550 lines
20 KiB
Rust
550 lines
20 KiB
Rust
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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/*!
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* # Representation of Algebraic Data Types
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*
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* This module determines how to represent enums, structs, and tuples
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* based on their monomorphized types; it is responsible both for
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* choosing a representation and translating basic operations on
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* values of those types.
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*
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* Note that the interface treats everything as a general case of an
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* enum, so structs/tuples/etc. have one pseudo-variant with
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* discriminant 0; i.e., as if they were a univariant enum.
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*
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* Having everything in one place will enable improvements to data
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* structure representation; possibilities include:
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*
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* - Aligning enum bodies correctly, which in turn makes possible SIMD
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* vector types (which are strict-alignment even on x86) and ports
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* to strict-alignment architectures (PowerPC, SPARC, etc.).
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*
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* - User-specified alignment (e.g., cacheline-aligning parts of
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* concurrently accessed data structures); LLVM can't represent this
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* directly, so we'd have to insert padding fields in any structure
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* that might contain one and adjust GEP indices accordingly. See
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* issue #4578.
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*
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* - Rendering `Option<&T>` as a possibly-null `*T` instead of using
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* an extra word (and likewise for `@T` and `~T`). Can and probably
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* should also apply to any enum with one empty case and one case
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* starting with a non-null pointer (e.g., `Result<(), ~str>`).
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*
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* - Using smaller integer types for discriminants.
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*
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* - Store nested enums' discriminants in the same word. Rather, if
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* some variants start with enums, and those enums representations
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* have unused alignment padding between discriminant and body, the
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* outer enum's discriminant can be stored there and those variants
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* can start at offset 0. Kind of fancy, and might need work to
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* make copies of the inner enum type cooperate, but it could help
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* with `Option` or `Result` wrapped around another enum.
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*
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* - Tagged pointers would be neat, but given that any type can be
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* used unboxed and any field can have pointers (including mutable)
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* taken to it, implementing them for Rust seems difficult.
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*/
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use core::container::Map;
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use core::libc::c_ulonglong;
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use core::option::{Option, Some, None};
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use core::vec;
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use lib::llvm::{ValueRef, TypeRef, True, False};
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use middle::trans::_match;
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use middle::trans::build::*;
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use middle::trans::common::*;
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use middle::trans::machine;
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use middle::trans::type_of;
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use middle::ty;
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use syntax::ast;
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use util::ppaux::ty_to_str;
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/// Representations.
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pub enum Repr {
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/**
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* `Unit` exists only so that an enum with a single C-like variant
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* can occupy no space, for ABI compatibility with rustc from
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* before (and during) the creation of this module. It may not be
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* worth keeping around; `CEnum` and `Univariant` cover it
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* overwise.
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*/
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Unit(int),
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/// C-like enums; basically an int.
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CEnum(int, int), // discriminant range
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/// Single-case variants, and structs/tuples/records.
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Univariant(Struct, Destructor),
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/**
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* General-case enums: discriminant as int, followed by fields.
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* The fields start immediately after the discriminant, meaning
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* that they may not be correctly aligned for the platform's ABI;
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* see above.
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*/
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General(~[Struct])
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}
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/**
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* Structs without destructors have historically had an extra layer of
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* LLVM-struct to make accessing them work the same as structs with
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* destructors. This could probably be flattened to a boolean now
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* that this module exists.
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*/
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enum Destructor {
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StructWithDtor,
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StructWithoutDtor,
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NonStruct
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}
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/// For structs, and struct-like parts of anything fancier.
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struct Struct {
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size: u64,
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align: u64,
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fields: ~[ty::t]
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}
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/**
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* Convenience for `represent_type`. There should probably be more or
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* these, for places in trans where the `ty::t` isn't directly
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* available.
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*/
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pub fn represent_node(bcx: block, node: ast::node_id) -> @Repr {
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represent_type(bcx.ccx(), node_id_type(bcx, node))
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}
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/// Decides how to represent a given type.
