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rust/src/librustc_trans/trans/adt.rs

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// Copyright 2013 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.
//! # Representation of Algebraic Data Types
//!
//! This module determines how to represent enums, structs, and tuples
//! based on their monomorphized types; it is responsible both for
//! choosing a representation and translating basic operations on
//! values of those types. (Note: exporting the representations for
//! debuggers is handled in debuginfo.rs, not here.)
//!
//! Note that the interface treats everything as a general case of an
//! enum, so structs/tuples/etc. have one pseudo-variant with
//! discriminant 0; i.e., as if they were a univariant enum.
//!
//! Having everything in one place will enable improvements to data
//! structure representation; possibilities include:
//!
//! - User-specified alignment (e.g., cacheline-aligning parts of
//! concurrently accessed data structures); LLVM can't represent this
//! directly, so we'd have to insert padding fields in any structure
//! that might contain one and adjust GEP indices accordingly. See
//! issue #4578.
//!
//! - Store nested enums' discriminants in the same word. Rather, if
//! some variants start with enums, and those enums representations
//! have unused alignment padding between discriminant and body, the
//! outer enum's discriminant can be stored there and those variants
//! can start at offset 0. Kind of fancy, and might need work to
//! make copies of the inner enum type cooperate, but it could help
//! with `Option` or `Result` wrapped around another enum.
//!
//! - Tagged pointers would be neat, but given that any type can be
//! used unboxed and any field can have pointers (including mutable)
//! taken to it, implementing them for Rust seems difficult.
#![allow(unsigned_negation)]
pub use self::Repr::*;
use std::rc::Rc;
use llvm::{ValueRef, True, IntEQ, IntNE};
use back::abi::FAT_PTR_ADDR;
use middle::subst;
use middle::ty::{self, Ty, ClosureTyper};
use middle::ty::Disr;
use syntax::ast;
use syntax::attr;
use syntax::attr::IntType;
use trans::_match;
use trans::build::*;
use trans::cleanup;
use trans::cleanup::CleanupMethods;
use trans::common::*;
use trans::datum;
use trans::debuginfo::DebugLoc;
use trans::machine;
use trans::monomorphize;
use trans::type_::Type;
use trans::type_of;
use util::ppaux::Repr as PrettyPrintRepr;
type Hint = attr::ReprAttr;
/// Representations.
#[derive(Eq, PartialEq, Debug)]
pub enum Repr<'tcx> {
/// C-like enums; basically an int.
CEnum(IntType, Disr, Disr), // discriminant range (signedness based on the IntType)
/// Single-case variants, and structs/tuples/records.
///
/// Structs with destructors need a dynamic destroyedness flag to
/// avoid running the destructor too many times; this is included
/// in the `Struct` if present.
/// (The flag if nonzero, represents the initialization value to use;
/// if zero, then use no flag at all.)
Univariant(Struct<'tcx>, u8),
/// General-case enums: for each case there is a struct, and they
/// all start with a field for the discriminant.
///
/// Types with destructors need a dynamic destroyedness flag to
/// avoid running the destructor too many times; the last argument
/// indicates whether such a flag is present.
/// (The flag, if nonzero, represents the initialization value to use;
/// if zero, then use no flag at all.)
General(IntType, Vec<Struct<'tcx>>, u8),
/// Two cases distinguished by a nullable pointer: the case with discriminant
/// `nndiscr` must have single field which is known to be nonnull due to its type.
/// The other case is known to be zero sized. Hence we represent the enum
/// as simply a nullable pointer: if not null it indicates the `nndiscr` variant,
/// otherwise it indicates the other case.
RawNullablePointer {
nndiscr: Disr,
nnty: Ty<'tcx>,
nullfields: Vec<Ty<'tcx>>
},
/// Two cases distinguished by a nullable pointer: the case with discriminant
/// `nndiscr` is represented by the struct `nonnull`, where the `discrfield`th
/// field is known to be nonnull due to its type; if that field is null, then
/// it represents the other case, which is inhabited by at most one value
/// (and all other fields are undefined/unused).
///
/// For example, `std::option::Option` instantiated at a safe pointer type
/// is represented such that `None` is a null pointer and `Some` is the
/// identity function.
StructWrappedNullablePointer {
nonnull: Struct<'tcx>,
nndiscr: Disr,
discrfield: DiscrField,
nullfields: Vec<Ty<'tcx>>,
}
}
/// For structs, and struct-like parts of anything fancier.
#[derive(Eq, PartialEq, Debug)]
pub struct Struct<'tcx> {
// If the struct is DST, then the size and alignment do not take into
// account the unsized fields of the struct.
pub size: u64,
pub align: u32,
pub sized: bool,
pub packed: bool,
pub fields: Vec<Ty<'tcx>>
}
/// Convenience for `represent_type`. There should probably be more or
/// these, for places in trans where the `Ty` isn't directly
/// available.
pub fn represent_node<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
node: ast::NodeId) -> Rc<Repr<'tcx>> {
represent_type(bcx.ccx(), node_id_type(bcx, node))
}
/// Decides how to represent a given type.
