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//! A pass that simplifies branches when their condition is known.
use rustc::ty::{TyCtxt, ParamEnv};
use rustc::mir::*;
use crate::transform::{MirPass, MirSource};
use std::borrow::Cow;
pub struct SimplifyBranches { label: String }
impl SimplifyBranches {
pub fn new(label: &str) -> Self {
SimplifyBranches { label: format!("SimplifyBranches-{}", label) }
}
}
impl MirPass for SimplifyBranches {
fn name<'a>(&'a self) -> Cow<'a, str> {
Cow::Borrowed(&self.label)
}
fn run_pass<'a, 'tcx>(&self,
tcx: TyCtxt<'a, 'tcx, 'tcx>,
_src: MirSource<'tcx>,
mir: &mut Mir<'tcx>) {
for block in mir.basic_blocks_mut() {
let terminator = block.terminator_mut();
terminator.kind = match terminator.kind {
TerminatorKind::SwitchInt {
discr: Operand::Constant(ref c), switch_ty, ref values, ref targets, ..
} => {
let switch_ty = ParamEnv::empty().and(switch_ty);
let constant = c.literal.map_evaluated(|c| c.assert_bits(tcx, switch_ty));
if let Some(constant) = constant {
let (otherwise, targets) = targets.split_last().unwrap();
let mut ret = TerminatorKind::Goto { target: *otherwise };
for (&v, t) in values.iter().zip(targets.iter()) {
if v == constant {
ret = TerminatorKind::Goto { target: *t };
break;
}
}
ret
} else {
continue
}
},
TerminatorKind::Assert {
target, cond: Operand::Constant(ref c), expected, ..
} if (c.literal.map_evaluated(|e| e.assert_bool(tcx)) == Some(true)) == expected =>
TerminatorKind::Goto { target },
TerminatorKind::FalseEdges { real_target, .. } => {
TerminatorKind::Goto { target: real_target }
},
TerminatorKind::FalseUnwind { real_target, .. } => {
TerminatorKind::Goto { target: real_target }
},
_ => continue
};
}
}
}
|
