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Skip drop elaboration for drop-free bodies [-0.12% avg, -0.21% debug] #55

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Skip drop elaboration for drop-free bodies [-0.12% avg, -0.21% debug] #55

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12 changes: 12 additions & 0 deletions compiler/rustc_mir_transform/src/elaborate_drops.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,18 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateDrops {
#[instrument(level = "trace", skip(self, tcx, body))]
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!("elaborate_drops({:?} @ {:?})", body.source, body.span);
// A body without `Drop` terminators has nothing to elaborate: the
// patch below could only ever come out empty. Skip the move-path
// construction and the two dataflow fixpoints, which are among the
// most expensive parts of the whole unoptimized pipeline, for the
// large class of drop-free bodies.
if !body
.basic_blocks
.iter()
.any(|block| matches!(block.terminator().kind, TerminatorKind::Drop { .. }))
{
return;
}
// FIXME(#132279): This is used during the phase transition from analysis
// to runtime, so we have to manually specify the correct typing mode.
let typing_env = ty::TypingEnv::post_analysis(tcx, body.source.def_id());
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