pub fn represent_type<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
t: Ty<'tcx>)
-> Rc<Repr<'tcx>> {
debug!("Representing: {}", t.repr());
match cx.adt_reprs().borrow().get(&t) {
Some(repr) => return repr.clone(),
None => {}
}
let repr = Rc::new(represent_type_uncached(cx, t));
debug!("Represented as: {:?}", repr);
cx.adt_reprs().borrow_mut().insert(t, repr.clone());
repr
}
macro_rules! repeat_u8_as_u32 {
($name:expr) => { (($name as u32) << 24 |
($name as u32) << 16 |
($name as u32) << 8 |
($name as u32)) }
}
macro_rules! repeat_u8_as_u64 {
($name:expr) => { ((repeat_u8_as_u32!($name) as u64) << 32 |
(repeat_u8_as_u32!($name) as u64)) }
}
pub const DTOR_NEEDED: u8 = 0xd4;
pub const DTOR_NEEDED_U32: u32 = repeat_u8_as_u32!(DTOR_NEEDED);
pub const DTOR_NEEDED_U64: u64 = repeat_u8_as_u64!(DTOR_NEEDED);
#[allow(dead_code)]
pub fn dtor_needed_usize(ccx: &CrateContext) -> usize {
match &ccx.tcx().sess.target.target.target_pointer_width[..] {
"32" => DTOR_NEEDED_U32 as usize,
"64" => DTOR_NEEDED_U64 as usize,
tws => panic!("Unsupported target word size for int: {}", tws),
}
}
pub const DTOR_DONE: u8 = 0x1d;
pub const DTOR_DONE_U32: u32 = repeat_u8_as_u32!(DTOR_DONE);
pub const DTOR_DONE_U64: u64 = repeat_u8_as_u64!(DTOR_DONE);
#[allow(dead_code)]
pub fn dtor_done_usize(ccx: &CrateContext) -> usize {
match &ccx.tcx().sess.target.target.target_pointer_width[..] {
"32" => DTOR_DONE_U32 as usize,
"64" => DTOR_DONE_U64 as usize,
tws => panic!("Unsupported target word size for int: {}", tws),
}
}
fn dtor_to_init_u8(dtor: bool) -> u8 {
if dtor { DTOR_NEEDED } else { 0 }
}
pub trait GetDtorType<'tcx> { fn dtor_type(&self) -> Ty<'tcx>; }
impl<'tcx> GetDtorType<'tcx> for ty::ctxt<'tcx> {
fn dtor_type(&self) -> Ty<'tcx> { self.types.u8 }
}
fn dtor_active(flag: u8) -> bool {
flag != 0
}
fn represent_type_uncached<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
t: Ty<'tcx>) -> Repr<'tcx> {
match t.sty {
ty::TyTuple(ref elems) => {
Univariant(mk_struct(cx, &elems[..], false, t), 0)
}
ty::TyStruct(def_id, substs) => {
let fields = ty::lookup_struct_fields(cx.tcx(), def_id);
let mut ftys = fields.iter().map(|field| {
let fty = ty::lookup_field_type(cx.tcx(), def_id, field.id, substs);
monomorphize::normalize_associated_type(cx.tcx(), &fty)
}).collect::<Vec<_>>();
let packed = ty::lookup_packed(cx.tcx(), def_id);
let dtor = ty::ty_dtor(cx.tcx(), def_id).has_drop_flag();
if dtor {
ftys.push(cx.tcx().dtor_type());
}
Univariant(mk_struct(cx, &ftys[..], packed, t), dtor_to_init_u8(dtor))
}
ty::TyClosure(def_id, substs) => {
let typer = NormalizingClosureTyper::new(cx.tcx());
let upvars = typer.closure_upvars(def_id, substs).unwrap();
let upvar_types = upvars.iter().map(|u| u.ty).collect::<Vec<_>>();
Univariant(mk_struct(cx, &upvar_types[..], false, t), 0)
}
ty::TyEnum(def_id, substs) => {
let cases = get_cases(cx.tcx(), def_id, substs);
let hint = *ty::lookup_repr_hints(cx.tcx(), def_id).get(0)
.unwrap_or(&attr::ReprAny);
let dtor = ty::ty_dtor(cx.tcx(), def_id).has_drop_flag();
if cases.is_empty() {
// Uninhabitable; represent as unit
// (Typechecking will reject discriminant-sizing attrs.)
assert_eq!(hint, attr::ReprAny);
let ftys = if dtor { vec!(cx.tcx().dtor_type()) } else { vec!() };
return Univariant(mk_struct(cx, &ftys[..], false, t),
dtor_to_init_u8(dtor));
}
if !dtor && cases.iter().all(|c| c.tys.is_empty()) {
// All bodies empty -> intlike
let discrs: Vec<u64> = cases.iter().map(|c| c.discr).collect();
let bounds = IntBounds {
ulo: *discrs.iter().min().unwrap(),
uhi: *discrs.iter().max().unwrap(),
slo: discrs.iter().map(|n| *n as i64).min().unwrap(),
shi: discrs.iter().map(|n| *n as i64).max().unwrap()
};
return mk_cenum(cx, hint, &bounds);
}
// Since there's at least one
// non-empty body, explicit discriminants should have
// been rejected by a checker before this point.
if !cases.iter().enumerate().all(|(i,c)| c.discr == (i as Disr)) {
cx.sess().bug(&format!("non-C-like enum {} with specified \
discriminants",
ty::item_path_str(cx.tcx(),
def_id)));
}
if cases.len() == 1 {
// Equivalent to a struct/tuple/newtype.
// (Typechecking will reject discriminant-sizing attrs.)
assert_eq!(hint, attr::ReprAny);
let mut ftys = cases[0].tys.clone();
if dtor { ftys.push(cx.tcx().dtor_type()); }
return Univariant(mk_struct(cx, &ftys[..], false, t),
dtor_to_init_u8(dtor));
}
if !dtor && cases.len() == 2 && hint == attr::ReprAny {
// Nullable pointer optimization
let mut discr = 0;
while discr < 2 {
if cases[1 - discr].is_zerolen(cx, t) {
let st = mk_struct(cx, &cases[discr].tys,
false, t);
match cases[discr].find_ptr(cx) {
Some(ref df) if df.len() == 1 && st.fields.len() == 1 => {
return RawNullablePointer {
nndiscr: discr as Disr,
nnty: st.fields[0],
nullfields: cases[1 - discr].tys.clone()
};
}
Some(mut discrfield) => {
discrfield.push(0);
discrfield.reverse();
return StructWrappedNullablePointer {
nndiscr: discr as Disr,
nonnull: st,
discrfield: discrfield,
nullfields: cases[1 - discr].tys.clone()
};
}
None => {}
}
}
discr += 1;
}
}
// The general case.
assert!((cases.len() - 1) as i64 >= 0);
let bounds = IntBounds { ulo: 0, uhi: (cases.len() - 1) as u64,
slo: 0, shi: (cases.len() - 1) as i64 };
let min_ity = range_to_inttype(cx, hint, &bounds);
// Create the set of structs that represent each variant
// Use the minimum integer type we figured out above
let fields : Vec<_> = cases.iter().map(|c| {
let mut ftys = vec!(ty_of_inttype(cx.tcx(), min_ity));
ftys.push_all(&c.tys);
if dtor { ftys.push(cx.tcx().dtor_type()); }
mk_struct(cx, &ftys, false, t)
}).collect();
// Check to see if we should use a different type for the
// discriminant. If the overall alignment of the type is
// the same as the first field in each variant, we can safely use
// an alignment-sized type.
