bjoernager/rust
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Auto merge of #73210 - wesleywiser:consts_in_debuginfo, r=oli-obk

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[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.
This commit is contained in:
bors 2020-12-15 08:46:00 +00:00
commit e99a89c7c0
16 changed files with 398 additions and 79 deletions
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21
compiler/rustc_middle/src/mir/mod.rs
View file

@ -1060,6 +1060,23 @@ impl<'tcx> LocalDecl<'tcx> {
}
}
#[derive(Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
pub enum VarDebugInfoContents<'tcx> {
/// NOTE(eddyb) There's an unenforced invariant that this `Place` is
/// based on a `Local`, not a `Static`, and contains no indexing.
Place(Place<'tcx>),
Const(Constant<'tcx>),
}
impl<'tcx> Debug for VarDebugInfoContents<'tcx> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
match self {
VarDebugInfoContents::Const(c) => write!(fmt, "{}", c),
VarDebugInfoContents::Place(p) => write!(fmt, "{:?}", p),
}
}
}
/// Debug information pertaining to a user variable.
#[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
pub struct VarDebugInfo<'tcx> {
@ -1071,9 +1088,7 @@ pub struct VarDebugInfo<'tcx> {
pub source_info: SourceInfo,
/// Where the data for this user variable is to be found.
/// NOTE(eddyb) There's an unenforced invariant that this `Place` is
/// based on a `Local`, not a `Static`, and contains no indexing.
pub place: Place<'tcx>,
pub value: VarDebugInfoContents<'tcx>,
}
///////////////////////////////////////////////////////////////////////////

16
compiler/rustc_middle/src/mir/visit.rs
View file

@ -829,16 +829,20 @@ macro_rules! make_mir_visitor {
let VarDebugInfo {
name: _,
source_info,
place,
value,
} = var_debug_info;
self.visit_source_info(source_info);
let location = START_BLOCK.start_location();
self.visit_place(
place,
PlaceContext::NonUse(NonUseContext::VarDebugInfo),
location,
);
match value {
VarDebugInfoContents::Const(c) => self.visit_constant(c, location),
VarDebugInfoContents::Place(place) =>
self.visit_place(
place,
PlaceContext::NonUse(NonUseContext::VarDebugInfo),
location
),
}
}
fn super_source_scope(&mut self,