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pub fn represent_type(cx: @CrateContext, t: ty::t) -> @Repr {
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debug!("Representing: %s", ty_to_str(cx.tcx, t));
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match cx.adt_reprs.find(&t) {
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Some(repr) => return *repr,
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None => { }
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}
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let repr = @match ty::get(t).sty {
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ty::ty_tup(ref elems) => {
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Univariant(mk_struct(cx, *elems), NonStruct)
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}
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ty::ty_struct(def_id, ref substs) => {
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let fields = ty::lookup_struct_fields(cx.tcx, def_id);
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let dt = ty::ty_dtor(cx.tcx, def_id).is_present();
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Univariant(mk_struct(cx, fields.map(|field| {
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ty::lookup_field_type(cx.tcx, def_id, field.id, substs)
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})), if dt { StructWithDtor } else { StructWithoutDtor })
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}
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ty::ty_enum(def_id, ref substs) => {
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struct Case { discr: int, tys: ~[ty::t] };
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let cases = do ty::enum_variants(cx.tcx, def_id).map |vi| {
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let arg_tys = do vi.args.map |&raw_ty| {
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ty::subst(cx.tcx, substs, raw_ty)
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};
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Case { discr: vi.disr_val, tys: arg_tys }
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};
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if cases.len() == 0 {
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// Uninhabitable; represent as unit
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Unit(0)
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} else if cases.len() == 1 && cases[0].tys.len() == 0 {
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// `()`-like; see comment on definition of `Unit`.
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Unit(cases[0].discr)
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} else if cases.len() == 1 {
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// Equivalent to a struct/tuple/newtype.
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assert cases[0].discr == 0;
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Univariant(mk_struct(cx, cases[0].tys), NonStruct)
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} else if cases.all(|c| c.tys.len() == 0) {
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// All bodies empty -> intlike
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let discrs = cases.map(|c| c.discr);
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CEnum(discrs.min(), discrs.max())
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} else {
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// The general case. Since there's at least one
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// non-empty body, explicit discriminants should have
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// been rejected by a checker before this point.
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if !cases.alli(|i,c| c.discr == (i as int)) {
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cx.sess.bug(fmt!("non-C-like enum %s with specified \
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discriminants",
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ty::item_path_str(cx.tcx, def_id)))
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}
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General(cases.map(|c| mk_struct(cx, c.tys)))
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}
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}
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_ => cx.sess.bug(~"adt::represent_type called on non-ADT type")
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};
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cx.adt_reprs.insert(t, repr);
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return repr;
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}
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fn mk_struct(cx: @CrateContext, tys: &[ty::t]) -> Struct {
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let lltys = tys.map(|&ty| type_of::sizing_type_of(cx, ty));
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let llty_rec = T_struct(lltys);
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Struct {
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size: machine::llsize_of_alloc(cx, llty_rec) /*bad*/as u64,
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align: machine::llalign_of_min(cx, llty_rec) /*bad*/as u64,
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fields: vec::from_slice(tys)
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}
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}
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/**
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* Returns the fields of a struct for the given representation.
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* All nominal types are LLVM structs, in order to be able to use
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* forward-declared opaque types to prevent circularity in `type_of`.
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*/
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pub fn fields_of(cx: @CrateContext, r: &Repr) -> ~[TypeRef] {
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generic_fields_of(cx, r, false)
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}
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/// Like `fields_of`, but for `type_of::sizing_type_of` (q.v.).
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pub fn sizing_fields_of(cx: @CrateContext, r: &Repr) -> ~[TypeRef] {
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generic_fields_of(cx, r, true)
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}
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fn generic_fields_of(cx: @CrateContext, r: &Repr, sizing: bool)
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-> ~[TypeRef] {
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match *r {
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Unit(*) => ~[],
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CEnum(*) => ~[T_enum_discrim(cx)],
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Univariant(ref st, dt) => {
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let f = if sizing {
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st.fields.map(|&ty| type_of::sizing_type_of(cx, ty))
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} else {
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st.fields.map(|&ty| type_of::type_of(cx, ty))
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};
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match dt {
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NonStruct => f,
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StructWithoutDtor => ~[T_struct(f)],
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StructWithDtor => ~[T_struct(f), T_i8()]
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}
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}
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General(ref sts) => {
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~[T_enum_discrim(cx),
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T_array(T_i8(), sts.map(|st| st.size).max() /*bad*/as uint)]
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}
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}
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}
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/**
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* Obtain a representation of the discriminant sufficient to translate
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* destructuring; this may or may not involve the actual discriminant.
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*
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* This should ideally be less tightly tied to `_match`.
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*/
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pub fn trans_switch(bcx: block, r: &Repr, scrutinee: ValueRef)
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-> (_match::branch_kind, Option<ValueRef>) {
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match *r {
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CEnum(*) | General(*) => {
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(_match::switch, Some(trans_get_discr(bcx, r, scrutinee)))
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}
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Unit(*) | Univariant(*) => {
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(_match::single, None)
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}
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}
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}
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/// Obtain the actual discriminant of a value.
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pub fn trans_get_discr(bcx: block, r: &Repr, scrutinee: ValueRef)
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-> ValueRef {
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match *r {
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Unit(the_disc) => C_int(bcx.ccx(), the_disc),
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CEnum(min, max) => load_discr(bcx, scrutinee, min, max),
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Univariant(*) => C_int(bcx.ccx(), 0),
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General(ref cases) => load_discr(bcx, scrutinee, 0,
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(cases.len() - 1) as int)
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}
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}
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/// Helper for cases where the discriminant is simply loaded.
