charon_lib/transform/

ctx.rs

use crate::ast::*;
use crate::errors::{ErrorCtx, Level};
use crate::formatter::{FmtCtx, IntoFormatter};
use crate::llbc_ast;
use crate::options::TranslateOptions;
use crate::pretty::FmtWithCtx;
use crate::ullbc_ast;
use std::cell::RefCell;
use std::{fmt, mem};

/// Simpler context used for rustc-independent code transformation. This only depends on rustc for
/// its error reporting machinery.
pub struct TransformCtx {
    /// The options that control transformation.
    pub options: TranslateOptions,
    /// The translated data.
    pub translated: TranslatedCrate,
    /// Context for tracking and reporting errors.
    pub errors: RefCell<ErrorCtx>,
}

/// A pass that modifies ullbc bodies.
pub trait UllbcPass: Sync {
    /// Transform a body.
    fn transform_body(&self, _ctx: &mut TransformCtx, _body: &mut ullbc_ast::ExprBody) {}

    /// Transform a function declaration. This forwards to `transform_body` by default.
    fn transform_function(&self, ctx: &mut TransformCtx, decl: &mut FunDecl) {
        if let Ok(body) = &mut decl.body {
            self.transform_body(ctx, body.as_unstructured_mut().unwrap())
        }
    }

    /// Transform the given context. This forwards to the other methods by default.
    fn transform_ctx(&self, ctx: &mut TransformCtx) {
        ctx.for_each_fun_decl(|ctx, decl| {
            let body = decl
                .body
                .as_mut()
                .map(|body| body.as_unstructured_mut().unwrap())
                .map_err(|opaque| *opaque);
            self.log_before_body(ctx, &decl.item_meta.name, body.as_deref());
            self.transform_function(ctx, decl);
        });
    }

    /// The name of the pass, used for debug logging. The default implementation uses the type
    /// name.
    fn name(&self) -> &str {
        std::any::type_name::<Self>()
    }

    /// Log that the pass is about to be run on this body.
    fn log_before_body(
        &self,
        ctx: &TransformCtx,
        name: &Name,
        body: Result<&ullbc_ast::ExprBody, &Opaque>,
    ) {
        let fmt_ctx = &ctx.into_fmt();
        let body_str = if let Ok(body) = body {
            body.to_string_with_ctx(fmt_ctx)
        } else {
            "<opaque>".to_owned()
        };
        trace!(
            "# About to run pass [{}] on `{}`:\n{}",
            self.name(),
            name.with_ctx(fmt_ctx),
            body_str,
        );
    }
}

/// A pass that modifies llbc bodies.
pub trait LlbcPass: Sync {
    /// Transform a body.
    fn transform_body(&self, _ctx: &mut TransformCtx, _body: &mut llbc_ast::ExprBody) {}

    /// Transform a function declaration. This forwards to `transform_body` by default.
    fn transform_function(&self, ctx: &mut TransformCtx, decl: &mut FunDecl) {
        if let Ok(body) = &mut decl.body {
            self.transform_body(ctx, body.as_structured_mut().unwrap())
        }
    }

    /// Transform the given context. This forwards to the other methods by default.
    fn transform_ctx(&self, ctx: &mut TransformCtx) {
        ctx.for_each_fun_decl(|ctx, decl| {
            let body = decl
                .body
                .as_mut()
                .map(|body| body.as_structured_mut().unwrap())
                .map_err(|opaque| *opaque);
            self.log_before_body(ctx, &decl.item_meta.name, body.as_deref());
            self.transform_function(ctx, decl);
        });
    }

    /// The name of the pass, used for debug logging. The default implementation uses the type
    /// name.
    fn name(&self) -> &str {
        std::any::type_name::<Self>()
    }

    /// Log that the pass is about to be run on this body.
    fn log_before_body(
        &self,
        ctx: &TransformCtx,
        name: &Name,
        body: Result<&llbc_ast::ExprBody, &Opaque>,
    ) {
        let fmt_ctx = &ctx.into_fmt();
        let body_str = if let Ok(body) = body {
            body.to_string_with_ctx(fmt_ctx)
        } else {
            "<opaque>".to_owned()
        };
        trace!(
            "# About to run pass [{}] on `{}`:\n{}",
            self.name(),
            name.with_ctx(fmt_ctx),
            body_str,
        );
    }
}

