103 lines
3.4 KiB
Rust
103 lines
3.4 KiB
Rust
//! Finds locals which are assigned once to a const and unused except for debuginfo and converts
|
|
//! their debuginfo to use the const directly, allowing the local to be removed.
|
|
|
|
use rustc_middle::{
|
|
mir::{
|
|
visit::{PlaceContext, Visitor},
|
|
Body, Constant, Local, Location, Operand, Rvalue, StatementKind, VarDebugInfoContents,
|
|
},
|
|
ty::TyCtxt,
|
|
};
|
|
|
|
use crate::MirPass;
|
|
use rustc_index::{bit_set::BitSet, vec::IndexVec};
|
|
|
|
pub struct ConstDebugInfo;
|
|
|
|
impl<'tcx> MirPass<'tcx> for ConstDebugInfo {
|
|
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
|
|
if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
|
|
return;
|
|
}
|
|
|
|
trace!("running ConstDebugInfo on {:?}", body.source);
|
|
|
|
for (local, constant) in find_optimization_oportunities(body) {
|
|
for debuginfo in &mut body.var_debug_info {
|
|
if let VarDebugInfoContents::Place(p) = debuginfo.value {
|
|
if p.local == local && p.projection.is_empty() {
|
|
trace!(
|
|
"changing debug info for {:?} from place {:?} to constant {:?}",
|
|
debuginfo.name,
|
|
p,
|
|
constant
|
|
);
|
|
debuginfo.value = VarDebugInfoContents::Const(constant);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
struct LocalUseVisitor {
|
|
local_mutating_uses: IndexVec<Local, u8>,
|
|
local_assignment_locations: IndexVec<Local, Option<Location>>,
|
|
}
|
|
|
|
fn find_optimization_oportunities<'tcx>(body: &Body<'tcx>) -> Vec<(Local, Constant<'tcx>)> {
|
|
let mut visitor = LocalUseVisitor {
|
|
local_mutating_uses: IndexVec::from_elem(0, &body.local_decls),
|
|
local_assignment_locations: IndexVec::from_elem(None, &body.local_decls),
|
|
};
|
|
|
|
visitor.visit_body(body);
|
|
|
|
let mut locals_to_debuginfo = BitSet::new_empty(body.local_decls.len());
|
|
for debuginfo in &body.var_debug_info {
|
|
if let VarDebugInfoContents::Place(p) = debuginfo.value {
|
|
if let Some(l) = p.as_local() {
|
|
locals_to_debuginfo.insert(l);
|
|
}
|
|
}
|
|
}
|
|
|
|
let mut eligable_locals = Vec::new();
|
|
for (local, mutating_uses) in visitor.local_mutating_uses.drain_enumerated(..) {
|
|
if mutating_uses != 1 || !locals_to_debuginfo.contains(local) {
|
|
continue;
|
|
}
|
|
|
|
if let Some(location) = visitor.local_assignment_locations[local] {
|
|
let bb = &body[location.block];
|
|
|
|
// The value is assigned as the result of a call, not a constant
|
|
if bb.statements.len() == location.statement_index {
|
|
continue;
|
|
}
|
|
|
|
if let StatementKind::Assign(box (p, Rvalue::Use(Operand::Constant(box c)))) =
|
|
&bb.statements[location.statement_index].kind
|
|
{
|
|
if let Some(local) = p.as_local() {
|
|
eligable_locals.push((local, *c));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
eligable_locals
|
|
}
|
|
|
|
impl<'tcx> Visitor<'tcx> for LocalUseVisitor {
|
|
fn visit_local(&mut self, local: &Local, context: PlaceContext, location: Location) {
|
|
if context.is_mutating_use() {
|
|
self.local_mutating_uses[*local] = self.local_mutating_uses[*local].saturating_add(1);
|
|
|
|
if context.is_place_assignment() {
|
|
self.local_assignment_locations[*local] = Some(location);
|
|
}
|
|
}
|
|
}
|
|
}
|