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Fix incorrect double assignment in MIR for while loops

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This commit is contained in:
Matthew Jasper 2019-06-15 10:08:20 +01:00
parent 5f9c0448dd
commit 62bec71446
2 changed files with 25 additions and 6 deletions
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20
src/librustc_mir/build/expr/into.rs
View File

@ -184,15 +184,23 @@ pub fn into_expr(
loop_block_end = this.as_local_operand(loop_block, cond_expr)
);
body_block = this.cfg.start_new_block();
let term =
TerminatorKind::if_(this.hir.tcx(), cond, body_block, exit_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);
// if the test is false, there's no `break` to assign `destination`, so
// we have to do it; this overwrites any `break`-assigned value but it's
// always `()` anyway
this.cfg
.push_assign_unit(exit_block, source_info, destination);
// we have to do it
this.cfg.push_assign_unit(false_block, source_info, destination);
this.cfg.terminate(
false_block,
source_info,
TerminatorKind::Goto { target: exit_block },
);
} else {
body_block = this.cfg.start_new_block();
let diverge_cleanup = this.diverge_cleanup();

11
src/test/ui/nll/assign-while-to-immutable.rs Normal file
View File

@ -0,0 +1,11 @@
// We used to incorrectly assign to `x` twice when generating MIR for this
// function, preventing this from compiling.
// check-pass
fn main() {
let x = while false {
break;
};
let y = 'l: while break 'l {};
}