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fn load_discr(bcx: block, scrutinee: ValueRef, min: int, max: int)
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-> ValueRef {
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let ptr = GEPi(bcx, scrutinee, [0, 0]);
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if max + 1 == min {
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// i.e., if the range is everything. The lo==hi case would be
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// rejected by the LLVM verifier (it would mean either an
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// empty set, which is impossible, or the entire range of the
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// type, which is pointless).
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Load(bcx, ptr)
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} else {
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// llvm::ConstantRange can deal with ranges that wrap around,
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// so an overflow on (max + 1) is fine.
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LoadRangeAssert(bcx, ptr, min as c_ulonglong,
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(max + 1) as c_ulonglong,
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/* signed: */ True)
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}
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}
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/**
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* Yield information about how to dispatch a case of the
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* discriminant-like value returned by `trans_switch`.
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*
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* This should ideally be less tightly tied to `_match`.
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*/
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pub fn trans_case(bcx: block, r: &Repr, discr: int) -> _match::opt_result {
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match *r {
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CEnum(*) => {
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_match::single_result(rslt(bcx, C_int(bcx.ccx(), discr)))
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}
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Unit(*) | Univariant(*)=> {
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bcx.ccx().sess.bug(~"no cases for univariants or structs")
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}
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General(*) => {
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_match::single_result(rslt(bcx, C_int(bcx.ccx(), discr)))
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}
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}
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}
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/**
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* Begin initializing a new value of the given case of the given
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* representation. The fields, if any, should then be initialized via
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* `trans_field_ptr`.
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*/
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pub fn trans_start_init(bcx: block, r: &Repr, val: ValueRef, discr: int) {
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match *r {
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Unit(the_discr) => {
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assert discr == the_discr;
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}
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CEnum(min, max) => {
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assert min <= discr && discr <= max;
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Store(bcx, C_int(bcx.ccx(), discr), GEPi(bcx, val, [0, 0]))
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}
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Univariant(_, StructWithDtor) => {
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assert discr == 0;
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Store(bcx, C_u8(1), GEPi(bcx, val, [0, 1]))
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}
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Univariant(*) => {
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assert discr == 0;
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}
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General(*) => {
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Store(bcx, C_int(bcx.ccx(), discr), GEPi(bcx, val, [0, 0]))
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}
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}
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}
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/**
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* The number of fields in a given case; for use when obtaining this
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* information from the type or definition is less convenient.
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*/
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pub fn num_args(r: &Repr, discr: int) -> uint {
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match *r {
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Unit(*) | CEnum(*) => 0,
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Univariant(ref st, _dt) => { assert discr == 0; st.fields.len() }
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General(ref cases) => cases[discr as uint].fields.len()
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}
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}
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/// Access a field, at a point when the value's case is known.
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pub fn trans_field_ptr(bcx: block, r: &Repr, val: ValueRef, discr: int,
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ix: uint) -> ValueRef {
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// Note: if this ever needs to generate conditionals (e.g., if we
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// decide to do some kind of cdr-coding-like non-unique repr
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// someday), it will need to return a possibly-new bcx as well.
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match *r {
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Unit(*) | CEnum(*) => {
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bcx.ccx().sess.bug(~"element access in C-like enum")
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}
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Univariant(ref st, dt) => {
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assert discr == 0;
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let val = match dt {
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NonStruct => val,
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StructWithDtor | StructWithoutDtor => GEPi(bcx, val, [0, 0])
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};
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struct_field_ptr(bcx, st, val, ix, false)
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}
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General(ref cases) => {
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struct_field_ptr(bcx, &cases[discr as uint],
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GEPi(bcx, val, [0, 1]), ix, true)
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}
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}
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}
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fn struct_field_ptr(bcx: block, st: &Struct, val: ValueRef, ix: uint,
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needs_cast: bool) -> ValueRef {
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let ccx = bcx.ccx();
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let val = if needs_cast {
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let real_llty = T_struct(st.fields.map(
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|&ty| type_of::type_of(ccx, ty)));
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PointerCast(bcx, val, T_ptr(real_llty))
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} else {
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val
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};
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GEPi(bcx, val, [0, ix])
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}
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/// Access the struct drop flag, if present.
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pub fn trans_drop_flag_ptr(bcx: block, r: &Repr, val: ValueRef) -> ValueRef {
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match *r {
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Univariant(_, StructWithDtor) => GEPi(bcx, val, [0, 1]),
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_ => bcx.ccx().sess.bug(~"tried to get drop flag of non-droppable \
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type")
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}
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}
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/**
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* Construct a constant value, suitable for initializing a
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* GlobalVariable, given a case and constant values for its fields.
