use crate::MirPass;
+// These constants are somewhat random guesses and have not been optimized.
+// If `tcx.sess.mir_opt_level() >= 4`, we ignore the limits (this can become very expensive).
const BLOCK_LIMIT: usize = 100;
const PLACE_LIMIT: usize = 100;
impl<'tcx> MirPass<'tcx> for DataflowConstProp {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
- sess.mir_opt_level() >= 1
+ sess.mir_opt_level() >= 3
}
#[instrument(skip_all level = "debug")]
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
- if body.basic_blocks.len() > BLOCK_LIMIT {
+ if tcx.sess.mir_opt_level() < 4 && body.basic_blocks.len() > BLOCK_LIMIT {
debug!("aborted dataflow const prop due too many basic blocks");
return;
}
// `O(num_nodes * tracked_places * n)` in terms of time complexity. Since the number of
// map nodes is strongly correlated to the number of tracked places, this becomes more or
// less `O(n)` if we place a constant limit on the number of tracked places.
- if map.tracked_places() > PLACE_LIMIT {
+ if tcx.sess.mir_opt_level() < 4 && map.tracked_places() > PLACE_LIMIT {
debug!("aborted dataflow const prop due to too many tracked places");
return;
}
FlatSet::Top => FlatSet::Top,
FlatSet::Elem(overflow) => {
if overflow {
- // Overflow cannot be reliable propagated. See: https://github.com/rust-lang/rust/pull/101168#issuecomment-1288091446
+ // Overflow cannot be reliably propagated. See: https://github.com/rust-lang/rust/pull/101168#issuecomment-1288091446
FlatSet::Top
} else {
self.wrap_scalar(Scalar::from_bool(false), self.tcx.types.bool)
/// For a given MIR location, this stores the values of the operands used by that location. In
/// particular, this is before the effect, such that the operands of `_1 = _1 + _2` are
- /// properly captured.
+ /// properly captured. (This may become UB soon, but it is currently emitted even by safe code.)
before_effect: FxHashMap<(Location, Place<'tcx>), ScalarTy<'tcx>>,
/// Stores the assigned values for assignments where the Rvalue is constant.