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use rustc::ty::TyCtxt;
use rustc::mir::*;
use rustc_data_structures::bitvec::BitVector;
use rustc_data_structures::indexed_vec::Idx;
use transform::{MirPass, MirSource};
use util::patch::MirPatch;
pub struct RemoveNoopLandingPads;
pub fn remove_noop_landing_pads<'a, 'tcx>(
tcx: TyCtxt<'a, 'tcx, 'tcx>,
mir: &mut Mir<'tcx>)
{
if tcx.sess.no_landing_pads() {
return
}
debug!("remove_noop_landing_pads({:?})", mir);
RemoveNoopLandingPads.remove_nop_landing_pads(mir)
}
impl MirPass for RemoveNoopLandingPads {
fn run_pass<'a, 'tcx>(&self,
tcx: TyCtxt<'a, 'tcx, 'tcx>,
_src: MirSource,
mir: &mut Mir<'tcx>) {
remove_noop_landing_pads(tcx, mir);
}
}
impl RemoveNoopLandingPads {
fn is_nop_landing_pad(&self, bb: BasicBlock, mir: &Mir, nop_landing_pads: &BitVector)
-> bool
{
for stmt in &mir[bb].statements {
match stmt.kind {
StatementKind::ReadForMatch(_) |
StatementKind::StorageLive(_) |
StatementKind::StorageDead(_) |
StatementKind::EndRegion(_) |
StatementKind::UserAssertTy(..) |
StatementKind::Nop => {
}
StatementKind::Assign(Place::Local(_), Rvalue::Use(_)) => {
}
StatementKind::Assign(_, _) |
StatementKind::SetDiscriminant { .. } |
StatementKind::InlineAsm { .. } |
StatementKind::Validate { .. } => {
return false;
}
}
}
let terminator = mir[bb].terminator();
match terminator.kind {
TerminatorKind::Goto { .. } |
TerminatorKind::Resume |
TerminatorKind::SwitchInt { .. } |
TerminatorKind::FalseEdges { .. } |
TerminatorKind::FalseUnwind { .. } => {
terminator.successors().all(|succ| {
nop_landing_pads.contains(succ.index())
})
},
TerminatorKind::GeneratorDrop |
TerminatorKind::Yield { .. } |
TerminatorKind::Return |
TerminatorKind::Abort |
TerminatorKind::Unreachable |
TerminatorKind::Call { .. } |
TerminatorKind::Assert { .. } |
TerminatorKind::DropAndReplace { .. } |
TerminatorKind::Drop { .. } => {
false
}
}
}
fn remove_nop_landing_pads(&self, mir: &mut Mir) {
let resume_block = {
let patch = MirPatch::new(mir);
let resume_block = patch.resume_block();
patch.apply(mir);
resume_block
};
debug!("remove_noop_landing_pads: resume block is {:?}", resume_block);
let mut jumps_folded = 0;
let mut landing_pads_removed = 0;
let mut nop_landing_pads = BitVector::new(mir.basic_blocks().len());
let postorder: Vec<_> = traversal::postorder(mir).map(|(bb, _)| bb).collect();
for bb in postorder {
debug!(" processing {:?}", bb);
for target in mir[bb].terminator_mut().successors_mut() {
if *target != resume_block && nop_landing_pads.contains(target.index()) {
debug!(" folding noop jump to {:?} to resume block", target);
*target = resume_block;
jumps_folded += 1;
}
}
match mir[bb].terminator_mut().unwind_mut() {
Some(unwind) => {
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, mir, &nop_landing_pads);
if is_nop_landing_pad {
nop_landing_pads.insert(bb.index());
}
debug!(" is_nop_landing_pad({:?}) = {}", bb, is_nop_landing_pad);
}
debug!("removed {:?} jumps and {:?} landing pads", jumps_folded, landing_pads_removed);
}
}