Implement references VarDebugInfo.

Author: cjgillot

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -41,6 +41,9 @@ pub struct PerLocalVarDebugInfo<'tcx, D> {
 
     /// `.place.projection` from `mir::VarDebugInfo`.
     pub projection: &'tcx ty::List<mir::PlaceElem<'tcx>>,
+
+    /// `references` from `mir::VarDebugInfo`.
+    pub references: u8,
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -293,6 +296,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     dbg_var,
                     fragment: None,
                     projection: ty::List::empty(),
+                    references: 0,
                 })
             }
         } else {
@@ -366,14 +370,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         &self,
         bx: &mut Bx,
         local: mir::Local,
-        base: PlaceRef<'tcx, Bx::Value>,
+        mut base: PlaceRef<'tcx, Bx::Value>,
         var: PerLocalVarDebugInfo<'tcx, Bx::DIVariable>,
     ) {
         let Some(dbg_var) = var.dbg_var else { return };
         let Some(dbg_loc) = self.dbg_loc(var.source_info) else { return };
 
-        let DebugInfoOffset { direct_offset, indirect_offsets, result: _ } =
+        let DebugInfoOffset { mut direct_offset, indirect_offsets, result: _ } =
             calculate_debuginfo_offset(bx, local, &var, base.layout);
+        let mut indirect_offsets = &indirect_offsets[..];
 
         // When targeting MSVC, create extra allocas for arguments instead of pointing multiple
         // dbg_var_addr() calls into the same alloca with offsets. MSVC uses CodeView records
@@ -387,28 +392,44 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             // LLVM can handle simple things but anything more complex than just a direct
             // offset or one indirect offset of 0 is too complex for it to generate CV records
             // correctly.
-            && (direct_offset != Size::ZERO || !matches!(&indirect_offsets[..], [Size::ZERO] | []));
-
-        if should_create_individual_allocas {
-            let DebugInfoOffset { direct_offset: _, indirect_offsets: _, result: place } =
-                calculate_debuginfo_offset(bx, local, &var, base);
+            && (direct_offset != Size::ZERO || !matches!(indirect_offsets, [Size::ZERO] | []));
 
+        let create_alloca = |bx: &mut Bx, place: PlaceRef<'tcx, Bx::Value>, refcount| {
             // Create a variable which will be a pointer to the actual value
             let ptr_ty = bx
                 .tcx()
                 .mk_ptr(ty::TypeAndMut { mutbl: mir::Mutability::Mut, ty: place.layout.ty });
             let ptr_layout = bx.layout_of(ptr_ty);
             let alloca = PlaceRef::alloca(bx, ptr_layout);
-            bx.set_var_name(alloca.llval, &(var.name.to_string() + ".dbg.spill"));
+            bx.set_var_name(alloca.llval, &format!("{}.ref{}.dbg.spill", var.name, refcount));
 
             // Write the pointer to the variable
             bx.store(place.llval, alloca.llval, alloca.align);
 
             // Point the debug info to `*alloca` for the current variable
-            bx.dbg_var_addr(dbg_var, dbg_loc, alloca.llval, Size::ZERO, &[Size::ZERO], None);
-        } else {
-            bx.dbg_var_addr(dbg_var, dbg_loc, base.llval, direct_offset, &indirect_offsets, None);
+            alloca
+        };
+
+        if var.references > 0 {
+            base = calculate_debuginfo_offset(bx, local, &var, base).result;
+
+            // Point the debug info to `&...&base == alloca` for the current variable
+            for refcount in 0..var.references {
+                base = create_alloca(bx, base, refcount);
+            }
+
+            direct_offset = Size::ZERO;
+            indirect_offsets = &[];
+        } else if should_create_individual_allocas {
+            let place = calculate_debuginfo_offset(bx, local, &var, base).result;
+
+            // Point the debug info to `*alloca` for the current variable
+            base = create_alloca(bx, place, 0);
+            direct_offset = Size::ZERO;
+            indirect_offsets = &[Size::ZERO];
         }
+
+        bx.dbg_var_addr(dbg_var, dbg_loc, base.llval, direct_offset, indirect_offsets, None);
     }
 
