rust/src/librustc/middle/trans/expr.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.

/*!

# Translation of expressions.

## Recommended entry point

If you wish to translate an expression, the preferred way to do
so is to use:

    expr::trans_into(block, expr, Dest) -> block

This will generate code that evaluates `expr`, storing the result into
`Dest`, which must either be the special flag ignore (throw the result
away) or be a pointer to memory of the same type/size as the
expression.  It returns the resulting basic block.  This form will
handle all automatic adjustments and moves for you.

## Translation to a datum

In some cases, `trans_into()` is too narrow of an interface.
Generally this occurs either when you know that the result value is
going to be a scalar, or when you need to evaluate the expression into
some memory location so you can go and inspect it (e.g., assignments,
`match` expressions, the `&` operator).

In such cases, you want the following function:

    trans_to_datum(block, expr) -> DatumBlock

This function generates code to evaluate the expression and return a
`Datum` describing where the result is to be found.  This function
tries to return its result in the most efficient way possible, without
introducing extra copies or sacrificing information.  Therefore, for
lvalue expressions, you always get a by-ref `Datum` in return that
points at the memory for this lvalue (almost, see [1]).  For rvalue
expressions, we will return a by-value `Datum` whenever possible, but
it is often necessary to allocate a stack slot, store the result of
the rvalue in there, and then return a pointer to the slot (see the
discussion later on about the different kinds of rvalues).

NB: The `trans_to_datum()` function does perform adjustments, but
since it returns a pointer to the value "in place" it does not handle
any moves that may be relevant.  If you are transing an expression
whose result should be moved, you should either use the Datum methods
`move_to()` (for unconditional moves) or `store_to()` (for moves
conditioned on the type of the expression) at some point.

## Translating local variables

`trans_local_var()` can be used to trans a ref to a local variable
that is not an expression.  This is needed for captures.

## Ownership and cleanups

The current system for cleanups associates required cleanups with
block contexts.  Block contexts are structured into a tree that
resembles the code itself.  Not every block context has cleanups
associated with it, only those blocks that have a kind of
`block_scope`.  See `common::block_kind` for more details.

If you invoke `trans_into()`, no cleanup is scheduled for you.  The
value is written into the given destination and is assumed to be owned
by that destination.

When you invoke `trans_to_datum()` on an rvalue, the resulting
datum/value will have an appropriate cleanup scheduled for the
innermost cleanup scope.  If you later use `move_to()` or
`drop_val()`, this cleanup will be canceled.

During the evaluation of an expression, temporary cleanups are created
and later canceled.  These represent intermediate or partial results
which must be cleaned up in the event of task failure.

## Implementation details

We divide expressions into three categories, based on how they are most
naturally implemented:

1. Lvalues
2. Datum rvalues
3. DPS rvalues
4. Statement rvalues

Lvalues always refer to user-assignable memory locations.
Translating those always results in a by-ref datum; this introduces
no inefficiencies into the generated code, because all lvalues are
naturally addressable.

Datum rvalues are rvalues that always generate datums as a result.
These are generally scalar results, such as `a+b` where `a` and `b`
are integers.

DPS rvalues are rvalues that, when translated, must be given a
memory location to write into (or the Ignore flag).  These are
generally expressions that produce structural results that are
larger than one word (e.g., a struct literal), but also expressions
(like `if`) that involve control flow (otherwise we'd have to
generate phi nodes).

Finally, statement rvalues are rvalues that always produce a nil
return type, such as `while` loops or assignments (`a = b`).

## Caveats

[1] Actually, some lvalues are only stored by value and not by
reference.  An example (as of this writing) would be immutable
arguments or pattern bindings of immediate type.  However, mutable
lvalues are *never* stored by value.

*/

use core::prelude::*;

use back::abi;
use lib;
use lib::llvm::{ValueRef, TypeRef, llvm, True};
use middle::borrowck::root_map_key;
use middle::trans::_match;
use middle::trans::adt;
use middle::trans::base;
use middle::trans::base::*;
use middle::trans::build::*;
use middle::trans::callee::{AutorefArg, DoAutorefArg, DontAutorefArg};
use middle::trans::callee;
use middle::trans::closure;
use middle::trans::common::*;
use middle::trans::consts;
use middle::trans::controlflow;
use middle::trans::datum::*;
use middle::trans::debuginfo;
use middle::trans::machine;
use middle::trans::meth;
use middle::trans::tvec;
use middle::trans::type_of;
use middle::ty;
use middle::ty::struct_mutable_fields;
use middle::ty::{AutoPtr, AutoBorrowVec, AutoBorrowVecRef, AutoBorrowFn,
                 AutoDerefRef, AutoAddEnv};
use util::common::indenter;
use util::ppaux::ty_to_str;

use std::oldmap::HashMap;
use syntax::print::pprust::{expr_to_str};
use syntax::ast;
use syntax::codemap;

// Destinations

// These are passed around by the code generating functions to track the
// destination of a computation's value.

pub enum Dest {
    SaveIn(ValueRef),
    Ignore,
}

pub impl Dest {
    fn to_str(&self, ccx: @CrateContext) -> ~str {
        match *self {
            SaveIn(v) => fmt!("SaveIn(%s)", val_str(ccx.tn, v)),
            Ignore => ~"Ignore"
        }
    }
}

impl cmp::Eq for Dest {
    pure fn eq(&self, other: &Dest) -> bool {
        match ((*self), (*other)) {
            (SaveIn(e0a), SaveIn(e0b)) => e0a == e0b,
            (Ignore, Ignore) => true,
            (SaveIn(*), _) => false,
            (Ignore, _) => false,
        }
    }
    pure fn ne(&self, other: &Dest) -> bool { !(*self).eq(other) }
}

fn drop_and_cancel_clean(bcx: block, dat: Datum) -> block {
    let bcx = dat.drop_val(bcx);
    dat.cancel_clean(bcx);
    return bcx;
}

pub fn trans_to_datum(bcx: block, expr: @ast::expr) -> DatumBlock {
    debug!("trans_to_datum(expr=%s)", bcx.expr_to_str(expr));
    return match bcx.tcx().adjustments.find(&expr.id) {
        None => {
            trans_to_datum_unadjusted(bcx, expr)
        }
        Some(@AutoAddEnv(*)) => {
            let mut bcx = bcx;
            let mut datum = unpack_datum!(bcx, {
                trans_to_datum_unadjusted(bcx, expr)
            });
            add_env(bcx, expr, datum)
        }
        Some(@AutoDerefRef(ref adj)) => {
            let mut bcx = bcx;
            let mut datum = unpack_datum!(bcx, {
                trans_to_datum_unadjusted(bcx, expr)
            });

            if adj.autoderefs > 0 {
                let DatumBlock { bcx: new_bcx, datum: new_datum } =
                    datum.autoderef(bcx, expr.id, adj.autoderefs);
                datum = new_datum;
                bcx = new_bcx;
            }

            datum = match adj.autoref {
                None => datum,
                Some(ref autoref) => {
                    match autoref.kind {
                        AutoPtr => {
                            unpack_datum!(bcx, auto_ref(bcx, datum))
                        }
                        AutoBorrowVec => {
                            unpack_datum!(bcx, auto_slice(bcx, datum))
                        }
                        AutoBorrowVecRef => {
                            unpack_datum!(bcx, auto_slice_and_ref(bcx, datum))
                        }
                        AutoBorrowFn => {
                            // currently, all closure types are
                            // represented precisely the same, so no
                            // runtime adjustment is required:
                            datum
                        }
                    }
                }
            };

            debug!("after adjustments, datum=%s", datum.to_str(bcx.ccx()));

            return DatumBlock {bcx: bcx, datum: datum};
        }
    };

    fn auto_ref(bcx: block, datum: Datum) -> DatumBlock {
        DatumBlock {bcx: bcx, datum: datum.to_rptr(bcx)}
    }

    fn auto_slice(bcx: block, datum: Datum) -> DatumBlock {
        // This is not the most efficient thing possible; since slices
        // are two words it'd be better if this were compiled in
        // 'dest' mode, but I can't find a nice way to structure the
        // code and keep it DRY that accommodates that use case at the
        // moment.

