rust/src/librustc/middle/trans/closure.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


use back::abi;
use back::link::{mangle_internal_name_by_path_and_seq};
use lib::llvm::ValueRef;
use middle::moves;
use middle::trans::base::*;
use middle::trans::build::*;
use middle::trans::common::*;
use middle::trans::datum::{Datum, INIT};
use middle::trans::debuginfo;
use middle::trans::expr;
use middle::trans::glue;
use middle::trans::type_of::*;
use middle::ty;
use util::ppaux::ty_to_str;

use std::vec;
use syntax::ast;
use syntax::ast_map::path_name;
use syntax::ast_util;
use syntax::parse::token::special_idents;

// ___Good to know (tm)__________________________________________________
//
// The layout of a closure environment in memory is
// roughly as follows:
//
// struct rust_opaque_box {         // see rust_internal.h
//   unsigned ref_count;            // only used for @fn()
//   type_desc *tydesc;             // describes closure_data struct
//   rust_opaque_box *prev;         // (used internally by memory alloc)
//   rust_opaque_box *next;         // (used internally by memory alloc)
//   struct closure_data {
//       type_desc *bound_tdescs[]; // bound descriptors
//       struct {
//         upvar1_t upvar1;
//         ...
//         upvarN_t upvarN;
//       } bound_data;
//    }
// };
//
// Note that the closure is itself a rust_opaque_box.  This is true
// even for ~fn and ||, because we wish to keep binary compatibility
// between all kinds of closures.  The allocation strategy for this
// closure depends on the closure type.  For a sendfn, the closure
// (and the referenced type descriptors) will be allocated in the
// exchange heap.  For a fn, the closure is allocated in the task heap
// and is reference counted.  For a block, the closure is allocated on
// the stack.
//
// ## Opaque closures and the embedded type descriptor ##
//
// One interesting part of closures is that they encapsulate the data
// that they close over.  So when I have a ptr to a closure, I do not
// know how many type descriptors it contains nor what upvars are
// captured within.  That means I do not know precisely how big it is
// nor where its fields are located.  This is called an "opaque
// closure".
//
// Typically an opaque closure suffices because we only manipulate it
// by ptr.  The routine Type::opaque_box().ptr_to() returns an
// appropriate type for such an opaque closure; it allows access to
// the box fields, but not the closure_data itself.
//
// But sometimes, such as when cloning or freeing a closure, we need
// to know the full information.  That is where the type descriptor
// that defines the closure comes in handy.  We can use its take and
// drop glue functions to allocate/free data as needed.
//
// ## Subtleties concerning alignment ##
//
// It is important that we be able to locate the closure data *without
// knowing the kind of data that is being bound*.  This can be tricky
// because the alignment requirements of the bound data affects the
// alignment requires of the closure_data struct as a whole.  However,
// right now this is a non-issue in any case, because the size of the
// rust_opaque_box header is always a mutiple of 16-bytes, which is
// the maximum alignment requirement we ever have to worry about.
//
// The only reason alignment matters is that, in order to learn what data
// is bound, we would normally first load the type descriptors: but their
// location is ultimately depend on their content!  There is, however, a
// workaround.  We can load the tydesc from the rust_opaque_box, which
// describes the closure_data struct and has self-contained derived type
// descriptors, and read the alignment from there.   It's just annoying to
// do.  Hopefully should this ever become an issue we'll have monomorphized
// and type descriptors will all be a bad dream.
//
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

pub enum EnvAction {
    /// Copy the value from this llvm ValueRef into the environment.
    EnvCopy,

    /// Move the value from this llvm ValueRef into the environment.
    EnvMove,

    /// Access by reference (used for stack closures).
    EnvRef
}

pub struct EnvValue {
    action: EnvAction,
    datum: Datum
}

impl EnvAction {
    pub fn to_str(&self) -> ~str {
        match *self {
            EnvCopy => ~"EnvCopy",
            EnvMove => ~"EnvMove",
            EnvRef => ~"EnvRef"
        }
    }
}

impl EnvValue {
    pub fn to_str(&self, ccx: &CrateContext) -> ~str {
        format!("{}({})", self.action.to_str(), self.datum.to_str(ccx))
    }
}

pub fn mk_tuplified_uniq_cbox_ty(tcx: ty::ctxt, cdata_ty: ty::t) -> ty::t {
    let cbox_ty = tuplify_box_ty(tcx, cdata_ty);
    return ty::mk_imm_uniq(tcx, cbox_ty);
}