// We increase the size of the discriminant to avoid LLVM copying
// padding when it doesn't need to. This normally causes unaligned
// load/stores and excessive memcpy/memset operations. By using a
// bigger integer size, LLVM can be sure about it's contents and
// won't be so conservative.
// This check is needed to avoid increasing the size of types when
// the alignment of the first field is smaller than the overall
// alignment of the type.
let (_, align) = union_size_and_align(&fields);
let mut use_align = true;
for st in &fields {
// Get the first non-zero-sized field
let field = st.fields.iter().skip(1).filter(|ty| {
let t = type_of::sizing_type_of(cx, **ty);
machine::llsize_of_real(cx, t) != 0 ||
// This case is only relevant for zero-sized types with large alignment
machine::llalign_of_min(cx, t) != 1
}).next();
if let Some(field) = field {
let field_align = type_of::align_of(cx, *field);
if field_align != align {
use_align = false;
break;
}
}
}
let ity = if use_align {
// Use the overall alignment
match align {
1 => attr::UnsignedInt(ast::TyU8),
2 => attr::UnsignedInt(ast::TyU16),
4 => attr::UnsignedInt(ast::TyU32),
8 if machine::llalign_of_min(cx, Type::i64(cx)) == 8 =>
attr::UnsignedInt(ast::TyU64),
_ => min_ity // use min_ity as a fallback
}
} else {
min_ity
};
let fields : Vec<_> = cases.iter().map(|c| {
let mut ftys = vec!(ty_of_inttype(cx.tcx(), ity));
ftys.push_all(&c.tys);
if dtor { ftys.push(cx.tcx().dtor_type()); }
mk_struct(cx, &ftys[..], false, t)
}).collect();
ensure_enum_fits_in_address_space(cx, &fields[..], t);
General(ity, fields, dtor_to_init_u8(dtor))
}
_ => cx.sess().bug(&format!("adt::represent_type called on non-ADT type: {}",
t.repr()))
}
}
// this should probably all be in ty
struct Case<'tcx> {
discr: Disr,
tys: Vec<Ty<'tcx>>
}
/// This represents the (GEP) indices to follow to get to the discriminant field
pub type DiscrField = Vec<usize>;
fn find_discr_field_candidate<'tcx>(tcx: &ty::ctxt<'tcx>,
ty: Ty<'tcx>,
mut path: DiscrField) -> Option<DiscrField> {
match ty.sty {
// Fat &T/&mut T/Box<T> i.e. T is [T], str, or Trait
ty::TyRef(_, ty::mt { ty, .. }) | ty::TyBox(ty) if !type_is_sized(tcx, ty) => {
path.push(FAT_PTR_ADDR);
Some(path)
},
// Regular thin pointer: &T/&mut T/Box<T>
ty::TyRef(..) | ty::TyBox(..) => Some(path),
// Functions are just pointers
ty::TyBareFn(..) => Some(path),
// Is this the NonZero lang item wrapping a pointer or integer type?
ty::TyStruct(did, substs) if Some(did) == tcx.lang_items.non_zero() => {
let nonzero_fields = ty::lookup_struct_fields(tcx, did);
assert_eq!(nonzero_fields.len(), 1);
let nonzero_field = ty::lookup_field_type(tcx, did, nonzero_fields[0].id, substs);
match nonzero_field.sty {
ty::TyRawPtr(ty::mt { ty, .. }) if !type_is_sized(tcx, ty) => {
path.push_all(&[0, FAT_PTR_ADDR]);
Some(path)
},
ty::TyRawPtr(..) | ty::TyInt(..) | ty::TyUint(..) => {
path.push(0);
Some(path)
},
_ => None
}
},
// Perhaps one of the fields of this struct is non-zero
// let's recurse and find out
ty::TyStruct(def_id, substs) => {
let fields = ty::lookup_struct_fields(tcx, def_id);
for (j, field) in fields.iter().enumerate() {
let field_ty = ty::lookup_field_type(tcx, def_id, field.id, substs);
if let Some(mut fpath) = find_discr_field_candidate(tcx, field_ty, path.clone()) {
fpath.push(j);
return Some(fpath);
}
}
None
},
// Perhaps one of the upvars of this struct is non-zero
// Let's recurse and find out!
ty::TyClosure(def_id, substs) => {
let typer = NormalizingClosureTyper::new(tcx);
let upvars = typer.closure_upvars(def_id, substs).unwrap();
let upvar_types = upvars.iter().map(|u| u.ty).collect::<Vec<_>>();
for (j, &ty) in upvar_types.iter().enumerate() {
if let Some(mut fpath) = find_discr_field_candidate(tcx, ty, path.clone()) {
fpath.push(j);
return Some(fpath);
}
}
None
},
// Can we use one of the fields in this tuple?
ty::TyTuple(ref tys) => {
for (j, &ty) in tys.iter().enumerate() {
if let Some(mut fpath) = find_discr_field_candidate(tcx, ty, path.clone()) {
fpath.push(j);
return Some(fpath);
}
}
None
},
// Is this a fixed-size array of something non-zero
// with at least one element?