        let tcx = bcx.tcx();
        let unit_ty = ty::sequence_element_type(tcx, datum.ty);
        let (base, len) = datum.get_base_and_len(bcx);

        // this type may have a different region/mutability than the
        // real one, but it will have the same runtime representation
        let slice_ty = ty::mk_evec(tcx,
                                   ty::mt { ty: unit_ty, mutbl: ast::m_imm },
                                   ty::vstore_slice(ty::re_static));

        let scratch = scratch_datum(bcx, slice_ty, false);
        Store(bcx, base, GEPi(bcx, scratch.val, [0u, abi::slice_elt_base]));
        Store(bcx, len, GEPi(bcx, scratch.val, [0u, abi::slice_elt_len]));
        DatumBlock {bcx: bcx, datum: scratch}
    }

    fn add_env(bcx: block, expr: @ast::expr, datum: Datum) -> DatumBlock {
        // This is not the most efficient thing possible; since closures
        // are two words it'd be better if this were compiled in
        // 'dest' mode, but I can't find a nice way to structure the
        // code and keep it DRY that accommodates that use case at the
        // moment.

        let tcx = bcx.tcx();
        let closure_ty = expr_ty_adjusted(bcx, expr);
        debug!("add_env(closure_ty=%s)", ty_to_str(tcx, closure_ty));
        let scratch = scratch_datum(bcx, closure_ty, false);
        let llfn = GEPi(bcx, scratch.val, [0u, abi::fn_field_code]);
        assert datum.appropriate_mode() == ByValue;
        Store(bcx, datum.to_appropriate_llval(bcx), llfn);
        let llenv = GEPi(bcx, scratch.val, [0u, abi::fn_field_box]);
        Store(bcx, base::null_env_ptr(bcx), llenv);
        DatumBlock {bcx: bcx, datum: scratch}
    }

    fn auto_slice_and_ref(bcx: block, datum: Datum) -> DatumBlock {
        let DatumBlock { bcx, datum } = auto_slice(bcx, datum);
        auto_ref(bcx, datum)
    }
}

pub fn trans_into(bcx: block, expr: @ast::expr, dest: Dest) -> block {
    if bcx.tcx().adjustments.contains_key(&expr.id) {
        // use trans_to_datum, which is mildly less efficient but
        // which will perform the adjustments:
        let datumblock = trans_to_datum(bcx, expr);
        return match dest {
            Ignore => datumblock.bcx,
            SaveIn(lldest) => datumblock.store_to(expr.id, INIT, lldest)
        };
    }

    let ty = expr_ty(bcx, expr);

    debug!("trans_into_unadjusted(expr=%s, dest=%s)",
           bcx.expr_to_str(expr),
           dest.to_str(bcx.ccx()));
    let _indenter = indenter();

    debuginfo::update_source_pos(bcx, expr.span);

    let dest = {
        if ty::type_is_nil(ty) || ty::type_is_bot(ty) {
            Ignore
        } else {
            dest
        }
    };

    let kind = bcx.expr_kind(expr);
    debug!("expr kind = %?", kind);
    return match kind {
        ty::LvalueExpr => {
            let datumblock = trans_lvalue_unadjusted(bcx, expr);
            match dest {
                Ignore => datumblock.bcx,
                SaveIn(lldest) => datumblock.store_to(expr.id, INIT, lldest)
            }
        }
        ty::RvalueDatumExpr => {
            let datumblock = trans_rvalue_datum_unadjusted(bcx, expr);
            match dest {
                Ignore => datumblock.drop_val(),

                // NB: We always do `move_to()` regardless of the
                // moves_map because we're processing an rvalue
                SaveIn(lldest) => datumblock.move_to(INIT, lldest)
            }
        }
        ty::RvalueDpsExpr => {
            trans_rvalue_dps_unadjusted(bcx, expr, dest)
        }
        ty::RvalueStmtExpr => {
            trans_rvalue_stmt_unadjusted(bcx, expr)
        }
    };
}

fn trans_lvalue(bcx: block, expr: @ast::expr) -> DatumBlock {
    /*!
     *
     * Translates an lvalue expression, always yielding a by-ref
     * datum.  Generally speaking you should call trans_to_datum()
     * instead, but sometimes we call trans_lvalue() directly as a
     * means of asserting that a particular expression is an lvalue. */

    return match bcx.tcx().adjustments.find(&expr.id) {
        None => trans_lvalue_unadjusted(bcx, expr),
        Some(_) => {
            bcx.sess().span_bug(
                expr.span,
                fmt!("trans_lvalue() called on an expression \
                      with adjustments"));
        }
    };
}

fn trans_to_datum_unadjusted(bcx: block, expr: @ast::expr) -> DatumBlock {
    /*!
     *
     * Translates an expression into a datum.  If this expression
     * is an rvalue, this will result in a temporary value being
     * created.  If you already know where the result should be stored,
     * you should use `trans_into()` instead. */

    let mut bcx = bcx;

    debug!("trans_to_datum_unadjusted(expr=%s)", bcx.expr_to_str(expr));
    let _indenter = indenter();

    debuginfo::update_source_pos(bcx, expr.span);

    match ty::expr_kind(bcx.tcx(), bcx.ccx().maps.method_map, expr) {
        ty::LvalueExpr => {
            return trans_lvalue_unadjusted(bcx, expr);
        }

        ty::RvalueDatumExpr => {
            let datum = unpack_datum!(bcx, {
                trans_rvalue_datum_unadjusted(bcx, expr)
            });
            datum.add_clean(bcx);
            return DatumBlock {bcx: bcx, datum: datum};
        }

        ty::RvalueStmtExpr => {
            bcx = trans_rvalue_stmt_unadjusted(bcx, expr);
            return nil(bcx, expr_ty(bcx, expr));
        }

        ty::RvalueDpsExpr => {
            let ty = expr_ty(bcx, expr);
            if ty::type_is_nil(ty) || ty::type_is_bot(ty) {
                bcx = trans_rvalue_dps_unadjusted(bcx, expr, Ignore);
                return nil(bcx, ty);
            } else {
                let scratch = scratch_datum(bcx, ty, false);
                bcx = trans_rvalue_dps_unadjusted(
                    bcx, expr, SaveIn(scratch.val));