     pub fn debug_introduce_locals(&self, bx: &mut Bx) {
@@ -441,7 +462,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             };
 
             let dbg_var = dbg_scope_and_span.map(|(dbg_scope, _, span)| {
-                let (var_ty, var_kind) = match var.value {
+                let (mut var_ty, var_kind) = match var.value {
                     mir::VarDebugInfoContents::Place(place) => {
                         let var_ty = self.monomorphized_place_ty(place.as_ref());
                         let var_kind = if let Some(arg_index) = var.argument_index
@@ -478,6 +499,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     }
                 };
 
+                for _ in 0..var.references {
+                    var_ty =
+                        bx.tcx().mk_ptr(ty::TypeAndMut { mutbl: mir::Mutability::Mut, ty: var_ty });
+                }
+
                 self.cx.create_dbg_var(var.name, var_ty, dbg_scope, var_kind, span)
             });
 
@@ -489,6 +515,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         dbg_var,
                         fragment: None,
                         projection: place.projection,
+                        references: var.references,
                     });
                 }
                 mir::VarDebugInfoContents::Const(c) => {
@@ -542,6 +569,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                 Some(fragment_start..fragment_start + fragment_layout.size)
                             },
                             projection: place.projection,
+                            references: var.references,
                         });
                     }
                 }

compiler/rustc_const_eval/src/transform/validate.rs

@@ -448,7 +448,15 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
         };
         match debuginfo.value {
             VarDebugInfoContents::Const(_) => {}
-            VarDebugInfoContents::Place(place) => check_place(place),
+            VarDebugInfoContents::Place(place) => {
+                check_place(place);
+                if debuginfo.references != 0 && place.projection.last() == Some(&PlaceElem::Deref) {
+                    self.fail(
+                        START_BLOCK.start_location(),
+                        format!("debuginfo {:?}, has both ref and deref", debuginfo),
+                    );
+                }
+            }
             VarDebugInfoContents::Composite { ty, ref fragments } => {
                 for f in fragments {
                     check_place(f.contents);

compiler/rustc_middle/src/mir/mod.rs

@@ -1111,6 +1111,10 @@ pub struct VarDebugInfo<'tcx> {
     /// originated from (starting from 1). Note, if MIR inlining is enabled, then this is the
     /// argument number in the original function before it was inlined.
     pub argument_index: Option<u16>,
+
+    /// The data represents `name` dereferenced `references` times,
+    /// and not the direct value.
+    pub references: u8,
 }
 
 ///////////////////////////////////////////////////////////////////////////
@@ -1639,18 +1643,7 @@ impl<'tcx> Place<'tcx> {
             return self;
         }
 
-        let mut v: Vec<PlaceElem<'tcx>>;
-
-        let new_projections = if self.projection.is_empty() {
-            more_projections
-        } else {
-            v = Vec::with_capacity(self.projection.len() + more_projections.len());
-            v.extend(self.projection);
-            v.extend(more_projections);
-            &v
-        };
-
-        Place { local: self.local, projection: tcx.mk_place_elems(new_projections) }
+        self.as_ref().project_deeper(more_projections, tcx)
     }
 }
 
@@ -1721,6 +1714,27 @@ impl<'tcx> PlaceRef<'tcx> {
             (base, *proj)
         })
     }
+
+    /// Generates a new place by appending `more_projections` to the existing ones
+    /// and interning the result.
+    pub fn project_deeper(
+        self,
+        more_projections: &[PlaceElem<'tcx>],
+        tcx: TyCtxt<'tcx>,
+    ) -> Place<'tcx> {
+        let mut v: Vec<PlaceElem<'tcx>>;
+
+        let new_projections = if self.projection.is_empty() {
+            more_projections
+        } else {
+            v = Vec::with_capacity(self.projection.len() + more_projections.len());
+            v.extend(self.projection);
+            v.extend(more_projections);
+            &v
+        };
+
+        Place { local: self.local, projection: tcx.mk_place_elems(new_projections) }
+    }
 }
 