ty::TyArray(ety, d) if d > 0 => {
if let Some(mut vpath) = find_discr_field_candidate(tcx, ety, path) {
vpath.push(0);
Some(vpath)
} else {
None
}
},
// Anything else is not a pointer
_ => None
}
}
impl<'tcx> Case<'tcx> {
fn is_zerolen<'a>(&self, cx: &CrateContext<'a, 'tcx>, scapegoat: Ty<'tcx>) -> bool {
mk_struct(cx, &self.tys, false, scapegoat).size == 0
}
fn find_ptr<'a>(&self, cx: &CrateContext<'a, 'tcx>) -> Option<DiscrField> {
for (i, &ty) in self.tys.iter().enumerate() {
if let Some(mut path) = find_discr_field_candidate(cx.tcx(), ty, vec![]) {
path.push(i);
return Some(path);
}
}
None
}
}
fn get_cases<'tcx>(tcx: &ty::ctxt<'tcx>,
def_id: ast::DefId,
substs: &subst::Substs<'tcx>)
-> Vec<Case<'tcx>> {
ty::enum_variants(tcx, def_id).iter().map(|vi| {
let arg_tys = vi.args.iter().map(|&raw_ty| {
monomorphize::apply_param_substs(tcx, substs, &raw_ty)
}).collect();
Case { discr: vi.disr_val, tys: arg_tys }
}).collect()
}
fn mk_struct<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
tys: &[Ty<'tcx>], packed: bool,
scapegoat: Ty<'tcx>)
-> Struct<'tcx> {
let sized = tys.iter().all(|&ty| type_is_sized(cx.tcx(), ty));
let lltys : Vec<Type> = if sized {
tys.iter().map(|&ty| type_of::sizing_type_of(cx, ty)).collect()
} else {
tys.iter().filter(|&ty| type_is_sized(cx.tcx(), *ty))
.map(|&ty| type_of::sizing_type_of(cx, ty)).collect()
};
ensure_struct_fits_in_address_space(cx, &lltys[..], packed, scapegoat);
let llty_rec = Type::struct_(cx, &lltys[..], packed);
Struct {
size: machine::llsize_of_alloc(cx, llty_rec),
align: machine::llalign_of_min(cx, llty_rec),
sized: sized,
packed: packed,
fields: tys.to_vec(),
}
}
#[derive(Debug)]
struct IntBounds {
slo: i64,
shi: i64,
ulo: u64,
uhi: u64
}
fn mk_cenum<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
hint: Hint, bounds: &IntBounds)
-> Repr<'tcx> {
let it = range_to_inttype(cx, hint, bounds);
match it {
attr::SignedInt(_) => CEnum(it, bounds.slo as Disr, bounds.shi as Disr),
attr::UnsignedInt(_) => CEnum(it, bounds.ulo, bounds.uhi)
}
}
fn range_to_inttype(cx: &CrateContext, hint: Hint, bounds: &IntBounds) -> IntType {
debug!("range_to_inttype: {:?} {:?}", hint, bounds);
// Lists of sizes to try. u64 is always allowed as a fallback.
#[allow(non_upper_case_globals)]
const choose_shortest: &'static [IntType] = &[
attr::UnsignedInt(ast::TyU8), attr::SignedInt(ast::TyI8),
attr::UnsignedInt(ast::TyU16), attr::SignedInt(ast::TyI16),
attr::UnsignedInt(ast::TyU32), attr::SignedInt(ast::TyI32)];
#[allow(non_upper_case_globals)]
const at_least_32: &'static [IntType] = &[
attr::UnsignedInt(ast::TyU32), attr::SignedInt(ast::TyI32)];
let attempts;
match hint {
attr::ReprInt(span, ity) => {
if !bounds_usable(cx, ity, bounds) {
cx.sess().span_bug(span, "representation hint insufficient for discriminant range")
}
return ity;
}
attr::ReprExtern => {
attempts = match &cx.sess().target.target.arch[..] {
// WARNING: the ARM EABI has two variants; the one corresponding to `at_least_32`
// appears to be used on Linux and NetBSD, but some systems may use the variant
// corresponding to `choose_shortest`. However, we don't run on those yet...?
"arm" => at_least_32,
_ => at_least_32,
}
}
attr::ReprAny => {
attempts = choose_shortest;
},
attr::ReprPacked => {
cx.tcx().sess.bug("range_to_inttype: found ReprPacked on an enum");
}
}
for &ity in attempts {
if bounds_usable(cx, ity, bounds) {
return ity;
}
}
return attr::UnsignedInt(ast::TyU64);
}
pub fn ll_inttype(cx: &CrateContext, ity: IntType) -> Type {
match ity {
attr::SignedInt(t) => Type::int_from_ty(cx, t),
attr::UnsignedInt(t) => Type::uint_from_ty(cx, t)
}
}
fn bounds_usable(cx: &CrateContext, ity: IntType, bounds: &IntBounds) -> bool {
debug!("bounds_usable: {:?} {:?}", ity, bounds);
match ity {
attr::SignedInt(_) => {
let lllo = C_integral(ll_inttype(cx, ity), bounds.slo as u64, true);
let llhi = C_integral(ll_inttype(cx, ity), bounds.shi as u64, true);
bounds.slo == const_to_int(lllo) as i64 && bounds.shi == const_to_int(llhi) as i64
}
attr::UnsignedInt(_) => {
let lllo = C_integral(ll_inttype(cx, ity), bounds.ulo, false);
let llhi = C_integral(ll_inttype(cx, ity), bounds.uhi, false);
bounds.ulo == const_to_uint(lllo) as u64 && bounds.uhi == const_to_uint(llhi) as u64
}
}
}
pub fn ty_of_inttype<'tcx>(tcx: &ty::ctxt<'tcx>, ity: IntType) -> Ty<'tcx> {
match ity {
attr::SignedInt(t) => ty::mk_mach_int(tcx, t),
attr::UnsignedInt(t) => ty::mk_mach_uint(tcx, t)
}
}
// LLVM doesn't like types that don't fit in the address space
fn ensure_struct_fits_in_address_space<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
fields: &[Type],
packed: bool,
scapegoat: Ty<'tcx>) {
let mut offset = 0;
for &llty in fields {
// Invariant: offset < ccx.obj_size_bound() <= 1<<61
if !packed {
let type_align = machine::llalign_of_min(ccx, llty);
offset = roundup(offset, type_align);
}
// type_align is a power-of-2, so still offset < ccx.obj_size_bound()
// llsize_of_alloc(ccx, llty) is also less than ccx.obj_size_bound()
// so the sum is less than 1<<62 (and therefore can't overflow).
offset += machine::llsize_of_alloc(ccx, llty);
if offset >= ccx.obj_size_bound() {
ccx.report_overbig_object(scapegoat);
}
}
}
fn union_size_and_align(sts: &[Struct]) -> (machine::llsize, machine::llalign) {
let size = sts.iter().map(|st| st.size).max().unwrap();
let align = sts.iter().map(|st| st.align).max().unwrap();
(roundup(size, align), align)
}
fn ensure_enum_fits_in_address_space<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
fields: &[Struct],
scapegoat: Ty<'tcx>) {
let (total_size, _) = union_size_and_align(fields);
if total_size >= ccx.obj_size_bound() {
ccx.report_overbig_object(scapegoat);
}
}
/// LLVM-level types are a little complicated.