// Given a closure ty, emits a corresponding tuple ty
pub fn mk_closure_tys(tcx: ty::ctxt,
                      bound_values: &[EnvValue])
                   -> ty::t {
    // determine the types of the values in the env.  Note that this
    // is the actual types that will be stored in the map, not the
    // logical types as the user sees them, so by-ref upvars must be
    // converted to ptrs.
    let bound_tys = bound_values.map(|bv| {
        match bv.action {
            EnvCopy | EnvMove => bv.datum.ty,
            EnvRef => ty::mk_mut_ptr(tcx, bv.datum.ty)
        }
    });
    let cdata_ty = ty::mk_tup(tcx, bound_tys);
    debug!("cdata_ty={}", ty_to_str(tcx, cdata_ty));
    return cdata_ty;
}

fn heap_for_unique_closure(bcx: @Block, t: ty::t) -> heap {
    if ty::type_contents(bcx.tcx(), t).owns_managed() {
        heap_managed_unique
    } else {
        heap_exchange_closure
    }
}

pub fn allocate_cbox(bcx: @Block, sigil: ast::Sigil, cdata_ty: ty::t)
                  -> Result {
    let _icx = push_ctxt("closure::allocate_cbox");
    let ccx = bcx.ccx();
    let tcx = ccx.tcx;

    // Allocate and initialize the box:
    match sigil {
        ast::ManagedSigil => {
            tcx.sess.bug("trying to trans allocation of @fn")
        }
        ast::OwnedSigil => {
            malloc_raw(bcx, cdata_ty, heap_for_unique_closure(bcx, cdata_ty))
        }
        ast::BorrowedSigil => {
            let cbox_ty = tuplify_box_ty(tcx, cdata_ty);
            let llbox = alloc_ty(bcx, cbox_ty, "__closure");
            rslt(bcx, llbox)
        }
    }
}

pub struct ClosureResult {
    llbox: ValueRef, // llvalue of ptr to closure
    cdata_ty: ty::t, // type of the closure data
    bcx: @Block       // final bcx
}

// Given a block context and a list of tydescs and values to bind
// construct a closure out of them. If copying is true, it is a
// heap allocated closure that copies the upvars into environment.
// Otherwise, it is stack allocated and copies pointers to the upvars.
pub fn store_environment(bcx: @Block,
                         bound_values: ~[EnvValue],
                         sigil: ast::Sigil)
                         -> ClosureResult {
    let _icx = push_ctxt("closure::store_environment");
    let ccx = bcx.ccx();
    let tcx = ccx.tcx;

    // compute the type of the closure
    let cdata_ty = mk_closure_tys(tcx, bound_values);

    // cbox_ty has the form of a tuple: (a, b, c) we want a ptr to a
    // tuple.  This could be a ptr in uniq or a box or on stack,
    // whatever.
    let cbox_ty = tuplify_box_ty(tcx, cdata_ty);
    let cboxptr_ty = ty::mk_ptr(tcx, ty::mt {ty:cbox_ty, mutbl:ast::MutImmutable});
    let llboxptr_ty = type_of(ccx, cboxptr_ty);

    // If there are no bound values, no point in allocating anything.
    if bound_values.is_empty() {
        return ClosureResult {llbox: C_null(llboxptr_ty),
                              cdata_ty: cdata_ty,
                              bcx: bcx};
    }

    // allocate closure in the heap
    let Result {bcx: bcx, val: llbox} = allocate_cbox(bcx, sigil, cdata_ty);

    let llbox = PointerCast(bcx, llbox, llboxptr_ty);
    debug!("tuplify_box_ty = {}", ty_to_str(tcx, cbox_ty));

    // Copy expr values into boxed bindings.
    let mut bcx = bcx;
    for (i, bv) in bound_values.iter().enumerate() {
        debug!("Copy {} into closure", bv.to_str(ccx));

        if ccx.sess.asm_comments() {
            add_comment(bcx, format!("Copy {} into closure",
                                  bv.to_str(ccx)));
        }

        let bound_data = GEPi(bcx, llbox, [0u, abi::box_field_body, i]);

        match bv.action {
            EnvCopy => {
                bcx = bv.datum.copy_to(bcx, INIT, bound_data);
            }
            EnvMove => {
                bcx = bv.datum.move_to(bcx, INIT, bound_data);
            }
            EnvRef => {
                Store(bcx, bv.datum.to_ref_llval(bcx), bound_data);
            }
        }

