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Add StorageDead statements for while conditions
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@matthewjasper
matthewjasper committed Jun 25, 2019
1 parent be23bd4 commit b86e675
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Showing 8 changed files with 172 additions and 128 deletions.
17 changes: 4 additions & 13 deletions src/librustc_mir/build/expr/into.rs
View file
Expand Up @@ -179,19 +179,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// conduct the test, if necessary
let body_block;
if let Some(cond_expr) = opt_cond_expr {
let loop_block_end;
let cond = unpack!(
loop_block_end = this.as_local_operand(loop_block, cond_expr)
);
body_block = this.cfg.start_new_block();
let false_block = this.cfg.start_new_block();
let term = TerminatorKind::if_(
this.hir.tcx(),
cond,
body_block,
false_block,
);
this.cfg.terminate(loop_block_end, source_info, term);
let cond_expr = this.hir.mirror(cond_expr);
let (true_block, false_block)
= this.test_bool(loop_block, cond_expr, source_info);
body_block = true_block;

// if the test is false, there's no `break` to assign `destination`, so
// we have to do it
Expand Down
49 changes: 11 additions & 38 deletions src/librustc_mir/build/matches/mod.rs
View file
Expand Up @@ -1490,15 +1490,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
};
let source_info = self.source_info(guard.span);
let guard_end = self.source_info(tcx.sess.source_map().end_point(guard.span));
let cond = unpack!(block = self.as_local_operand(block, guard));
let (post_guard_block, otherwise_post_guard_block)
= self.test_bool(block, guard, source_info);
let guard_frame = self.guard_context.pop().unwrap();
debug!(
"Exiting guard building context with locals: {:?}",
guard_frame
);

for &(_, temp) in fake_borrows {
self.cfg.push(block, Statement {
self.cfg.push(post_guard_block, Statement {
source_info: guard_end,
kind: StatementKind::FakeRead(
FakeReadCause::ForMatchGuard,
Expand All @@ -1507,6 +1508,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
});
}

self.exit_scope(
source_info.span,
region_scope,
otherwise_post_guard_block,
candidate.otherwise_block.unwrap(),
);

// We want to ensure that the matched candidates are bound
// after we have confirmed this candidate *and* any
// associated guard; Binding them on `block` is too soon,
Expand All @@ -1533,41 +1541,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// ```
//
// and that is clearly not correct.
let post_guard_block = self.cfg.start_new_block();
let otherwise_post_guard_block = self.cfg.start_new_block();
self.cfg.terminate(
block,
source_info,
TerminatorKind::if_(
self.hir.tcx(),
cond.clone(),
post_guard_block,
otherwise_post_guard_block,
),
);

self.exit_scope(
source_info.span,
region_scope,
otherwise_post_guard_block,
candidate.otherwise_block.unwrap(),
);

if let Operand::Copy(cond_place) | Operand::Move(cond_place) = cond {
if let Place::Base(PlaceBase::Local(cond_temp)) = cond_place {
// We will call `clear_top_scope` if there's another guard. So
// we have to drop this variable now or it will be "storage
// leaked".
self.pop_variable(
post_guard_block,
region_scope.0,
cond_temp
);
} else {
bug!("Expected as_local_operand to produce a temporary");
}
}

let by_value_bindings = candidate.bindings.iter().filter(|binding| {
if let BindingMode::ByValue = binding.binding_mode { true } else { false }
});
Expand All @@ -1577,7 +1550,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
let local_id = self.var_local_id(binding.var_id, RefWithinGuard);
let place = Place::from(local_id);
self.cfg.push(
block,
post_guard_block,
Statement {
source_info: guard_end,
kind: StatementKind::FakeRead(FakeReadCause::ForGuardBinding, place),
Expand Down
125 changes: 73 additions & 52 deletions src/librustc_mir/build/scope.rs
View file
Expand Up @@ -83,7 +83,7 @@ should go to.
*/

use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder, CFG};
use crate::hair::{ExprRef, LintLevel};
use crate::hair::{Expr, ExprRef, LintLevel};
use rustc::middle::region;
use rustc::ty::Ty;
use rustc::hir;
Expand Down Expand Up @@ -829,6 +829,78 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {

