Auto merge of #866 - photoszzt:can_derive_copy_array, r=fitzgen

Can derive copy analysis

r? @fitzgen  or @emilio. Fix: #766

Author: bors-servo

src/codegen/mod.rs

@@ -1424,7 +1424,7 @@ impl CodeGenerator for CompInfo {
             needs_default_impl = ctx.options().derive_default;
         }
 
-        if item.can_derive_copy(ctx, ()) &&
+        if item.can_derive_copy(ctx) &&
            !item.annotations().disallow_copy() {
             derives.push("Copy");
             if used_template_params.is_some() {

src/ir/analysis/derive_copy.rs

@@ -0,0 +1,309 @@
+//! Determining which types for which we can emit `#[derive(Copy)]`.
+
+use super::{ConstrainResult, MonotoneFramework, generate_dependencies};
+use std::collections::HashSet;
+use std::collections::HashMap;
+use ir::context::{BindgenContext, ItemId};
+use ir::item::IsOpaque;
+use ir::traversal::EdgeKind;
+use ir::ty::TypeKind;
+use ir::comp::Field;
+use ir::comp::FieldMethods;
+use ir::derive::CanTriviallyDeriveCopy;
+use ir::comp::CompKind;
+use ir::template::TemplateParameters;
+
+/// An analysis that finds for each IR item whether copy cannot be derived.
+///
+/// We use the monotone constraint function `cannot_derive_copy`, defined as
+/// follows:
+///
+/// * If T is Opaque and layout of the type is known, get this layout as opaque
+///   type and check whether it can be derived using trivial checks.
+/// * If T is Array type, copy cannot be derived if the length of the array is
+///   larger than the limit or the type of data the array contains cannot derive
+///   copy.
+/// * If T is a type alias, a templated alias or an indirection to another type,
+///   copy cannot be derived if the type T refers to cannot be derived copy.
+/// * If T is a compound type, copy cannot be derived if any of its base member
+///   or field cannot be derived copy.
+/// * If T is an instantiation of an abstract template definition, T cannot be
+///   derived copy if any of the template arguments or template definition
+///   cannot derive copy.
+#[derive(Debug, Clone)]
+pub struct CannotDeriveCopy<'ctx, 'gen>
+    where 'gen: 'ctx
+{
+    ctx: &'ctx BindgenContext<'gen>,
+
+    // The incremental result of this analysis's computation. Everything in this
+    // set cannot derive copy.
+    cannot_derive_copy: HashSet<ItemId>,
+
+    // Dependencies saying that if a key ItemId has been inserted into the
+    // `cannot_derive_copy` 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
+    // can derive copy or not.
+    dependencies: HashMap<ItemId, Vec<ItemId>>,
+}
+
+impl<'ctx, 'gen> CannotDeriveCopy<'ctx, 'gen> {
+    fn consider_edge(kind: EdgeKind) -> bool {
+        match kind {
+            // These are the only edges that can affect whether a type can derive
+            // copy or not.
+            EdgeKind::BaseMember |
+            EdgeKind::Field |
+            EdgeKind::TypeReference |
+            EdgeKind::VarType |
+            EdgeKind::TemplateArgument |
+            EdgeKind::TemplateDeclaration |
+            EdgeKind::TemplateParameterDefinition => true,
+
+            EdgeKind::Constructor |
+            EdgeKind::Destructor |
+            EdgeKind::FunctionReturn |
+            EdgeKind::FunctionParameter |
+            EdgeKind::InnerType |
+            EdgeKind::InnerVar |
+            EdgeKind::Method => false,
+            EdgeKind::Generic => false,
+        }
+    }
+
+    fn insert(&mut self, id: ItemId) -> ConstrainResult {
+        trace!("inserting {:?} into the cannot_derive_copy set", id);
+
+        let was_not_already_in_set = self.cannot_derive_copy.insert(id);
+        assert!(
+            was_not_already_in_set,
+            "We shouldn't try and insert {:?} twice because if it was \
+             already in the set, `constrain` should have exited early.",
+            id
+        );
+
+        ConstrainResult::Changed
+    }
+}
+
+impl<'ctx, 'gen> MonotoneFramework for CannotDeriveCopy<'ctx, 'gen> {
+    type Node = ItemId;
+    type Extra = &'ctx BindgenContext<'gen>;
+    type Output = HashSet<ItemId>;
+
+    fn new(ctx: &'ctx BindgenContext<'gen>) -> CannotDeriveCopy<'ctx, 'gen> {
+        let cannot_derive_copy = HashSet::new();
+        let dependencies = generate_dependencies(ctx, Self::consider_edge);
+
+        CannotDeriveCopy {
+            ctx,
+            cannot_derive_copy,
+            dependencies,
+        }
+    }
+
+    fn initial_worklist(&self) -> Vec<ItemId> {
+        self.ctx.whitelisted_items().iter().cloned().collect()
+    }
+
+    fn constrain(&mut self, id: ItemId) -> ConstrainResult {
+        trace!("constrain: {:?}", id);
+
+        if self.cannot_derive_copy.contains(&id) {
+            trace!("    already know it cannot derive Copy");
+            return ConstrainResult::Same;
+        }
+
+        let item = self.ctx.resolve_item(id);
+        let ty = match item.as_type() {
+            Some(ty) => ty,
+            None => {
+                trace!("    not a type; ignoring");
+                return ConstrainResult::Same;
+            }
+        };
+
+        if item.is_opaque(self.ctx, &()) {
+            let layout_can_derive = ty.layout(self.ctx).map_or(true, |l| {
+                l.opaque().can_trivially_derive_copy()
+            });
+            return if layout_can_derive {
+                trace!("    we can trivially derive Copy for the layout");
+                ConstrainResult::Same
+            } else {
+                trace!("    we cannot derive Copy for the layout");
+                self.insert(id)
+            };
+        }
+
+        match *ty.kind() {
+            // Handle the simple cases. These can derive copy without further
+            // information.
+            TypeKind::Void |
+            TypeKind::NullPtr |
+            TypeKind::Int(..) |
+            TypeKind::Float(..) |
+            TypeKind::Complex(..) |
+            TypeKind::Function(..) |
+            TypeKind::Enum(..) |
+            TypeKind::Reference(..) |
+            TypeKind::Named |
+            TypeKind::BlockPointer |
+            TypeKind::Pointer(..) |
+            TypeKind::UnresolvedTypeRef(..) |
