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Move trans, back, driver, and back into a new crate, rustc_trans. Reduces memory usage significantly and opens opportunities for more parallel compilation.

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This commit is contained in:
Niko Matsakis
2014-11-15 20:30:33 -05:00
parent f637f1c5a2
commit dc6e414e6f
80 changed files with 640 additions and 532 deletions
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src/librustc_trans/trans/meth.rs Normal file
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// 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 llvm;
use llvm::ValueRef;
use metadata::csearch;
use middle::subst::{Subst,Substs};
use middle::subst::VecPerParamSpace;
use middle::subst;
use middle::traits;
use trans::base::*;
use trans::build::*;
use trans::callee::*;
use trans::callee;
use trans::cleanup;
use trans::common::*;
use trans::datum::*;
use trans::expr::{SaveIn, Ignore};
use trans::expr;
use trans::glue;
use trans::machine;
use trans::type_::Type;
use trans::type_of::*;
use middle::ty;
use middle::typeck;
use middle::typeck::MethodCall;
use util::ppaux::Repr;
use std::c_str::ToCStr;
use std::rc::Rc;
use syntax::abi::{Rust, RustCall};
use syntax::parse::token;
use syntax::{ast, ast_map, attr, visit};
use syntax::ast_util::PostExpansionMethod;
use syntax::codemap::DUMMY_SP;
// drop_glue pointer, size, align.
static VTABLE_OFFSET: uint = 3;
/**
The main "translation" pass for methods. Generates code
for non-monomorphized methods only. Other methods will
be generated once they are invoked with specific type parameters,
see `trans::base::lval_static_fn()` or `trans::base::monomorphic_fn()`.
*/
pub fn trans_impl(ccx: &CrateContext,
name: ast::Ident,
impl_items: &[ast::ImplItem],
generics: &ast::Generics,
id: ast::NodeId) {
let _icx = push_ctxt("meth::trans_impl");
let tcx = ccx.tcx();
debug!("trans_impl(name={}, id={})", name.repr(tcx), id);
// Both here and below with generic methods, be sure to recurse and look for
// items that we need to translate.
if !generics.ty_params.is_empty() {
let mut v = TransItemVisitor{ ccx: ccx };
for impl_item in impl_items.iter() {
match *impl_item {
ast::MethodImplItem(ref method) => {
visit::walk_method_helper(&mut v, &**method);
}
ast::TypeImplItem(_) => {}
}
}
return;
}
for impl_item in impl_items.iter() {
match *impl_item {
ast::MethodImplItem(ref method) => {
if method.pe_generics().ty_params.len() == 0u {
let trans_everywhere = attr::requests_inline(method.attrs.as_slice());
for (ref ccx, is_origin) in ccx.maybe_iter(trans_everywhere) {
let llfn = get_item_val(ccx, method.id);
trans_fn(ccx,
method.pe_fn_decl(),
method.pe_body(),
llfn,
&param_substs::empty(),
method.id,
&[]);
update_linkage(ccx,
llfn,
Some(method.id),
if is_origin { OriginalTranslation } else { InlinedCopy });
}
}
let mut v = TransItemVisitor {
ccx: ccx,
};
visit::walk_method_helper(&mut v, &**method);
}
ast::TypeImplItem(_) => {}
}
}
}
pub fn trans_method_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
method_call: MethodCall,
self_expr: Option<&ast::Expr>,
arg_cleanup_scope: cleanup::ScopeId)
-> Callee<'blk, 'tcx> {
let _icx = push_ctxt("meth::trans_method_callee");
let (origin, method_ty) =
bcx.tcx().method_map
.borrow()
.get(&method_call)
.map(|method| (method.origin.clone(), method.ty))
.unwrap();
match origin {
typeck::MethodStatic(did) |
typeck::MethodStaticUnboxedClosure(did) => {
Callee {
bcx: bcx,
data: Fn(callee::trans_fn_ref(bcx,
did,
MethodCall(method_call))),
}
}
typeck::MethodTypeParam(typeck::MethodParam {
ref trait_ref,
method_num
}) => {
let trait_ref =
Rc::new(trait_ref.subst(bcx.tcx(),
&bcx.fcx.param_substs.substs));
let span = bcx.tcx().map.span(method_call.expr_id);
let origin = fulfill_obligation(bcx.ccx(),
span,
(*trait_ref).clone());
debug!("origin = {}", origin.repr(bcx.tcx()));
trans_monomorphized_callee(bcx, method_call, trait_ref.def_id,
method_num, origin)
}
typeck::MethodTraitObject(ref mt) => {
let self_expr = match self_expr {
Some(self_expr) => self_expr,
None => {
bcx.sess().span_bug(bcx.tcx().map.span(method_call.expr_id),
"self expr wasn't provided for trait object \
callee (trying to call overloaded op?)")
