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mir: Add false edge cleanup out of infinite loops

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Fixes #46036
This commit is contained in:
bobtwinkles 2018-01-26 18:25:25 -05:00
parent bdc37aa057
commit ed6a2ebcd6
1 changed files with 17 additions and 5 deletions
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22
src/librustc_mir/build/expr/into.rs
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@ -156,11 +156,15 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
//
// If `opt_cond_expr` is `None`, then the graph is somewhat simplified:
//
// [block] --> [loop_block / body_block ] ~~> [body_block_end] [exit_block]
// ^ |
// | |
// +--------------------------+
// [block] --> [loop_block] ~~> [loop_block_end]
// | ^ |
// false link | |
// | +-------------------+
// v
// [cleanup_block]
//
// The false link is required in case something results in
// unwinding through the body.
let loop_block = this.cfg.start_new_block();
let exit_block = this.cfg.start_new_block();
@ -174,6 +178,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
move |this| {
// conduct the test, if necessary
let body_block;
let out_terminator;
if let Some(cond_expr) = opt_cond_expr {
let loop_block_end;
let cond = unpack!(
@ -187,8 +192,15 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
// 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);
out_terminator = TerminatorKind::Goto { target: loop_block };
} else {
body_block = loop_block;
let diverge_cleanup = this.diverge_cleanup();
out_terminator = TerminatorKind::FalseUnwind {
real_target: loop_block,
unwind: Some(diverge_cleanup)
}
}
// The “return” value of the loop body must always be an unit. We therefore
@ -197,7 +209,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
// Execute the body, branching back to the test.
let body_block_end = unpack!(this.into(&tmp, body_block, body));
this.cfg.terminate(body_block_end, source_info,
TerminatorKind::Goto { target: loop_block });
out_terminator);
}
);
exit_block.unit()