// 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 or the MIT license // , 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. */ use std::container::Map; use std::libc::c_ulonglong; use std::option::{Option, Some, None}; use lib::llvm::{ValueRef, True, IntEQ, IntNE}; use middle::trans::_match; use middle::trans::build::*; use middle::trans::common::*; use middle::trans::machine; use middle::trans::type_of; use middle::ty; use middle::ty::Disr; use syntax::abi::{X86, X86_64, Arm, Mips}; use syntax::ast; use syntax::attr; use syntax::attr::IntType; use util::ppaux::ty_to_str; use middle::trans::type_::Type; type Hint = attr::ReprAttr; /// Representations. pub enum Repr { /// 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. */ Univariant(Struct, bool), /** * General-case enums: for each case there is a struct, and they * all start with a field for the discriminant. */ General(IntType, ~[Struct]), /** * Two cases distinguished by a nullable pointer: the case with discriminant * `nndiscr` is represented by the struct `nonnull`, where the `ptrfield`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. */ NullablePointer{ nonnull: Struct, nndiscr: Disr, ptrfield: uint, nullfields: ~[ty::t] } } /// For structs, and struct-like parts of anything fancier. pub struct Struct { size: u64, align: u64, packed: bool, fields: ~[ty::t] } /** * Convenience for `represent_type`. There should probably be more or * these, for places in trans where the `ty::t` isn't directly * available. */ pub fn represent_node(bcx: @mut Block, node: ast::NodeId) -> @Repr { represent_type(bcx.ccx(), node_id_type(bcx, node)) } /// Decides how to represent a given type. pub fn represent_type(cx: &mut CrateContext, t: ty::t) -> @Repr { debug!("Representing: {}", ty_to_str(cx.tcx, t)); match cx.adt_reprs.find(&t) { Some(repr) => return *repr, None => { } } let repr = @represent_type_uncached(cx, t); debug!("Represented as: {:?}", repr) cx.adt_reprs.insert(t, repr); return repr; } fn represent_type_uncached(cx: &mut CrateContext, t: ty::t) -> Repr { match ty::get(t).sty { ty::ty_tup(ref elems) => { return Univariant(mk_struct(cx, *elems, false), false) } ty::ty_struct(def_id, ref substs) => { let fields = ty::lookup_struct_fields(cx.tcx, def_id); let mut ftys = do fields.map |field| { ty::lookup_field_type(cx.tcx, def_id, field.id, substs) }; 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(ty::mk_bool()); } return Univariant(mk_struct(cx, ftys, packed), dtor) } ty::ty_enum(def_id, ref substs) => { let cases = get_cases(cx.tcx, def_id, substs); let hint = ty::lookup_repr_hint(cx.tcx, def_id); if cases.len() == 0 { // Uninhabitable; represent as unit // (Typechecking will reject discriminant-sizing attrs.) assert_eq!(hint, attr::ReprAny); return Univariant(mk_struct(cx, [], false), false); } if cases.iter().all(|c| c.tys.len() == 0) { // All bodies empty -> intlike let discrs = cases.map(|c| c.discr); 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); return Univariant(mk_struct(cx, cases[0].tys, false), false) } if cases.len() == 2 && hint == attr::ReprAny { // Nullable pointer optimization let mut discr = 0; while discr < 2 { if cases[1 - discr].is_zerolen(cx) { match cases[discr].find_ptr() { Some(ptrfield) => { return NullablePointer { nndiscr: discr, nonnull: mk_struct(cx, cases[discr].tys, false), ptrfield: ptrfield, 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 ity = range_to_inttype(cx, hint, &bounds); let discr = ~[ty_of_inttype(ity)]; return General(ity, cases.map(|c| mk_struct(cx, discr + c.tys, false))) } _ => cx.sess.bug("adt::represent_type called on non-ADT type") } } /// Determine, without doing translation, whether an ADT must be FFI-safe. /// For use in lint or similar, where being sound but slightly incomplete is acceptable. pub fn is_ffi_safe(tcx: ty::ctxt, def_id: ast::DefId) -> bool { match ty::get(ty::lookup_item_type(tcx, def_id).ty).sty { ty::ty_enum(def_id, _) => { let variants = ty::enum_variants(tcx, def_id); // Univariant => like struct/tuple. if variants.len() <= 1 { return true; } let hint = ty::lookup_repr_hint(tcx, def_id); // Appropriate