///
/// C-like enums need to be actual ints, not wrapped in a struct,
/// because that changes the ABI on some platforms (see issue #10308).
///
/// For nominal types, in some cases, we need to use LLVM named structs
/// and fill in the actual contents in a second pass to prevent
/// unbounded recursion; see also the comments in `trans::type_of`.
pub fn type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, r: &Repr<'tcx>) -> Type {
generic_type_of(cx, r, None, false, false)
}
// Pass dst=true if the type you are passing is a DST. Yes, we could figure
// this out, but if you call this on an unsized type without realising it, you
// are going to get the wrong type (it will not include the unsized parts of it).
pub fn sizing_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
r: &Repr<'tcx>, dst: bool) -> Type {
generic_type_of(cx, r, None, true, dst)
}
pub fn incomplete_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
r: &Repr<'tcx>, name: &str) -> Type {
generic_type_of(cx, r, Some(name), false, false)
}
pub fn finish_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
r: &Repr<'tcx>, llty: &mut Type) {
match *r {
CEnum(..) | General(..) | RawNullablePointer { .. } => { }
Univariant(ref st, _) | StructWrappedNullablePointer { nonnull: ref st, .. } =>
llty.set_struct_body(&struct_llfields(cx, st, false, false),
st.packed)
}
}
fn generic_type_of<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
r: &Repr<'tcx>,
name: Option<&str>,
sizing: bool,
dst: bool) -> Type {
match *r {
CEnum(ity, _, _) => ll_inttype(cx, ity),
RawNullablePointer { nnty, .. } => type_of::sizing_type_of(cx, nnty),
Univariant(ref st, _) | StructWrappedNullablePointer { nonnull: ref st, .. } => {
match name {
None => {
Type::struct_(cx, &struct_llfields(cx, st, sizing, dst),
st.packed)
}
Some(name) => { assert_eq!(sizing, false); Type::named_struct(cx, name) }
}
}
General(ity, ref sts, _) => {
// We need a representation that has:
// * The alignment of the most-aligned field
// * The size of the largest variant (rounded up to that alignment)
// * No alignment padding anywhere any variant has actual data
// (currently matters only for enums small enough to be immediate)
// * The discriminant in an obvious place.
//
// So we start with the discriminant, pad it up to the alignment with
// more of its own type, then use alignment-sized ints to get the rest
// of the size.
//
// FIXME #10604: this breaks when vector types are present.
let (size, align) = union_size_and_align(&sts[..]);
let align_s = align as u64;
assert_eq!(size % align_s, 0);
let align_units = size / align_s - 1;
let discr_ty = ll_inttype(cx, ity);
let discr_size = machine::llsize_of_alloc(cx, discr_ty);
let fill_ty = match align_s {
1 => Type::array(&Type::i8(cx), align_units),
2 => Type::array(&Type::i16(cx), align_units),
4 => Type::array(&Type::i32(cx), align_units),
8 if machine::llalign_of_min(cx, Type::i64(cx)) == 8 =>
Type::array(&Type::i64(cx), align_units),
a if a.count_ones() == 1 => Type::array(&Type::vector(&Type::i32(cx), a / 4),
align_units),
_ => panic!("unsupported enum alignment: {}", align)
};
assert_eq!(machine::llalign_of_min(cx, fill_ty), align);
assert_eq!(align_s % discr_size, 0);
let fields = [discr_ty,
Type::array(&discr_ty, align_s / discr_size - 1),
fill_ty];
match name {
None => Type::struct_(cx, &fields[..], false),
Some(name) => {
let mut llty = Type::named_struct(cx, name);
llty.set_struct_body(&fields[..], false);
llty
}
}
}
}
}
fn struct_llfields<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, st: &Struct<'tcx>,
sizing: bool, dst: bool) -> Vec<Type> {
if sizing {
st.fields.iter().filter(|&ty| !dst || type_is_sized(cx.tcx(), *ty))
.map(|&ty| type_of::sizing_type_of(cx, ty)).collect()
} else {
st.fields.iter().map(|&ty| type_of::in_memory_type_of(cx, ty)).collect()
}
}
/// Obtain a representation of the discriminant sufficient to translate
/// destructuring; this may or may not involve the actual discriminant.
///
/// This should ideally be less tightly tied to `_match`.
pub fn trans_switch<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
r: &Repr<'tcx>, scrutinee: ValueRef)
-> (_match::BranchKind, Option<ValueRef>) {
match *r {
CEnum(..) | General(..) |
RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => {
(_match::Switch, Some(trans_get_discr(bcx, r, scrutinee, None)))
}
Univariant(..) => {
// N.B.: Univariant means <= 1 enum variants (*not* == 1 variants).
(_match::Single, None)
}
}
}
pub fn is_discr_signed<'tcx>(r: &Repr<'tcx>) -> bool {
match *r {
CEnum(ity, _, _) => ity.is_signed(),
General(ity, _, _) => ity.is_signed(),
Univariant(..) => false,
RawNullablePointer { .. } => false,
StructWrappedNullablePointer { .. } => false,
}
}
/// Obtain the actual discriminant of a value.
