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Auto merge of #81122 - tmiasko:no-drop, r=davidtwco

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Visit only terminators when removing unneeded drops

No functional changes intended
This commit is contained in:
bors 2021-01-21 17:02:49 +00:00
commit 65767e5653
1 changed files with 20 additions and 41 deletions
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61
compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
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@ -1,9 +1,8 @@
//! This pass replaces a drop of a type that does not need dropping, with a goto
use crate::transform::MirPass;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::ty::{ParamEnv, TyCtxt};
use rustc_middle::ty::TyCtxt;
use super::simplify::simplify_cfg;
@ -12,24 +11,26 @@ pub struct RemoveUnneededDrops;
impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
trace!("Running RemoveUnneededDrops on {:?}", body.source);
let mut opt_finder = RemoveUnneededDropsOptimizationFinder {
tcx,
body,
param_env: tcx.param_env(body.source.def_id()),
optimizations: vec![],
};
opt_finder.visit_body(body);
let should_simplify = !opt_finder.optimizations.is_empty();
for (loc, target) in opt_finder.optimizations {
if !tcx
.consider_optimizing(|| format!("RemoveUnneededDrops {:?} ", body.source.def_id()))
{
break;
}
let terminator = body.basic_blocks_mut()[loc.block].terminator_mut();
debug!("SUCCESS: replacing `drop` with goto({:?})", target);
terminator.kind = TerminatorKind::Goto { target };
let did = body.source.def_id();
let param_env = tcx.param_env(did);
let mut should_simplify = false;
let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
for block in basic_blocks {
let terminator = block.terminator_mut();
if let TerminatorKind::Drop { place, target, .. } = terminator.kind {
let ty = place.ty(local_decls, tcx);
if ty.ty.needs_drop(tcx, param_env) {
continue;
}
if !tcx.consider_optimizing(|| format!("RemoveUnneededDrops {:?} ", did)) {
continue;
}
debug!("SUCCESS: replacing `drop` with goto({:?})", target);
terminator.kind = TerminatorKind::Goto { target };
should_simplify = true;
}
}
// if we applied optimizations, we potentially have some cfg to cleanup to
@ -39,25 +40,3 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for RemoveUnneededDropsOptimizationFinder<'a, 'tcx> {
fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
match terminator.kind {
TerminatorKind::Drop { place, target, .. } => {
let ty = place.ty(self.body, self.tcx);
let needs_drop = ty.ty.needs_drop(self.tcx, self.param_env);
if !needs_drop {
self.optimizations.push((location, target));
}
}
_ => {}
}
self.super_terminator(terminator, location);
}
}
pub struct RemoveUnneededDropsOptimizationFinder<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
body: &'a Body<'tcx>,
optimizations: Vec<(Location, BasicBlock)>,
param_env: ParamEnv<'tcx>,
}