                // Note: this is not obviously a good idea.  It causes
                // immediate values to be loaded immediately after a
                // return from a call or other similar expression,
                // which in turn leads to alloca's having shorter
                // lifetimes and hence larger stack frames.  However,
                // in turn it can lead to more register pressure.
                // Still, in practice it seems to increase
                // performance, since we have fewer problems with
                // morestack churn.
                let scratch = scratch.to_appropriate_datum(bcx);

                scratch.add_clean(bcx);
                return DatumBlock {bcx: bcx, datum: scratch};
            }
        }
    }

    fn nil(bcx: block, ty: ty::t) -> DatumBlock {
        let datum = immediate_rvalue(C_nil(), ty);
        DatumBlock {bcx: bcx, datum: datum}
    }
}

fn trans_rvalue_datum_unadjusted(bcx: block, expr: @ast::expr) -> DatumBlock {
    let _icx = bcx.insn_ctxt("trans_rvalue_datum_unadjusted");

    trace_span!(bcx, expr.span, @shorten(bcx.expr_to_str(expr)));

    match expr.node {
        ast::expr_path(_) => {
            return trans_def_datum_unadjusted(bcx, expr, bcx.def(expr.id));
        }
        ast::expr_vstore(contents, ast::expr_vstore_box) |
        ast::expr_vstore(contents, ast::expr_vstore_mut_box) => {
            return tvec::trans_uniq_or_managed_vstore(bcx, heap_managed,
                                                      expr, contents);
        }
        ast::expr_vstore(contents, ast::expr_vstore_uniq) => {
            let heap = heap_for_unique(bcx, expr_ty(bcx, contents));
            return tvec::trans_uniq_or_managed_vstore(bcx, heap,
                                                      expr, contents);
        }
        ast::expr_lit(lit) => {
            return trans_immediate_lit(bcx, expr, *lit);
        }
        ast::expr_binary(op, lhs, rhs) => {
            // if overloaded, would be RvalueDpsExpr
            assert !bcx.ccx().maps.method_map.contains_key(&expr.id);

            return trans_binary(bcx, expr, op, lhs, rhs);
        }
        ast::expr_unary(op, x) => {
            return trans_unary_datum(bcx, expr, op, x);
        }
        ast::expr_addr_of(_, x) => {
            return trans_addr_of(bcx, expr, x);
        }
        ast::expr_cast(val, _) => {
            return trans_imm_cast(bcx, val, expr.id);
        }
        ast::expr_paren(e) => {
            return trans_rvalue_datum_unadjusted(bcx, e);
        }
        _ => {
            bcx.tcx().sess.span_bug(
                expr.span,
                fmt!("trans_rvalue_datum_unadjusted reached \
                      fall-through case: %?",
                     expr.node));
        }
    }
}

fn trans_rvalue_stmt_unadjusted(bcx: block, expr: @ast::expr) -> block {
    let mut bcx = bcx;
    let _icx = bcx.insn_ctxt("trans_rvalue_stmt");

    trace_span!(bcx, expr.span, @shorten(bcx.expr_to_str(expr)));

    match expr.node {
        ast::expr_break(label_opt) => {
            return controlflow::trans_break(bcx, label_opt);
        }
        ast::expr_again(label_opt) => {
            return controlflow::trans_cont(bcx, label_opt);
        }
        ast::expr_ret(ex) => {
            return controlflow::trans_ret(bcx, ex);
        }
        ast::expr_log(_, lvl, a) => {
            return controlflow::trans_log(expr, lvl, bcx, a);
        }
        ast::expr_assert(a) => {
            return controlflow::trans_check_expr(bcx, expr, a, ~"Assertion");
        }
        ast::expr_while(cond, ref body) => {
            return controlflow::trans_while(bcx, cond, body);
        }
        ast::expr_loop(ref body, opt_label) => {
            return controlflow::trans_loop(bcx, body, opt_label);
        }
        ast::expr_assign(dst, src) => {
            let src_datum = unpack_datum!(
                bcx, trans_to_datum(bcx, src));
            let dst_datum = unpack_datum!(
                bcx, trans_lvalue(bcx, dst));
            return src_datum.store_to_datum(
                bcx, src.id, DROP_EXISTING, dst_datum);
        }
        ast::expr_swap(dst, src) => {
            let dst_datum = unpack_datum!(bcx, trans_lvalue(bcx, dst));
            let src_datum = unpack_datum!(bcx, trans_lvalue(bcx, src));

            // If the source and destination are the same, then don't swap.
            // Avoids performing an overlapping memcpy
            let dst_datum_ref = dst_datum.to_ref_llval(bcx);
            let src_datum_ref = src_datum.to_ref_llval(bcx);
            let cmp = ICmp(bcx, lib::llvm::IntEQ,
                           src_datum_ref,
                           dst_datum_ref);

            let swap_cx = base::sub_block(bcx, ~"swap");
            let next_cx = base::sub_block(bcx, ~"next");

            CondBr(bcx, cmp, next_cx.llbb, swap_cx.llbb);

            let scratch = scratch_datum(swap_cx, dst_datum.ty, false);

            let swap_cx = dst_datum.move_to_datum(swap_cx, INIT, scratch);
            let swap_cx = src_datum.move_to_datum(swap_cx, INIT, dst_datum);
            let swap_cx = scratch.move_to_datum(swap_cx, INIT, src_datum);

            Br(swap_cx, next_cx.llbb);

            return next_cx;
        }
        ast::expr_assign_op(op, dst, src) => {
            return trans_assign_op(bcx, expr, op, dst, src);
        }
        ast::expr_paren(a) => {
            return trans_rvalue_stmt_unadjusted(bcx, a);
        }
        _ => {
            bcx.tcx().sess.span_bug(
                expr.span,
                fmt!("trans_rvalue_stmt_unadjusted reached \
                      fall-through case: %?",
                     expr.node));
        }
    };
}

fn trans_rvalue_dps_unadjusted(bcx: block, expr: @ast::expr,
                               dest: Dest) -> block {
    let mut bcx = bcx;
    let _icx = bcx.insn_ctxt("trans_rvalue_dps_unadjusted");
    let tcx = bcx.tcx();

    trace_span!(bcx, expr.span, @shorten(bcx.expr_to_str(expr)));