 impl Debug for Place<'_> {

compiler/rustc_middle/src/mir/pretty.rs

@@ -551,8 +551,13 @@ fn write_scope_tree(
         }
 
         let indented_debug_info = format!(
-            "{0:1$}debug {2} => {3:?};",
-            INDENT, indent, var_debug_info.name, var_debug_info.value,
+            "{0:1$}debug {2} => {3:&<4$}{5:?};",
+            INDENT,
+            indent,
+            var_debug_info.name,
+            "",
+            var_debug_info.references as usize,
+            var_debug_info.value,
         );
 
         writeln!(

compiler/rustc_middle/src/mir/visit.rs

@@ -842,6 +842,7 @@ macro_rules! make_mir_visitor {
                     source_info,
                     value,
                     argument_index: _,
+                    references: _,
                 } = var_debug_info;
 
                 self.visit_source_info(source_info);

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -204,6 +204,7 @@ CloneLiftImpls! {
     (),
     bool,
     usize,
+    u8,
     u16,
     u32,
     u64,

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -2241,6 +2241,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         self.var_debug_info.push(VarDebugInfo {
             name,
             source_info: debug_source_info,
+            references: 0,
             value: VarDebugInfoContents::Place(for_arm_body.into()),
             argument_index: None,
         });
@@ -2260,6 +2261,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             self.var_debug_info.push(VarDebugInfo {
                 name,
                 source_info: debug_source_info,
+                references: 0,
                 value: VarDebugInfoContents::Place(ref_for_guard.into()),
                 argument_index: None,
             });

compiler/rustc_mir_build/src/build/mod.rs

@@ -798,6 +798,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 };
                 self.var_debug_info.push(VarDebugInfo {
                     name,
+                    references: 0,
                     source_info: SourceInfo::outermost(captured_place.var_ident.span),
                     value: VarDebugInfoContents::Place(use_place),
                     argument_index: None,
@@ -828,6 +829,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 self.var_debug_info.push(VarDebugInfo {
                     name,
                     source_info,
+                    references: 0,
                     value: VarDebugInfoContents::Place(arg_local.into()),
                     argument_index: Some(argument_index as u16 + 1),
                 });

compiler/rustc_mir_transform/src/ref_prop.rs

@@ -263,6 +263,7 @@ fn compute_replacement<'tcx>(
         targets,
         storage_to_remove,
         allowed_replacements,
+        fully_replacable_locals,
         any_replacement: false,
     };
 
@@ -343,13 +344,31 @@ struct Replacer<'tcx> {
     storage_to_remove: BitSet<Local>,
     allowed_replacements: FxHashSet<(Local, Location)>,
     any_replacement: bool,
+    fully_replacable_locals: BitSet<Local>,
 }
 
 impl<'tcx> MutVisitor<'tcx> for Replacer<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
+    fn visit_var_debug_info(&mut self, debuginfo: &mut VarDebugInfo<'tcx>) {
+        if let VarDebugInfoContents::Place(ref mut place) = debuginfo.value
+            && place.projection.is_empty()
+            && let Value::Pointer(target, _) = self.targets[place.local]
+            && target.projection.iter().all(|p| p.can_use_in_debuginfo())
+        {
+            if let Some((&PlaceElem::Deref, rest)) = target.projection.split_last() {
+                *place = Place::from(target.local).project_deeper(rest, self.tcx);
+                self.any_replacement = true;
+            } else if self.fully_replacable_locals.contains(place.local) {
+                debuginfo.references += 1;
+                *place = target;
+                self.any_replacement = true;
+            }
+        }
+    }
+
     fn visit_place(&mut self, place: &mut Place<'tcx>, ctxt: PlaceContext, loc: Location) {
         if place.projection.first() != Some(&PlaceElem::Deref) {
             return;

compiler/rustc_type_ir/src/structural_impls.rs

@@ -21,6 +21,7 @@ TrivialTypeTraversalImpls! {
     (),
     bool,
     usize,
+    u8,
     u16,
     u32,
     u64,