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MIR-opt: Generalize &(*_1) optimization to mutable references #76802

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MIR-opt: Generalize &(*_1) optimization to mutable references #76802

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12a77b7
Add test demonstrating missing optimization
simonvandel Sep 16, 2020
5b354ed
Generalize &(*_1) optimization to mutable references
simonvandel Sep 16, 2020
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8 changes: 8 additions & 0 deletions compiler/rustc_middle/src/mir/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -649,6 +649,14 @@ impl BorrowKind {
BorrowKind::Mut { allow_two_phase_borrow } => allow_two_phase_borrow,
}
}

/// Returns the mutability of the borrow
pub fn mutability(&self) -> Mutability {
match self {
BorrowKind::Shared | BorrowKind::Shallow | BorrowKind::Unique => Mutability::Not,
BorrowKind::Mut { .. } => Mutability::Mut,
}
}
}

///////////////////////////////////////////////////////////////////////////
Expand Down
23 changes: 13 additions & 10 deletions compiler/rustc_mir/src/transform/instcombine.rs
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
//! Performs various peephole optimizations.

use crate::transform::{MirPass, MirSource};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::Mutability;
use rustc_ast::Mutability;
use rustc_data_structures::fx::FxHashMap;
use rustc_index::vec::Idx;
use rustc_middle::mir::visit::{MutVisitor, Visitor};
use rustc_middle::mir::{
Expand Down Expand Up @@ -40,8 +40,9 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
}

fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
if self.optimizations.and_stars.remove(&location) {
debug!("replacing `&*`: {:?}", rvalue);
if let Some(mutability) = self.optimizations.and_stars.remove(&location) {
let type_to_print = if mutability == Mutability::Not { "&" } else { "&mut" };
debug!("replacing `{}*`: {:?}", type_to_print, rvalue);
let new_place = match rvalue {
Rvalue::Ref(_, _, place) => {
if let &[ref proj_l @ .., proj_r] = place.projection.as_ref() {
Expand All @@ -56,7 +57,7 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
unreachable!();
}
}
_ => bug!("Detected `&*` but didn't find `&*`!"),
_ => bug!("Detected `{}*` but didn't find `{}*`!", type_to_print, type_to_print),
};
*rvalue = Rvalue::Use(Operand::Copy(new_place))
}
Expand Down Expand Up @@ -132,14 +133,16 @@ impl OptimizationFinder<'b, 'tcx> {

impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
if let Rvalue::Ref(_, _, place) = rvalue {
if let Rvalue::Ref(_, borrowkind, place) = rvalue {
if let PlaceRef { local, projection: &[ref proj_base @ .., ProjectionElem::Deref] } =
place.as_ref()
{
// The dereferenced place must have type `&_`.
// The dereferenced place must have a reference type with the same mutability
let ty = Place::ty_from(local, proj_base, self.body, self.tcx).ty;
if let ty::Ref(_, _, Mutability::Not) = ty.kind() {
self.optimizations.and_stars.insert(location);
let mutability = borrowkind.mutability();
if matches!(ty.kind(), ty::Ref(_, _, derefed_place_mutability) if *derefed_place_mutability == mutability)
{
self.optimizations.and_stars.insert(location, mutability);
}
}
}
Expand All @@ -161,7 +164,7 @@ impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {

#[derive(Default)]
struct OptimizationList<'tcx> {
and_stars: FxHashSet<Location>,
and_stars: FxHashMap<Location, Mutability>,
arrays_lengths: FxHashMap<Location, Constant<'tcx>>,
unneeded_equality_comparison: FxHashMap<Location, Operand<'tcx>>,
}
44 changes: 44 additions & 0 deletions src/test/mir-opt/and_star.opt_immutable.InstCombine.diff
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@@ -0,0 +1,44 @@
- // MIR for `opt_immutable` before InstCombine
+ // MIR for `opt_immutable` after InstCombine

