Auto merge of #73210 - wesleywiser:consts_in_debuginfo, r=oli-obk
[mir-opt] Allow debuginfo to be generated for a constant or a Place Prior to this commit, debuginfo was always generated by mapping a name to a Place. This has the side-effect that `SimplifyLocals` cannot remove locals that are only used for debuginfo because their other uses have been const-propagated. To allow these locals to be removed, we now allow debuginfo to point to a constant value. The `ConstProp` pass detects when debuginfo points to a local with a known constant value and replaces it with the value. This allows the later `SimplifyLocals` pass to remove the local.
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commit
e99a89c7c0
16 changed files with 398 additions and 79 deletions
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@ -12,7 +12,7 @@ use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
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use rustc_middle::hir::place::PlaceBase as HirPlaceBase;
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use rustc_middle::mir::{
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traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
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PlaceRef,
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PlaceRef, VarDebugInfoContents,
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};
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use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
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use rustc_middle::mir::{Field, ProjectionElem, Promoted, Rvalue, Statement, StatementKind};
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@ -135,19 +135,21 @@ fn do_mir_borrowck<'a, 'tcx>(
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let mut local_names = IndexVec::from_elem(None, &input_body.local_decls);
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for var_debug_info in &input_body.var_debug_info {
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if let Some(local) = var_debug_info.place.as_local() {
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if let Some(prev_name) = local_names[local] {
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if var_debug_info.name != prev_name {
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span_bug!(
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var_debug_info.source_info.span,
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"local {:?} has many names (`{}` vs `{}`)",
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local,
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prev_name,
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var_debug_info.name
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);
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if let VarDebugInfoContents::Place(place) = var_debug_info.value {
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if let Some(local) = place.as_local() {
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if let Some(prev_name) = local_names[local] {
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if var_debug_info.name != prev_name {
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span_bug!(
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var_debug_info.source_info.span,
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"local {:?} has many names (`{}` vs `{}`)",
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local,
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prev_name,
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var_debug_info.name
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);
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}
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}
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local_names[local] = Some(var_debug_info.name);
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}
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local_names[local] = Some(var_debug_info.name);
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}
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}
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102
compiler/rustc_mir/src/transform/const_debuginfo.rs
Normal file
102
compiler/rustc_mir/src/transform/const_debuginfo.rs
Normal file
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@ -0,0 +1,102 @@
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//! Finds locals which are assigned once to a const and unused except for debuginfo and converts
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//! their debuginfo to use the const directly, allowing the local to be removed.
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use rustc_middle::{
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mir::{
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visit::{PlaceContext, Visitor},
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Body, Constant, Local, Location, Operand, Rvalue, StatementKind, VarDebugInfoContents,
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},
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ty::TyCtxt,
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};
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use crate::transform::MirPass;
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use rustc_index::{bit_set::BitSet, vec::IndexVec};
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pub struct ConstDebugInfo;
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impl<'tcx> MirPass<'tcx> for ConstDebugInfo {
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fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
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return;
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}
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trace!("running ConstDebugInfo on {:?}", body.source);
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for (local, constant) in find_optimization_oportunities(body) {
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for debuginfo in &mut body.var_debug_info {
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if let VarDebugInfoContents::Place(p) = debuginfo.value {
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if p.local == local && p.projection.is_empty() {
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trace!(
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"changing debug info for {:?} from place {:?} to constant {:?}",
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debuginfo.name,
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p,
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constant
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);
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debuginfo.value = VarDebugInfoContents::Const(constant);
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}
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}
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}
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}
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}
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}
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struct LocalUseVisitor {
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local_mutating_uses: IndexVec<Local, u8>,
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local_assignment_locations: IndexVec<Local, Option<Location>>,
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}
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fn find_optimization_oportunities<'tcx>(body: &Body<'tcx>) -> Vec<(Local, Constant<'tcx>)> {
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let mut visitor = LocalUseVisitor {
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local_mutating_uses: IndexVec::from_elem(0, &body.local_decls),
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local_assignment_locations: IndexVec::from_elem(None, &body.local_decls),
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};
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visitor.visit_body(body);
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let mut locals_to_debuginfo = BitSet::new_empty(body.local_decls.len());
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for debuginfo in &body.var_debug_info {
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if let VarDebugInfoContents::Place(p) = debuginfo.value {
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if let Some(l) = p.as_local() {
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locals_to_debuginfo.insert(l);
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}
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}
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}
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let mut eligable_locals = Vec::new();
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for (local, mutating_uses) in visitor.local_mutating_uses.drain_enumerated(..) {
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if mutating_uses != 1 || !locals_to_debuginfo.contains(local) {
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continue;
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}
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if let Some(location) = visitor.local_assignment_locations[local] {