+            TypeKind::ObjCInterface(..) |
+            TypeKind::ObjCId |
+            TypeKind::ObjCSel => {
+                trace!("    simple type that can always derive Copy");
+                ConstrainResult::Same
+            }
+
+            TypeKind::Array(t, len) => {
+                let cant_derive_copy = self.cannot_derive_copy.contains(&t);
+                if  cant_derive_copy {
+                    trace!("    arrays of T for which we cannot derive Copy \
+                            also cannot derive Copy");
+                    return self.insert(id);
+                }
+
+                if len > 0 {
+                    trace!("    array can derive Copy with positive length");
+                    ConstrainResult::Same
+                } else {
+                    trace!("    array cannot derive Copy with 0 length");
+                    self.insert(id)
+                }
+            }
+
+            TypeKind::ResolvedTypeRef(t) |
+            TypeKind::TemplateAlias(t, _) |
+            TypeKind::Alias(t) => {
+                let cant_derive_copy = self.cannot_derive_copy.contains(&t);
+                if  cant_derive_copy {
+                    trace!("    arrays of T for which we cannot derive Copy \
+                            also cannot derive Copy");
+                    return self.insert(id);
+                }
+                trace!("    aliases and type refs to T which can derive \
+                        Copy can also derive Copy");
+                ConstrainResult::Same
+            }
+
+            TypeKind::Comp(ref info) => {
+                assert!(
+                    !info.has_non_type_template_params(),
+                    "The early ty.is_opaque check should have handled this case"
+                );
+
+                // NOTE: Take into account that while unions in C and C++ are copied by
+                // default, the may have an explicit destructor in C++, so we can't
+                // defer this check just for the union case.
+                if info.has_destructor(self.ctx) {
+                    trace!("    comp has destructor which cannot derive copy");
+                    return self.insert(id);
+                }
+
+                if info.kind() == CompKind::Union {
+                    if !self.ctx.options().unstable_rust {
+                        // NOTE: If there's no template parameters we can derive copy
+                        // unconditionally, since arrays are magical for rustc, and
+                        // __BindgenUnionField always implements copy.
+                        trace!("    comp can always derive debug if it's a Union and no template parameters");
+                        return ConstrainResult::Same
+                    }
+
+                    // https://github.com/rust-lang/rust/issues/36640
+                    if info.self_template_params(self.ctx).is_some() ||
+                       item.used_template_params(self.ctx).is_some() {
+                        trace!("    comp cannot derive copy because issue 36640");
+                        return self.insert(id);
+                    }
+                }
+
+                let bases_cannot_derive = info.base_members()
+                    .iter()
+                    .any(|base| self.cannot_derive_copy.contains(&base.ty));
+                if bases_cannot_derive {
+                    trace!("    base members cannot derive Copy, so we can't \
+                            either");
+                    return self.insert(id);
+                }
+
+                let fields_cannot_derive = info.fields()
+                    .iter()
+                    .any(|f| {
+                        match *f {
+                            Field::DataMember(ref data) => {
+                                self.cannot_derive_copy.contains(&data.ty())
+                            }
+                            Field::Bitfields(ref bfu) => {
+                                bfu.bitfields()
+                                    .iter().any(|b| {
+                                        self.cannot_derive_copy.contains(&b.ty())
+                                    })
+                            }
+                        }
+                    });
+                if fields_cannot_derive {
+                    trace!("    fields cannot derive Copy, so we can't either");
+                    return self.insert(id);
+                }
+
+                trace!("    comp can derive Copy");
+                ConstrainResult::Same
+            }
+
+            TypeKind::TemplateInstantiation(ref template) => {
+                let args_cannot_derive = template.template_arguments()
+                    .iter()
+                    .any(|arg| self.cannot_derive_copy.contains(&arg));
+                if args_cannot_derive {
+                    trace!("    template args cannot derive Copy, so \
+                            insantiation can't either");
+                    return self.insert(id);
+                }
+
+                assert!(
+                    !template.template_definition().is_opaque(self.ctx, &()),
+                    "The early ty.is_opaque check should have handled this case"
+                );
+                let def_cannot_derive = self.cannot_derive_copy
+                    .contains(&template.template_definition());
+                if def_cannot_derive {
+                    trace!("    template definition cannot derive Copy, so \
+                            insantiation can't either");
+                    return self.insert(id);
+                }
+
+                trace!("    template instantiation can derive Copy");
+                ConstrainResult::Same
+            }
+
+            TypeKind::Opaque => {
+                unreachable!(
+                    "The early ty.is_opaque check should have handled this case"
+                )
+            }
+        }
+    }
+
+    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, 'gen> From<CannotDeriveCopy<'ctx, 'gen>> for HashSet<ItemId> {
+    fn from(analysis: CannotDeriveCopy<'ctx, 'gen>) -> Self {
+        analysis.cannot_derive_copy
+    }
+}