    match expr.node {
        ast::expr_paren(e) => {
            return trans_rvalue_dps_unadjusted(bcx, e, dest);
        }
        ast::expr_path(_) => {
            return trans_def_dps_unadjusted(bcx, expr,
                                            bcx.def(expr.id), dest);
        }
        ast::expr_if(cond, ref thn, els) => {
            return controlflow::trans_if(bcx, cond, thn, els, dest);
        }
        ast::expr_match(discr, ref arms) => {
            return _match::trans_match(bcx, expr, discr, /*bad*/copy *arms,
                                       dest);
        }
        ast::expr_block(ref blk) => {
            return do base::with_scope(bcx, blk.info(),
                                       ~"block-expr body") |bcx| {
                controlflow::trans_block(bcx, blk, dest)
            };
        }
        ast::expr_rec(ref fields, base) |
        ast::expr_struct(_, ref fields, base) => {
            return trans_rec_or_struct(bcx, (*fields), base, expr.id, dest);
        }
        ast::expr_tup(ref args) => {
            let repr = adt::represent_type(bcx.ccx(), expr_ty(bcx, expr));
            return trans_adt(bcx, &repr, 0, args.mapi(|i, arg| (i, *arg)),
                             None, dest);
        }
        ast::expr_lit(@codemap::spanned {node: ast::lit_str(s), _}) => {
            return tvec::trans_lit_str(bcx, expr, s, dest);
        }
        ast::expr_vstore(contents, ast::expr_vstore_slice) |
        ast::expr_vstore(contents, ast::expr_vstore_mut_slice) => {
            return tvec::trans_slice_vstore(bcx, expr, contents, dest);
        }
        ast::expr_vstore(contents, ast::expr_vstore_fixed(_)) => {
            return tvec::trans_fixed_vstore(bcx, expr, contents, dest);
        }
        ast::expr_vec(*) | ast::expr_repeat(*) => {
            return tvec::trans_fixed_vstore(bcx, expr, expr, dest);
        }
        ast::expr_fn_block(ref decl, ref body) => {
            let expr_ty = expr_ty(bcx, expr);
            let sigil = ty::ty_closure_sigil(expr_ty);
            debug!("translating fn_block %s with type %s",
                   expr_to_str(expr, tcx.sess.intr()),
                   ty_to_str(tcx, expr_ty));
            return closure::trans_expr_fn(bcx, sigil, decl, body,
                                          expr.id, expr.id,
                                          None, dest);
        }
        ast::expr_loop_body(blk) => {
            let expr_ty = expr_ty(bcx, expr);
            let sigil = ty::ty_closure_sigil(expr_ty);
            match blk.node {
                ast::expr_fn_block(ref decl, ref body) => {
                    return closure::trans_expr_fn(bcx, sigil,
                                                  decl, body,
                                                  expr.id, blk.id,
                                                  Some(None), dest);
                }
                _ => {
                    bcx.sess().impossible_case(
                        expr.span,
                        "loop_body has the wrong kind of contents")
                }
            }
        }
        ast::expr_do_body(blk) => {
            return trans_into(bcx, blk, dest);
        }
        ast::expr_copy(a) => {
            return trans_into(bcx, a, dest);
        }
        ast::expr_call(f, ref args, _) => {
            return callee::trans_call(
                bcx, expr, f, callee::ArgExprs(*args), expr.id, dest);
        }
        ast::expr_method_call(rcvr, _, _, ref args, _) => {
            return callee::trans_method_call(bcx,
                                             expr,
                                             rcvr,
                                             callee::ArgExprs(*args),
                                             dest);
        }
        ast::expr_binary(_, lhs, rhs) => {
            // if not overloaded, would be RvalueDatumExpr
            return trans_overloaded_op(bcx, expr, lhs, ~[rhs], dest,
                                       DoAutorefArg);
        }
        ast::expr_unary(_, subexpr) => {
            // if not overloaded, would be RvalueDatumExpr
            return trans_overloaded_op(bcx, expr, subexpr, ~[], dest,
                                       DontAutorefArg);
        }
        ast::expr_index(base, idx) => {
            // if not overloaded, would be RvalueDatumExpr
            return trans_overloaded_op(bcx, expr, base, ~[idx], dest,
                                       DontAutorefArg);
        }
        ast::expr_cast(val, _) => {
            match ty::get(node_id_type(bcx, expr.id)).sty {
                ty::ty_trait(_, _, vstore) => {
                    return meth::trans_trait_cast(bcx, val, expr.id, dest,
                                                  vstore);
                }
                _ => {
                    bcx.tcx().sess.span_bug(expr.span,
                                            ~"expr_cast of non-trait");
                }
            }
        }
        ast::expr_assign_op(op, dst, src) => {
            return trans_assign_op(bcx, expr, op, dst, src);
        }
        _ => {
            bcx.tcx().sess.span_bug(
                expr.span,
                fmt!("trans_rvalue_dps_unadjusted reached \
                      fall-through case: %?",
                     expr.node));
        }
    }
}

fn trans_def_dps_unadjusted(bcx: block, ref_expr: @ast::expr,
                            def: ast::def, dest: Dest) -> block {
    let _icx = bcx.insn_ctxt("trans_def_dps_unadjusted");
    let ccx = bcx.ccx();

    let lldest = match dest {
        SaveIn(lldest) => lldest,
        Ignore => { return bcx; }
    };

    match def {
        ast::def_variant(tid, vid) => {
            let variant_info = ty::enum_variant_with_id(ccx.tcx, tid, vid);
            if variant_info.args.len() > 0u {
                // N-ary variant.
                let fn_data = callee::trans_fn_ref(bcx, vid, ref_expr.id);
                Store(bcx, fn_data.llfn, lldest);
                return bcx;
            } else {
                // Nullary variant.
                let ty = expr_ty(bcx, ref_expr);
                let repr = adt::represent_type(ccx, ty);
                adt::trans_set_discr(bcx, &repr, lldest,
                                     variant_info.disr_val);
                return bcx;
            }
        }
        ast::def_struct(*) => {
            // Nothing to do here.
            // XXX: May not be true in the case of classes with destructors.
            return bcx;
        }
        _ => {
            bcx.tcx().sess.span_bug(ref_expr.span, fmt!(
                "Non-DPS def %? referened by %s",
                def, bcx.node_id_to_str(ref_expr.id)));
        }
    }
}

fn trans_def_datum_unadjusted(bcx: block,
                              ref_expr: @ast::expr,
                              def: ast::def) -> DatumBlock
{
    let _icx = bcx.insn_ctxt("trans_def_datum_unadjusted");

    match def {
        ast::def_fn(did, _) | ast::def_static_method(did, None, _) => {
            let fn_data = callee::trans_fn_ref(bcx, did, ref_expr.id);
            return fn_data_to_datum(bcx, ref_expr, did, fn_data);
        }
        ast::def_static_method(impl_did, Some(trait_did), _) => {
            let fn_data = meth::trans_static_method_callee(bcx, impl_did,
                                                           trait_did,
                                                           ref_expr.id);
            return fn_data_to_datum(bcx, ref_expr, impl_did, fn_data);
        }
        _ => {
            bcx.tcx().sess.span_bug(ref_expr.span, fmt!(
                "Non-DPS def %? referened by %s",
                def, bcx.node_id_to_str(ref_expr.id)));
        }
    }

    fn fn_data_to_datum(bcx: block,
                        ref_expr: @ast::expr,
                        def_id: ast::def_id,
                        fn_data: callee::FnData) -> DatumBlock {
        /*!
        *
        * Translates a reference to a top-level fn item into a rust
        * value.  This is just a fn pointer.
        */

        let is_extern = {
            let fn_tpt = ty::lookup_item_type(bcx.tcx(), def_id);
            ty::ty_fn_purity(fn_tpt.ty) == ast::extern_fn
        };
        let (rust_ty, llval) = if is_extern {
            let rust_ty = ty::mk_ptr(
                bcx.tcx(),
                ty::mt {
                    ty: ty::mk_mach_uint(bcx.tcx(), ast::ty_u8),
                    mutbl: ast::m_imm
                }); // *u8
            (rust_ty, PointerCast(bcx, fn_data.llfn, T_ptr(T_i8())))
        } else {
            let fn_ty = expr_ty(bcx, ref_expr);
            (fn_ty, fn_data.llfn)
        };
        return DatumBlock {
            bcx: bcx,
            datum: Datum {val: llval,
                          ty: rust_ty,
                          mode: ByValue,
                          source: RevokeClean}
        };
    }
}

fn trans_lvalue_unadjusted(bcx: block, expr: @ast::expr) -> DatumBlock {
    /*!
     *
     * Translates an lvalue expression, always yielding a by-ref
     * datum.  Does not apply any adjustments. */

    let _icx = bcx.insn_ctxt("trans_lval");
    let mut bcx = bcx;

    debug!("trans_lvalue(expr=%s)", bcx.expr_to_str(expr));
    let _indenter = indenter();

    trace_span!(bcx, expr.span, @shorten(bcx.expr_to_str(expr)));

    let unrooted_datum = unpack_datum!(bcx, unrooted(bcx, expr));

