46 lines
1.7 KiB
Rust
46 lines
1.7 KiB
Rust
//! This pass replaces a drop of a type that does not need dropping, with a goto.
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//!
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//! When the MIR is built, we check `needs_drop` before emitting a `Drop` for a place. This pass is
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//! useful because (unlike MIR building) it runs after type checking, so it can make use of
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//! `Reveal::All` to provide more precies type information.
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use crate::MirPass;
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use rustc_middle::mir::*;
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use rustc_middle::ty::TyCtxt;
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use super::simplify::simplify_cfg;
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pub struct RemoveUnneededDrops;
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impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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trace!("Running RemoveUnneededDrops on {:?}", body.source);
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let did = body.source.def_id();
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let param_env = tcx.param_env_reveal_all_normalized(did);
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let mut should_simplify = false;
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let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
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for block in basic_blocks {
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let terminator = block.terminator_mut();
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if let TerminatorKind::Drop { place, target, .. } = terminator.kind {
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let ty = place.ty(local_decls, tcx);
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if ty.ty.needs_drop(tcx, param_env) {
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continue;
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}
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if !tcx.consider_optimizing(|| format!("RemoveUnneededDrops {:?} ", did)) {
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continue;
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}
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debug!("SUCCESS: replacing `drop` with goto({:?})", target);
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terminator.kind = TerminatorKind::Goto { target };
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should_simplify = true;
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}
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}
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// if we applied optimizations, we potentially have some cfg to cleanup to
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// make it easier for further passes
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if should_simplify {
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simplify_cfg(tcx, body);
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}
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}
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}
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