    }

    ClosureResult { llbox: llbox, cdata_ty: cdata_ty, bcx: bcx }
}

// Given a context and a list of upvars, build a closure. This just
// collects the upvars and packages them up for store_environment.
pub fn build_closure(bcx0: @Block,
                     cap_vars: &[moves::CaptureVar],
                     sigil: ast::Sigil) -> ClosureResult {
    let _icx = push_ctxt("closure::build_closure");

    // If we need to, package up the iterator body to call
    let bcx = bcx0;

    // Package up the captured upvars
    let mut env_vals = ~[];
    for cap_var in cap_vars.iter() {
        debug!("Building closure: captured variable {:?}", *cap_var);
        let datum = expr::trans_local_var(bcx, cap_var.def);
        match cap_var.mode {
            moves::CapRef => {
                assert_eq!(sigil, ast::BorrowedSigil);
                env_vals.push(EnvValue {action: EnvRef,
                                        datum: datum});
            }
            moves::CapCopy => {
                env_vals.push(EnvValue {action: EnvCopy,
                                        datum: datum});
            }
            moves::CapMove => {
                env_vals.push(EnvValue {action: EnvMove,
                                        datum: datum});
            }
        }
    }

    return store_environment(bcx, env_vals, sigil);
}

// Given an enclosing block context, a new function context, a closure type,
// and a list of upvars, generate code to load and populate the environment
// with the upvars and type descriptors.
pub fn load_environment(fcx: @mut FunctionContext,
                        cdata_ty: ty::t,
                        cap_vars: &[moves::CaptureVar],
                        sigil: ast::Sigil) {
    let _icx = push_ctxt("closure::load_environment");

    // Don't bother to create the block if there's nothing to load
    if cap_vars.len() == 0 {
        return;
    }

    let bcx = fcx.entry_bcx.unwrap();

    // Load a pointer to the closure data, skipping over the box header:
    let llcdata = opaque_box_body(bcx, cdata_ty, fcx.llenv.get());

    // Store the pointer to closure data in an alloca for debug info because that's what the
    // llvm.dbg.declare intrinsic expects
    let env_pointer_alloca = if fcx.ccx.sess.opts.extra_debuginfo {
        let alloc = alloc_ty(bcx, ty::mk_mut_ptr(bcx.tcx(), cdata_ty), "__debuginfo_env_ptr");
        Store(bcx, llcdata, alloc);
        Some(alloc)
    } else {
        None
    };

    // Populate the upvars from the environment
    let mut i = 0u;
    for cap_var in cap_vars.iter() {
        let mut upvarptr = GEPi(bcx, llcdata, [0u, i]);
        match sigil {
            ast::BorrowedSigil => { upvarptr = Load(bcx, upvarptr); }
            ast::ManagedSigil | ast::OwnedSigil => {}
        }
        let def_id = ast_util::def_id_of_def(cap_var.def);

        {
            let mut llupvars = fcx.llupvars.borrow_mut();
            llupvars.get().insert(def_id.node, upvarptr);
        }

        for &env_pointer_alloca in env_pointer_alloca.iter() {
            debuginfo::create_captured_var_metadata(
                bcx,
                def_id.node,
                cdata_ty,
                env_pointer_alloca,
                i,
                sigil,
                cap_var.span);
        }

        i += 1u;
    }
}

pub fn trans_expr_fn(bcx: @Block,
                     sigil: ast::Sigil,
                     decl: &ast::fn_decl,
                     body: &ast::Block,
                     outer_id: ast::NodeId,
                     user_id: ast::NodeId,
                     dest: expr::Dest) -> @Block {
    /*!
     *
     * Translates the body of a closure expression.
     *
     * - `sigil`
     * - `decl`
     * - `body`
     * - `outer_id`: The id of the closure expression with the correct
     *   type.  This is usually the same as `user_id`, but in the
     *   case of a `for` loop, the `outer_id` will have the return
     *   type of boolean, and the `user_id` will have the return type
     *   of `nil`.
     * - `user_id`: The id of the closure as the user expressed it.
         Generally the same as `outer_id`
     * - `cap_clause`: information about captured variables, if any.
     * - `dest`: where to write the closure value, which must be a
         (fn ptr, env) pair
     */

    let _icx = push_ctxt("closure::trans_expr_fn");

    let dest_addr = match dest {
        expr::SaveIn(p) => p,
        expr::Ignore => {
            return bcx; // closure construction is non-side-effecting
        }
    };

    let ccx = bcx.ccx();
    let fty = node_id_type(bcx, outer_id);
    let f = match ty::get(fty).sty {
        ty::ty_closure(ref f) => f,
        _ => fail!("expected closure")
    };

    let sub_path = vec::append_one(bcx.fcx.path.clone(),
                                   path_name(special_idents::anon));
    // XXX: Bad copy.
    let s = mangle_internal_name_by_path_and_seq(ccx,
                                                 sub_path.clone(),
                                                 "expr_fn");
    let llfn = decl_internal_rust_fn(ccx, f.sig.inputs, f.sig.output, s);

