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Add peephold optimization that simplifies Ne(_1, false) and Ne(false, _1) into _1

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This was observed emitted from the MatchBranchSimplification pass.
This commit is contained in:
Simon Vandel Sillesen 2020-08-29 14:16:39 +02:00
parent ffaf158608
commit c2693db264
5 changed files with 128 additions and 2 deletions
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9
compiler/rustc_middle/src/mir/mod.rs
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@ -1954,6 +1954,15 @@ impl<'tcx> Operand<'tcx> {
Operand::Constant(_) => None,
}
}
/// Returns the `Constant` that is the target of this `Operand`, or `None` if this `Operand` is a
/// place.
pub fn constant(&self) -> Option<&Constant<'tcx>> {
match self {
Operand::Constant(x) => Some(&**x),
Operand::Copy(_) | Operand::Move(_) => None,
}
}
}
///////////////////////////////////////////////////////////////////////////

37
compiler/rustc_mir/src/transform/instcombine.rs
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@ -6,7 +6,7 @@ use rustc_hir::Mutability;
use rustc_index::vec::Idx;
use rustc_middle::mir::visit::{MutVisitor, Visitor};
use rustc_middle::mir::{
Body, Constant, Local, Location, Operand, Place, PlaceRef, ProjectionElem, Rvalue,
BinOp, Body, Constant, Local, Location, Operand, Place, PlaceRef, ProjectionElem, Rvalue,
};
use rustc_middle::ty::{self, TyCtxt};
use std::mem;
@ -66,6 +66,11 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
*rvalue = Rvalue::Use(Operand::Constant(box constant));
}
if let Some(operand) = self.optimizations.unneeded_not_equal.remove(&location) {
debug!("replacing {:?} with {:?}", rvalue, operand);
*rvalue = Rvalue::Use(operand);
}
self.super_rvalue(rvalue, location)
}
}
@ -81,6 +86,23 @@ impl OptimizationFinder<'b, 'tcx> {
fn new(body: &'b Body<'tcx>, tcx: TyCtxt<'tcx>) -> OptimizationFinder<'b, 'tcx> {
OptimizationFinder { body, tcx, optimizations: OptimizationList::default() }
}
fn find_operand_in_ne_false_pattern(
&self,
l: &Operand<'tcx>,
r: &'a Operand<'tcx>,
) -> Option<&'a Operand<'tcx>> {
let const_ = l.constant()?;
if const_.literal.ty == self.tcx.types.bool
&& const_.literal.val.try_to_bool() == Some(false)
{
if r.place().is_some() {
return Some(r);
}
}
return None;
}
}
impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
@ -106,6 +128,18 @@ impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
}
}
// find Ne(_place, false) or Ne(false, _place)
if let Rvalue::BinaryOp(BinOp::Ne, l, r) = rvalue {
// (false, _place)
if let Some(o) = self.find_operand_in_ne_false_pattern(l, r) {
self.optimizations.unneeded_not_equal.insert(location, o.clone());
}
// (_place, false)
else if let Some(o) = self.find_operand_in_ne_false_pattern(r, l) {
self.optimizations.unneeded_not_equal.insert(location, o.clone());
}
}
self.super_rvalue(rvalue, location)
}
}
@ -114,4 +148,5 @@ impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
struct OptimizationList<'tcx> {
and_stars: FxHashSet<Location>,
arrays_lengths: FxHashMap<Location, Constant<'tcx>>,
unneeded_not_equal: FxHashMap<Location, Operand<'tcx>>,
}

3
compiler/rustc_mir/src/transform/mod.rs
View File

@ -453,8 +453,9 @@ fn run_optimization_passes<'tcx>(
// The main optimizations that we do on MIR.
let optimizations: &[&dyn MirPass<'tcx>] = &[
&instcombine::InstCombine,
&match_branches::MatchBranchSimplification,
// inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
&instcombine::InstCombine,
&const_prop::ConstProp,
&simplify_branches::SimplifyBranches::new("after-const-prop"),
&simplify_comparison_integral::SimplifyComparisonIntegral,

72
src/test/mir-opt/not_equal_false.opt.InstCombine.diff Normal file
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@ -0,0 +1,72 @@
- // MIR for `opt` before InstCombine
+ // MIR for `opt` after InstCombine
fn opt(_1: Option<()>) -> bool {
debug x => _1; // in scope 0 at $DIR/not_equal_false.rs:3:8: 3:9
let mut _0: bool; // return place in scope 0 at $DIR/not_equal_false.rs:3:26: 3:30
let mut _2: bool; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
let mut _3: isize; // in scope 0 at $DIR/not_equal_false.rs:4:17: 4:21
let mut _4: bool; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
let mut _5: isize; // in scope 0 at $DIR/not_equal_false.rs:4:38: 4:45
bb0: {
StorageLive(_2); // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
_3 = discriminant(_1); // scope 0 at $DIR/not_equal_false.rs:4:17: 4:21
_2 = Eq(_3, const 0_isize); // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
goto -> bb7; // scope 0 at $DIR/not_equal_false.rs:4:17: 4:21
}
bb1: {
_0 = const true; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
goto -> bb4; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
}
bb2: {
_0 = const false; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
goto -> bb4; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
}
bb3: {
StorageLive(_4); // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
_5 = discriminant(_1); // scope 0 at $DIR/not_equal_false.rs:4:38: 4:45
_4 = Eq(_5, const 1_isize); // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
goto -> bb10; // scope 0 at $DIR/not_equal_false.rs:4:38: 4:45
}
bb4: {
StorageDead(_4); // scope 0 at $DIR/not_equal_false.rs:4:45: 4:46
StorageDead(_2); // scope 0 at $DIR/not_equal_false.rs:4:45: 4:46
return; // scope 0 at $DIR/not_equal_false.rs:5:2: 5:2
}
bb5: {
_2 = const false; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
goto -> bb7; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
}
bb6: {
_2 = const true; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
goto -> bb7; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
}
bb7: {
switchInt(move _2) -> [false: bb3, otherwise: bb1]; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
}
bb8: {
_4 = const false; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
goto -> bb10; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
}
bb9: {
_4 = const true; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
goto -> bb10; // scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
}
bb10: {
- _0 = Ne(_4, const false); // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
+ _0 = _4; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
goto -> bb4; // scope 0 at $DIR/not_equal_false.rs:4:5: 4:46
}
}

9
src/test/mir-opt/not_equal_false.rs Normal file
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@ -0,0 +1,9 @@
// EMIT_MIR not_equal_false.opt.InstCombine.diff
fn opt(x: Option<()>) -> bool {
matches!(x, None) || matches!(x, Some(_))
}
fn main() {
opt(None);
}