}
};
trans_trait_callee(bcx,
monomorphize_type(bcx, method_ty),
mt.real_index,
self_expr,
arg_cleanup_scope)
}
}
}
pub fn trans_static_method_callee(bcx: Block,
method_id: ast::DefId,
trait_id: ast::DefId,
expr_id: ast::NodeId)
-> ValueRef
{
let _icx = push_ctxt("meth::trans_static_method_callee");
let ccx = bcx.ccx();
debug!("trans_static_method_callee(method_id={}, trait_id={}, \
expr_id={})",
method_id,
ty::item_path_str(bcx.tcx(), trait_id),
expr_id);
let mname = if method_id.krate == ast::LOCAL_CRATE {
match bcx.tcx().map.get(method_id.node) {
ast_map::NodeTraitItem(method) => {
let ident = match *method {
ast::RequiredMethod(ref m) => m.ident,
ast::ProvidedMethod(ref m) => m.pe_ident(),
ast::TypeTraitItem(_) => {
bcx.tcx().sess.bug("trans_static_method_callee() on \
an associated type?!")
}
};
ident.name
}
_ => panic!("callee is not a trait method")
}
} else {
csearch::get_item_path(bcx.tcx(), method_id).last().unwrap().name()
};
debug!("trans_static_method_callee: method_id={}, expr_id={}, \
name={}", method_id, expr_id, token::get_name(mname));
// Find the substitutions for the fn itself. This includes
// type parameters that belong to the trait but also some that
// belong to the method:
let rcvr_substs = node_id_substs(bcx, ExprId(expr_id));
let subst::SeparateVecsPerParamSpace {
types: rcvr_type,
selfs: rcvr_self,
assocs: rcvr_assoc,
fns: rcvr_method
} = rcvr_substs.types.split();
// Lookup the precise impl being called. To do that, we need to
// create a trait reference identifying the self type and other
// input type parameters. To create that trait reference, we have
// to pick apart the type parameters to identify just those that
// pertain to the trait. This is easiest to explain by example:
//
// trait Convert {
// fn from<U:Foo>(n: U) -> Option<Self>;
// }
// ...
// let f = <Vec<int> as Convert>::from::<String>(...)
//
// Here, in this call, which I've written with explicit UFCS
// notation, the set of type parameters will be:
//
// rcvr_type: [] <-- nothing declared on the trait itself
// rcvr_self: [Vec<int>] <-- the self type
// rcvr_method: [String] <-- method type parameter
//
// So we create a trait reference using the first two,
// basically corresponding to `<Vec<int> as Convert>`.
// The remaining type parameters (`rcvr_method`) will be used below.
let trait_substs =
Substs::erased(VecPerParamSpace::new(rcvr_type,
rcvr_self,
rcvr_assoc,
Vec::new()));
debug!("trait_substs={}", trait_substs.repr(bcx.tcx()));
let trait_ref = Rc::new(ty::TraitRef { def_id: trait_id,
substs: trait_substs });
let vtbl = fulfill_obligation(bcx.ccx(),
DUMMY_SP,
trait_ref);
// Now that we know which impl is being used, we can dispatch to
// the actual function:
match vtbl {
traits::VtableImpl(traits::VtableImplData {
impl_def_id: impl_did,
substs: impl_substs,
nested: _ }) =>
{
assert!(impl_substs.types.all(|t| !ty::type_needs_infer(*t)));
// Create the substitutions that are in scope. This combines
// the type parameters from the impl with those declared earlier.