/// A pass that transforms the crate data.
pub trait TransformPass: Sync {
    fn transform_ctx(&self, ctx: &mut TransformCtx);

    /// The name of the pass, used for debug logging. The default implementation uses the type
    /// name.
    fn name(&self) -> &str {
        std::any::type_name::<Self>()
    }
}

impl<'ctx> TransformCtx {
    pub(crate) fn has_errors(&self) -> bool {
        self.errors.borrow().has_errors()
    }

    /// Span an error and register the error.
    pub(crate) fn span_err(&self, span: Span, msg: &str, level: Level) -> Error {
        self.errors
            .borrow_mut()
            .span_err(&self.translated, span, msg, level)
    }

    pub(crate) fn opacity_for_name(&self, name: &Name) -> ItemOpacity {
        self.options.opacity_for_name(&self.translated, name)
    }

    pub(crate) fn with_def_id<F, T>(
        &mut self,
        def_id: impl Into<ItemId>,
        def_id_is_local: bool,
        f: F,
    ) -> T
    where
        F: FnOnce(&mut Self) -> T,
    {
        let mut errors = self.errors.borrow_mut();
        let current_def_id = mem::replace(&mut errors.def_id, Some(def_id.into()));
        let current_def_id_is_local = mem::replace(&mut errors.def_id_is_local, def_id_is_local);
        drop(errors); // important: release the refcell "lock"
        let ret = f(self);
        let mut errors = self.errors.borrow_mut();
        errors.def_id = current_def_id;
        errors.def_id_is_local = current_def_id_is_local;
        ret
    }

    /// Mutably iterate over the bodies.
    /// Warning: we replace each body with `Err(Opaque)` while inspecting it so we can keep access
    /// to the rest of the crate.
    pub(crate) fn for_each_body(&mut self, mut f: impl FnMut(&mut Self, &mut Body)) {
        let fn_ids = self.translated.fun_decls.all_indices();
        for id in fn_ids {
            if let Some(decl) = self.translated.fun_decls.get_mut(id) {
                if let Ok(mut body) = mem::replace(&mut decl.body, Err(Opaque)) {
                    let fun_decl_id = decl.def_id;
                    let is_local = decl.item_meta.is_local;
                    self.with_def_id(fun_decl_id, is_local, |ctx| f(ctx, &mut body));
                    self.translated.fun_decls[id].body = Ok(body);
                }
            }
        }
    }

    /// Mutably iterate over the function declarations.
    /// Warning: each inspected fundecl becomes inaccessible from `ctx` during the course of this function.
    pub(crate) fn for_each_fun_decl(&mut self, mut f: impl FnMut(&mut Self, &mut FunDecl)) {
        let fn_ids = self.translated.fun_decls.all_indices();
        for id in fn_ids {
            if let Some(mut decl) = self.translated.fun_decls.remove(id) {
                let fun_decl_id = decl.def_id;
                let is_local = decl.item_meta.is_local;
                self.with_def_id(fun_decl_id, is_local, |ctx| f(ctx, &mut decl));
                self.translated.fun_decls.set_slot(id, decl);
            }
        }
    }

    /// Iterate mutably over all items, keeping access to `self`. To make this work, we move out
    /// each item before iterating over it. Items added during traversal will not be iterated over.
    pub fn for_each_item_mut(&mut self, mut f: impl for<'a> FnMut(&'a mut Self, ItemRefMut<'a>)) {
        for id in self.translated.all_ids() {
            if let Some(mut decl) = self.translated.remove_item(id) {
                f(self, decl.as_mut());
                self.translated.set_item_slot(id, decl);
            }
        }
    }
}

impl<'a> IntoFormatter for &'a TransformCtx {
    type C = FmtCtx<'a>;

    fn into_fmt(self) -> Self::C {
        self.translated.into_fmt()
    }
}

impl fmt::Display for TransformCtx {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.translated.fmt(f)
    }
}

/// A helper trait that captures the usual operation in body transformation.
pub trait BodyTransformCtx: Sized {
    fn get_ctx(&self) -> &TransformCtx;
    fn get_params(&self) -> &GenericParams;
    fn get_locals_mut(&mut self) -> &mut Locals;

    fn insert_storage_live_stmt(&mut self, local: LocalId);
    fn insert_storage_dead_stmt(&mut self, local: LocalId);
    fn insert_assn_stmt(&mut self, place: Place, rvalue: Rvalue);