    // If the lvalue must remain rooted, create a scratch datum, copy
    // the lvalue in there, and then arrange for it to be cleaned up
    // at the end of the scope with id `scope_id`:
    let root_key = root_map_key { id: expr.id, derefs: 0u };
    for bcx.ccx().maps.root_map.find(&root_key).each |&root_info| {
        bcx = unrooted_datum.root(bcx, root_info);
    }

    return DatumBlock {bcx: bcx, datum: unrooted_datum};

    fn unrooted(bcx: block, expr: @ast::expr) -> DatumBlock {
        /*!
         *
         * Translates `expr`.  Note that this version generally
         * yields an unrooted, unmoved version.  Rooting and possible
         * moves are dealt with above in trans_lvalue_unadjusted().
         *
         * One exception is if `expr` refers to a local variable,
         * in which case the source may already be FromMovedLvalue
         * if appropriate.
         */

        let mut bcx = bcx;

        match expr.node {
            ast::expr_paren(e) => {
                return unrooted(bcx, e);
            }
            ast::expr_path(_) => {
                return trans_def_lvalue(bcx, expr, bcx.def(expr.id));
            }
            ast::expr_field(base, ident, _) => {
                return trans_rec_field(bcx, base, ident);
            }
            ast::expr_index(base, idx) => {
                return trans_index(bcx, expr, base, idx);
            }
            ast::expr_unary(ast::deref, base) => {
                let basedatum = unpack_datum!(bcx, trans_to_datum(bcx, base));
                return basedatum.deref(bcx, base, 0);
            }
            _ => {
                bcx.tcx().sess.span_bug(
                    expr.span,
                    fmt!("trans_lvalue reached fall-through case: %?",
                         expr.node));
            }
        }
    }

    fn trans_rec_field(bcx: block,
                       base: @ast::expr,
                       field: ast::ident) -> DatumBlock {
        /*!
         *
         * Translates `base.field`.  Note that this version always
         * yields an unrooted, unmoved version.  Rooting and possible
         * moves are dealt with above in trans_lvalue_unadjusted().
         */

        let mut bcx = bcx;
        let _icx = bcx.insn_ctxt("trans_rec_field");

        let base_datum = unpack_datum!(bcx, trans_to_datum(bcx, base));
        let repr = adt::represent_type(bcx.ccx(), base_datum.ty);
        do with_field_tys(bcx.tcx(), base_datum.ty, None) |discr, field_tys| {
            let ix = ty::field_idx_strict(bcx.tcx(), field, field_tys);
            DatumBlock {
                datum: do base_datum.get_element(bcx,
                                                 field_tys[ix].mt.ty,
                                                 ZeroMem) |srcval| {
                    adt::trans_GEP(bcx, &repr, srcval, discr, ix)
                },
                bcx: bcx
            }
        }
    }

    fn trans_index(bcx: block,
                   index_expr: @ast::expr,
                   base: @ast::expr,
                   idx: @ast::expr) -> DatumBlock {
        /*!
         *
         * Translates `base[idx]`.  Note that this version always
         * yields an unrooted, unmoved version.  Rooting and possible
         * moves are dealt with above in trans_lvalue_unadjusted().
         */

        let _icx = bcx.insn_ctxt("trans_index");
        let ccx = bcx.ccx();
        let base_ty = expr_ty(bcx, base);
        let mut bcx = bcx;

        let base_datum = unpack_datum!(bcx, trans_to_datum(bcx, base));

        // Translate index expression and cast to a suitable LLVM integer.
        // Rust is less strict than LLVM in this regard.
        let Result {bcx, val: ix_val} = trans_to_datum(bcx, idx).to_result();
        let ix_size = machine::llbitsize_of_real(bcx.ccx(), val_ty(ix_val));
        let int_size = machine::llbitsize_of_real(bcx.ccx(), ccx.int_type);
        let ix_val = {
            if ix_size < int_size {
                if ty::type_is_signed(expr_ty(bcx, idx)) {
                    SExt(bcx, ix_val, ccx.int_type)
                } else { ZExt(bcx, ix_val, ccx.int_type) }
            } else if ix_size > int_size {
                Trunc(bcx, ix_val, ccx.int_type)
            } else {
                ix_val
            }
        };

        let vt = tvec::vec_types(bcx, base_datum.ty);
        base::maybe_name_value(bcx.ccx(), vt.llunit_size, ~"unit_sz");
        let scaled_ix = Mul(bcx, ix_val, vt.llunit_size);
        base::maybe_name_value(bcx.ccx(), scaled_ix, ~"scaled_ix");

        let mut (base, len) = base_datum.get_base_and_len(bcx);

        if ty::type_is_str(base_ty) {
            // acccount for null terminator in the case of string
            len = Sub(bcx, len, C_uint(bcx.ccx(), 1u));
        }

        debug!("trans_index: base %s", val_str(bcx.ccx().tn, base));
        debug!("trans_index: len %s", val_str(bcx.ccx().tn, len));

        let bounds_check = ICmp(bcx, lib::llvm::IntUGE, scaled_ix, len);
        let bcx = do with_cond(bcx, bounds_check) |bcx| {
            let unscaled_len = UDiv(bcx, len, vt.llunit_size);
            controlflow::trans_fail_bounds_check(bcx, index_expr.span,
                                                 ix_val, unscaled_len)
        };
        let elt = InBoundsGEP(bcx, base, ~[ix_val]);
        let elt = PointerCast(bcx, elt, T_ptr(vt.llunit_ty));
        return DatumBlock {
            bcx: bcx,
            datum: Datum {val: elt,
                          ty: vt.unit_ty,
                          mode: ByRef,
                          source: ZeroMem}
        };
    }

    fn trans_def_lvalue(bcx: block,
                        ref_expr: @ast::expr,
                        def: ast::def)
        -> DatumBlock
    {
        /*!
         *
         * Translates a reference to a path.  Note that this version
         * generally yields an unrooted, unmoved version.  Rooting and
         * possible moves are dealt with above in
         * trans_lvalue_unadjusted(), with the caveat that local variables
         * may already be in move mode.
         */

        let _icx = bcx.insn_ctxt("trans_def_lvalue");
        let ccx = bcx.ccx();
        match def {
            ast::def_const(did) => {
                let const_ty = expr_ty(bcx, ref_expr);
                let val = if did.crate == ast::local_crate {
                    // The LLVM global has the type of its initializer,
                    // which may not be equal to the enum's type for
                    // non-C-like enums.
                    PointerCast(bcx, base::get_item_val(ccx, did.node),
                                T_ptr(type_of(bcx.ccx(), const_ty)))
                } else {
                    base::trans_external_path(ccx, did, const_ty)
                };
                DatumBlock {
                    bcx: bcx,
                    datum: Datum {val: val,
                                  ty: const_ty,
                                  mode: ByRef,
                                  source: ZeroMem}
                }
            }
            _ => {
                DatumBlock {
                    bcx: bcx,
                    datum: trans_local_var(bcx, def)
                }
            }
        }
    }
}

pub fn trans_local_var(bcx: block, def: ast::def) -> Datum {
    let _icx = bcx.insn_ctxt("trans_local_var");

    return match def {
        ast::def_upvar(nid, _, _, _) => {
            // Can't move upvars, so this is never a ZeroMemLastUse.
            let local_ty = node_id_type(bcx, nid);
            match bcx.fcx.llupvars.find(&nid) {
                Some(val) => {
                    Datum {
                        val: val,
                        ty: local_ty,
                        mode: ByRef,
                        source: ZeroMem
                    }
                }
                None => {
                    bcx.sess().bug(fmt!(
                        "trans_local_var: no llval for upvar %? found", nid));
                }
            }
        }
        ast::def_arg(nid, _, _) => {
            take_local(bcx, *bcx.fcx.llargs, nid)
        }
        ast::def_local(nid, _) | ast::def_binding(nid, _) => {
            take_local(bcx, *bcx.fcx.lllocals, nid)
        }
        ast::def_self(nid, _) => {
            let self_info: ValSelfData = match bcx.fcx.llself {
                Some(ref self_info) => *self_info,
                None => {
                    bcx.sess().bug(fmt!(
                        "trans_local_var: reference to self \
                         out of context with id %?", nid));
                }
            };