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let bb = &body[location.block];
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// The value is assigned as the result of a call, not a constant
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if bb.statements.len() == location.statement_index {
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continue;
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}
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if let StatementKind::Assign(box (p, Rvalue::Use(Operand::Constant(box c)))) =
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&bb.statements[location.statement_index].kind
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{
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if let Some(local) = p.as_local() {
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eligable_locals.push((local, *c));
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}
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}
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}
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}
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eligable_locals
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}
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impl<'tcx> Visitor<'tcx> for LocalUseVisitor {
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fn visit_local(&mut self, local: &Local, context: PlaceContext, location: Location) {
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if context.is_mutating_use() {
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self.local_mutating_uses[*local] = self.local_mutating_uses[*local].saturating_add(1);
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if context.is_place_assignment() {
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self.local_assignment_locations[*local] = Some(location);
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}
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}
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}
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}
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@ -21,6 +21,7 @@ pub mod check_consts;
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pub mod check_packed_ref;
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pub mod check_unsafety;
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pub mod cleanup_post_borrowck;
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pub mod const_debuginfo;
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pub mod const_prop;
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pub mod coverage;
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pub mod deaggregator;
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@ -408,6 +409,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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&remove_noop_landing_pads::RemoveNoopLandingPads,
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&simplify::SimplifyCfg::new("final"),
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&nrvo::RenameReturnPlace,
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&const_debuginfo::ConstDebugInfo,
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&simplify::SimplifyLocals,
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&multiple_return_terminators::MultipleReturnTerminators,
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];
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@ -246,14 +246,19 @@ fn get_arm_identity_info<'a, 'tcx>(
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tmp_assigned_vars.insert(*r);
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}
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let dbg_info_to_adjust: Vec<_> =
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debug_info
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.iter()
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.enumerate()
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.filter_map(|(i, var_info)| {
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if tmp_assigned_vars.contains(var_info.place.local) { Some(i) } else { None }
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})
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.collect();
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let dbg_info_to_adjust: Vec<_> = debug_info
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.iter()
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.enumerate()
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.filter_map(|(i, var_info)| {
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if let VarDebugInfoContents::Place(p) = var_info.value {
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if tmp_assigned_vars.contains(p.local) {
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return Some(i);
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}
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}
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None
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})
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.collect();
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Some(ArmIdentityInfo {
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local_temp_0: local_tmp_s0,
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@ -340,9 +345,11 @@ fn optimization_applies<'tcx>(
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// Check that debug info only points to full Locals and not projections.
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for dbg_idx in &opt_info.dbg_info_to_adjust {
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let dbg_info = &var_debug_info[*dbg_idx];
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if !dbg_info.place.projection.is_empty() {
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trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, dbg_info.place);
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return false;
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if let VarDebugInfoContents::Place(p) = dbg_info.value {
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if !p.projection.is_empty() {
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trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, p);
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return false;
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}
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}
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}
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@ -423,9 +430,15 @@ impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
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// Fix the debug info to point to the right local
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for dbg_index in opt_info.dbg_info_to_adjust {
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let dbg_info = &mut debug_info[dbg_index];
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assert!(dbg_info.place.projection.is_empty());
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dbg_info.place.local = opt_info.local_0;
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dbg_info.place.projection = opt_info.dbg_projection;
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assert!(
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matches!(dbg_info.value, VarDebugInfoContents::Place(_)),
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"value was not a Place"
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);
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if let VarDebugInfoContents::Place(p) = &mut dbg_info.value {
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assert!(p.projection.is_empty());
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p.local = opt_info.local_0;
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p.projection = opt_info.dbg_projection;
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}
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}
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trace!("block is now {:?}", bb.statements);
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@ -220,7 +220,7 @@ fn write_graph_label<'tcx, W: Write>(
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w,
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r#"debug {} => {};<br align="left"/>"#,
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var_debug_info.name,
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escape(&var_debug_info.place)
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escape(&var_debug_info.value),
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)?;
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}
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@ -495,7 +495,7 @@ fn write_scope_tree(
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let indented_debug_info = format!(
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"{0:1$}debug {2} => {3:?};",
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INDENT, indent, var_debug_info.name, var_debug_info.place,
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INDENT, indent, var_debug_info.name, var_debug_info.value,
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);
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writeln!(
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