representation explicitly selected? if hint.is_ffi_safe() { return true; } // Option<~T> and similar are used in FFI. Rather than try to resolve type parameters // and recognize this case exactly, this overapproximates -- assuming that if a // non-C-like enum is being used in FFI then the user knows what they're doing. if variants.iter().any(|vi| !vi.args.is_empty()) { return true; } false } // struct, tuple, etc. // (is this right in the present of typedefs?) _ => true } } // NOTE this should probably all be in ty struct Case { discr: Disr, tys: ~[ty::t] } impl Case { fn is_zerolen(&self, cx: &mut CrateContext) -> bool { mk_struct(cx, self.tys, false).size == 0 } fn find_ptr(&self) -> Option { self.tys.iter().position(|&ty| mono_data_classify(ty) == MonoNonNull) } } fn get_cases(tcx: ty::ctxt, def_id: ast::DefId, substs: &ty::substs) -> ~[Case] { do ty::enum_variants(tcx, def_id).map |vi| { let arg_tys = do vi.args.map |&raw_ty| { ty::subst(tcx, substs, raw_ty) }; Case { discr: vi.disr_val, tys: arg_tys } } } fn mk_struct(cx: &mut CrateContext, tys: &[ty::t], packed: bool) -> Struct { let lltys = tys.map(|&ty| type_of::sizing_type_of(cx, ty)); let llty_rec = Type::struct_(lltys, packed); Struct { size: machine::llsize_of_alloc(cx, llty_rec) /*bad*/as u64, align: machine::llalign_of_min(cx, llty_rec) /*bad*/as u64, packed: packed, fields: tys.to_owned(), } } struct IntBounds { slo: i64, shi: i64, ulo: u64, uhi: u64 } fn mk_cenum(cx: &mut CrateContext, hint: Hint, bounds: &IntBounds) -> Repr { 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: &mut CrateContext, hint: Hint, bounds: &IntBounds) -> IntType { debug!("range_to_inttype: {:?} {:?}", hint, bounds); // Lists of sizes to try. u64 is always allowed as a fallback. static choose_shortest: &'static[IntType] = &[ attr::UnsignedInt(ast::ty_u8), attr::SignedInt(ast::ty_i8), attr::UnsignedInt(ast::ty_u16), attr::SignedInt(ast::ty_i16), attr::UnsignedInt(ast::ty_u32), attr::SignedInt(ast::ty_i32)]; static at_least_32: &'static[IntType] = &[ attr::UnsignedInt(ast::ty_u32), attr::SignedInt(ast::ty_i32)]; 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.targ_cfg.arch { X86 | X86_64 => at_least_32, // 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, Mips => at_least_32, } } attr::ReprAny => { attempts = choose_shortest; } } for &ity in attempts.iter() { if bounds_usable(cx, ity, bounds) { return ity; } } return attr::UnsignedInt(ast::ty_u64); } pub fn ll_inttype(cx: &mut 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: &mut 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(ity: IntType) -> ty::t { match ity { attr::SignedInt(t) => ty::mk_mach_int(t), attr::UnsignedInt(t) => ty::mk_mach_uint(t) } } /** * 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(cx: &mut CrateContext, r: &Repr) -> Type { generic_type_of(cx, r, None, false) } pub fn sizing_type_of(cx: &mut CrateContext, r: &Repr) -> Type { generic_type_of(cx, r, None, true) } pub fn incomplete_type_of(cx: &mut CrateContext, r: &Repr, name: &str) -> Type { generic_type_of(cx, r, Some(name), false) } pub fn finish_type_of(cx: &mut CrateContext, r: &Repr, llty: &mut Type) { match *r { CEnum(*) | General(*) => { } Univariant(ref st, _) | NullablePointer{ nonnull: ref st, _ } => llty.set_struct_body(struct_llfields(cx, st, false), st.packed) } } fn generic_type_of(cx: &mut CrateContext, r: &Repr, name: Option<&str>, sizing: bool) -> Type { match *r { CEnum(ity, _, _) => ll_inttype(cx, ity), Univariant(ref st, _) | NullablePointer{ nonnull: ref st, _ } => { match name { None => Type::struct_(struct_llfields(cx, st, sizing), st.packed), Some(name) => { assert_eq!(sizing, false); Type::named_struct(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 = sts.iter().map(|st| st.size).max().unwrap(); let most_aligned = sts.iter().max_by(|st| st.align).unwrap(); let align = most_aligned.align; let discr_ty = ll_inttype(cx, ity); let discr_size = machine::llsize_of_alloc(cx, discr_ty) as u64; let pad_ty = match align { 1 => Type::i8(), 2 => Type::i16(), 4 => Type::i32(), 8 if machine::llalign_of_min(cx, Type::i64()) == 8 => Type::i64(), _ => fail!