// To see what I mean, consider a possible impl:
//
// impl<T> Convert for Vec<T> {
// fn from<U:Foo>(n: U) { ... }
// }
//
// Recall that we matched `<Vec<int> as Convert>`. Trait
// resolution will have given us a substitution
// containing `impl_substs=[[T=int],[],[]]` (the type
// parameters defined on the impl). We combine
// that with the `rcvr_method` from before, which tells us
// the type parameters from the *method*, to yield
// `callee_substs=[[T=int],[],[U=String]]`.
let subst::SeparateVecsPerParamSpace {
types: impl_type,
selfs: impl_self,
assocs: impl_assoc,
fns: _
} = impl_substs.types.split();
let callee_substs =
Substs::erased(VecPerParamSpace::new(impl_type,
impl_self,
impl_assoc,
rcvr_method));
let mth_id = method_with_name(ccx, impl_did, mname);
let llfn = trans_fn_ref_with_substs(bcx, mth_id, ExprId(expr_id),
callee_substs);
let callee_ty = node_id_type(bcx, expr_id);
let llty = type_of_fn_from_ty(ccx, callee_ty).ptr_to();
PointerCast(bcx, llfn, llty)
}
_ => {
bcx.tcx().sess.bug(
format!("static call to invalid vtable: {}",
vtbl.repr(bcx.tcx())).as_slice());
}
}
}
fn method_with_name(ccx: &CrateContext, impl_id: ast::DefId, name: ast::Name)
-> ast::DefId {
match ccx.impl_method_cache().borrow().get(&(impl_id, name)).cloned() {
Some(m) => return m,
None => {}
}
let impl_items = ccx.tcx().impl_items.borrow();
let impl_items =
impl_items.get(&impl_id)
.expect("could not find impl while translating");
let meth_did = impl_items.iter()
.find(|&did| {
ty::impl_or_trait_item(ccx.tcx(), did.def_id()).name() == name
}).expect("could not find method while \
translating");
ccx.impl_method_cache().borrow_mut().insert((impl_id, name),
meth_did.def_id());
meth_did.def_id()
}
fn trans_monomorphized_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
method_call: MethodCall,
trait_id: ast::DefId,
n_method: uint,
vtable: traits::Vtable<()>)
-> Callee<'blk, 'tcx> {
let _icx = push_ctxt("meth::trans_monomorphized_callee");
match vtable {
traits::VtableImpl(vtable_impl) => {
let ccx = bcx.ccx();
let impl_did = vtable_impl.impl_def_id;
let mname = match ty::trait_item(ccx.tcx(), trait_id, n_method) {
ty::MethodTraitItem(method) => method.name,
ty::TypeTraitItem(_) => {
bcx.tcx().sess.bug("can't monomorphize an associated \
type")
}
};
let mth_id = method_with_name(bcx.ccx(), impl_did, mname);
// create a concatenated set of substitutions which includes
// those from the impl and those from the method:
let callee_substs =
combine_impl_and_methods_tps(
bcx, MethodCall(method_call), vtable_impl.substs);
// translate the function
let llfn = trans_fn_ref_with_substs(bcx,
mth_id,
MethodCall(method_call),
callee_substs);
Callee { bcx: bcx, data: Fn(llfn) }
}
traits::VtableUnboxedClosure(closure_def_id, substs) => {
// The substitutions should have no type parameters remaining
// after passing through fulfill_obligation
let llfn = trans_fn_ref_with_substs(bcx,
closure_def_id,
MethodCall(method_call),
substs);
Callee {
bcx: bcx,
data: Fn(llfn),
}
}
_ => {
bcx.tcx().sess.bug(
"vtable_param left in monomorphized function's vtable substs");
}
}
}
fn combine_impl_and_methods_tps(bcx: Block,
node: ExprOrMethodCall,
rcvr_substs: subst::Substs)
-> subst::Substs
{
/*!
* Creates a concatenated set of substitutions which includes
* those from the impl and those from the method. This are
* some subtle complications here. Statically, we have a list
* of type parameters like `[T0, T1, T2, M1, M2, M3]` where
* `Tn` are type parameters that appear on the receiver. For
* example, if the receiver is a method parameter `A` with a
* bound like `trait<B,C,D>` then `Tn` would be `[B,C,D]`.
*
* The weird part is that the type `A` might now be bound to
* any other type, such as `foo<X>`. In that case, the vector
* we want is: `[X, M1, M2, M3]`. Therefore, what we do now is
* to slice off the method type parameters and append them to
* the type parameters from the type that the receiver is
* mapped to.
