diff options
7 files changed, 209 insertions, 0 deletions
diff --git a/compiler/rustc_mir/src/transform/mod.rs b/compiler/rustc_mir/src/transform/mod.rs index abe2dc496a6..17ef98c176d 100644 --- a/compiler/rustc_mir/src/transform/mod.rs +++ b/compiler/rustc_mir/src/transform/mod.rs @@ -38,6 +38,7 @@ pub mod nrvo; pub mod promote_consts; pub mod qualify_min_const_fn; pub mod remove_noop_landing_pads; +pub mod remove_unneeded_drops; pub mod required_consts; pub mod rustc_peek; pub mod simplify; @@ -461,6 +462,7 @@ fn run_optimization_passes<'tcx>( // The main optimizations that we do on MIR. let optimizations: &[&dyn MirPass<'tcx>] = &[ + &remove_unneeded_drops::RemoveUnneededDrops::new(def_id), &match_branches::MatchBranchSimplification, // inst combine is after MatchBranchSimplification to clean up Ne(_1, false) &instcombine::InstCombine, diff --git a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs new file mode 100644 index 00000000000..0f023d71dd1 --- /dev/null +++ b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs @@ -0,0 +1,57 @@ +//! 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; + +pub struct RemoveUnneededDrops { + def_id: LocalDefId, +} + +impl RemoveUnneededDrops { + pub fn new(def_id: LocalDefId) -> Self { + Self { def_id } + } +} + +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 }; + } + } +} + +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, +} diff --git a/src/test/mir-opt/remove_unneeded_drops.cannot_opt_generic.RemoveUnneededDrops.diff b/src/test/mir-opt/remove_unneeded_drops.cannot_opt_generic.RemoveUnneededDrops.diff new file mode 100644 index 00000000000..545ad2794ee --- /dev/null +++ b/src/test/mir-opt/remove_unneeded_drops.cannot_opt_generic.RemoveUnneededDrops.diff @@ -0,0 +1,32 @@ +- // MIR for `cannot_opt_generic` before RemoveUnneededDrops ++ // MIR for `cannot_opt_generic` after RemoveUnneededDrops + + 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 + } + + 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 + } + + bb1 (cleanup): { + resume; // scope 0 at $DIR/remove_unneeded_drops.rs:19:1: 21:2 + } + + 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 + } + } + diff --git a/src/test/mir-opt/remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff b/src/test/mir-opt/remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff new file mode 100644 index 00000000000..78d65d13bd1 --- /dev/null +++ b/src/test/mir-opt/remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff @@ -0,0 +1,32 @@ +- // MIR for `dont_opt` before RemoveUnneededDrops ++ // MIR for `dont_opt` after RemoveUnneededDrops + + 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 + } + + 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 + } + + bb1 (cleanup): { + resume; // scope 0 at $DIR/remove_unneeded_drops.rs:7:1: 9:2 + } + + 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 + } + } + diff --git a/src/test/mir-opt/remove_unneeded_drops.opt.RemoveUnneededDrops.diff b/src/test/mir-opt/remove_unneeded_drops.opt.RemoveUnneededDrops.diff new file mode 100644 index 00000000000..34193ccc5c7 --- /dev/null +++ b/src/test/mir-opt/remove_unneeded_drops.opt.RemoveUnneededDrops.diff @@ -0,0 +1,29 @@ +- // MIR for `opt` before RemoveUnneededDrops ++ // MIR for `opt` after RemoveUnneededDrops + + 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 + } + + 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 + } + + 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 + } + } + diff --git a/src/test/mir-opt/remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff b/src/test/mir-opt/remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff new file mode 100644 index 00000000000..2e6c8c8a78a --- /dev/null +++ b/src/test/mir-opt/remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff @@ -0,0 +1,29 @@ +- // MIR for `opt_generic_copy` before RemoveUnneededDrops ++ // MIR for `opt_generic_copy` after RemoveUnneededDrops + + 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 + } + + 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 + } + + 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 + } + } + diff --git a/src/test/mir-opt/remove_unneeded_drops.rs b/src/test/mir-opt/remove_unneeded_drops.rs new file mode 100644 index 00000000000..17d7e79a1eb --- /dev/null +++ b/src/test/mir-opt/remove_unneeded_drops.rs @@ -0,0 +1,28 @@ +// EMIT_MIR remove_unneeded_drops.opt.RemoveUnneededDrops.diff +fn opt(x: bool) { + drop(x); +} + +// EMIT_MIR remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff +fn dont_opt(x: Vec<bool>) { + drop(x); +} + +// EMIT_MIR remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff +fn opt_generic_copy<T: Copy>(x: T) { + drop(x); +} + +// 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); +} + +fn main() { + opt(true); + opt_generic_copy(42); + cannot_opt_generic(42); + dont_opt(vec![true]); +} |