fn opt_immutable(_1: &[u8]) -> () {
debug dst => _1; // in scope 0 at $DIR/and_star.rs:7:18: 7:21
let mut _0: (); // return place in scope 0 at $DIR/and_star.rs:7:30: 7:30
let _2: std::option::Option<&u8>; // in scope 0 at $DIR/and_star.rs:8:5: 8:15
let mut _3: &[u8]; // in scope 0 at $DIR/and_star.rs:8:5: 8:8
let mut _6: usize; // in scope 0 at $DIR/and_star.rs:8:5: 8:15
scope 1 {
debug self => _3; // in scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
debug index => _6; // in scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
let mut _4: usize; // in scope 1 at $DIR/and_star.rs:8:5: 8:15
let mut _5: &[u8]; // in scope 1 at $DIR/and_star.rs:8:5: 8:15
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/and_star.rs:8:5: 8:15
StorageLive(_3); // scope 0 at $DIR/and_star.rs:8:5: 8:8
- _3 = &(*_1); // scope 0 at $DIR/and_star.rs:8:5: 8:8
+ _3 = _1; // scope 0 at $DIR/and_star.rs:8:5: 8:8
StorageLive(_6); // scope 0 at $DIR/and_star.rs:8:5: 8:15
_6 = const 0_usize; // scope 0 at $DIR/and_star.rs:8:5: 8:15
StorageLive(_4); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
_4 = move _6; // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
StorageLive(_5); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
_5 = _3; // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
_2 = <usize as SliceIndex<[u8]>>::get(move _4, move _5) -> bb1; // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
// mir::Constant
// + span: $SRC_DIR/core/src/slice/mod.rs:LL:COL
// + literal: Const { ty: for<'r> fn(usize, &'r [u8]) -> std::option::Option<&'r <usize as std::slice::SliceIndex<[u8]>>::Output> {<usize as std::slice::SliceIndex<[u8]>>::get}, val: Value(Scalar(<ZST>)) }
}

bb1: {
StorageDead(_5); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
StorageDead(_4); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
StorageDead(_6); // scope 0 at $DIR/and_star.rs:8:5: 8:15
StorageDead(_3); // scope 0 at $DIR/and_star.rs:8:14: 8:15
StorageDead(_2); // scope 0 at $DIR/and_star.rs:8:15: 8:16
_0 = const (); // scope 0 at $DIR/and_star.rs:7:30: 9:2
return; // scope 0 at $DIR/and_star.rs:9:2: 9:2
}
}

44 changes: 44 additions & 0 deletions src/test/mir-opt/and_star.opt_mutable.InstCombine.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
- // MIR for `opt_mutable` before InstCombine
+ // MIR for `opt_mutable` after InstCombine

fn opt_mutable(_1: &mut [u8]) -> () {
debug dst => _1; // in scope 0 at $DIR/and_star.rs:2:16: 2:19
let mut _0: (); // return place in scope 0 at $DIR/and_star.rs:2:32: 2:32
let _2: std::option::Option<&mut u8>; // in scope 0 at $DIR/and_star.rs:3:5: 3:19
let mut _3: &mut [u8]; // in scope 0 at $DIR/and_star.rs:3:5: 3:8
let mut _6: usize; // in scope 0 at $DIR/and_star.rs:3:5: 3:19
scope 1 {
debug self => _3; // in scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
debug index => _6; // in scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
let mut _4: usize; // in scope 1 at $DIR/and_star.rs:3:5: 3:19
let mut _5: &mut [u8]; // in scope 1 at $DIR/and_star.rs:3:5: 3:19
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/and_star.rs:3:5: 3:19
StorageLive(_3); // scope 0 at $DIR/and_star.rs:3:5: 3:8
- _3 = &mut (*_1); // scope 0 at $DIR/and_star.rs:3:5: 3:8
+ _3 = _1; // scope 0 at $DIR/and_star.rs:3:5: 3:8
StorageLive(_6); // scope 0 at $DIR/and_star.rs:3:5: 3:19
_6 = const 0_usize; // scope 0 at $DIR/and_star.rs:3:5: 3:19
StorageLive(_4); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
_4 = move _6; // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
StorageLive(_5); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
_5 = _3; // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
_2 = <usize as SliceIndex<[u8]>>::get_mut(move _4, move _5) -> bb1; // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
// mir::Constant
// + span: $SRC_DIR/core/src/slice/mod.rs:LL:COL
// + literal: Const { ty: for<'r> fn(usize, &'r mut [u8]) -> std::option::Option<&'r mut <usize as std::slice::SliceIndex<[u8]>>::Output> {<usize as std::slice::SliceIndex<[u8]>>::get_mut}, val: Value(Scalar(<ZST>)) }
}

bb1: {
StorageDead(_5); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
StorageDead(_4); // scope 1 at $SRC_DIR/core/src/slice/mod.rs:LL:COL
StorageDead(_6); // scope 0 at $DIR/and_star.rs:3:5: 3:19
StorageDead(_3); // scope 0 at $DIR/and_star.rs:3:18: 3:19
StorageDead(_2); // scope 0 at $DIR/and_star.rs:3:19: 3:20
_0 = const (); // scope 0 at $DIR/and_star.rs:2:32: 4:2
return; // scope 0 at $DIR/and_star.rs:4:2: 4:2
}
}

14 changes: 14 additions & 0 deletions src/test/mir-opt/and_star.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
// EMIT_MIR and_star.opt_mutable.InstCombine.diff
fn opt_mutable(dst: &mut [u8]) {
dst.get_mut(0);
}