*/
let ccx = bcx.ccx();
let node_substs = node_id_substs(bcx, node);
debug!("rcvr_substs={}", rcvr_substs.repr(ccx.tcx()));
debug!("node_substs={}", node_substs.repr(ccx.tcx()));
// Break apart the type parameters from the node and type
// parameters from the receiver.
let node_method = node_substs.types.split().fns;
let subst::SeparateVecsPerParamSpace {
types: rcvr_type,
selfs: rcvr_self,
assocs: rcvr_assoc,
fns: rcvr_method
} = rcvr_substs.types.clone().split();
assert!(rcvr_method.is_empty());
subst::Substs {
regions: subst::ErasedRegions,
types: subst::VecPerParamSpace::new(rcvr_type, rcvr_self, rcvr_assoc, node_method)
}
}
fn trans_trait_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
method_ty: ty::t,
n_method: uint,
self_expr: &ast::Expr,
arg_cleanup_scope: cleanup::ScopeId)
-> Callee<'blk, 'tcx> {
/*!
* Create a method callee where the method is coming from a trait
* object (e.g., Box<Trait> type). In this case, we must pull the fn
* pointer out of the vtable that is packaged up with the object.
* Objects are represented as a pair, so we first evaluate the self
* expression and then extract the self data and vtable out of the
* pair.
*/
let _icx = push_ctxt("meth::trans_trait_callee");
let mut bcx = bcx;
// Translate self_datum and take ownership of the value by
// converting to an rvalue.
let self_datum = unpack_datum!(
bcx, expr::trans(bcx, self_expr));
let llval = if ty::type_needs_drop(bcx.tcx(), self_datum.ty) {
let self_datum = unpack_datum!(
bcx, self_datum.to_rvalue_datum(bcx, "trait_callee"));
// Convert to by-ref since `trans_trait_callee_from_llval` wants it
// that way.
let self_datum = unpack_datum!(
bcx, self_datum.to_ref_datum(bcx));
// Arrange cleanup in case something should go wrong before the
// actual call occurs.
self_datum.add_clean(bcx.fcx, arg_cleanup_scope)
} else {
// We don't have to do anything about cleanups for &Trait and &mut Trait.
assert!(self_datum.kind.is_by_ref());
self_datum.val
};
trans_trait_callee_from_llval(bcx, method_ty, n_method, llval)
}
pub fn trans_trait_callee_from_llval<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
callee_ty: ty::t,
n_method: uint,
llpair: ValueRef)
-> Callee<'blk, 'tcx> {
/*!
* Same as `trans_trait_callee()` above, except that it is given
* a by-ref pointer to the object pair.
*/
let _icx = push_ctxt("meth::trans_trait_callee");
let ccx = bcx.ccx();
// Load the data pointer from the object.
debug!("(translating trait callee) loading second index from pair");
let llboxptr = GEPi(bcx, llpair, &[0u, abi::trt_field_box]);
let llbox = Load(bcx, llboxptr);
let llself = PointerCast(bcx, llbox, Type::i8p(ccx));
// Load the function from the vtable and cast it to the expected type.
debug!("(translating trait callee) loading method");
// Replace the self type (&Self or Box<Self>) with an opaque pointer.
let llcallee_ty = match ty::get(callee_ty).sty {
ty::ty_bare_fn(ref f) if f.abi == Rust || f.abi == RustCall => {
type_of_rust_fn(ccx,
Some(Type::i8p(ccx)),
f.sig.inputs.slice_from(1),
f.sig.output,
f.abi)
}
_ => {
ccx.sess().bug("meth::trans_trait_callee given non-bare-rust-fn");
}
};
let llvtable = Load(bcx,
PointerCast(bcx,
GEPi(bcx, llpair,
&[0u, abi::trt_field_vtable]),
Type::vtable(ccx).ptr_to().ptr_to()));
let mptr = Load(bcx, GEPi(bcx, llvtable, &[0u, n_method + VTABLE_OFFSET]));
let mptr = PointerCast(bcx, mptr, llcallee_ty.ptr_to());
return Callee {
bcx: bcx,
data: TraitItem(MethodData {
llfn: mptr,
llself: llself,
})
};
}
/// Creates a returns a dynamic vtable for the given type and vtable origin.
/// This is used only for objects.
///
/// The `trait_ref` encodes the erased self type. Hence if we are
/// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
/// `trait_ref` would map `T:Trait`, but `box_ty` would be
/// `Foo<T>`. This `box_ty` is primarily used to encode the destructor.
