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Optimize MIR for comparison of references #112542

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Optimize MIR for comparison of references #112542

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2 changes: 2 additions & 0 deletions compiler/rustc_mir_transform/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,7 @@ mod multiple_return_terminators;
mod normalize_array_len;
mod nrvo;
mod prettify;
mod ref_cmp_simplify;
mod ref_prop;
mod remove_noop_landing_pads;
mod remove_storage_markers;
Expand Down Expand Up @@ -561,6 +562,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
&instsimplify::InstSimplify,
&simplify::SimplifyLocals::BeforeConstProp,
&copy_prop::CopyProp,
&ref_cmp_simplify::RefCmpSimplify,
&ref_prop::ReferencePropagation,
// Perform `SeparateConstSwitch` after SSA-based analyses, as cloning blocks may
// destroy the SSA property. It should still happen before const-propagation, so the
Expand Down
93 changes: 93 additions & 0 deletions compiler/rustc_mir_transform/src/ref_cmp_simplify.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,93 @@
use crate::MirPass;
use rustc_middle::mir::patch::MirPatch;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;

pub struct RefCmpSimplify;

impl<'tcx> MirPass<'tcx> for RefCmpSimplify {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
self.simplify_ref_cmp(tcx, body)
}
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum MatchState {
Empty,
Deref { src_statement_idx: usize, dst: Local, src: Local },
CopiedFrom { src_statement_idx: usize, dst: Local, real_src: Local },
Completed { src_statement_idx: usize, dst: Local, real_src: Local },
}

impl RefCmpSimplify {
fn simplify_ref_cmp<'tcx>(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!("body: {:#?}", body);

let n_bbs = body.basic_blocks.len() as u32;
for bb in 0..n_bbs {
let bb = BasicBlock::from_u32(bb);
let mut max = Local::MAX;
'repeat: loop {
let mut state = MatchState::Empty;
let bb_data = &body.basic_blocks[bb];
for (i, stmt) in bb_data.statements.iter().enumerate().rev() {
state = match (state, &stmt.kind) {
(
MatchState::Empty,
StatementKind::Assign(box (lhs, Rvalue::Use(Operand::Copy(rhs)))),
) if rhs.has_deref() && lhs.ty(body, tcx).ty.is_primitive() => {
let Some(dst) = lhs.as_local() else {
continue
};
let Some(src) = rhs.local_or_deref_local() else {
continue;
};
if max <= dst {
continue;
}
max = dst;
MatchState::Deref { dst, src, src_statement_idx: i }
}
(
MatchState::Deref { src, dst, src_statement_idx },
StatementKind::Assign(box (lhs, Rvalue::CopyForDeref(rhs))),
) if lhs.as_local() == Some(src) && rhs.has_deref() => {
let Some(real_src) = rhs.local_or_deref_local() else{
continue;
};
MatchState::CopiedFrom { src_statement_idx, dst, real_src }
}
(
MatchState::CopiedFrom { src_statement_idx, dst, real_src },
StatementKind::Assign(box (
lhs,
Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, rhs),
)),
) if lhs.as_local() == Some(real_src) => {
let Some(real_src) = rhs.as_local() else {
continue;
};
MatchState::Completed { dst, real_src, src_statement_idx }
}
_ => continue,
};
if let MatchState::Completed { dst, real_src, src_statement_idx } = state {
let mut patch = MirPatch::new(&body);
let src = Place::from(real_src);
let src = src.project_deeper(&[PlaceElem::Deref], tcx);
let dst = Place::from(dst);
let new_stmt =
StatementKind::Assign(Box::new((dst, Rvalue::Use(Operand::Copy(src)))));
patch.add_statement(
Location { block: bb, statement_index: src_statement_idx + 1 },
new_stmt,
);
patch.apply(body);
continue 'repeat;
}
}
break;
}
}
}
}
50 changes: 50 additions & 0 deletions tests/mir-opt/ref_int_cmp.opt1.RefCmpSimplify.diff
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@@ -0,0 +1,50 @@
- // MIR for `opt1` before RefCmpSimplify
+ // MIR for `opt1` after RefCmpSimplify

fn opt1(_1: &u8, _2: &u8) -> bool {
debug x => _1; // in scope 0 at $DIR/ref_int_cmp.rs:+0:13: +0:14
debug y => _2; // in scope 0 at $DIR/ref_int_cmp.rs:+0:21: +0:22
let mut _0: bool; // return place in scope 0 at $DIR/ref_int_cmp.rs:+0:32: +0:36
let mut _3: &&u8; // in scope 0 at $DIR/ref_int_cmp.rs:+1:3: +1:4
let mut _4: &&u8; // in scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
let _5: &u8; // in scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
let mut _8: &u8; // in scope 0 at $SRC_DIR/core/src/cmp.rs:LL:COL
let mut _9: &u8; // in scope 0 at $SRC_DIR/core/src/cmp.rs:LL:COL
scope 1 (inlined cmp::impls::<impl PartialOrd for &u8>::lt) { // at $DIR/ref_int_cmp.rs:5:3: 5:8
debug self => _3; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
debug other => _4; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
let mut _6: &u8; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
let mut _7: &u8; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
scope 2 (inlined cmp::impls::<impl PartialOrd for u8>::lt) { // at $SRC_DIR/core/src/cmp.rs:LL:COL
debug self => _6; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
debug other => _7; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
let mut _10: u8; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
let mut _11: u8; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
}
}

bb0: {
StorageLive(_3); // scope 0 at $DIR/ref_int_cmp.rs:+1:3: +1:4
_3 = &_1; // scope 0 at $DIR/ref_int_cmp.rs:+1:3: +1:4
StorageLive(_4); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
StorageLive(_5); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
_5 = _2; // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
_4 = &_5; // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
_6 = deref_copy (*_3); // scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
_7 = deref_copy (*_4); // scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
StorageLive(_10); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
_10 = (*_6); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
+ _10 = (*_1); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
StorageLive(_11); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
_11 = (*_7); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
+ _11 = (*_5); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
_0 = Lt(move _10, move _11); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
StorageDead(_11); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
StorageDead(_10); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
StorageDead(_4); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
StorageDead(_3); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
StorageDead(_5); // scope 0 at $DIR/ref_int_cmp.rs:+2:1: +2:2
return; // scope 0 at $DIR/ref_int_cmp.rs:+2:2: +2:2
}
}

10 changes: 10 additions & 0 deletions tests/mir-opt/ref_int_cmp.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
// compile-flags: -O -Zmir-opt-level=3

// EMIT_MIR ref_int_cmp.opt1.RefCmpSimplify.diff
pub fn opt1(x: &u8, y: &u8) -> bool {
x < y
}

fn main() {
opt1(&1, &2);
}