bjoernager/rust
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[mir-opt] Allow debuginfo to be generated for a constant or a Place

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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.
This commit is contained in:
Wesley Wiser 2020-05-30 15:02:32 -04:00
parent b776d1c3e3
commit 01aec8d185
23 changed files with 406 additions and 127 deletions
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41
compiler/rustc_mir/src/transform/simplify_try.rs
View file

@ -246,14 +246,19 @@ fn get_arm_identity_info<'a, 'tcx>(
tmp_assigned_vars.insert(*r);
}
let dbg_info_to_adjust: Vec<_> =
debug_info
.iter()
.enumerate()
.filter_map(|(i, var_info)| {
if tmp_assigned_vars.contains(var_info.place.local) { Some(i) } else { None }
})
.collect();
let dbg_info_to_adjust: Vec<_> = debug_info
.iter()
.enumerate()
.filter_map(|(i, var_info)| {
if let VarDebugInfoContents::Place(p) = var_info.value {
if tmp_assigned_vars.contains(p.local) {
return Some(i);
}
}
None
})
.collect();
Some(ArmIdentityInfo {
local_temp_0: local_tmp_s0,
@ -340,9 +345,11 @@ fn optimization_applies<'tcx>(
// Check that debug info only points to full Locals and not projections.
for dbg_idx in &opt_info.dbg_info_to_adjust {
let dbg_info = &var_debug_info[*dbg_idx];
if !dbg_info.place.projection.is_empty() {
trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, dbg_info.place);
return false;
if let VarDebugInfoContents::Place(p) = dbg_info.value {
if !p.projection.is_empty() {
trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, p);
return false;
}
}
}
@ -423,9 +430,15 @@ impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity {
// Fix the debug info to point to the right local
for dbg_index in opt_info.dbg_info_to_adjust {
let dbg_info = &mut debug_info[dbg_index];
assert!(dbg_info.place.projection.is_empty());
dbg_info.place.local = opt_info.local_0;
dbg_info.place.projection = opt_info.dbg_projection;
assert!(
matches!(dbg_info.value, VarDebugInfoContents::Place(_)),
"value was not a Place"
);
if let VarDebugInfoContents::Place(p) = &mut dbg_info.value {
assert!(p.projection.is_empty());
p.local = opt_info.local_0;
p.projection = opt_info.dbg_projection;
}
}
trace!("block is now {:?}", bb.statements);