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use crate::MirPass;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
/// A pass that replaces a branch with a goto when its condition is known.
pub struct SimplifyConstCondition {
label: String,
}
impl SimplifyConstCondition {
pub fn new(label: &str) -> Self {
SimplifyConstCondition { label: format!("SimplifyConstCondition-{}", label) }
}
}
impl<'tcx> MirPass<'tcx> for SimplifyConstCondition {
fn name(&self) -> &str {
&self.label
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env(body.source.def_id());
for block in body.basic_blocks_mut() {
let terminator = block.terminator_mut();
terminator.kind = match terminator.kind {
TerminatorKind::SwitchInt {
discr: Operand::Constant(ref c), ref targets, ..
} => {
let constant = c.literal.try_eval_bits(tcx, param_env, c.ty());
if let Some(constant) = constant {
let target = targets.target_for_value(constant);
TerminatorKind::Goto { target }
} else {
continue;
}
}
TerminatorKind::Assert {
target, cond: Operand::Constant(ref c), expected, ..
} => match c.literal.try_eval_bool(tcx, param_env) {
Some(v) if v == expected => TerminatorKind::Goto { target },
_ => continue,
},
_ => continue,
};
}
}
}
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