rustc_mir: do not remove dead user variables if debuginfo needs them.

Author: eddyb

src/librustc_mir/transform/simplify.rs

@@ -42,6 +42,7 @@ use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc::ty::TyCtxt;
 use rustc::mir::*;
 use rustc::mir::visit::{MutVisitor, Visitor, PlaceContext};
+use rustc::session::config::FullDebugInfo;
 use std::borrow::Cow;
 use transform::{MirPass, MirSource};
 
@@ -281,16 +282,24 @@ pub struct SimplifyLocals;
 
 impl MirPass for SimplifyLocals {
  fn run_pass<'a, 'tcx>(&self,
- _: TyCtxt<'a, 'tcx, 'tcx>,
+ tcx: TyCtxt<'a, 'tcx, 'tcx>,
  _: MirSource,
  mir: &mut Mir<'tcx>) {
  let mut marker = DeclMarker { locals: BitVector::new(mir.local_decls.len()) };
  marker.visit_mir(mir);
  // Return pointer and arguments are always live
- marker.locals.insert(0);
- for idx in mir.args_iter() {
- marker.locals.insert(idx.index());
+ marker.locals.insert(RETURN_PLACE.index());
+ for arg in mir.args_iter() {
+ marker.locals.insert(arg.index());
  }
+
+ // We may need to keep dead user variables live for debuginfo.
+ if tcx.sess.opts.debuginfo == FullDebugInfo {
+ for local in mir.vars_iter() {
+ marker.locals.insert(local.index());
+ }
+ }
+
  let map = make_local_map(&mut mir.local_decls, marker.locals);
  // Update references to all vars and tmps now
  LocalUpdater { map: map }.visit_mir(mir);