    // set an inline hint for all closures
    set_inline_hint(llfn);

    let Result {bcx: bcx, val: closure} = match sigil {
        ast::BorrowedSigil | ast::ManagedSigil | ast::OwnedSigil => {
            let cap_vars = {
                let capture_map = ccx.maps.capture_map.borrow();
                capture_map.get().get_copy(&user_id)
            };
            let ClosureResult {llbox, cdata_ty, bcx}
                = build_closure(bcx, cap_vars, sigil);
            trans_closure(ccx,
                          sub_path,
                          decl,
                          body,
                          llfn,
                          no_self,
                          bcx.fcx.param_substs,
                          user_id,
                          [],
                          ty::ty_fn_ret(fty),
                          |fcx| load_environment(fcx, cdata_ty, cap_vars, sigil));
            rslt(bcx, llbox)
        }
    };
    fill_fn_pair(bcx, dest_addr, llfn, closure);

    return bcx;
}

pub fn make_closure_glue(cx: @Block,
                         v: ValueRef,
                         t: ty::t,
                         glue_fn: |@Block, v: ValueRef, t: ty::t|
                                   -> @Block)
                         -> @Block {
    let _icx = push_ctxt("closure::make_closure_glue");
    let bcx = cx;
    let tcx = cx.tcx();

    let sigil = ty::ty_closure_sigil(t);
    match sigil {
        ast::BorrowedSigil => bcx,
        ast::OwnedSigil | ast::ManagedSigil => {
            let box_cell_v = GEPi(cx, v, [0u, abi::fn_field_box]);
            let box_ptr_v = Load(cx, box_cell_v);
            with_cond(cx, IsNotNull(cx, box_ptr_v), |bcx| {
                let closure_ty = ty::mk_opaque_closure_ptr(tcx, sigil);
                glue_fn(bcx, box_cell_v, closure_ty)
            })
        }
    }
}

pub fn make_opaque_cbox_drop_glue(
    bcx: @Block,
    sigil: ast::Sigil,
    cboxptr: ValueRef)     // ptr to the opaque closure
    -> @Block {
    let _icx = push_ctxt("closure::make_opaque_cbox_drop_glue");
    match sigil {
        ast::BorrowedSigil => bcx,
        ast::ManagedSigil => {
            bcx.tcx().sess.bug("trying to trans drop glue of @fn")
        }
        ast::OwnedSigil => {
            glue::free_ty(
                bcx, cboxptr,
                ty::mk_opaque_closure_ptr(bcx.tcx(), sigil))
        }
    }
}

/// `cbox` is a pointer to a pointer to an opaque closure.
pub fn make_opaque_cbox_free_glue(bcx: @Block,
                                  sigil: ast::Sigil,
                                  cbox: ValueRef)
                                  -> @Block {
    let _icx = push_ctxt("closure::make_opaque_cbox_free_glue");
    match sigil {
        ast::BorrowedSigil => {
            return bcx;
        }
        ast::ManagedSigil | ast::OwnedSigil => {
            /* hard cases: fallthrough to code below */
        }
    }

    let ccx = bcx.ccx();
    with_cond(bcx, IsNotNull(bcx, cbox), |bcx| {
        // Load the type descr found in the cbox
        let lltydescty = ccx.tydesc_type.ptr_to();
        let cbox = Load(bcx, cbox);
        let tydescptr = GEPi(bcx, cbox, [0u, abi::box_field_tydesc]);
        let tydesc = Load(bcx, tydescptr);
        let tydesc = PointerCast(bcx, tydesc, lltydescty);

        // Drop the tuple data then free the descriptor
        let cdata = GEPi(bcx, cbox, [0u, abi::box_field_body]);
        glue::call_tydesc_glue_full(bcx, cdata, tydesc,
                                    abi::tydesc_field_drop_glue, None);

        // Free the ty descr (if necc) and the box itself
        glue::trans_exchange_free(bcx, cbox);

        bcx
    })
}