// 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. #![allow(unsigned_negation)] pub use self::Repr::*; #[allow(deprecated)] use std::num::Int; 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::ty_to_string; 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>, 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> }, /// 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>, } } /// 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> } /// 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> { 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> { debug!("Representing: {}", ty_to_string(cx.tcx(), t)); 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::ty_tup(ref elems) => { Univariant(mk_struct(cx, &elems[..], false, t), 0) } ty::ty_struct(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::>(); 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::ty_closure(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::>(); Univariant(mk_struct(cx, &upvar_types[..], false, t), 0) } ty::ty_enum(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 = 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: {}", ty_to_string(cx.tcx(), t))) } } // this should probably all be in ty struct Case<'tcx> { discr: Disr, tys: Vec> } /// This represents the (GEP) indices to follow to get to the discriminant field pub type DiscrField = Vec; fn find_discr_field_candidate<'tcx>(tcx: &ty::ctxt<'tcx>, ty: Ty<'tcx>, mut path: DiscrField) -> Option { match ty.sty { // Fat &T/&mut T/Box i.e. T is [T], str, or Trait ty::ty_rptr(_, ty::mt { ty, .. }) | ty::ty_uniq(ty) if !type_is_sized(tcx, ty) => { path.push(FAT_PTR_ADDR); Some(path) }, // Regular thin pointer: &T/&mut T/Box ty::ty_rptr(..) | ty::ty_uniq(..) => Some(path), // Functions are just pointers ty::ty_bare_fn(..) => Some(path), // Is this the NonZero lang item wrapping a pointer or integer type? ty::ty_struct(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::ty_ptr(..) | ty::ty_int(..) | ty::ty_uint(..) => { path.push(0); Some(path) }, _ => None } }, // Perhaps one of the fields of this struct is non-zero // let's recurse and find out ty::ty_struct(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 }, // Can we use one of the fields in this tuple? ty::ty_tup(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::ty_vec(ety, Some(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 { 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> { 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 = 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 { 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) { match *r { CEnum(..) | General(..) | RawNullablePointer { .. } | StructWrappedNullablePointer { .. } => { (_match::Switch, Some(trans_get_discr(bcx, r, scrutinee, None))) } Univariant(..) => { (_match::Single, None) } } } /// 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) -> ValueRef { let signed; let val; debug!("trans_get_discr r: {:?}", r); 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(bcx.ccx(), 0); signed = false; } RawNullablePointer { nndiscr, nnty, .. } => { let cmp = if nndiscr == 0 { IntEQ } else { IntNE }; let llptrty = type_of::sizing_type_of(bcx.ccx(), nnty); val = ICmp(bcx, cmp, Load(bcx, scrutinee), C_null(llptrty), DebugLoc::None); signed = false; } StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => { val = struct_wrapped_nullable_bitdiscr(bcx, nndiscr, discrfield, scrutinee); signed = false; } } match cast_to { None => val, Some(llty) => if signed { 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::>(); 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(); let unr_cx = fcx.new_temp_block("enum-variant-iter-unr"); Unreachable(unr_cx); let discr_val = trans_get_discr(bcx, r, value, None); let llswitch = Switch(bcx, discr_val, unr_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::>(); 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::Rvalue::new(datum::ByRef)) .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::>(); 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 { 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 { 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.iter()) { 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; } }