/// This will hopefully change now that DST is underway.
pub fn get_vtable(bcx: Block,
box_ty: ty::t,
trait_ref: Rc<ty::TraitRef>)
-> ValueRef
{
debug!("get_vtable(box_ty={}, trait_ref={})",
box_ty.repr(bcx.tcx()),
trait_ref.repr(bcx.tcx()));
let tcx = bcx.tcx();
let ccx = bcx.ccx();
let _icx = push_ctxt("meth::get_vtable");
// Check the cache.
let cache_key = (box_ty, trait_ref.clone());
match ccx.vtables().borrow().get(&cache_key) {
Some(&val) => { return val }
None => { }
}
// Not in the cache. Build it.
let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
let vtable = fulfill_obligation(bcx.ccx(),
DUMMY_SP,
trait_ref.clone());
match vtable {
traits::VtableBuiltin(_) => {
Vec::new().into_iter()
}
traits::VtableImpl(
traits::VtableImplData {
impl_def_id: id,
substs,
nested: _ }) => {
emit_vtable_methods(bcx, id, substs).into_iter()
}
traits::VtableUnboxedClosure(closure_def_id, substs) => {
// Look up closure type
let self_ty = ty::node_id_to_type(bcx.tcx(), closure_def_id.node);
// Apply substitutions from closure param environment.
// The substitutions should have no type parameters
// remaining after passing through fulfill_obligation
let self_ty = self_ty.subst(bcx.tcx(), &substs);
let mut llfn = trans_fn_ref_with_substs(
bcx,
closure_def_id,
ExprId(0),
substs.clone());
{
let unboxed_closures = bcx.tcx()
.unboxed_closures
.borrow();
let closure_info =
unboxed_closures.get(&closure_def_id)
.expect("get_vtable(): didn't find \
unboxed closure");
if closure_info.kind == ty::FnOnceUnboxedClosureKind {
// Untuple the arguments and create an unboxing shim.
let (new_inputs, new_output) = match ty::get(self_ty).sty {
ty::ty_unboxed_closure(_, _, ref substs) => {
let mut new_inputs = vec![self_ty.clone()];
match ty::get(closure_info.closure_type
.sig
.inputs[0]).sty {
ty::ty_tup(ref elements) => {
for element in elements.iter() {
new_inputs.push(element.subst(bcx.tcx(), substs));
}
}
_ => {
bcx.tcx().sess.bug("get_vtable(): closure \
type wasn't a tuple")
}
}
(new_inputs,
closure_info.closure_type.sig.output.subst(bcx.tcx(), substs))
},
_ => bcx.tcx().sess.bug("get_vtable(): def wasn't an unboxed closure")
};
let closure_type = ty::BareFnTy {
fn_style: closure_info.closure_type.fn_style,
abi: Rust,
sig: ty::FnSig {
binder_id: closure_info.closure_type
.sig
.binder_id,
inputs: new_inputs,
output: new_output,
variadic: false,
},
};
debug!("get_vtable(): closure type is {}",
closure_type.repr(bcx.tcx()));
llfn = trans_unboxing_shim(bcx,
llfn,
&closure_type,
closure_def_id,
&substs);
}
}
(vec!(llfn)).into_iter()
}
traits::VtableParam(..) => {
bcx.sess().bug(
format!("resolved vtable for {} to bad vtable {} in trans",
trait_ref.repr(bcx.tcx()),
vtable.repr(bcx.tcx())).as_slice());
}
}
});
let size_ty = sizing_type_of(ccx, trait_ref.self_ty());
let size = machine::llsize_of_alloc(ccx, size_ty);
let ll_size = C_uint(ccx, size);
let align = align_of(ccx, trait_ref.self_ty());
let ll_align = C_uint(ccx, align);
// Generate a destructor for the vtable.
let drop_glue = glue::get_drop_glue(ccx, box_ty);
let vtable = make_vtable(ccx, drop_glue, ll_size, ll_align, methods);
ccx.vtables().borrow_mut().insert(cache_key, vtable);
vtable
}
/// Helper function to declare and initialize the vtable.
