Vendor things

third-party/vendor/bindgen/ir/analysis/has_vtable.rs

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+//! Determining which types has vtable
+
+use super::{generate_dependencies, ConstrainResult, MonotoneFramework};
+use crate::ir::context::{BindgenContext, ItemId};
+use crate::ir::traversal::EdgeKind;
+use crate::ir::ty::TypeKind;
+use crate::{Entry, HashMap};
+use std::cmp;
+use std::ops;
+
+/// The result of the `HasVtableAnalysis` for an individual item.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum HasVtableResult {
+    /// The item does not have a vtable pointer.
+    No,
+
+    /// The item has a vtable and the actual vtable pointer is within this item.
+    SelfHasVtable,
+
+    /// The item has a vtable, but the actual vtable pointer is in a base
+    /// member.
+    BaseHasVtable,
+}
+
+impl Default for HasVtableResult {
+    fn default() -> Self {
+        HasVtableResult::No
+    }
+}
+
+impl HasVtableResult {
+    /// Take the least upper bound of `self` and `rhs`.
+    pub fn join(self, rhs: Self) -> Self {
+        cmp::max(self, rhs)
+    }
+}
+
+impl ops::BitOr for HasVtableResult {
+    type Output = Self;
+
+    fn bitor(self, rhs: HasVtableResult) -> Self::Output {
+        self.join(rhs)
+    }
+}
+
+impl ops::BitOrAssign for HasVtableResult {
+    fn bitor_assign(&mut self, rhs: HasVtableResult) {
+        *self = self.join(rhs)
+    }
+}
+
+/// An analysis that finds for each IR item whether it has vtable or not
+///
+/// We use the monotone function `has vtable`, defined as follows:
+///
+/// * If T is a type alias, a templated alias, an indirection to another type,
+///   or a reference of a type, T has vtable if the type T refers to has vtable.
+/// * If T is a compound type, T has vtable if we saw a virtual function when
+///   parsing it or any of its base member has vtable.
+/// * If T is an instantiation of an abstract template definition, T has
+///   vtable if template definition has vtable
+#[derive(Debug, Clone)]
+pub struct HasVtableAnalysis<'ctx> {
+    ctx: &'ctx BindgenContext,
+
+    // The incremental result of this analysis's computation. Everything in this
+    // set definitely has a vtable.
+    have_vtable: HashMap<ItemId, HasVtableResult>,
+
+    // Dependencies saying that if a key ItemId has been inserted into the
+    // `have_vtable` set, then each of the ids in Vec<ItemId> need to be
+    // considered again.
+    //
+    // This is a subset of the natural IR graph with reversed edges, where we
+    // only include the edges from the IR graph that can affect whether a type
+    // has a vtable or not.
+    dependencies: HashMap<ItemId, Vec<ItemId>>,
+}
+
+impl<'ctx> HasVtableAnalysis<'ctx> {
+    fn consider_edge(kind: EdgeKind) -> bool {
+        // These are the only edges that can affect whether a type has a
+        // vtable or not.
