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Fix underflow when calculating the number of no-op jumps folded #76748

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Sep 24, 2020
Merged

Fix underflow when calculating the number of no-op jumps folded #76748

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19 changes: 10 additions & 9 deletions compiler/rustc_mir/src/transform/remove_noop_landing_pads.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,16 @@ impl RemoveNoopLandingPads {
let postorder: Vec<_> = traversal::postorder(body).map(|(bb, _)| bb).collect();
for bb in postorder {
debug!(" processing {:?}", bb);
if let Some(unwind) = body[bb].terminator_mut().unwind_mut() {
if let Some(unwind_bb) = *unwind {
if nop_landing_pads.contains(unwind_bb) {
debug!(" removing noop landing pad");
landing_pads_removed += 1;
*unwind = None;
}
}
}

for target in body[bb].terminator_mut().successors_mut() {
if *target != resume_block && nop_landing_pads.contains(*target) {
debug!(" folding noop jump to {:?} to resume block", target);
Expand All @@ -110,15 +120,6 @@ impl RemoveNoopLandingPads {
}
}

if let Some(unwind) = body[bb].terminator_mut().unwind_mut() {
if *unwind == Some(resume_block) {
debug!(" removing noop landing pad");
jumps_folded -= 1;
landing_pads_removed += 1;
*unwind = None;
}
}

let is_nop_landing_pad = self.is_nop_landing_pad(bb, body, &nop_landing_pads);
if is_nop_landing_pad {
nop_landing_pads.insert(bb);
Expand Down