pub fn make_vtable<I: Iterator<ValueRef>>(ccx: &CrateContext,
drop_glue: ValueRef,
size: ValueRef,
align: ValueRef,
ptrs: I)
-> ValueRef {
let _icx = push_ctxt("meth::make_vtable");
let head = vec![drop_glue, size, align];
let components: Vec<_> = head.into_iter().chain(ptrs).collect();
unsafe {
let tbl = C_struct(ccx, components.as_slice(), false);
let sym = token::gensym("vtable");
let vt_gvar = format!("vtable{}", sym.uint()).with_c_str(|buf| {
llvm::LLVMAddGlobal(ccx.llmod(), val_ty(tbl).to_ref(), buf)
});
llvm::LLVMSetInitializer(vt_gvar, tbl);
llvm::LLVMSetGlobalConstant(vt_gvar, llvm::True);
llvm::SetLinkage(vt_gvar, llvm::InternalLinkage);
vt_gvar
}
}
fn emit_vtable_methods(bcx: Block,
impl_id: ast::DefId,
substs: subst::Substs)
-> Vec<ValueRef> {
let ccx = bcx.ccx();
let tcx = ccx.tcx();
let trt_id = match ty::impl_trait_ref(tcx, impl_id) {
Some(t_id) => t_id.def_id,
None => ccx.sess().bug("make_impl_vtable: don't know how to \
make a vtable for a type impl!")
};
ty::populate_implementations_for_trait_if_necessary(bcx.tcx(), trt_id);
let trait_item_def_ids = ty::trait_item_def_ids(tcx, trt_id);
trait_item_def_ids.iter().flat_map(|method_def_id| {
let method_def_id = method_def_id.def_id();
let name = ty::impl_or_trait_item(tcx, method_def_id).name();
// The substitutions we have are on the impl, so we grab
// the method type from the impl to substitute into.
let m_id = method_with_name(ccx, impl_id, name);
let ti = ty::impl_or_trait_item(tcx, m_id);
match ti {
ty::MethodTraitItem(m) => {
debug!("(making impl vtable) emitting method {} at subst {}",
m.repr(tcx),
substs.repr(tcx));
if m.generics.has_type_params(subst::FnSpace) ||
ty::type_has_self(ty::mk_bare_fn(tcx, m.fty.clone())) {
debug!("(making impl vtable) method has self or type \
params: {}",
token::get_name(name));
Some(C_null(Type::nil(ccx).ptr_to())).into_iter()
} else {
let mut fn_ref = trans_fn_ref_with_substs(
bcx,
m_id,
ExprId(0),
substs.clone());
if m.explicit_self == ty::ByValueExplicitSelfCategory {
fn_ref = trans_unboxing_shim(bcx,
fn_ref,
&m.fty,
m_id,
&substs);
}
Some(fn_ref).into_iter()
}
}
ty::TypeTraitItem(_) => {
None.into_iter()
}
}
}).collect()
}
pub fn trans_trait_cast<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
datum: Datum<Expr>,
id: ast::NodeId,
trait_ref: Rc<ty::TraitRef>,
dest: expr::Dest)
-> Block<'blk, 'tcx> {
/*!
* Generates the code to convert from a pointer (`Box<T>`, `&T`, etc)
* into an object (`Box<Trait>`, `&Trait`, etc). This means creating a
* pair where the first word is the vtable and the second word is
* the pointer.
*/
let mut bcx = bcx;
let _icx = push_ctxt("meth::trans_trait_cast");
let lldest = match dest {
Ignore => {
return datum.clean(bcx, "trait_trait_cast", id);
}
SaveIn(dest) => dest
};
debug!("trans_trait_cast: trait_ref={}",
trait_ref.repr(bcx.tcx()));
let datum_ty = datum.ty;
let llbox_ty = type_of(bcx.ccx(), datum_ty);
// Store the pointer into the first half of pair.
let llboxdest = GEPi(bcx, lldest, &[0u, abi::trt_field_box]);
let llboxdest = PointerCast(bcx, llboxdest, llbox_ty.ptr_to());
bcx = datum.store_to(bcx, llboxdest);
// Store the vtable into the second half of pair.
let vtable = get_vtable(bcx, datum_ty, trait_ref);
let llvtabledest = GEPi(bcx, lldest, &[0u, abi::trt_field_vtable]);
let llvtabledest = PointerCast(bcx, llvtabledest, val_ty(vtable).ptr_to());
Store(bcx, vtable, llvtabledest);
bcx
}