+        matches!(
+            kind,
+            EdgeKind::TypeReference |
+                EdgeKind::BaseMember |
+                EdgeKind::TemplateDeclaration
+        )
+    }
+
+    fn insert<Id: Into<ItemId>>(
+        &mut self,
+        id: Id,
+        result: HasVtableResult,
+    ) -> ConstrainResult {
+        if let HasVtableResult::No = result {
+            return ConstrainResult::Same;
+        }
+
+        let id = id.into();
+        match self.have_vtable.entry(id) {
+            Entry::Occupied(mut entry) => {
+                if *entry.get() < result {
+                    entry.insert(result);
+                    ConstrainResult::Changed
+                } else {
+                    ConstrainResult::Same
+                }
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(result);
+                ConstrainResult::Changed
+            }
+        }
+    }
+
+    fn forward<Id1, Id2>(&mut self, from: Id1, to: Id2) -> ConstrainResult
+    where
+        Id1: Into<ItemId>,
+        Id2: Into<ItemId>,
+    {
+        let from = from.into();
+        let to = to.into();
+
+        match self.have_vtable.get(&from).cloned() {
+            None => ConstrainResult::Same,
+            Some(r) => self.insert(to, r),
+        }
+    }
+}
+
+impl<'ctx> MonotoneFramework for HasVtableAnalysis<'ctx> {
+    type Node = ItemId;
+    type Extra = &'ctx BindgenContext;
+    type Output = HashMap<ItemId, HasVtableResult>;
+
+    fn new(ctx: &'ctx BindgenContext) -> HasVtableAnalysis<'ctx> {
+        let have_vtable = HashMap::default();
+        let dependencies = generate_dependencies(ctx, Self::consider_edge);
+
+        HasVtableAnalysis {
+            ctx,
+            have_vtable,
+            dependencies,
+        }
+    }
+
+    fn initial_worklist(&self) -> Vec<ItemId> {
+        self.ctx.allowlisted_items().iter().cloned().collect()
+    }
+
+    fn constrain(&mut self, id: ItemId) -> ConstrainResult {
+        trace!("constrain {:?}", id);
+
+        let item = self.ctx.resolve_item(id);
+        let ty = match item.as_type() {
+            None => return ConstrainResult::Same,
+            Some(ty) => ty,
+        };
+
+        // TODO #851: figure out a way to handle deriving from template type parameters.
+        match *ty.kind() {
+            TypeKind::TemplateAlias(t, _) |
+            TypeKind::Alias(t) |
+            TypeKind::ResolvedTypeRef(t) |
+            TypeKind::Reference(t) => {
+                trace!(
+                    "    aliases and references forward to their inner type"
+                );
+                self.forward(t, id)
+            }
+
+            TypeKind::Comp(ref info) => {
+                trace!("    comp considers its own methods and bases");
+                let mut result = HasVtableResult::No;
+
+                if info.has_own_virtual_method() {
+                    trace!("    comp has its own virtual method");
+                    result |= HasVtableResult::SelfHasVtable;
+                }
+
+                let bases_has_vtable = info.base_members().iter().any(|base| {
+                    trace!("    comp has a base with a vtable: {:?}", base);
+                    self.have_vtable.contains_key(&base.ty.into())
+                });
+                if bases_has_vtable {
+                    result |= HasVtableResult::BaseHasVtable;
+                }
+
+                self.insert(id, result)
+            }
+
+            TypeKind::TemplateInstantiation(ref inst) => {
+                self.forward(inst.template_definition(), id)
+            }
+
+            _ => ConstrainResult::Same,
+        }
+    }
+
+    fn each_depending_on<F>(&self, id: ItemId, mut f: F)
+    where
+        F: FnMut(ItemId),
+    {
+        if let Some(edges) = self.dependencies.get(&id) {
+            for item in edges {
+                trace!("enqueue {:?} into worklist", item);
+                f(*item);
+            }
+        }
+    }
+}
+
+impl<'ctx> From<HasVtableAnalysis<'ctx>> for HashMap<ItemId, HasVtableResult> {
+    fn from(analysis: HasVtableAnalysis<'ctx>) -> Self {
+        // We let the lack of an entry mean "No" to save space.
+        extra_assert!(analysis
+            .have_vtable
+            .values()
+            .all(|v| { *v != HasVtableResult::No }));
+
+        analysis.have_vtable
+    }
+}
+
+/// A convenience trait for the things for which we might wonder if they have a
+/// vtable during codegen.
+///
+/// This is not for _computing_ whether the thing has a vtable, it is for
+/// looking up the results of the HasVtableAnalysis's computations for a
+/// specific thing.
+pub trait HasVtable {
+    /// Return `true` if this thing has vtable, `false` otherwise.
+    fn has_vtable(&self, ctx: &BindgenContext) -> bool;
+
+    /// Return `true` if this thing has an actual vtable pointer in itself, as
+    /// opposed to transitively in a base member.
+    fn has_vtable_ptr(&self, ctx: &BindgenContext) -> bool;
+}