Rollup merge of rust-lang#96432 - SparrowLii:dbg_scope, r=davidtwco

not need `Option` for `dbg_scope`

This PR fixes a few FIXME about not using `Option` in `dbg_scope` field of `DebugScope`, during `create_function_debug_context` func in codegen parts.
Added a `BitSet<SourceScope>` parameter to `make_mir_scope` to indicate whether the `DebugScope` has been instantiated.
cc ```@eddyb```

compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs

@@ -20,7 +20,6 @@ pub fn compute_mir_scopes<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     instance: Instance<'tcx>,
     mir: &Body<'tcx>,
-    fn_dbg_scope: &'ll DIScope,
     debug_context: &mut FunctionDebugContext<&'ll DIScope, &'ll DILocation>,
 ) {
     // Find all scopes with variables defined in them.
@@ -38,47 +37,49 @@ pub fn compute_mir_scopes<'ll, 'tcx>(
         // Nothing to emit, of course.
         None
     };
-
+    let mut instantiated = BitSet::new_empty(mir.source_scopes.len());
     // Instantiate all scopes.
     for idx in 0..mir.source_scopes.len() {
         let scope = SourceScope::new(idx);
-        make_mir_scope(cx, instance, mir, fn_dbg_scope, &variables, debug_context, scope);
+        make_mir_scope(cx, instance, mir, &variables, debug_context, &mut instantiated, scope);
     }
+    assert!(instantiated.count() == mir.source_scopes.len());
 }
 
 fn make_mir_scope<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     instance: Instance<'tcx>,
     mir: &Body<'tcx>,
-    fn_dbg_scope: &'ll DIScope,
     variables: &Option<BitSet<SourceScope>>,
     debug_context: &mut FunctionDebugContext<&'ll DIScope, &'ll DILocation>,
+    instantiated: &mut BitSet<SourceScope>,
     scope: SourceScope,
 ) {
-    if debug_context.scopes[scope].dbg_scope.is_some() {
+    if instantiated.contains(scope) {
         return;
     }
 
     let scope_data = &mir.source_scopes[scope];
     let parent_scope = if let Some(parent) = scope_data.parent_scope {
-        make_mir_scope(cx, instance, mir, fn_dbg_scope, variables, debug_context, parent);
+        make_mir_scope(cx, instance, mir, variables, debug_context, instantiated, parent);
         debug_context.scopes[parent]
     } else {
         // The root is the function itself.
         let loc = cx.lookup_debug_loc(mir.span.lo());
         debug_context.scopes[scope] = DebugScope {
-            dbg_scope: Some(fn_dbg_scope),
-            inlined_at: None,
             file_start_pos: loc.file.start_pos,
             file_end_pos: loc.file.end_pos,
+            ..debug_context.scopes[scope]
         };
+        instantiated.insert(scope);
         return;
     };
 
     if let Some(vars) = variables && !vars.contains(scope) && scope_data.inlined.is_none() {
         // Do not create a DIScope if there are no variables defined in this
         // MIR `SourceScope`, and it's not `inlined`, to avoid debuginfo bloat.
         debug_context.scopes[scope] = parent_scope;
+        instantiated.insert(scope);
         return;
     }
 
@@ -100,7 +101,7 @@ fn make_mir_scope<'ll, 'tcx>(
         None => unsafe {
             llvm::LLVMRustDIBuilderCreateLexicalBlock(
                 DIB(cx),
-                parent_scope.dbg_scope.unwrap(),
+                parent_scope.dbg_scope,
                 file_metadata,
                 loc.line,
                 loc.col,
@@ -116,9 +117,10 @@ fn make_mir_scope<'ll, 'tcx>(
     });
 
     debug_context.scopes[scope] = DebugScope {
-        dbg_scope: Some(dbg_scope),
+        dbg_scope,
         inlined_at: inlined_at.or(parent_scope.inlined_at),
         file_start_pos: loc.file.start_pos,
         file_end_pos: loc.file.end_pos,
     };
+    instantiated.insert(scope);
 }

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -286,9 +286,8 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         }
 
         // Initialize fn debug context (including scopes).
-        // FIXME(eddyb) figure out a way to not need `Option` for `dbg_scope`.
         let empty_scope = DebugScope {
-            dbg_scope: None,
+            dbg_scope: self.dbg_scope_fn(instance, fn_abi, Some(llfn)),
             inlined_at: None,
             file_start_pos: BytePos(0),
             file_end_pos: BytePos(0),
@@ -297,13 +296,7 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             FunctionDebugContext { scopes: IndexVec::from_elem(empty_scope, &mir.source_scopes) };
 
         // Fill in all the scopes, with the information from the MIR body.
-        compute_mir_scopes(
-            self,
-            instance,
-            mir,
-            self.dbg_scope_fn(instance, fn_abi, Some(llfn)),
-            &mut fn_debug_context,
-        );
+        compute_mir_scopes(self, instance, mir, &mut fn_debug_context);
 
         Some(fn_debug_context)
     }

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -39,8 +39,7 @@ pub struct PerLocalVarDebugInfo<'tcx, D> {
 
 #[derive(Clone, Copy, Debug)]
 pub struct DebugScope<S, L> {
-    // FIXME(eddyb) this should never be `None`, after initialization.
-    pub dbg_scope: Option<S>,
+    pub dbg_scope: S,
 
     /// Call site location, if this scope was inlined from another function.
     pub inlined_at: Option<L>,
@@ -61,17 +60,12 @@ impl<'tcx, S: Copy, L: Copy> DebugScope<S, L> {
         cx: &Cx,
         span: Span,
     ) -> S {
-        // FIXME(eddyb) this should never be `None`.
-        let dbg_scope = self
-            .dbg_scope
-            .unwrap_or_else(|| bug!("`dbg_scope` is only `None` during initialization"));
-
         let pos = span.lo();
         if pos < self.file_start_pos || pos >= self.file_end_pos {
             let sm = cx.sess().source_map();
-            cx.extend_scope_to_file(dbg_scope, &sm.lookup_char_pos(pos).file)
+            cx.extend_scope_to_file(self.dbg_scope, &sm.lookup_char_pos(pos).file)
         } else {
-            dbg_scope
+            self.dbg_scope
         }
     }
 }