pub fn trans_get_discr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
scrutinee: ValueRef, cast_to: Option<Type>)
-> ValueRef {
debug!("trans_get_discr r: {:?}", r);
let val = match *r {
CEnum(ity, min, max) => load_discr(bcx, ity, scrutinee, min, max),
General(ity, ref cases, _) => {
let ptr = GEPi(bcx, scrutinee, &[0, 0]);
load_discr(bcx, ity, ptr, 0, (cases.len() - 1) as Disr)
}
Univariant(..) => C_u8(bcx.ccx(), 0),
RawNullablePointer { nndiscr, nnty, .. } => {
let cmp = if nndiscr == 0 { IntEQ } else { IntNE };
let llptrty = type_of::sizing_type_of(bcx.ccx(), nnty);
ICmp(bcx, cmp, Load(bcx, scrutinee), C_null(llptrty), DebugLoc::None)
}
StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
struct_wrapped_nullable_bitdiscr(bcx, nndiscr, discrfield, scrutinee)
}
};
match cast_to {
None => val,
Some(llty) => if is_discr_signed(r) { SExt(bcx, val, llty) } else { ZExt(bcx, val, llty) }
}
}
fn struct_wrapped_nullable_bitdiscr(bcx: Block, nndiscr: Disr, discrfield: &DiscrField,
scrutinee: ValueRef) -> ValueRef {
let llptrptr = GEPi(bcx, scrutinee, &discrfield[..]);
let llptr = Load(bcx, llptrptr);
let cmp = if nndiscr == 0 { IntEQ } else { IntNE };
ICmp(bcx, cmp, llptr, C_null(val_ty(llptr)), DebugLoc::None)
}
/// Helper for cases where the discriminant is simply loaded.
fn load_discr(bcx: Block, ity: IntType, ptr: ValueRef, min: Disr, max: Disr)
-> ValueRef {
let llty = ll_inttype(bcx.ccx(), ity);
assert_eq!(val_ty(ptr), llty.ptr_to());
let bits = machine::llbitsize_of_real(bcx.ccx(), llty);
assert!(bits <= 64);
let bits = bits as usize;
let mask = (!0u64 >> (64 - bits)) as Disr;
// For a (max) discr of -1, max will be `-1 as usize`, which overflows.
// However, that is fine here (it would still represent the full range),
if (max.wrapping_add(1)) & mask == min & mask {
// i.e., if the range is everything. The lo==hi case would be
// rejected by the LLVM verifier (it would mean either an
// empty set, which is impossible, or the entire range of the
// type, which is pointless).
Load(bcx, ptr)
} else {
// llvm::ConstantRange can deal with ranges that wrap around,
// so an overflow on (max + 1) is fine.
LoadRangeAssert(bcx, ptr, min, (max.wrapping_add(1)), /* signed: */ True)
}
}
/// Yield information about how to dispatch a case of the
/// discriminant-like value returned by `trans_switch`.
///
/// This should ideally be less tightly tied to `_match`.
pub fn trans_case<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr, discr: Disr)
-> _match::OptResult<'blk, 'tcx> {
match *r {
CEnum(ity, _, _) => {
_match::SingleResult(Result::new(bcx, C_integral(ll_inttype(bcx.ccx(), ity),
discr as u64, true)))
}
General(ity, _, _) => {
_match::SingleResult(Result::new(bcx, C_integral(ll_inttype(bcx.ccx(), ity),
discr as u64, true)))
}
Univariant(..) => {
bcx.ccx().sess().bug("no cases for univariants or structs")
}
RawNullablePointer { .. } |
StructWrappedNullablePointer { .. } => {
assert!(discr == 0 || discr == 1);
_match::SingleResult(Result::new(bcx, C_bool(bcx.ccx(), discr != 0)))
}
}
}
/// Set the discriminant for a new value of the given case of the given
/// representation.
pub fn trans_set_discr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
val: ValueRef, discr: Disr) {
match *r {
CEnum(ity, min, max) => {
assert_discr_in_range(ity, min, max, discr);
Store(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true),
val);
}
General(ity, ref cases, dtor) => {
if dtor_active(dtor) {
let ptr = trans_field_ptr(bcx, r, val, discr,
cases[discr as usize].fields.len() - 2);
Store(bcx, C_u8(bcx.ccx(), DTOR_NEEDED as usize), ptr);
}
Store(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true),
GEPi(bcx, val, &[0, 0]));
}
Univariant(ref st, dtor) => {
assert_eq!(discr, 0);
if dtor_active(dtor) {
Store(bcx, C_u8(bcx.ccx(), DTOR_NEEDED as usize),
GEPi(bcx, val, &[0, st.fields.len() - 1]));
}
}
RawNullablePointer { nndiscr, nnty, ..} => {
if discr != nndiscr {
let llptrty = type_of::sizing_type_of(bcx.ccx(), nnty);
Store(bcx, C_null(llptrty), val);
}
}
StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
if discr != nndiscr {
let llptrptr = GEPi(bcx, val, &discrfield[..]);
let llptrty = val_ty(llptrptr).element_type();
Store(bcx, C_null(llptrty), llptrptr);
}
}
}
}
fn assert_discr_in_range(ity: IntType, min: Disr, max: Disr, discr: Disr) {
match ity {
attr::UnsignedInt(_) => assert!(min <= discr && discr <= max),
attr::SignedInt(_) => assert!(min as i64 <= discr as i64 && discr as i64 <= max as i64)
}
}
/// The number of fields in a given case; for use when obtaining this
/// information from the type or definition is less convenient.
pub fn num_args(r: &Repr, discr: Disr) -> usize {
match *r {
CEnum(..) => 0,
Univariant(ref st, dtor) => {
assert_eq!(discr, 0);
st.fields.len() - (if dtor_active(dtor) { 1 } else { 0 })
}
General(_, ref cases, dtor) => {
cases[discr as usize].fields.len() - 1 - (if dtor_active(dtor) { 1 } else { 0 })
}
RawNullablePointer { nndiscr, ref nullfields, .. } => {
if discr == nndiscr { 1 } else { nullfields.len() }
}
StructWrappedNullablePointer { ref nonnull, nndiscr,
ref nullfields, .. } => {
if discr == nndiscr { nonnull.fields.len() } else { nullfields.len() }
}
}
}
/// Access a field, at a point when the value's case is known.
pub fn trans_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
val: ValueRef, discr: Disr, ix: usize) -> ValueRef {
// Note: if this ever needs to generate conditionals (e.g., if we
// decide to do some kind of cdr-coding-like non-unique repr
// someday), it will need to return a possibly-new bcx as well.
match *r {
CEnum(..) => {
bcx.ccx().sess().bug("element access in C-like enum")
}
Univariant(ref st, _dtor) => {
assert_eq!(discr, 0);
struct_field_ptr(bcx, st, val, ix, false)
}
General(_, ref cases, _) => {
struct_field_ptr(bcx, &cases[discr as usize], val, ix + 1, true)
}
RawNullablePointer { nndiscr, ref nullfields, .. } |
StructWrappedNullablePointer { nndiscr, ref nullfields, .. } if discr != nndiscr => {
// The unit-like case might have a nonzero number of unit-like fields.