// Other
// =====
/// Branch based on a boolean condition.
///
/// This is a special case because the temporary for the condition needs to
/// be dropped on both the true and the false arm.
pub fn test_bool(
&mut self,
mut block: BasicBlock,
condition: Expr<'tcx>,
source_info: SourceInfo,
) -> (BasicBlock, BasicBlock) {
let cond = unpack!(block = self.as_local_operand(block, condition));
let true_block = self.cfg.start_new_block();
let false_block = self.cfg.start_new_block();
let term = TerminatorKind::if_(
self.hir.tcx(),
cond.clone(),
true_block,
false_block,
);
self.cfg.terminate(block, source_info, term);

match cond {
// Don't try to drop a constant
Operand::Constant(_) => (),
// If constants and statics, we don't generate StorageLive for this
// temporary, so don't try to generate StorageDead for it either.
_ if self.local_scope().is_none() => (),
Operand::Copy(Place::Base(PlaceBase::Local(cond_temp)))
| Operand::Move(Place::Base(PlaceBase::Local(cond_temp))) => {
// Manually drop the condition on both branches.
let top_scope = self.scopes.scopes.last_mut().unwrap();
let top_drop_data = top_scope.drops.pop().unwrap();

match top_drop_data.kind {
DropKind::Value { .. } => {
bug!("Drop scheduled on top of condition variable")
}
DropKind::Storage => {
// Drop the storage for both value and storage drops.
// Only temps and vars need their storage dead.
match top_drop_data.location {
Place::Base(PlaceBase::Local(index)) => {
let source_info = top_scope.source_info(top_drop_data.span);
assert_eq!(index, cond_temp, "Drop scheduled on top of condition");
self.cfg.push(
true_block,
Statement {
source_info,
kind: StatementKind::StorageDead(index)
},
);
self.cfg.push(
false_block,
Statement {
source_info,
kind: StatementKind::StorageDead(index)
},
);
}
_ => unreachable!(),
}
}
}

top_scope.invalidate_cache(true, self.is_generator, true);
}
_ => bug!("Expected as_local_operand to produce a temporary"),
}

(true_block, false_block)
}

/// Creates a path that performs all required cleanup for unwinding.
///
/// This path terminates in Resume. Returns the start of the path.
Expand Down Expand Up @@ -942,57 +1014,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
top_scope.drops.clear();
top_scope.invalidate_cache(false, self.is_generator, true);
}

/// Drops the single variable provided
///
/// * The scope must be the top scope.
/// * The variable must be in that scope.
/// * The variable must be at the top of that scope: it's the next thing
/// scheduled to drop.
/// * The drop must be of `DropKind::Storage`.
///
/// This is used for the boolean holding the result of the match guard. We
/// do this because:
///
/// * The boolean is different for each pattern
/// * There is only one exit for the arm scope
/// * The guard expression scope is too short, it ends just before the
/// boolean is tested.
pub(crate) fn pop_variable(
&mut self,
block: BasicBlock,
region_scope: region::Scope,
variable: Local,
) {
let top_scope = self.scopes.scopes.last_mut().unwrap();

assert_eq!(top_scope.region_scope, region_scope);

let top_drop_data = top_scope.drops.pop().unwrap();

match top_drop_data.kind {
DropKind::Value { .. } => {
bug!("Should not be calling pop_top_variable on non-copy type!")
}
DropKind::Storage => {
// Drop the storage for both value and storage drops.
// Only temps and vars need their storage dead.
match top_drop_data.location {
Place::Base(PlaceBase::Local(index)) => {
let source_info = top_scope.source_info(top_drop_data.span);
assert_eq!(index, variable);
self.cfg.push(block, Statement {
source_info,
kind: StatementKind::StorageDead(index)
});
}
_ => unreachable!(),
}
}
}

