From ff1a9e406bfccefedb6c4f2cabc0c4d59ac947d4 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= Date: Wed, 16 Sep 2020 00:00:00 +0000 Subject: [PATCH] Fix underflow when calculating the number of no-op jumps folded When removing unwinds to no-op blocks and folding jumps to no-op blocks, remove the unwind target first. Otherwise we cannot determine if target has been already folded or not. Previous implementation incorrectly assumed that all resume targets had been folded already, occasionally resulting in an underflow: remove_noop_landing_pads: removed 18446744073709551613 jumps and 3 landing pads --- .../src/transform/remove_noop_landing_pads.rs | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/compiler/rustc_mir/src/transform/remove_noop_landing_pads.rs b/compiler/rustc_mir/src/transform/remove_noop_landing_pads.rs index 0bad1e5037a..4079f0110e2 100644 --- a/compiler/rustc_mir/src/transform/remove_noop_landing_pads.rs +++ b/compiler/rustc_mir/src/transform/remove_noop_landing_pads.rs @@ -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); @@ -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);