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//! This pass removes jumps to basic blocks containing only a return, and replaces them with a
//! return instead.
use crate::{simplify, MirPass};
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
pub struct MultipleReturnTerminators;
impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.mir_opt_level() >= 4
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// find basic blocks with no statement and a return terminator
let mut bbs_simple_returns = BitSet::new_empty(body.basic_blocks.len());
let def_id = body.source.def_id();
let bbs = body.basic_blocks_mut();
for idx in bbs.indices() {
if bbs[idx].statements.is_empty()
&& bbs[idx].terminator().kind == TerminatorKind::Return
{
bbs_simple_returns.insert(idx);
}
}
for bb in bbs {
if !tcx.consider_optimizing(|| format!("MultipleReturnTerminators {:?} ", def_id)) {
break;
}
if let TerminatorKind::Goto { target } = bb.terminator().kind {
if bbs_simple_returns.contains(target) {
bb.terminator_mut().kind = TerminatorKind::Return;
}
}
}
simplify::remove_dead_blocks(tcx, body)
}
}
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