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MIR pass to remove unneeded drops on types not needing drop
This is heavily dependent on MIR inlining running to actually see the drop statement
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//! This pass replaces a drop of a type that does not need dropping, with a goto | ||
use crate::transform::{MirPass, MirSource}; | ||
use rustc_hir::def_id::LocalDefId; | ||
use rustc_middle::mir::visit::Visitor; | ||
use rustc_middle::mir::*; | ||
use rustc_middle::ty::TyCtxt; | ||
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pub struct RemoveUnneededDrops { | ||
def_id: LocalDefId, | ||
} | ||
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impl RemoveUnneededDrops { | ||
pub fn new(def_id: LocalDefId) -> Self { | ||
Self { def_id } | ||
} | ||
} | ||
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impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops { | ||
fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) { | ||
trace!("Running SimplifyComparisonIntegral on {:?}", source); | ||
let mut opt_finder = RemoveUnneededDropsOptimizationFinder { | ||
tcx, | ||
body, | ||
optimizations: vec![], | ||
def_id: self.def_id, | ||
}; | ||
opt_finder.visit_body(body); | ||
for (loc, target) in opt_finder.optimizations { | ||
let terminator = body.basic_blocks_mut()[loc.block].terminator_mut(); | ||
debug!("SUCCESS: replacing `drop` with goto({:?})", target); | ||
terminator.kind = TerminatorKind::Goto { target }; | ||
} | ||
} | ||
} | ||
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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.tcx.param_env(self.def_id)); | ||
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)>, | ||
def_id: LocalDefId, | ||
} |
32 changes: 32 additions & 0 deletions
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src/test/mir-opt/remove_unneeded_drops.cannot_opt_generic.RemoveUnneededDrops.diff
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- // MIR for `cannot_opt_generic` before RemoveUnneededDrops | ||
+ // MIR for `cannot_opt_generic` after RemoveUnneededDrops | ||
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fn cannot_opt_generic(_1: T) -> () { | ||
debug x => _1; // in scope 0 at $DIR/remove_unneeded_drops.rs:19:26: 19:27 | ||
let mut _0: (); // return place in scope 0 at $DIR/remove_unneeded_drops.rs:19:32: 19:32 | ||
let _2: (); // in scope 0 at $DIR/remove_unneeded_drops.rs:20:5: 20:12 | ||
let mut _3: T; // in scope 0 at $DIR/remove_unneeded_drops.rs:20:10: 20:11 | ||
scope 1 { | ||
debug _x => _3; // in scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb0: { | ||
StorageLive(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:20:5: 20:12 | ||
StorageLive(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:20:10: 20:11 | ||
_3 = move _1; // scope 0 at $DIR/remove_unneeded_drops.rs:20:10: 20:11 | ||
_2 = const (); // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
drop(_3) -> [return: bb2, unwind: bb1]; // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb1 (cleanup): { | ||
resume; // scope 0 at $DIR/remove_unneeded_drops.rs:19:1: 21:2 | ||
} | ||
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bb2: { | ||
StorageDead(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:20:11: 20:12 | ||
StorageDead(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:20:12: 20:13 | ||
_0 = const (); // scope 0 at $DIR/remove_unneeded_drops.rs:19:32: 21:2 | ||
return; // scope 0 at $DIR/remove_unneeded_drops.rs:21:2: 21:2 | ||
} | ||
} | ||
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32 changes: 32 additions & 0 deletions
32
src/test/mir-opt/remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff
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- // MIR for `dont_opt` before RemoveUnneededDrops | ||
+ // MIR for `dont_opt` after RemoveUnneededDrops | ||
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fn dont_opt(_1: Vec<bool>) -> () { | ||
debug x => _1; // in scope 0 at $DIR/remove_unneeded_drops.rs:7:13: 7:14 | ||
let mut _0: (); // return place in scope 0 at $DIR/remove_unneeded_drops.rs:7:27: 7:27 | ||
let _2: (); // in scope 0 at $DIR/remove_unneeded_drops.rs:8:5: 8:12 | ||
let mut _3: std::vec::Vec<bool>; // in scope 0 at $DIR/remove_unneeded_drops.rs:8:10: 8:11 | ||
scope 1 { | ||
debug _x => _3; // in scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb0: { | ||
StorageLive(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:8:5: 8:12 | ||
StorageLive(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:8:10: 8:11 | ||
_3 = move _1; // scope 0 at $DIR/remove_unneeded_drops.rs:8:10: 8:11 | ||
_2 = const (); // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
drop(_3) -> [return: bb2, unwind: bb1]; // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb1 (cleanup): { | ||