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* Note that this may have a different LLVM type (and different
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* alignment!) from the representation's `type_of`, so it needs a
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* pointer cast before use.
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*
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* The LLVM type system does not directly support unions, and only
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* pointers can be bitcast, so a constant (and, by extension, the
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* GlobalVariable initialized by it) will have a type that can vary
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* depending on which case of an enum it is.
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*
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* To understand the alignment situation, consider `enum E { V64(u64),
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* V32(u32, u32) }` on win32. The type should have 8-byte alignment
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* to accommodate the u64 (currently it doesn't; this is a known bug),
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* but `V32(x, y)` would have LLVM type `{i32, i32, i32}`, which is
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* 4-byte aligned.
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*
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* Currently the returned value has the same size as the type, but
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* this may be changed in the future to avoid allocating unnecessary
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* space after values of shorter-than-maximum cases.
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*/
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pub fn trans_const(ccx: @CrateContext, r: &Repr, discr: int,
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vals: &[ValueRef]) -> ValueRef {
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match *r {
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Unit(*) => {
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C_struct(~[])
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}
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CEnum(min, max) => {
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assert vals.len() == 0;
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assert min <= discr && discr <= max;
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C_int(ccx, discr)
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}
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Univariant(ref st, dt) => {
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assert discr == 0;
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let s = C_struct(build_const_struct(ccx, st, vals));
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match dt {
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NonStruct => s,
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// The actual destructor flag doesn't need to be present.
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// But add an extra struct layer for compatibility.
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StructWithDtor | StructWithoutDtor => C_struct(~[s])
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}
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}
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General(ref cases) => {
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let case = &cases[discr as uint];
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let max_sz = cases.map(|s| s.size).max();
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let body = build_const_struct(ccx, case, vals);
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// The unary packed struct has alignment 1 regardless of
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// its contents, so it will always be located at the
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// expected offset at runtime.
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C_struct([C_int(ccx, discr),
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C_packed_struct([C_struct(body)]),
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padding(max_sz - case.size)])
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}
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}
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}
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/**
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* Building structs is a little complicated, because we might need to
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* insert padding if a field's value is less aligned than its type.
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*
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* Continuing the example from `trans_const`, a value of type `(u32,
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* E)` should have the `E` at offset 8, but if that field's
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* initializer is 4-byte aligned then simply translating the tuple as
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* a two-element struct will locate it at offset 4, and accesses to it
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* will read the wrong memory.
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*/
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fn build_const_struct(ccx: @CrateContext, st: &Struct, vals: &[ValueRef])
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-> ~[ValueRef] {
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assert vals.len() == st.fields.len();
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let mut offset = 0;
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let mut cfields = ~[];
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for st.fields.eachi |i, &ty| {
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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;
|
|
}
|
|
assert !is_undef(vals[i]);
|
|
// If that assert fails, could change it to wrap in a struct?
|
|
// (See `const_struct_field` for why real fields must not be undef.)
|
|
cfields.push(vals[i]);
|
|
}
|
|
|
|
return cfields;
|
|
}
|
|
|
|
fn padding(size: u64) -> ValueRef {
|
|
C_undef(T_array(T_i8(), size /*bad*/as uint))
|
|
}
|
|
|
|
// XXX this utility routine should be somewhere more general
|
|
#[always_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: @CrateContext, r: &Repr, val: ValueRef)
|
|
-> int {
|
|
match *r {
|
|
Unit(discr) => discr,
|
|
CEnum(*) => const_to_int(val) as int,
|
|
Univariant(*) => 0,
|
|
General(*) => const_to_int(const_get_elt(ccx, val, [0])) as int,
|
|
}
|
|
}
|
|
|
|
/**
|
|
* 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: int, ix: uint) -> ValueRef {
|
|
match *r {
|
|
Unit(*) | CEnum(*) => ccx.sess.bug(~"element access in C-like enum \
|
|
const"),
|
|
Univariant(_, NonStruct) => const_struct_field(ccx, val, ix),
|
|
Univariant(*) => const_struct_field(ccx, const_get_elt(ccx, val,
|
|
[0]), ix),
|
|
General(*) => const_struct_field(ccx, const_get_elt(ccx, val,
|
|
[1, 0]), ix)
|
|
}
|
|
}
|
|
|
|
/// Extract field of struct-like const, skipping our alignment padding.
|
|
fn const_struct_field(ccx: @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, StructWithoutDtor)
|
|
| Univariant(ref st, NonStruct) => st.fields.len() == 1,
|
|
_ => false
|
|
}
|
|
}
|