    /// Create a local & return the place pointing to it
    fn fresh_var(&mut self, name: Option<String>, ty: Ty) -> Place {
        let var = self.get_locals_mut().new_var(name, ty);
        self.insert_storage_live_stmt(var.local_id().unwrap());
        var
    }

    /// When `from_end` is true, we need to compute `len(p) - last_arg` instead of just using `last_arg`.
    /// Otherwise, we simply return `last_arg`.
    /// New local variables are created as needed.
    ///
    /// The `last_arg` is either the `offset` for `Index` or the `to` for `Subslice` for the projections.
    fn compute_subslice_end_idx(
        &mut self,
        len_place: &Place,
        last_arg: Operand,
        from_end: bool,
    ) -> Operand {
        if from_end {
            // `storage_live(len_var)`
            // `len_var = len(p)`
            let len_var = self.fresh_var(None, Ty::mk_usize());
            self.insert_assn_stmt(
                len_var.clone(),
                Rvalue::Len(
                    len_place.clone(),
                    len_place.ty().clone(),
                    len_place
                        .ty()
                        .as_adt()
                        .unwrap()
                        .generics
                        .const_generics
                        .get(0.into())
                        .cloned(),
                ),
            );

            // `storage_live(index_var)`
            // `index_var = len_var - last_arg`
            // `storage_dead(len_var)`
            let index_var = self.fresh_var(None, Ty::mk_usize());
            self.insert_assn_stmt(
                index_var.clone(),
                Rvalue::BinaryOp(
                    BinOp::Sub(OverflowMode::UB),
                    Operand::Copy(len_var.clone()),
                    last_arg,
                ),
            );
            self.insert_storage_dead_stmt(len_var.local_id().unwrap());
            Operand::Copy(index_var)
        } else {
            last_arg
        }
    }

    fn is_sized_type_var(&mut self, ty: &Ty) -> bool {
        match ty.kind() {
            TyKind::TypeVar(..) => {
                if self.get_ctx().options.hide_marker_traits {
                    // If we're hiding `Sized`, let's consider everything to be sized.
                    return true;
                }
                let params = self.get_params();
                for clause in &params.trait_clauses {
                    let tref = clause.trait_.clone().erase();
                    // Check if it is `Sized<T>`
                    if tref.generics.types[0] == *ty
                        && self
                            .get_ctx()
                            .translated
                            .trait_decls
                            .get(tref.id)
                            .and_then(|decl| decl.item_meta.lang_item.clone())
                            == Some("sized".into())
                    {
                        return true;
                    }
                }
                false
            }
            _ => false,
        }
    }

    /// Emit statements that compute the metadata of the given place. Returns an operand containing the
    /// metadata value.
    fn compute_place_metadata(&mut self, place: &Place) -> Operand {
        /// No metadata. We use the `unit_metadata` global to avoid having to define unit locals
        /// everywhere.
        fn no_metadata<T: BodyTransformCtx>(ctx: &T) -> Operand {
            let unit_meta = ctx.get_ctx().translated.unit_metadata.clone().unwrap();
            Operand::Copy(Place::new_global(unit_meta, Ty::mk_unit()))
        }