            // This cast should not be necessary. We should cast self *once*,
            // but right now this conflicts with default methods.
            let real_self_ty = monomorphize_type(bcx, self_info.t);
            let llselfty = T_ptr(type_of::type_of(bcx.ccx(), real_self_ty));

            let casted_val = PointerCast(bcx, self_info.v, llselfty);
            Datum {
                val: casted_val,
                ty: self_info.t,
                mode: ByRef,
                source: ZeroMem
            }
        }
        _ => {
            bcx.sess().unimpl(fmt!(
                "unsupported def type in trans_local_var: %?", def));
        }
    };

    fn take_local(bcx: block,
                  table: HashMap<ast::node_id, local_val>,
                  nid: ast::node_id) -> Datum {
        let (v, mode) = match table.find(&nid) {
            Some(local_mem(v)) => (v, ByRef),
            Some(local_imm(v)) => (v, ByValue),
            None => {
                bcx.sess().bug(fmt!(
                    "trans_local_var: no llval for local/arg %? found", nid));
            }
        };
        let ty = node_id_type(bcx, nid);

        debug!("take_local(nid=%?, v=%s, mode=%?, ty=%s)",
               nid, bcx.val_str(v), mode, bcx.ty_to_str(ty));

        Datum {
            val: v,
            ty: ty,
            mode: mode,
            source: ZeroMem
        }
    }
}

// The optional node ID here is the node ID of the path identifying the enum
// variant in use. If none, this cannot possibly an enum variant (so, if it
// is and `node_id_opt` is none, this function fails).
pub fn with_field_tys<R>(tcx: ty::ctxt,
                         ty: ty::t,
                         node_id_opt: Option<ast::node_id>,
                         op: fn(int, (&[ty::field])) -> R) -> R {
    match ty::get(ty).sty {
        ty::ty_rec(ref fields) => {
            op(0, *fields)
        }

        ty::ty_struct(did, ref substs) => {
            op(0, struct_mutable_fields(tcx, did, substs))
        }

        ty::ty_enum(_, ref substs) => {
            // We want the *variant* ID here, not the enum ID.
            match node_id_opt {
                None => {
                    tcx.sess.bug(fmt!(
                        "cannot get field types from the enum type %s \
                         without a node ID",
                        ty_to_str(tcx, ty)));
                }
                Some(node_id) => {
                    match tcx.def_map.get(&node_id) {
                        ast::def_variant(enum_id, variant_id) => {
                            let variant_info = ty::enum_variant_with_id(
                                tcx, enum_id, variant_id);
                            op(variant_info.disr_val, struct_mutable_fields(
                                tcx, variant_id, substs))
                        }
                        _ => {
                            tcx.sess.bug(~"resolve didn't map this expr to a \
                                           variant ID")
                        }
                    }
                }
            }
        }

        _ => {
            tcx.sess.bug(fmt!(
                "cannot get field types from the type %s",
                ty_to_str(tcx, ty)));
        }
    }
}

fn trans_rec_or_struct(bcx: block,
                       fields: &[ast::field],
                       base: Option<@ast::expr>,
                       id: ast::node_id,
                       dest: Dest) -> block
{
    let _icx = bcx.insn_ctxt("trans_rec");
    let mut bcx = bcx;

    let ty = node_id_type(bcx, id);
    let tcx = bcx.tcx();
    do with_field_tys(tcx, ty, Some(id)) |discr, field_tys| {
        let mut need_base = vec::from_elem(field_tys.len(), true);

        let numbered_fields = do fields.map |field| {
            match do vec::position(field_tys) |field_ty| {
                field_ty.ident == field.node.ident
            } {
                Some(i) => {
                    need_base[i] = false;
                    (i, field.node.expr)
                }
                None => {
                    tcx.sess.span_bug(field.span,
                                      ~"Couldn't find field in struct type")
                }
            }
        };
        let optbase = match base {
            Some(base_expr) => {
                let mut leftovers = ~[];
                for need_base.eachi |i, b| {
                    if *b {
                        leftovers.push((i, field_tys[i].mt.ty))
                    }
                }
                Some(StructBaseInfo {expr: base_expr,
                                     fields: leftovers })
            }
            None => {
                if need_base.any(|b| *b) {
                    // XXX should be span bug
                    tcx.sess.bug(~"missing fields and no base expr")
                }
                None
            }
        };

        let repr = adt::represent_type(bcx.ccx(), ty);
        trans_adt(bcx, &repr, discr, numbered_fields, optbase, dest)
    }
}

struct StructBaseInfo {
    expr: @ast::expr,
    fields: ~[(uint, ty::t)]
}

fn trans_adt(bcx: block, repr: &adt::Repr, discr: int,
             fields: &[(uint, @ast::expr)],
             optbase: Option<StructBaseInfo>,
             dest: Dest) -> block {
    let _icx = bcx.insn_ctxt("trans_adt");
    let mut bcx = bcx;
    let addr = match dest {
        Ignore => {
            for fields.each |&(_i, e)| {
                bcx = trans_into(bcx, e, Ignore);
            }
            for optbase.each |sbi| {
                bcx = trans_into(bcx, sbi.expr, Ignore);
            }
            return bcx;
        }
        SaveIn(pos) => pos
    };
    let mut temp_cleanups = ~[];
    adt::trans_set_discr(bcx, repr, addr, discr);
    for fields.each |&(i, e)| {
        let dest = adt::trans_GEP(bcx, repr, addr, discr, i);
        let e_ty = expr_ty(bcx, e);
        bcx = trans_into(bcx, e, SaveIn(dest));
        add_clean_temp_mem(bcx, dest, e_ty);
        temp_cleanups.push(dest);
    }
    for optbase.each |base| {
        // XXX is it sound to use the destination's repr on the base?
        // XXX would it ever be reasonable to be here with discr != 0?
        let base_datum = unpack_datum!(bcx, trans_to_datum(bcx, base.expr));
        for base.fields.each |&(i, t)| {
            let datum = do base_datum.get_element(bcx, t, ZeroMem) |srcval| {
                adt::trans_GEP(bcx, repr, srcval, discr, i)
            };
            let dest = adt::trans_GEP(bcx, repr, addr, discr, i);
            bcx = datum.store_to(bcx, base.expr.id, INIT, dest);
        }
    }

    for vec::each(temp_cleanups) |cleanup| {
        revoke_clean(bcx, *cleanup);
    }
    return bcx;
}


fn trans_immediate_lit(bcx: block, expr: @ast::expr,
                       lit: ast::lit) -> DatumBlock {
    // must not be a string constant, that is a RvalueDpsExpr
    let _icx = bcx.insn_ctxt("trans_immediate_lit");
    let ty = expr_ty(bcx, expr);
    immediate_rvalue_bcx(bcx, consts::const_lit(bcx.ccx(), expr, lit), ty)
}

fn trans_unary_datum(bcx: block,
                     un_expr: @ast::expr,
                     op: ast::unop,
                     sub_expr: @ast::expr) -> DatumBlock {
    let _icx = bcx.insn_ctxt("trans_unary_datum");

    // if deref, would be LvalueExpr
    assert op != ast::deref;

    // if overloaded, would be RvalueDpsExpr
    assert !bcx.ccx().maps.method_map.contains_key(&un_expr.id);

    let un_ty = expr_ty(bcx, un_expr);
    let sub_ty = expr_ty(bcx, sub_expr);

    return match op {
        ast::not => {
            let Result {bcx, val} = trans_to_datum(bcx, sub_expr).to_result();

