bjoernager/rust
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Turn copy into moves during DSE.

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This commit is contained in:
Camille GILLOT 2023-07-16 13:11:10 +00:00
parent b657dc555b
commit f5feb3e3ca
32 changed files with 129 additions and 31 deletions
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40
compiler/rustc_mir_transform/src/dead_store_elimination.rs
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@ -13,9 +13,12 @@
//!
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use rustc_mir_dataflow::impls::{borrowed_locals, MaybeTransitiveLiveLocals};
use rustc_mir_dataflow::impls::{
borrowed_locals, LivenessTransferFunction, MaybeTransitiveLiveLocals,
};
use rustc_mir_dataflow::Analysis;
/// Performs the optimization on the body
@ -28,8 +31,33 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, borrowed: &BitS
.iterate_to_fixpoint()
.into_results_cursor(body);
// For blocks with a call terminator, if an argument copy can be turned into a move,
// record it as (block, argument index).
let mut call_operands_to_move = Vec::new();
let mut patch = Vec::new();
for (bb, bb_data) in traversal::preorder(body) {
if let TerminatorKind::Call { ref args, .. } = bb_data.terminator().kind {
let loc = Location { block: bb, statement_index: bb_data.statements.len() };
// Position ourselves between the evaluation of `args` and the write to `destination`.
live.seek_to_block_end(bb);
let mut state = live.get().clone();
for (index, arg) in args.iter().enumerate().rev() {
if let Operand::Copy(place) = *arg
&& !place.is_indirect()
&& !borrowed.contains(place.local)
&& !state.contains(place.local)
{
call_operands_to_move.push((bb, index));
}
// Account that `arg` is read from, so we don't promote another argument to a move.
LivenessTransferFunction(&mut state).visit_operand(arg, loc);
}
}
for (statement_index, statement) in bb_data.statements.iter().enumerate().rev() {
let loc = Location { block: bb, statement_index };
if let StatementKind::Assign(assign) = &statement.kind {
@ -64,7 +92,7 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, borrowed: &BitS
}
}
if patch.is_empty() {
if patch.is_empty() && call_operands_to_move.is_empty() {
return;
}
@ -72,6 +100,14 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, borrowed: &BitS
for Location { block, statement_index } in patch {
bbs[block].statements[statement_index].make_nop();
}
for (block, argument_index) in call_operands_to_move {
let TerminatorKind::Call { ref mut args, .. } = bbs[block].terminator_mut().kind else {
bug!()
};
let arg = &mut args[argument_index];
let Operand::Copy(place) = *arg else { bug!() };
*arg = Operand::Move(place);
}
crate::simplify::simplify_locals(body, tcx)
}