// EMIT_MIR and_star.opt_immutable.InstCombine.diff
fn opt_immutable(dst: &[u8]) {
dst.get(0);
}

fn main() {
opt_mutable(&mut [1]);
opt_immutable(&[1])
}
4 changes: 2 additions & 2 deletions src/test/mir-opt/funky_arms.float_to_exponential_common.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,7 @@

bb6: {
StorageLive(_18); // scope 2 at $DIR/funky_arms.rs:28:46: 28:49
_18 = &mut (*_1); // scope 2 at $DIR/funky_arms.rs:28:46: 28:49
_18 = _1; // scope 2 at $DIR/funky_arms.rs:28:46: 28:49
StorageLive(_19); // scope 2 at $DIR/funky_arms.rs:28:51: 28:54
_19 = _2; // scope 2 at $DIR/funky_arms.rs:28:51: 28:54
StorageLive(_20); // scope 2 at $DIR/funky_arms.rs:28:56: 28:60
Expand All @@ -95,7 +95,7 @@
StorageLive(_10); // scope 2 at $DIR/funky_arms.rs:24:17: 24:26
_10 = ((_7 as Some).0: usize); // scope 2 at $DIR/funky_arms.rs:24:17: 24:26
StorageLive(_11); // scope 3 at $DIR/funky_arms.rs:26:43: 26:46
_11 = &mut (*_1); // scope 3 at $DIR/funky_arms.rs:26:43: 26:46
_11 = _1; // scope 3 at $DIR/funky_arms.rs:26:43: 26:46
StorageLive(_12); // scope 3 at $DIR/funky_arms.rs:26:48: 26:51
_12 = _2; // scope 3 at $DIR/funky_arms.rs:26:48: 26:51
StorageLive(_13); // scope 3 at $DIR/funky_arms.rs:26:53: 26:57
Expand Down
6 changes: 1 addition & 5 deletions src/test/mir-opt/inline/issue_58867_inline_as_ref_as_mut.a.Inline.after.mir
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Expand Up @@ -8,18 +8,14 @@ fn a(_1: &mut [T]) -> &mut [T] {
let mut _4: &mut [T]; // in scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:6
scope 1 {
debug self => _4; // in scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
let mut _5: &mut [T]; // in scope 1 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
StorageLive(_3); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
StorageLive(_4); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:6
_4 = &mut (*_1); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:6
StorageLive(_5); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_5 = &mut (*_4); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_3 = &mut (*_5); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
StorageDead(_5); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_3 = _4; // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_2 = &mut (*_3); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
StorageDead(_4); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:14: 3:15
_0 = &mut (*_2); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
Expand Down
8 changes: 2 additions & 6 deletions src/test/mir-opt/inline/issue_58867_inline_as_ref_as_mut.b.Inline.after.mir
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Expand Up @@ -9,7 +9,6 @@ fn b(_1: &mut Box<T>) -> &mut T {
scope 1 {
debug self => _4; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _5: &mut T; // in scope 1 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:15
let mut _6: &mut T; // in scope 1 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:15
}

bb0: {
Expand All @@ -18,11 +17,8 @@ fn b(_1: &mut Box<T>) -> &mut T {
StorageLive(_4); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:6
_4 = &mut (*_1); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:6
StorageLive(_5); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
StorageLive(_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_6 = &mut (*(*_4)); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_5 = &mut (*_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_3 = &mut (*_5); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
StorageDead(_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_5 = &mut (*(*_4)); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_3 = _5; // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
StorageDead(_5); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_2 = &mut (*_3); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:15
StorageDead(_4); // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:14: 8:15
Expand Down
7 changes: 1 addition & 6 deletions src/test/mir-opt/nrvo_simple.nrvo.RenameReturnPlace.diff
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Expand Up @@ -20,17 +20,12 @@
- _2 = [const 0_u8; 1024]; // scope 0 at $DIR/nrvo-simple.rs:3:19: 3:28
+ _0 = [const 0_u8; 1024]; // scope 0 at $DIR/nrvo-simple.rs:3:19: 3:28
StorageLive(_3); // scope 1 at $DIR/nrvo-simple.rs:4:5: 4:19
StorageLive(_5); // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
StorageLive(_6); // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
- _6 = &mut _2; // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
+ _6 = &mut _0; // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
_5 = &mut (*_6); // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
_3 = move _1(move _5) -> bb1; // scope 1 at $DIR/nrvo-simple.rs:4:5: 4:19
_3 = move _1(move _6) -> bb1; // scope 1 at $DIR/nrvo-simple.rs:4:5: 4:19
}

bb1: {
StorageDead(_5); // scope 1 at $DIR/nrvo-simple.rs:4:18: 4:19
StorageDead(_6); // scope 1 at $DIR/nrvo-simple.rs:4:19: 4:20
StorageDead(_3); // scope 1 at $DIR/nrvo-simple.rs:4:19: 4:20
- _0 = _2; // scope 1 at $DIR/nrvo-simple.rs:5:5: 5:8
- StorageDead(_2); // scope 0 at $DIR/nrvo-simple.rs:6:1: 6:2
Expand Down