resume; // scope 0 at $DIR/remove_unneeded_drops.rs:7:1: 9:2 | ||
} | ||
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bb2: { | ||
StorageDead(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:8:11: 8:12 | ||
StorageDead(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:8:12: 8:13 | ||
_0 = const (); // scope 0 at $DIR/remove_unneeded_drops.rs:7:27: 9:2 | ||
return; // scope 0 at $DIR/remove_unneeded_drops.rs:9:2: 9:2 | ||
} | ||
} | ||
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29 changes: 29 additions & 0 deletions
29
src/test/mir-opt/remove_unneeded_drops.opt.RemoveUnneededDrops.diff
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- // MIR for `opt` before RemoveUnneededDrops | ||
+ // MIR for `opt` after RemoveUnneededDrops | ||
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fn opt(_1: bool) -> () { | ||
debug x => _1; // in scope 0 at $DIR/remove_unneeded_drops.rs:2:8: 2:9 | ||
let mut _0: (); // return place in scope 0 at $DIR/remove_unneeded_drops.rs:2:17: 2:17 | ||
let _2: (); // in scope 0 at $DIR/remove_unneeded_drops.rs:3:5: 3:12 | ||
let mut _3: bool; // in scope 0 at $DIR/remove_unneeded_drops.rs:3:10: 3:11 | ||
scope 1 { | ||
debug _x => _3; // in scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb0: { | ||
StorageLive(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:3:5: 3:12 | ||
StorageLive(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:3:10: 3:11 | ||
_3 = _1; // scope 0 at $DIR/remove_unneeded_drops.rs:3:10: 3:11 | ||
_2 = const (); // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
- drop(_3) -> bb1; // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
+ goto -> bb1; // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb1: { | ||
StorageDead(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:3:11: 3:12 | ||
StorageDead(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:3:12: 3:13 | ||
_0 = const (); // scope 0 at $DIR/remove_unneeded_drops.rs:2:17: 4:2 | ||
return; // scope 0 at $DIR/remove_unneeded_drops.rs:4:2: 4:2 | ||
} | ||
} | ||
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29 changes: 29 additions & 0 deletions
29
src/test/mir-opt/remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff
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- // MIR for `opt_generic_copy` before RemoveUnneededDrops | ||
+ // MIR for `opt_generic_copy` after RemoveUnneededDrops | ||
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fn opt_generic_copy(_1: T) -> () { | ||
debug x => _1; // in scope 0 at $DIR/remove_unneeded_drops.rs:12:30: 12:31 | ||
let mut _0: (); // return place in scope 0 at $DIR/remove_unneeded_drops.rs:12:36: 12:36 | ||
let _2: (); // in scope 0 at $DIR/remove_unneeded_drops.rs:13:5: 13:12 | ||
let mut _3: T; // in scope 0 at $DIR/remove_unneeded_drops.rs:13:10: 13:11 | ||
scope 1 { | ||
debug _x => _3; // in scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb0: { | ||
StorageLive(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:13:5: 13:12 | ||
StorageLive(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:13:10: 13:11 | ||
_3 = _1; // scope 0 at $DIR/remove_unneeded_drops.rs:13:10: 13:11 | ||
_2 = const (); // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
- drop(_3) -> bb1; // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
+ goto -> bb1; // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL | ||
} | ||
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bb1: { | ||
StorageDead(_3); // scope 0 at $DIR/remove_unneeded_drops.rs:13:11: 13:12 | ||
StorageDead(_2); // scope 0 at $DIR/remove_unneeded_drops.rs:13:12: 13:13 | ||
_0 = const (); // scope 0 at $DIR/remove_unneeded_drops.rs:12:36: 14:2 | ||
return; // scope 0 at $DIR/remove_unneeded_drops.rs:14:2: 14:2 | ||
} | ||
} | ||
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// EMIT_MIR remove_unneeded_drops.opt.RemoveUnneededDrops.diff | ||
fn opt(x: bool) { | ||
drop(x); | ||
} | ||
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// EMIT_MIR remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff | ||
fn dont_opt(x: Vec<bool>) { | ||
drop(x); | ||
} | ||
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// EMIT_MIR remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff | ||
fn opt_generic_copy<T: Copy>(x: T) { | ||
drop(x); | ||
} | ||
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// EMIT_MIR remove_unneeded_drops.cannot_opt_generic.RemoveUnneededDrops.diff | ||
// since the pass is not running on monomorphisized code, | ||
// we can't (but probably should) optimize this | ||
fn cannot_opt_generic<T>(x: T) { | ||
drop(x); | ||
} | ||
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fn main() { | ||
opt(true); | ||
opt_generic_copy(42); | ||
cannot_opt_generic(42); | ||
dont_opt(vec![true]); | ||
} |