:+1:13: +1:22
StorageDead(_9); // scope 0 at $DIR/boxes.rs:+1:13: +1:26
_1 = Add(move _2, const 0_i32); // scope 0 at $DIR/boxes.rs:+1:13: +1:26
StorageDead(_2); // scope 0 at $DIR/boxes.rs:+1:25: +1:26
drop(_3) -> [return: bb2, unwind: bb3]; // scope 0 at $DIR/boxes.rs:+1:26: +1:27
Expand Down
2 changes: 0 additions & 2 deletions src/test/mir-opt/derefer_complex_case.main.Derefer.diff
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Expand Up @@ -68,10 +68,8 @@
bb4: {
StorageLive(_12); // scope 1 at $DIR/derefer_complex_case.rs:+1:10: +1:13
- _12 = (*((_7 as Some).0: &i32)); // scope 1 at $DIR/derefer_complex_case.rs:+1:10: +1:13
+ StorageLive(_15); // scope 1 at $DIR/derefer_complex_case.rs:+1:10: +1:13
+ _15 = deref_copy ((_7 as Some).0: &i32); // scope 1 at $DIR/derefer_complex_case.rs:+1:10: +1:13
+ _12 = (*_15); // scope 1 at $DIR/derefer_complex_case.rs:+1:10: +1:13
+ StorageDead(_15); // scope 2 at $DIR/derefer_complex_case.rs:+1:34: +1:37
StorageLive(_13); // scope 2 at $DIR/derefer_complex_case.rs:+1:34: +1:37
_13 = _12; // scope 2 at $DIR/derefer_complex_case.rs:+1:34: +1:37
_6 = std::mem::drop::<i32>(move _13) -> bb7; // scope 2 at $DIR/derefer_complex_case.rs:+1:29: +1:38
Expand Down
7 changes: 0 additions & 7 deletions src/test/mir-opt/derefer_terminator_test.main.Derefer.diff
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Expand Up @@ -55,25 +55,18 @@
_5 = &_6; // scope 2 at $DIR/derefer_terminator_test.rs:+3:17: +3:21
_4 = &_5; // scope 2 at $DIR/derefer_terminator_test.rs:+3:15: +3:22
- switchInt((*(*(*(*_4))))) -> [false: bb3, otherwise: bb4]; // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ StorageLive(_10); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ _10 = deref_copy (*_4); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ StorageLive(_11); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ _11 = deref_copy (*_10); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ StorageDead(_10); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ StorageLive(_12); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ _12 = deref_copy (*_11); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ StorageDead(_11); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
+ switchInt((*_12)) -> [false: bb3, otherwise: bb4]; // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
}

bb3: {
+ StorageDead(_12); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
_3 = const (); // scope 2 at $DIR/derefer_terminator_test.rs:+5:18: +5:20
goto -> bb5; // scope 2 at $DIR/derefer_terminator_test.rs:+5:18: +5:20
}

bb4: {
+ StorageDead(_12); // scope 2 at $DIR/derefer_terminator_test.rs:+3:5: +3:22
StorageLive(_8); // scope 2 at $DIR/derefer_terminator_test.rs:+4:22: +4:23
_8 = const 5_i32; // scope 2 at $DIR/derefer_terminator_test.rs:+4:26: +4:27
_3 = const (); // scope 2 at $DIR/derefer_terminator_test.rs:+4:17: +4:29
Expand Down
4 changes: 0 additions & 4 deletions src/test/mir-opt/derefer_test.main.Derefer.diff
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Expand Up @@ -33,16 +33,12 @@
StorageDead(_3); // scope 1 at $DIR/derefer_test.rs:+2:28: +2:29
StorageLive(_4); // scope 2 at $DIR/derefer_test.rs:+3:9: +3:10
- _4 = &mut ((*(_2.1: &mut (i32, i32))).0: i32); // scope 2 at $DIR/derefer_test.rs:+3:13: +3:26
+ StorageLive(_6); // scope 2 at $DIR/derefer_test.rs:+3:13: +3:26
+ _6 = deref_copy (_2.1: &mut (i32, i32)); // scope 2 at $DIR/derefer_test.rs:+3:13: +3:26
+ _4 = &mut ((*_6).0: i32); // scope 2 at $DIR/derefer_test.rs:+3:13: +3:26