top_scope.invalidate_cache(true, self.is_generator, true);
}
}

/// Builds drops for pop_scope and exit_scope.
Expand Down
16 changes: 8 additions & 8 deletions src/test/mir-opt/match-arm-scopes.rs
View file
Expand Up @@ -103,10 +103,6 @@ fn main() {
// bb10: { // `else` block - first time
// _9 = (*_6);
// StorageDead(_10);
// FakeRead(ForMatchGuard, _3);
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// FakeRead(ForGuardBinding, _8);
// switchInt(move _9) -> [false: bb16, otherwise: bb15];
// }
// bb11: { // `return 3` - first time
Expand All @@ -128,6 +124,10 @@ fn main() {
// }
// bb15: {
// StorageDead(_9);
// FakeRead(ForMatchGuard, _3);
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// FakeRead(ForGuardBinding, _8);
// StorageLive(_5);
// _5 = (_2.1: bool);
// StorageLive(_7);
Expand Down Expand Up @@ -159,10 +159,6 @@ fn main() {
// bb19: { // `else` block - second time
// _12 = (*_6);
// StorageDead(_13);
// FakeRead(ForMatchGuard, _3);
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// FakeRead(ForGuardBinding, _8);
// switchInt(move _12) -> [false: bb22, otherwise: bb21];
// }
// bb20: {
Expand All @@ -175,6 +171,10 @@ fn main() {
// }
// bb21: { // bindings for arm 1
// StorageDead(_12);
// FakeRead(ForMatchGuard, _3);
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// FakeRead(ForGuardBinding, _8);
// StorageLive(_5);
// _5 = (_2.0: bool);
// StorageLive(_7);
Expand Down
16 changes: 8 additions & 8 deletions src/test/mir-opt/match_false_edges.rs
View file
Expand Up @@ -71,12 +71,12 @@ fn main() {
// _7 = const guard() -> [return: bb7, unwind: bb1];
// }
// bb7: { // end of guard
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// switchInt(move _7) -> [false: bb9, otherwise: bb8];
// }
// bb8: { // arm1
// StorageDead(_7);
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// StorageLive(_5);
// _5 = ((_2 as Some).0: i32);
// StorageLive(_8);
Expand Down Expand Up @@ -138,12 +138,12 @@ fn main() {
// _7 = const guard() -> [return: bb6, unwind: bb1];
// }
// bb6: { // end of guard
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// switchInt(move _7) -> [false: bb8, otherwise: bb7];
// }
// bb7: {
// StorageDead(_7);
// FakeRead(ForMatchGuard, _4);
// FakeRead(ForGuardBinding, _6);
// StorageLive(_5);
// _5 = ((_2 as Some).0: i32);
// StorageLive(_8);
Expand Down Expand Up @@ -209,12 +209,12 @@ fn main() {
// _8 = const guard() -> [return: bb6, unwind: bb1];
// }
// bb6: { //end of guard1
// FakeRead(ForMatchGuard, _5);
// FakeRead(ForGuardBinding, _7);
// switchInt(move _8) -> [false: bb8, otherwise: bb7];
// }
// bb7: {
// StorageDead(_8);
// FakeRead(ForMatchGuard, _5);
// FakeRead(ForGuardBinding, _7);
// StorageLive(_6);
// _6 = ((_2 as Some).0: i32);
// _1 = const 1i32;
Expand Down Expand Up @@ -245,12 +245,12 @@ fn main() {
// }
// bb11: { // end of guard2
// StorageDead(_13);
// FakeRead(ForMatchGuard, _5);
// FakeRead(ForGuardBinding, _11);
// switchInt(move _12) -> [false: bb13, otherwise: bb12];
// }
// bb12: { // binding4 & arm4
// StorageDead(_12);
// FakeRead(ForMatchGuard, _5);
// FakeRead(ForGuardBinding, _11);
// StorageLive(_10);
// _10 = ((_2 as Some).0: i32);
// _1 = const 3i32;
Expand Down
2 changes: 1 addition & 1 deletion src/test/mir-opt/match_test.rs
View file
Expand Up @@ -54,11 +54,11 @@ fn main() {
// _8 = &shallow _1;
// StorageLive(_9);
// _9 = _2;
// FakeRead(ForMatchGuard, _8);
// switchInt(move _9) -> [false: bb11, otherwise: bb10];
// }
// bb10: {
// StorageDead(_9);
// FakeRead(ForMatchGuard, _8);
// _3 = const 0i32;
// goto -> bb14;
// }
Expand Down

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