// (e.d., Result of Either with (), as one side.)
let ty = type_of::type_of(bcx.ccx(), nullfields[ix]);
assert_eq!(machine::llsize_of_alloc(bcx.ccx(), ty), 0);
// The contents of memory at this pointer can't matter, but use
// the value that's "reasonable" in case of pointer comparison.
PointerCast(bcx, val, ty.ptr_to())
}
RawNullablePointer { nndiscr, nnty, .. } => {
assert_eq!(ix, 0);
assert_eq!(discr, nndiscr);
let ty = type_of::type_of(bcx.ccx(), nnty);
PointerCast(bcx, val, ty.ptr_to())
}
StructWrappedNullablePointer { ref nonnull, nndiscr, .. } => {
assert_eq!(discr, nndiscr);
struct_field_ptr(bcx, nonnull, val, ix, false)
}
}
}
pub fn struct_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, st: &Struct<'tcx>, val: ValueRef,
ix: usize, needs_cast: bool) -> ValueRef {
let val = if needs_cast {
let ccx = bcx.ccx();
let fields = st.fields.iter().map(|&ty| type_of::type_of(ccx, ty)).collect::<Vec<_>>();
let real_ty = Type::struct_(ccx, &fields[..], st.packed);
PointerCast(bcx, val, real_ty.ptr_to())
} else {
val
};
GEPi(bcx, val, &[0, ix])
}
pub fn fold_variants<'blk, 'tcx, F>(bcx: Block<'blk, 'tcx>,
r: &Repr<'tcx>,
value: ValueRef,
mut f: F)
-> Block<'blk, 'tcx> where
F: FnMut(Block<'blk, 'tcx>, &Struct<'tcx>, ValueRef) -> Block<'blk, 'tcx>,
{
let fcx = bcx.fcx;
match *r {
Univariant(ref st, _) => {
f(bcx, st, value)
}
General(ity, ref cases, _) => {
let ccx = bcx.ccx();
// See the comments in trans/base.rs for more information (inside
// iter_structural_ty), but the gist here is that if the enum's
// discriminant is *not* in the range that we're expecting (in which
// case we'll take the fall-through branch on the switch
// instruction) then we can't just optimize this to an Unreachable
// block.
//
// Currently we still have filling drop, so this means that the drop
// glue for enums may be called when the enum has been paved over
// with the "I've been dropped" value. In this case the default
// branch of the switch instruction will actually be taken at
// runtime, so the basic block isn't actually unreachable, so we
// need to make it do something with defined behavior. In this case
// we just return early from the function.
let ret_void_cx = fcx.new_temp_block("enum-variant-iter-ret-void");
RetVoid(ret_void_cx, DebugLoc::None);
let discr_val = trans_get_discr(bcx, r, value, None);
let llswitch = Switch(bcx, discr_val, ret_void_cx.llbb, cases.len());
let bcx_next = fcx.new_temp_block("enum-variant-iter-next");
for (discr, case) in cases.iter().enumerate() {
let mut variant_cx = fcx.new_temp_block(
&format!("enum-variant-iter-{}", &discr.to_string())
);
let rhs_val = C_integral(ll_inttype(ccx, ity), discr as u64, true);
AddCase(llswitch, rhs_val, variant_cx.llbb);
let fields = case.fields.iter().map(|&ty|
type_of::type_of(bcx.ccx(), ty)).collect::<Vec<_>>();
let real_ty = Type::struct_(ccx, &fields[..], case.packed);
let variant_value = PointerCast(variant_cx, value, real_ty.ptr_to());
variant_cx = f(variant_cx, case, variant_value);
Br(variant_cx, bcx_next.llbb, DebugLoc::None);
}
bcx_next
}
_ => unreachable!()
}
}
/// Access the struct drop flag, if present.
pub fn trans_drop_flag_ptr<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
r: &Repr<'tcx>,
val: ValueRef)
-> datum::DatumBlock<'blk, 'tcx, datum::Expr>
{
let tcx = bcx.tcx();
let ptr_ty = ty::mk_imm_ptr(bcx.tcx(), tcx.dtor_type());
match *r {
Univariant(ref st, dtor) if dtor_active(dtor) => {
let flag_ptr = GEPi(bcx, val, &[0, st.fields.len() - 1]);
datum::immediate_rvalue_bcx(bcx, flag_ptr, ptr_ty).to_expr_datumblock()
}
General(_, _, dtor) if dtor_active(dtor) => {
let fcx = bcx.fcx;
let custom_cleanup_scope = fcx.push_custom_cleanup_scope();
let scratch = unpack_datum!(bcx, datum::lvalue_scratch_datum(
bcx, tcx.dtor_type(), "drop_flag",
cleanup::CustomScope(custom_cleanup_scope), (), |_, bcx, _| bcx
));
bcx = fold_variants(bcx, r, val, |variant_cx, st, value| {
let ptr = struct_field_ptr(variant_cx, st, value, (st.fields.len() - 1), false);
datum::Datum::new(ptr, ptr_ty, datum::Lvalue)
.store_to(variant_cx, scratch.val)
});
let expr_datum = scratch.to_expr_datum();
fcx.pop_custom_cleanup_scope(custom_cleanup_scope);
datum::DatumBlock::new(bcx, expr_datum)
}
_ => bcx.ccx().sess().bug("tried to get drop flag of non-droppable type")
}
}
/// Construct a constant value, suitable for initializing a
/// GlobalVariable, given a case and constant values for its fields.
/// Note that this may have a different LLVM type (and different
/// alignment!) from the representation's `type_of`, so it needs a
/// pointer cast before use.
///
/// The LLVM type system does not directly support unions, and only
/// pointers can be bitcast, so a constant (and, by extension, the
/// GlobalVariable initialized by it) will have a type that can vary
/// depending on which case of an enum it is.
///
/// To understand the alignment situation, consider `enum E { V64(u64),
/// V32(u32, u32) }` on Windows. The type has 8-byte alignment to
/// accommodate the u64, but `V32(x, y)` would have LLVM type `{i32,
/// i32, i32}`, which is 4-byte aligned.