        /// Compute the metadata for a place. Return `None` if the place has no metadata.
        fn compute_place_metadata_inner<T: BodyTransformCtx>(
            ctx: &mut T,
            place: &Place,
            metadata_ty: &Ty,
        ) -> Option<Operand> {
            let (subplace, proj) = place.as_projection()?;
            match proj {
                // The outermost deref we encountered gives us the metadata of the place.
                ProjectionElem::Deref => {
                    let metadata_place = subplace
                        .clone()
                        .project(ProjectionElem::PtrMetadata, metadata_ty.clone());
                    Some(Operand::Copy(metadata_place))
                }
                ProjectionElem::Field { .. } => {
                    compute_place_metadata_inner(ctx, subplace, metadata_ty)
                }
                // Indexing for array & slice will only result in sized types, hence no metadata
                ProjectionElem::Index { .. } => None,
                // Ptr metadata is always sized.
                ProjectionElem::PtrMetadata { .. } => None,
                // Subslice must have metadata length, compute the metadata here as `to` - `from`
                ProjectionElem::Subslice { from, to, from_end } => {
                    let to_idx = ctx.compute_subslice_end_idx(subplace, *to.clone(), *from_end);
                    let diff_place = ctx.fresh_var(None, Ty::mk_usize());
                    ctx.insert_assn_stmt(
                        diff_place.clone(),
                        // Overflow is UB and should have been prevented by a bound check beforehand.
                        Rvalue::BinaryOp(BinOp::Sub(OverflowMode::UB), to_idx, *from.clone()),
                    );
                    Some(Operand::Copy(diff_place))
                }
            }
        }
        trace!(
            "getting ptr metadata for place: {}",
            place.with_ctx(&self.get_ctx().into_fmt())
        );
        let metadata_ty = place
            .ty()
            .get_ptr_metadata(&self.get_ctx().translated)
            .into_type();
        if metadata_ty.is_unit()
            || matches!(metadata_ty.kind(), TyKind::PtrMetadata(ty) if self.is_sized_type_var(ty))
        {
            // If the type var is known to be `Sized`, then no metadata is needed
            return no_metadata(self);
        }
        trace!(
            "computed metadata type: {}",
            metadata_ty.with_ctx(&self.get_ctx().into_fmt())
        );
        compute_place_metadata_inner(self, place, &metadata_ty).unwrap_or_else(|| no_metadata(self))
    }
}

pub struct UllbcStatementTransformCtx<'a> {
    pub ctx: &'a mut TransformCtx,
    pub params: &'a GenericParams,
    pub locals: &'a mut Locals,
    /// Span of the statement being explored
    pub span: Span,
    /// Statements to prepend to the statement currently being explored.
    pub statements: Vec<ullbc_ast::Statement>,
}

impl BodyTransformCtx for UllbcStatementTransformCtx<'_> {
    fn get_ctx(&self) -> &TransformCtx {
        self.ctx
    }
    fn get_params(&self) -> &GenericParams {
        self.params
    }
    fn get_locals_mut(&mut self) -> &mut Locals {
        self.locals
    }

    fn insert_storage_live_stmt(&mut self, local: LocalId) {
        self.statements.push(ullbc_ast::Statement::new(
            self.span,
            ullbc_ast::StatementKind::StorageLive(local),
        ));
    }

    fn insert_assn_stmt(&mut self, place: Place, rvalue: Rvalue) {
        self.statements.push(ullbc_ast::Statement::new(
            self.span,
            ullbc_ast::StatementKind::Assign(place, rvalue),
        ));
    }

    fn insert_storage_dead_stmt(&mut self, local: LocalId) {
        self.statements.push(ullbc_ast::Statement::new(
            self.span,
            ullbc_ast::StatementKind::StorageDead(local),
        ));
    }
}

impl FunDecl {
    pub fn transform_ullbc_terminators(
        &mut self,
        ctx: &mut TransformCtx,
        mut f: impl FnMut(&mut UllbcStatementTransformCtx, &mut ullbc_ast::Terminator),
    ) {
        if let Ok(body) = &mut self.body {
            let params = &self.signature.generics;
            let body = body.as_unstructured_mut().unwrap();
            body.body.iter_mut().for_each(|block| {
                let span = block.terminator.span;
                let mut ctx = UllbcStatementTransformCtx {
                    ctx,
                    params,
                    locals: &mut body.locals,
                    span,
                    statements: std::mem::take(&mut block.statements),
                };
                f(&mut ctx, &mut block.terminator);
                block.statements = ctx.statements;
            });
        }
    }

    pub fn transform_ullbc_statements(
        &mut self,
        ctx: &mut TransformCtx,
        mut f: impl FnMut(&mut UllbcStatementTransformCtx, &mut ullbc_ast::Statement),
    ) {
        if let Ok(body) = &mut self.body {
            let params = &self.signature.generics;
            let body = body.as_unstructured_mut().unwrap();
            body.body.iter_mut().for_each(|block| {
                block.transform(|st: &mut ullbc_ast::Statement| {
                    let mut ctx = UllbcStatementTransformCtx {
                        ctx,
                        params,
                        locals: &mut body.locals,
                        span: st.span,
                        statements: Vec::new(),
                    };
                    f(&mut ctx, st);
                    ctx.statements
                });
            });
        }
    }
}