bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Auto merge of #107844 - Zeegomo:no-drop-and-rep, r=cjgillot

Browse source 
Desugaring of drop and replace at MIR build

This commit desugars the drop and replace deriving from an
assignment at MIR build, avoiding the construction of the
`DropAndReplace` terminator (which will be removed in a following PR).

In order to retain the same error messages for replaces a new
`DesugaringKind::Replace` variant is introduced.

The changes in the borrowck are also useful for future work in moving drop elaboration
before borrowck, as no `DropAndReplace` would be present there anymore.

Notes on test diffs:
*  `tests/ui/borrowck/issue-58776-borrowck-scans-children`: the assignment deriving from the desugaring kills the borrow.
*  `tests/ui/async-await/async-fn-size-uninit-locals.rs`, `tests/mir-opt/issue_41110.test.ElaborateDrops.after.mir`,  `tests/mir-opt/issue_41888.main.ElaborateDrops.after.mir`:  drop elaboration generates (or reads from) a useless drop flag due to an issue with the dataflow analysis. Will be fixed independently by https://github.com/rust-lang/rust/pull/106430.

See https://github.com/rust-lang/rust/pull/104488 for more context
This commit is contained in:
bors 2023-03-05 07:56:26 +00:00
commit 14c54b637b
22 changed files with 286 additions and 157 deletions
Download patch file Download diff file Expand all files Collapse all files

2
compiler/rustc_mir_build/src/build/expr/stmt.rs
View file

@ -40,7 +40,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// Generate better code for things that don't need to be
// dropped.
if lhs.ty.needs_drop(this.tcx, this.param_env) {
let rhs = unpack!(block = this.as_local_operand(block, rhs));
let rhs = unpack!(block = this.as_local_rvalue(block, rhs));
let lhs = unpack!(block = this.as_place(block, lhs));
unpack!(block = this.build_drop_and_replace(block, lhs_span, lhs, rhs));
} else {

32
compiler/rustc_mir_build/src/build/scope.rs
View file

@ -91,7 +91,7 @@ use rustc_middle::middle::region;
use rustc_middle::mir::*;
use rustc_middle::thir::{Expr, LintLevel};
use rustc_span::{Span, DUMMY_SP};
use rustc_span::{DesugaringKind, Span, DUMMY_SP};
#[derive(Debug)]
pub struct Scopes<'tcx> {
@ -1118,24 +1118,35 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
}
/// Utility function for *non*-scope code to build their own drops
/// Force a drop at this point in the MIR by creating a new block.
pub(crate) fn build_drop_and_replace(
&mut self,
block: BasicBlock,
span: Span,
place: Place<'tcx>,
value: Operand<'tcx>,
value: Rvalue<'tcx>,
) -> BlockAnd<()> {
let span = self.tcx.with_stable_hashing_context(|hcx| {
span.mark_with_reason(None, DesugaringKind::Replace, self.tcx.sess.edition(), hcx)
});
let source_info = self.source_info(span);
let next_target = self.cfg.start_new_block();
// create the new block for the assignment
let assign = self.cfg.start_new_block();
self.cfg.push_assign(assign, source_info, place, value.clone());
// create the new block for the assignment in the case of unwinding
let assign_unwind = self.cfg.start_new_cleanup_block();
self.cfg.push_assign(assign_unwind, source_info, place, value.clone());
self.cfg.terminate(
block,
source_info,
TerminatorKind::DropAndReplace { place, value, target: next_target, unwind: None },
TerminatorKind::Drop { place, target: assign, unwind: Some(assign_unwind) },
);
self.diverge_from(block);
next_target.unit()
assign.unit()
}
/// Creates an `Assert` terminator and return the success block.
@ -1413,8 +1424,15 @@ impl<'tcx> DropTreeBuilder<'tcx> for Unwind {
fn add_entry(cfg: &mut CFG<'tcx>, from: BasicBlock, to: BasicBlock) {
let term = &mut cfg.block_data_mut(from).terminator_mut();
match &mut term.kind {
TerminatorKind::Drop { unwind, .. }
| TerminatorKind::DropAndReplace { unwind, .. }
TerminatorKind::Drop { unwind, .. } => {
if let Some(unwind) = *unwind {
let source_info = term.source_info;
cfg.terminate(unwind, source_info, TerminatorKind::Goto { target: to });
} else {
*unwind = Some(to);
}
}
TerminatorKind::DropAndReplace { unwind, .. }
| TerminatorKind::FalseUnwind { unwind, .. }
| TerminatorKind::Call { cleanup: unwind, .. }
| TerminatorKind::Assert { cleanup: unwind, .. }