///
/// Currently the returned value has the same size as the type, but
/// this could be changed in the future to avoid allocating unnecessary
/// space after values of shorter-than-maximum cases.
pub fn trans_const<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, r: &Repr<'tcx>, discr: Disr,
vals: &[ValueRef]) -> ValueRef {
match *r {
CEnum(ity, min, max) => {
assert_eq!(vals.len(), 0);
assert_discr_in_range(ity, min, max, discr);
C_integral(ll_inttype(ccx, ity), discr as u64, true)
}
General(ity, ref cases, _) => {
let case = &cases[discr as usize];
let (max_sz, _) = union_size_and_align(&cases[..]);
let lldiscr = C_integral(ll_inttype(ccx, ity), discr as u64, true);
let mut f = vec![lldiscr];
f.push_all(vals);
let mut contents = build_const_struct(ccx, case, &f[..]);
contents.push_all(&[padding(ccx, max_sz - case.size)]);
C_struct(ccx, &contents[..], false)
}
Univariant(ref st, _dro) => {
assert!(discr == 0);
let contents = build_const_struct(ccx, st, vals);
C_struct(ccx, &contents[..], st.packed)
}
RawNullablePointer { nndiscr, nnty, .. } => {
if discr == nndiscr {
assert_eq!(vals.len(), 1);
vals[0]
} else {
C_null(type_of::sizing_type_of(ccx, nnty))
}
}
StructWrappedNullablePointer { ref nonnull, nndiscr, .. } => {
if discr == nndiscr {
C_struct(ccx, &build_const_struct(ccx,
nonnull,
vals),
false)
} else {
let vals = nonnull.fields.iter().map(|&ty| {
// Always use null even if it's not the `discrfield`th
// field; see #8506.
C_null(type_of::sizing_type_of(ccx, ty))
}).collect::<Vec<ValueRef>>();
C_struct(ccx, &build_const_struct(ccx,
nonnull,
&vals[..]),
false)
}
}
}
}
/// Compute struct field offsets relative to struct begin.
fn compute_struct_field_offsets<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
st: &Struct<'tcx>) -> Vec<u64> {
let mut offsets = vec!();
let mut offset = 0;
for &ty in &st.fields {
let llty = type_of::sizing_type_of(ccx, ty);
if !st.packed {
let type_align = type_of::align_of(ccx, ty);
offset = roundup(offset, type_align);
}
offsets.push(offset);
offset += machine::llsize_of_alloc(ccx, llty);
}
assert_eq!(st.fields.len(), offsets.len());
offsets
}
/// Building structs is a little complicated, because we might need to
/// insert padding if a field's value is less aligned than its type.
///
/// Continuing the example from `trans_const`, a value of type `(u32,
/// E)` should have the `E` at offset 8, but if that field's
/// initializer is 4-byte aligned then simply translating the tuple as
/// a two-element struct will locate it at offset 4, and accesses to it
/// will read the wrong memory.
fn build_const_struct<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
st: &Struct<'tcx>, vals: &[ValueRef])
-> Vec<ValueRef> {
assert_eq!(vals.len(), st.fields.len());
let target_offsets = compute_struct_field_offsets(ccx, st);
// offset of current value
let mut offset = 0;
let mut cfields = Vec::new();
for (&val, target_offset) in vals.iter().zip(target_offsets) {
if !st.packed {
let val_align = machine::llalign_of_min(ccx, val_ty(val));
offset = roundup(offset, val_align);
}
if offset != target_offset {
cfields.push(padding(ccx, target_offset - offset));
offset = target_offset;
}
assert!(!is_undef(val));
cfields.push(val);
offset += machine::llsize_of_alloc(ccx, val_ty(val));
}
assert!(st.sized && offset <= st.size);
if offset != st.size {
cfields.push(padding(ccx, st.size - offset));
}
cfields
}
fn padding(ccx: &CrateContext, size: u64) -> ValueRef {
C_undef(Type::array(&Type::i8(ccx), size))
}
// FIXME this utility routine should be somewhere more general
#[inline]
fn roundup(x: u64, a: u32) -> u64 { let a = a as u64; ((x + (a - 1)) / a) * a }
/// Get the discriminant of a constant value.
pub fn const_get_discrim(ccx: &CrateContext, r: &Repr, val: ValueRef) -> Disr {
match *r {
CEnum(ity, _, _) => {
match ity {
attr::SignedInt(..) => const_to_int(val) as Disr,
attr::UnsignedInt(..) => const_to_uint(val) as Disr
}
}
General(ity, _, _) => {
match ity {
attr::SignedInt(..) => const_to_int(const_get_elt(ccx, val, &[0])) as Disr,
attr::UnsignedInt(..) => const_to_uint(const_get_elt(ccx, val, &[0])) as Disr
}
}
Univariant(..) => 0,
RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => {
ccx.sess().bug("const discrim access of non c-like enum")
}
}
}
/// Extract a field of a constant value, as appropriate for its
/// representation.
///
/// (Not to be confused with `common::const_get_elt`, which operates on
/// raw LLVM-level structs and arrays.)
pub fn const_get_field(ccx: &CrateContext, r: &Repr, val: ValueRef,
_discr: Disr, ix: usize) -> ValueRef {
match *r {
CEnum(..) => ccx.sess().bug("element access in C-like enum const"),
Univariant(..) => const_struct_field(ccx, val, ix),
General(..) => const_struct_field(ccx, val, ix + 1),
RawNullablePointer { .. } => {
assert_eq!(ix, 0);
val
},
StructWrappedNullablePointer{ .. } => const_struct_field(ccx, val, ix)
}
}
/// Extract field of struct-like const, skipping our alignment padding.
fn const_struct_field(ccx: &CrateContext, val: ValueRef, ix: usize) -> ValueRef {
// Get the ix-th non-undef element of the struct.
let mut real_ix = 0; // actual position in the struct
let mut ix = ix; // logical index relative to real_ix
let mut field;
loop {
loop {
field = const_get_elt(ccx, val, &[real_ix]);
if !is_undef(field) {
break;
}
real_ix = real_ix + 1;
}
if ix == 0 {
return field;
}
ix = ix - 1;
real_ix = real_ix + 1;
}
}
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