+ StorageDead(_6); // scope 3 at $DIR/derefer_test.rs:+4:9: +4:10
StorageLive(_5); // scope 3 at $DIR/derefer_test.rs:+4:9: +4:10
- _5 = &mut ((*(_2.1: &mut (i32, i32))).1: i32); // scope 3 at $DIR/derefer_test.rs:+4:13: +4:26
+ StorageLive(_7); // scope 3 at $DIR/derefer_test.rs:+4:13: +4:26
+ _7 = deref_copy (_2.1: &mut (i32, i32)); // scope 3 at $DIR/derefer_test.rs:+4:13: +4:26
+ _5 = &mut ((*_7).1: i32); // scope 3 at $DIR/derefer_test.rs:+4:13: +4:26
+ StorageDead(_7); // scope 0 at $DIR/derefer_test.rs:+0:11: +5:2
_0 = const (); // scope 0 at $DIR/derefer_test.rs:+0:11: +5:2
StorageDead(_5); // scope 3 at $DIR/derefer_test.rs:+5:1: +5:2
StorageDead(_4); // scope 2 at $DIR/derefer_test.rs:+5:1: +5:2
Expand Down
12 changes: 0 additions & 12 deletions src/test/mir-opt/derefer_test_multiple.main.Derefer.diff
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Expand Up @@ -57,28 +57,16 @@
StorageDead(_7); // scope 3 at $DIR/derefer_test_multiple.rs:+4:28: +4:29
StorageLive(_8); // scope 4 at $DIR/derefer_test_multiple.rs:+5:9: +5:10
- _8 = &mut ((*((*((*(_6.1: &mut (i32, &mut (i32, &mut (i32, i32))))).1: &mut (i32, &mut (i32, i32)))).1: &mut (i32, i32))).1: i32); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ StorageLive(_10); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ _10 = deref_copy (_6.1: &mut (i32, &mut (i32, &mut (i32, i32)))); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ StorageLive(_11); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ _11 = deref_copy ((*_10).1: &mut (i32, &mut (i32, i32))); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ StorageDead(_10); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ StorageLive(_12); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ _12 = deref_copy ((*_11).1: &mut (i32, i32)); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ StorageDead(_11); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ _8 = &mut ((*_12).1: i32); // scope 4 at $DIR/derefer_test_multiple.rs:+5:13: +5:30
+ StorageDead(_12); // scope 5 at $DIR/derefer_test_multiple.rs:+6:9: +6:10
StorageLive(_9); // scope 5 at $DIR/derefer_test_multiple.rs:+6:9: +6:10
- _9 = &mut ((*((*((*(_6.1: &mut (i32, &mut (i32, &mut (i32, i32))))).1: &mut (i32, &mut (i32, i32)))).1: &mut (i32, i32))).1: i32); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ StorageLive(_13); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ _13 = deref_copy (_6.1: &mut (i32, &mut (i32, &mut (i32, i32)))); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ StorageLive(_14); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ _14 = deref_copy ((*_13).1: &mut (i32, &mut (i32, i32))); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ StorageDead(_13); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ StorageLive(_15); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ _15 = deref_copy ((*_14).1: &mut (i32, i32)); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ StorageDead(_14); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ _9 = &mut ((*_15).1: i32); // scope 5 at $DIR/derefer_test_multiple.rs:+6:13: +6:30
+ StorageDead(_15); // scope 0 at $DIR/derefer_test_multiple.rs:+0:12: +7:2
_0 = const (); // scope 0 at $DIR/derefer_test_multiple.rs:+0:12: +7:2
StorageDead(_9); // scope 5 at $DIR/derefer_test_multiple.rs:+7:1: +7:2
StorageDead(_8); // scope 4 at $DIR/derefer_test_multiple.rs:+7:1: +7:2
Expand Down
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