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Remove false edges in CleanupPostBorrowck

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This commit is contained in:
Tomasz Miąsko 2022-12-17 00:00:00 +00:00
parent 4c3efc7f1b
commit 62f9084dfa
3 changed files with 16 additions and 46 deletions
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28
compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs
View file

@ -1,32 +1,26 @@
//! This module provides a pass to replacing the following statements with
//! [`Nop`]s
//! This module provides a pass that removes parts of MIR that are no longer relevant after
//! analysis phase and borrowck. In particular, it removes false edges, user type annotations and
//! replaces following statements with [`Nop`]s:
//!
//! - [`AscribeUserType`]
//! - [`FakeRead`]
//! - [`Assign`] statements with a [`Shallow`] borrow
//!
//! The `CleanFakeReadsAndBorrows` "pass" is actually implemented as two
//! traversals (aka visits) of the input MIR. The first traversal,
//! `DeleteAndRecordFakeReads`, deletes the fake reads and finds the
//! temporaries read by [`ForMatchGuard`] reads, and `DeleteFakeBorrows`
//! deletes the initialization of those temporaries.
//!
//! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
//! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
//! [`Assign`]: rustc_middle::mir::StatementKind::Assign
//! [`ForMatchGuard`]: rustc_middle::mir::FakeReadCause::ForMatchGuard
//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
//! [`Nop`]: rustc_middle::mir::StatementKind::Nop
//! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
use crate::MirPass;
use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind};
use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::ty::TyCtxt;
pub struct CleanupPostBorrowck;
impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
for basic_block in body.basic_blocks.as_mut_preserves_cfg() {
for basic_block in body.basic_blocks.as_mut() {
for statement in basic_block.statements.iter_mut() {
match statement.kind {
StatementKind::AscribeUserType(..)
@ -35,6 +29,14 @@ impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
_ => (),
}
}
let terminator = basic_block.terminator_mut();
match terminator.kind {
TerminatorKind::FalseEdge { real_target, .. }
| TerminatorKind::FalseUnwind { real_target, .. } => {
terminator.kind = TerminatorKind::Goto { target: real_target };
}
_ => {}
}
}
body.user_type_annotations.raw.clear();

5
compiler/rustc_mir_transform/src/lib.rs
View file

@ -77,8 +77,6 @@ mod match_branches;
mod multiple_return_terminators;
mod normalize_array_len;
mod nrvo;
// This pass is public to allow external drivers to perform MIR cleanup
pub mod remove_false_edges;
mod remove_noop_landing_pads;
mod remove_storage_markers;
mod remove_uninit_drops;
@ -494,10 +492,9 @@ fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>
/// 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>] = &[
&remove_false_edges::RemoveFalseEdges,
&cleanup_post_borrowck::CleanupPostBorrowck,
&simplify_branches::SimplifyConstCondition::new("initial"),
&remove_noop_landing_pads::RemoveNoopLandingPads,
&cleanup_post_borrowck::CleanupPostBorrowck,
&simplify::SimplifyCfg::new("early-opt"),
&deref_separator::Derefer,
];

29
compiler/rustc_mir_transform/src/remove_false_edges.rs
View file

@ -1,29 +0,0 @@
use rustc_middle::mir::{Body, TerminatorKind};
use rustc_middle::ty::TyCtxt;
use crate::MirPass;
/// Removes `FalseEdge` and `FalseUnwind` terminators from the MIR.
///
/// These are only needed for borrow checking, and can be removed afterwards.
///
/// FIXME: This should probably have its own MIR phase.
pub struct RemoveFalseEdges;
impl<'tcx> MirPass<'tcx> for RemoveFalseEdges {
fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
for block in body.basic_blocks_mut() {
let terminator = block.terminator_mut();
terminator.kind = match terminator.kind {
TerminatorKind::FalseEdge { real_target, .. } => {
TerminatorKind::Goto { target: real_target }
}
TerminatorKind::FalseUnwind { real_target, .. } => {
TerminatorKind::Goto { target: real_target }
}
_ => continue,
}
}
}
}