("Unsupported enum alignment: {:?}", align) }; assert_eq!(machine::llalign_of_min(cx, pad_ty) as u64, align); let align_units = (size + align - 1) / align; assert_eq!(align % discr_size, 0); let fields = ~[discr_ty, Type::array(&discr_ty, align / discr_size - 1), Type::array(&pad_ty, align_units - 1)]; match name { None => Type::struct_(fields, false), Some(name) => { let mut llty = Type::named_struct(name); llty.set_struct_body(fields, false); llty } } } } } fn struct_llfields(cx: &mut CrateContext, st: &Struct, sizing: bool) -> ~[Type] { if sizing { st.fields.map(|&ty| type_of::sizing_type_of(cx, ty)) } else { st.fields.map(|&ty| type_of::type_of(cx, ty)) } } /** * 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(bcx: @mut Block, r: &Repr, scrutinee: ValueRef) -> (_match::branch_kind, Option) { match *r { CEnum(*) | General(*) => { (_match::switch, Some(trans_get_discr(bcx, r, scrutinee, None))) } NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => { (_match::switch, Some(nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee))) } Univariant(*) => { (_match::single, None) } } } /// Obtain the actual discriminant of a value. pub fn trans_get_discr(bcx: @mut Block, r: &Repr, scrutinee: ValueRef, cast_to: Option) -> ValueRef { let signed; let val; match *r { CEnum(ity, min, max) => { val = load_discr(bcx, ity, scrutinee, min, max); signed = ity.is_signed(); } General(ity, ref cases) => { let ptr = GEPi(bcx, scrutinee, [0, 0]); val = load_discr(bcx, ity, ptr, 0, (cases.len() - 1) as Disr); signed = ity.is_signed(); } Univariant(*) => { val = C_u8(0); signed = false; } NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => { val = nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee); signed = false; } } match cast_to { None => val, Some(llty) => if signed { SExt(bcx, val, llty) } else { ZExt(bcx, val, llty) } } } fn nullable_bitdiscr(bcx: @mut Block, nonnull: &Struct, nndiscr: Disr, ptrfield: uint, scrutinee: ValueRef) -> ValueRef { let cmp = if nndiscr == 0 { IntEQ } else { IntNE }; let llptr = Load(bcx, GEPi(bcx, scrutinee, [0, ptrfield])); let llptrty = type_of::type_of(bcx.ccx(), nonnull.fields[ptrfield]); ICmp(bcx, cmp, llptr, C_null(llptrty)) } /// Helper for cases where the discriminant is simply loaded. fn load_discr(bcx: @mut 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 mask = (-1u64 >> (64 - bits)) as Disr; if (max + 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 as c_ulonglong, (max + 1) as c_ulonglong, /* 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(bcx: @mut Block, r: &Repr, discr: Disr) -> _match::opt_result { match *r { CEnum(ity, _, _) => { _match::single_result(rslt(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true))) } General(ity, _) => { _match::single_result(rslt(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true))) } Univariant(*) => { bcx.ccx().sess.bug("no cases for univariants or structs") } NullablePointer{ _ } => { assert!(discr == 0 || discr == 1); _match::single_result(rslt(bcx, C_i1(discr != 0))) } } } /** * Begin initializing a new value of the given case of the given * representation. The fields, if any, should then be initialized via * `trans_field_ptr`. */ pub fn trans_start_init(bcx: @mut Block, r: &Repr, 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, _) => { Store(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true), GEPi(bcx, val, [0, 0])) } Univariant(ref st, true) => { assert_eq!(discr, 0); Store(bcx, C_bool(true), GEPi(bcx, val, [0, st.fields.len() - 1])) } Univariant(*) => { assert_eq!(discr, 0); } NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => { if discr != nndiscr { let llptrptr = GEPi(bcx, val, [0, ptrfield]); let llptrty = type_of::type_of(bcx.ccx(), nonnull.fields[ptrfield]); 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) -> uint { match *r { CEnum(*) => 0, Univariant(ref st, dtor) => { assert_eq!