            // If this is a boolean type, we must not use the LLVM Not
            // instruction, as that is a *bitwise* not and we want *logical*
            // not on our 8-bit boolean values.
            let llresult = match ty::get(un_ty).sty {
                ty::ty_bool => {
                    let llcond = ICmp(bcx,
                                      lib::llvm::IntEQ,
                                      val,
                                      C_bool(false));
                    Select(bcx, llcond, C_bool(true), C_bool(false))
                }
                _ => Not(bcx, val)
            };
            immediate_rvalue_bcx(bcx, llresult, un_ty)
        }
        ast::neg => {
            let Result {bcx, val} = trans_to_datum(bcx, sub_expr).to_result();
            let llneg = {
                if ty::type_is_fp(un_ty) {
                    FNeg(bcx, val)
                } else {
                    Neg(bcx, val)
                }
            };
            immediate_rvalue_bcx(bcx, llneg, un_ty)
        }
        ast::box(_) => {
            trans_boxed_expr(bcx, un_ty, sub_expr, sub_ty,
                             heap_managed)
        }
        ast::uniq(_) => {
            let heap  = heap_for_unique(bcx, un_ty);
            trans_boxed_expr(bcx, un_ty, sub_expr, sub_ty, heap)
        }
        ast::deref => {
            bcx.sess().bug(~"deref expressions should have been \
                             translated using trans_lvalue(), not \
                             trans_unary_datum()")
        }
    };

    fn trans_boxed_expr(bcx: block,
                        box_ty: ty::t,
                        contents: @ast::expr,
                        contents_ty: ty::t,
                        heap: heap) -> DatumBlock {
        let _icx = bcx.insn_ctxt("trans_boxed_expr");
        let base::MallocResult { bcx, box: bx, body } =
            base::malloc_general(bcx, contents_ty, heap);
        add_clean_free(bcx, bx, heap);
        let bcx = trans_into(bcx, contents, SaveIn(body));
        revoke_clean(bcx, bx);
        return immediate_rvalue_bcx(bcx, bx, box_ty);
    }
}

fn trans_addr_of(bcx: block, expr: @ast::expr,
                 subexpr: @ast::expr) -> DatumBlock {
    let _icx = bcx.insn_ctxt("trans_addr_of");
    let mut bcx = bcx;
    let sub_datum = unpack_datum!(bcx, trans_to_datum(bcx, subexpr));
    let llval = sub_datum.to_ref_llval(bcx);
    return immediate_rvalue_bcx(bcx, llval, expr_ty(bcx, expr));
}

// Important to get types for both lhs and rhs, because one might be _|_
// and the other not.
fn trans_eager_binop(bcx: block,
                     binop_expr: @ast::expr,
                     binop_ty: ty::t,
                     op: ast::binop,
                     lhs_datum: &Datum,
                     rhs_datum: &Datum)
                  -> DatumBlock {
    let mut bcx = bcx;
    let _icx = bcx.insn_ctxt("trans_eager_binop");

    let lhs = lhs_datum.to_appropriate_llval(bcx);
    let lhs_t = lhs_datum.ty;

    let rhs = rhs_datum.to_appropriate_llval(bcx);
    let rhs_t = rhs_datum.ty;

    let intype = {
        if ty::type_is_bot(lhs_t) { rhs_t }
        else { lhs_t }
    };
    let is_float = ty::type_is_fp(intype);

    let rhs = base::cast_shift_expr_rhs(bcx, op, lhs, rhs);

    let mut bcx = bcx;
    let val = match op {
      ast::add => {
        if is_float { FAdd(bcx, lhs, rhs) }
        else { Add(bcx, lhs, rhs) }
      }
      ast::subtract => {
        if is_float { FSub(bcx, lhs, rhs) }
        else { Sub(bcx, lhs, rhs) }
      }
      ast::mul => {
        if is_float { FMul(bcx, lhs, rhs) }
        else { Mul(bcx, lhs, rhs) }
      }
      ast::div => {
        if is_float {
            FDiv(bcx, lhs, rhs)
        } else {
            // Only zero-check integers; fp /0 is NaN
            bcx = base::fail_if_zero(bcx, binop_expr.span,
                                     op, rhs, rhs_t);
            if ty::type_is_signed(intype) {
                SDiv(bcx, lhs, rhs)
            } else {
                UDiv(bcx, lhs, rhs)
            }
        }
      }
      ast::rem => {
        if is_float {
            FRem(bcx, lhs, rhs)
        } else {
            // Only zero-check integers; fp %0 is NaN
            bcx = base::fail_if_zero(bcx, binop_expr.span,
                                     op, rhs, rhs_t);
            if ty::type_is_signed(intype) {
                SRem(bcx, lhs, rhs)
            } else {
                URem(bcx, lhs, rhs)
            }
        }
      }
      ast::bitor => Or(bcx, lhs, rhs),
      ast::bitand => And(bcx, lhs, rhs),
      ast::bitxor => Xor(bcx, lhs, rhs),
      ast::shl => Shl(bcx, lhs, rhs),
      ast::shr => {
        if ty::type_is_signed(intype) {
            AShr(bcx, lhs, rhs)
        } else { LShr(bcx, lhs, rhs) }
      }
      ast::eq | ast::ne | ast::lt | ast::ge | ast::le | ast::gt => {
        if ty::type_is_bot(rhs_t) {
            C_bool(false)
        } else {
            if !ty::type_is_scalar(rhs_t) {
                bcx.tcx().sess.span_bug(binop_expr.span,
                                        ~"non-scalar comparison");
            }
            let cmpr = base::compare_scalar_types(bcx, lhs, rhs, rhs_t, op);
            bcx = cmpr.bcx;
            ZExt(bcx, cmpr.val, T_i8())
        }
      }
      _ => {
        bcx.tcx().sess.span_bug(binop_expr.span, ~"unexpected binop");
      }
    };

    return immediate_rvalue_bcx(bcx, val, binop_ty);
}

// refinement types would obviate the need for this
enum lazy_binop_ty { lazy_and, lazy_or }

fn trans_lazy_binop(bcx: block,
                    binop_expr: @ast::expr,
                    op: lazy_binop_ty,
                    a: @ast::expr,
                    b: @ast::expr) -> DatumBlock {
    let _icx = bcx.insn_ctxt("trans_lazy_binop");
    let binop_ty = expr_ty(bcx, binop_expr);
    let mut bcx = bcx;

    let Result {bcx: past_lhs, val: lhs} = {
        do base::with_scope_result(bcx, a.info(), ~"lhs") |bcx| {
            trans_to_datum(bcx, a).to_result()
        }
    };

    if past_lhs.unreachable {
        return immediate_rvalue_bcx(past_lhs, lhs, binop_ty);
    }

    let join = base::sub_block(bcx, ~"join");
    let before_rhs = base::sub_block(bcx, ~"rhs");

    let lhs_i1 = bool_to_i1(past_lhs, lhs);
    match op {
      lazy_and => CondBr(past_lhs, lhs_i1, before_rhs.llbb, join.llbb),
      lazy_or => CondBr(past_lhs, lhs_i1, join.llbb, before_rhs.llbb)
    }

    let Result {bcx: past_rhs, val: rhs} = {
        do base::with_scope_result(before_rhs, b.info(), ~"rhs") |bcx| {
            trans_to_datum(bcx, b).to_result()
        }
    };

    if past_rhs.unreachable {
        return immediate_rvalue_bcx(join, lhs, binop_ty);
    }

