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

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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
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19
compiler/rustc_mir_transform/src/elaborate_drops.rs
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@ -14,7 +14,7 @@ use rustc_mir_dataflow::un_derefer::UnDerefer;
use rustc_mir_dataflow::MoveDataParamEnv;
use rustc_mir_dataflow::{on_all_children_bits, on_all_drop_children_bits};
use rustc_mir_dataflow::{Analysis, ResultsCursor};
use rustc_span::Span;
use rustc_span::{DesugaringKind, Span};
use rustc_target::abi::VariantIdx;
use std::fmt;
@ -425,10 +425,19 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
bb,
),
LookupResult::Parent(..) => {
self.tcx.sess.delay_span_bug(
terminator.source_info.span,
&format!("drop of untracked value {:?}", bb),
);
if !matches!(
terminator.source_info.span.desugaring_kind(),
Some(DesugaringKind::Replace),
) {
self.tcx.sess.delay_span_bug(
terminator.source_info.span,
&format!("drop of untracked value {:?}", bb),
);
}
// A drop and replace behind a pointer/array/whatever.
// The borrow checker requires that these locations are initialized before the assignment,
// so we just leave an unconditional drop.
assert!(!data.is_cleanup);
}
}
}