(discr, 0); st.fields.len() - (if dtor { 1 } else { 0 }) } General(_, ref cases) => cases[discr].fields.len() - 1, NullablePointer{ nonnull: ref nonnull, nndiscr, nullfields: 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(bcx: @mut Block, r: &Repr, val: ValueRef, discr: Disr, ix: uint) -> 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], val, ix + 1, true) } NullablePointer{ nonnull: ref nonnull, nullfields: ref nullfields, nndiscr, _ } => { if (discr == nndiscr) { struct_field_ptr(bcx, nonnull, val, ix, false) } else { // The unit-like case might have a nonzero number of unit-like fields. // (e.g., Result or 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()) } } } } fn struct_field_ptr(bcx: @mut Block, st: &Struct, val: ValueRef, ix: uint, needs_cast: bool) -> ValueRef { let ccx = bcx.ccx(); let val = if needs_cast { let fields = do st.fields.map |&ty| { type_of::type_of(ccx, ty) }; let real_ty = Type::struct_(fields, st.packed); PointerCast(bcx, val, real_ty.ptr_to()) } else { val }; GEPi(bcx, val, [0, ix]) } /// Access the struct drop flag, if present. pub fn trans_drop_flag_ptr(bcx: @mut Block, r: &Repr, val: ValueRef) -> ValueRef { match *r { Univariant(ref st, true) => GEPi(bcx, val, [0, st.fields.len() - 1]), _ => 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 win32. 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(ccx: &mut CrateContext, r: &Repr, 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]; let max_sz = cases.iter().map(|x| x.size).max().unwrap(); let lldiscr = C_integral(ll_inttype(ccx, ity), discr as u64, true); let contents = build_const_struct(ccx, case, ~[lldiscr] + vals); C_struct(contents + &[padding(max_sz - case.size)], false) } Univariant(ref st, _dro) => { assert!(discr == 0); let contents = build_const_struct(ccx, st, vals); C_struct(contents, st.packed) } NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => { if discr == nndiscr { C_struct(build_const_struct(ccx, nonnull, vals), false) } else { assert_eq!(vals.len(), 0); let vals = do nonnull.fields.iter().enumerate().map |(i, &ty)| { let llty = type_of::sizing_type_of(ccx, ty); if i == ptrfield { C_null(llty) } else { C_undef(llty) } }.collect::<~[ValueRef]>(); C_struct(build_const_struct(ccx, nonnull, vals), false) } } } } /** * 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(ccx: &mut CrateContext, st: &Struct, vals: &[ValueRef]) -> ~[ValueRef] { assert_eq!(vals.len(), st.fields.len()); let mut offset = 0; let mut cfields = ~[]; for (i, &ty) in st.fields.iter().enumerate() { let llty = type_of::sizing_type_of(ccx, ty); let type_align = machine::llalign_of_min(ccx, llty) /*bad*/as u64; let val_align = machine::llalign_of_min(ccx, val_ty(vals[i])) /*bad*/as u64; let target_offset = roundup(offset, type_align); offset = roundup(offset, val_align); if (offset != target_offset) { cfields.push(padding(target_offset - offset)); offset = target_offset; } let val = if is_undef(vals[i]) { let wrapped = C_struct([vals[i]], false); assert!(!is_undef(wrapped)); wrapped } else { vals[i] }; cfields.push(val); offset += machine::llsize_of_alloc(ccx, llty) as u64 } return cfields; } fn padding(size: u64) -> ValueRef { C_undef(Type::array(&Type::i8(), size)) } // XXX this utility routine should be somewhere more general #[inline] fn roundup(x: u64, a: u64) -> u64 { ((x + (a - 1)) / a) * a } /// Get the discriminant of a constant value. (Not currently used.) pub fn const_get_discrim(ccx: &mut 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, NullablePointer{ nndiscr, ptrfield, _ } => { if is_null(const_struct_field(ccx, val, ptrfield)) { /* subtraction as uint is ok because nndiscr is either 0 or 1 */ (1 - nndiscr) as Disr } else { nndiscr } } } } /** * 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: &mut CrateContext, r: &Repr, val: ValueRef, _discr: Disr, ix: uint) -> 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), NullablePointer{ _ } => const_struct_field(ccx, val, ix) } } /// Extract field of struct-like const, skipping our alignment padding. fn const_struct_field(ccx: &mut CrateContext, val: ValueRef, ix: uint) -> 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; } } /// Is it safe to bitcast a value to the one field of its one variant? pub fn is_newtypeish(r: &Repr) -> bool { match *r { Univariant(ref st, false) => st.fields.len() == 1, _ => false } }