    Br(past_rhs, join.llbb);
    let phi = Phi(join, T_bool(), ~[lhs, rhs], ~[past_lhs.llbb,
                                                 past_rhs.llbb]);

    return immediate_rvalue_bcx(join, phi, binop_ty);
}

fn trans_binary(bcx: block,
                binop_expr: @ast::expr,
                op: ast::binop,
                lhs: @ast::expr,
                rhs: @ast::expr) -> DatumBlock
{
    let _icx = bcx.insn_ctxt("trans_binary");

    match op {
        ast::and => {
            trans_lazy_binop(bcx, binop_expr, lazy_and, lhs, rhs)
        }
        ast::or => {
            trans_lazy_binop(bcx, binop_expr, lazy_or, lhs, rhs)
        }
        _ => {
            let mut bcx = bcx;
            let lhs_datum = unpack_datum!(bcx, trans_to_datum(bcx, lhs));
            let rhs_datum = unpack_datum!(bcx, trans_to_datum(bcx, rhs));
            let binop_ty = expr_ty(bcx, binop_expr);
            trans_eager_binop(bcx, binop_expr, binop_ty, op,
                              &lhs_datum, &rhs_datum)
        }
    }
}

fn trans_overloaded_op(bcx: block,
                       expr: @ast::expr,
                       rcvr: @ast::expr,
                       +args: ~[@ast::expr],
                       dest: Dest,
                       +autoref_arg: AutorefArg) -> block
{
    let origin = bcx.ccx().maps.method_map.get(&expr.id);
    let fty = node_id_type(bcx, expr.callee_id);
    return callee::trans_call_inner(
        bcx, expr.info(), fty,
        expr_ty(bcx, expr),
        |bcx| meth::trans_method_callee(bcx, expr.callee_id, rcvr, origin),
        callee::ArgExprs(args), dest, autoref_arg);
}

fn int_cast(bcx: block, lldsttype: TypeRef, llsrctype: TypeRef,
            llsrc: ValueRef, signed: bool) -> ValueRef {
    let _icx = bcx.insn_ctxt("int_cast");
    unsafe {
        let srcsz = llvm::LLVMGetIntTypeWidth(llsrctype);
        let dstsz = llvm::LLVMGetIntTypeWidth(lldsttype);
        return if dstsz == srcsz {
            BitCast(bcx, llsrc, lldsttype)
        } else if srcsz > dstsz {
            TruncOrBitCast(bcx, llsrc, lldsttype)
        } else if signed {
            SExtOrBitCast(bcx, llsrc, lldsttype)
        } else {
            ZExtOrBitCast(bcx, llsrc, lldsttype)
        };
    }
}

fn float_cast(bcx: block, lldsttype: TypeRef, llsrctype: TypeRef,
              llsrc: ValueRef) -> ValueRef {
    let _icx = bcx.insn_ctxt("float_cast");
    let srcsz = lib::llvm::float_width(llsrctype);
    let dstsz = lib::llvm::float_width(lldsttype);
    return if dstsz > srcsz {
        FPExt(bcx, llsrc, lldsttype)
    } else if srcsz > dstsz {
        FPTrunc(bcx, llsrc, lldsttype)
    } else { llsrc };
}

pub enum cast_kind {
    cast_pointer,
    cast_integral,
    cast_float,
    cast_enum,
    cast_other,
}

impl cmp::Eq for cast_kind {
    pure fn eq(&self, other: &cast_kind) -> bool {
        match ((*self), (*other)) {
            (cast_pointer, cast_pointer) => true,
            (cast_integral, cast_integral) => true,
            (cast_float, cast_float) => true,
            (cast_enum, cast_enum) => true,
            (cast_other, cast_other) => true,
            (cast_pointer, _) => false,
            (cast_integral, _) => false,
            (cast_float, _) => false,
            (cast_enum, _) => false,
            (cast_other, _) => false,
        }
    }
    pure fn ne(&self, other: &cast_kind) -> bool { !(*self).eq(other) }
}

pub fn cast_type_kind(t: ty::t) -> cast_kind {
    match ty::get(t).sty {
        ty::ty_float(*)   => cast_float,
        ty::ty_ptr(*)     => cast_pointer,
        ty::ty_rptr(*)    => cast_pointer,
        ty::ty_int(*)     => cast_integral,
        ty::ty_uint(*)    => cast_integral,
        ty::ty_bool       => cast_integral,
        ty::ty_enum(*)    => cast_enum,
        _                 => cast_other
    }
}

fn trans_imm_cast(bcx: block, expr: @ast::expr,
                  id: ast::node_id) -> DatumBlock {
    let _icx = bcx.insn_ctxt("trans_cast");
    let ccx = bcx.ccx();

    let t_out = node_id_type(bcx, id);

    let mut bcx = bcx;
    let llexpr = unpack_result!(bcx, trans_to_datum(bcx, expr).to_result());
    let ll_t_in = val_ty(llexpr);
    let t_in = expr_ty(bcx, expr);
    let ll_t_out = type_of::type_of(ccx, t_out);

    let k_in = cast_type_kind(t_in);
    let k_out = cast_type_kind(t_out);
    let s_in = k_in == cast_integral && ty::type_is_signed(t_in);

    let newval =
        match (k_in, k_out) {
            (cast_integral, cast_integral) => {
                int_cast(bcx, ll_t_out, ll_t_in, llexpr, s_in)
            }
            (cast_float, cast_float) => {
                float_cast(bcx, ll_t_out, ll_t_in, llexpr)
            }
            (cast_integral, cast_float) => {
                if s_in {
                    SIToFP(bcx, llexpr, ll_t_out)
                } else { UIToFP(bcx, llexpr, ll_t_out) }
            }
            (cast_float, cast_integral) => {
                if ty::type_is_signed(t_out) {
                    FPToSI(bcx, llexpr, ll_t_out)
                } else { FPToUI(bcx, llexpr, ll_t_out) }
            }
            (cast_integral, cast_pointer) => {
                IntToPtr(bcx, llexpr, ll_t_out)
            }
            (cast_pointer, cast_integral) => {
                PtrToInt(bcx, llexpr, ll_t_out)
            }
            (cast_pointer, cast_pointer) => {
                PointerCast(bcx, llexpr, ll_t_out)
            }
            (cast_enum, cast_integral) |
            (cast_enum, cast_float) => {
                let bcx = bcx;
                let repr = adt::represent_type(ccx, t_in);
                let lldiscrim_a = adt::trans_cast_to_int(bcx, &repr, llexpr);
                match k_out {
                    cast_integral => int_cast(bcx, ll_t_out,
                                              val_ty(lldiscrim_a),
                                              lldiscrim_a, true),
                    cast_float => SIToFP(bcx, lldiscrim_a, ll_t_out),
                    _ => ccx.sess.bug(~"translating unsupported cast.")
                }
            }
            _ => ccx.sess.bug(~"translating unsupported cast.")
        };
    return immediate_rvalue_bcx(bcx, newval, t_out);
}

fn trans_assign_op(bcx: block,
                   expr: @ast::expr,
                   op: ast::binop,
                   dst: @ast::expr,
                   src: @ast::expr) -> block
{
    let _icx = bcx.insn_ctxt("trans_assign_op");
    let mut bcx = bcx;

    debug!("trans_assign_op(expr=%s)", bcx.expr_to_str(expr));

    // Evaluate LHS (destination), which should be an lvalue
    let dst_datum = unpack_datum!(bcx, trans_lvalue_unadjusted(bcx, dst));

    // A user-defined operator method
    if bcx.ccx().maps.method_map.find(&expr.id).is_some() {
        // FIXME(#2528) evaluates the receiver twice!!
        let scratch = scratch_datum(bcx, dst_datum.ty, false);
        let bcx = trans_overloaded_op(bcx, expr, dst, ~[src],
                                      SaveIn(scratch.val), DoAutorefArg);
        return scratch.move_to_datum(bcx, DROP_EXISTING, dst_datum);
    }

    // Evaluate RHS (source)
    let src_datum = unpack_datum!(bcx, trans_to_datum(bcx, src));

    // Perform computation and store the result
    let result_datum =
        unpack_datum!(bcx,
                      trans_eager_binop(
                          bcx, expr, dst_datum.ty, op,
                          &dst_datum, &src_datum));
    return result_datum.copy_to_datum(bcx, DROP_EXISTING, dst_datum);
}

fn shorten(+x: ~str) -> ~str {
    if x.len() > 60 { x.substr(0, 60) } else { x }
}