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JulianKnodtJulianKnodt
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Optimize MIR for comparison of references
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4 files changed

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4 files changed

+155
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‎compiler/rustc_mir_transform/src/lib.rs

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Original file line numberDiff line numberDiff line change
@@ -86,6 +86,7 @@ mod multiple_return_terminators;
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mod normalize_array_len;
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mod nrvo;
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mod prettify;
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mod ref_cmp_simplify;
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mod ref_prop;
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mod remove_noop_landing_pads;
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mod remove_storage_markers;
@@ -561,6 +562,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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&instsimplify::InstSimplify,
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&simplify::SimplifyLocals::BeforeConstProp,
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&copy_prop::CopyProp,
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&ref_cmp_simplify::RefCmpSimplify,
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&ref_prop::ReferencePropagation,
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// Perform `SeparateConstSwitch` after SSA-based analyses, as cloning blocks may
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// destroy the SSA property. It should still happen before const-propagation, so the

‎compiler/rustc_mir_transform/src/ref_cmp_simplify.rs

Lines changed: 93 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,93 @@
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use crate::MirPass;
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use rustc_middle::mir::patch::MirPatch;
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use rustc_middle::mir::*;
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use rustc_middle::ty::TyCtxt;
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pub struct RefCmpSimplify;
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impl<'tcx> MirPass<'tcx> for RefCmpSimplify {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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self.simplify_ref_cmp(tcx, body)
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}
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}
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#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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enum MatchState {
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Empty,
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Deref { src_statement_idx: usize, dst: Local, src: Local },
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CopiedFrom { src_statement_idx: usize, dst: Local, real_src: Local },
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Completed { src_statement_idx: usize, dst: Local, real_src: Local },
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}
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impl RefCmpSimplify {
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fn simplify_ref_cmp<'tcx>(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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debug!("body: {:#?}", body);
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let n_bbs = body.basic_blocks.len() as u32;
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for bb in 0..n_bbs {
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let bb = BasicBlock::from_u32(bb);
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let mut max = Local::MAX;
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'repeat: loop {
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let mut state = MatchState::Empty;
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let bb_data = &body.basic_blocks[bb];
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for (i, stmt) in bb_data.statements.iter().enumerate().rev() {
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state = match (state, &stmt.kind) {
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(
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MatchState::Empty,
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StatementKind::Assign(box (lhs, Rvalue::Use(Operand::Copy(rhs)))),
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) if rhs.has_deref() && lhs.ty(body, tcx).ty.is_primitive() => {
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let Some(dst) = lhs.as_local() else {
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continue
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};
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let Some(src) = rhs.local_or_deref_local() else {
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continue;
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};
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if max <= dst {
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continue;
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}
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max = dst;
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MatchState::Deref { dst, src, src_statement_idx: i }
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}
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(
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MatchState::Deref { src, dst, src_statement_idx },
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StatementKind::Assign(box (lhs, Rvalue::CopyForDeref(rhs))),
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) if lhs.as_local() == Some(src) && rhs.has_deref() => {
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let Some(real_src) = rhs.local_or_deref_local() else{
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continue;
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};
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MatchState::CopiedFrom { src_statement_idx, dst, real_src }
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}
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(
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MatchState::CopiedFrom { src_statement_idx, dst, real_src },
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StatementKind::Assign(box (
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lhs,
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Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Shallow, rhs),
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)),
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) if lhs.as_local() == Some(real_src) => {
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let Some(real_src) = rhs.as_local() else {
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continue;
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};
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MatchState::Completed { dst, real_src, src_statement_idx }
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}
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_ => continue,
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};
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if let MatchState::Completed { dst, real_src, src_statement_idx } = state {
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let mut patch = MirPatch::new(&body);
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let src = Place::from(real_src);
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let src = src.project_deeper(&[PlaceElem::Deref], tcx);
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let dst = Place::from(dst);
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let new_stmt =
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StatementKind::Assign(Box::new((dst, Rvalue::Use(Operand::Copy(src)))));
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patch.add_statement(
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Location { block: bb, statement_index: src_statement_idx + 1 },
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new_stmt,
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);
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patch.apply(body);
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continue 'repeat;
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}
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}
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break;
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}
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}
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}
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}

‎tests/mir-opt/ref_int_cmp.opt1.RefCmpSimplify.diff

Lines changed: 50 additions & 0 deletions
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@@ -0,0 +1,50 @@
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- // MIR for `opt1` before RefCmpSimplify
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+ // MIR for `opt1` after RefCmpSimplify
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fn opt1(_1: &u8, _2: &u8) -> bool {
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debug x => _1; // in scope 0 at $DIR/ref_int_cmp.rs:+0:13: +0:14
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debug y => _2; // in scope 0 at $DIR/ref_int_cmp.rs:+0:21: +0:22
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let mut _0: bool; // return place in scope 0 at $DIR/ref_int_cmp.rs:+0:32: +0:36
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let mut _3: &&u8; // in scope 0 at $DIR/ref_int_cmp.rs:+1:3: +1:4
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let mut _4: &&u8; // in scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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let _5: &u8; // in scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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let mut _8: &u8; // in scope 0 at $SRC_DIR/core/src/cmp.rs:LL:COL
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let mut _9: &u8; // in scope 0 at $SRC_DIR/core/src/cmp.rs:LL:COL
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scope 1 (inlined cmp::impls::<impl PartialOrd for &u8>::lt) { // at $DIR/ref_int_cmp.rs:5:3: 5:8
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debug self => _3; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
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debug other => _4; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
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let mut _6: &u8; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
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let mut _7: &u8; // in scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
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scope 2 (inlined cmp::impls::<impl PartialOrd for u8>::lt) { // at $SRC_DIR/core/src/cmp.rs:LL:COL
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debug self => _6; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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debug other => _7; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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let mut _10: u8; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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let mut _11: u8; // in scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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}
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}
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bb0: {
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StorageLive(_3); // scope 0 at $DIR/ref_int_cmp.rs:+1:3: +1:4
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_3 = &_1; // scope 0 at $DIR/ref_int_cmp.rs:+1:3: +1:4
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StorageLive(_4); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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StorageLive(_5); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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_5 = _2; // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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_4 = &_5; // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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_6 = deref_copy (*_3); // scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
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_7 = deref_copy (*_4); // scope 1 at $SRC_DIR/core/src/cmp.rs:LL:COL
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StorageLive(_10); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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_10 = (*_6); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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+ _10 = (*_1); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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StorageLive(_11); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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_11 = (*_7); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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+ _11 = (*_5); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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_0 = Lt(move _10, move _11); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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StorageDead(_11); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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StorageDead(_10); // scope 2 at $SRC_DIR/core/src/cmp.rs:LL:COL
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StorageDead(_4); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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StorageDead(_3); // scope 0 at $DIR/ref_int_cmp.rs:+1:7: +1:8
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StorageDead(_5); // scope 0 at $DIR/ref_int_cmp.rs:+2:1: +2:2
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return; // scope 0 at $DIR/ref_int_cmp.rs:+2:2: +2:2
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}
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}
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‎tests/mir-opt/ref_int_cmp.rs

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@@ -0,0 +1,10 @@
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// compile-flags: -O -Zmir-opt-level=3
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// EMIT_MIR ref_int_cmp.opt1.RefCmpSimplify.diff
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pub fn opt1(x: &u8, y: &u8) -> bool {
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x < y
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}
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fn main() {
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opt1(&1, &2);
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}

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