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use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use tracing::trace;
use crate::patch::MirPatch;
pub(super) enum SimplifyConstCondition {
AfterConstProp,
Final,
}
/// A pass that replaces a branch with a goto when its condition is known.
impl<'tcx> crate::MirPass<'tcx> for SimplifyConstCondition {
fn name(&self) -> &'static str {
match self {
SimplifyConstCondition::AfterConstProp => "SimplifyConstCondition-after-const-prop",
SimplifyConstCondition::Final => "SimplifyConstCondition-final",
}
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
trace!("Running SimplifyConstCondition on {:?}", body.source);
let typing_env = body.typing_env(tcx);
let mut patch = MirPatch::new(body);
'blocks: for (bb, block) in body.basic_blocks.iter_enumerated() {
for (statement_index, stmt) in block.statements.iter().enumerate() {
// Simplify `assume` of a known value: either a NOP or unreachable.
if let StatementKind::Intrinsic(box ref intrinsic) = stmt.kind
&& let NonDivergingIntrinsic::Assume(discr) = intrinsic
&& let Operand::Constant(c) = discr
&& let Some(constant) = c.const_.try_eval_bool(tcx, typing_env)
{
if constant {
patch.nop_statement(Location { block: bb, statement_index });
} else {
patch.patch_terminator(bb, TerminatorKind::Unreachable);
continue 'blocks;
}
}
}
let terminator = block.terminator();
let terminator = match terminator.kind {
TerminatorKind::SwitchInt {
discr: Operand::Constant(ref c), ref targets, ..
} => {
let constant = c.const_.try_eval_bits(tcx, typing_env);
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.const_.try_eval_bool(tcx, typing_env) {
Some(v) if v == expected => TerminatorKind::Goto { target },
_ => continue,
},
_ => continue,
};
patch.patch_terminator(bb, terminator);
}
patch.apply(body);
}
fn is_required(&self) -> bool {
false
}
}
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