rust/src/comp/middle/shape.rs

// A "shape" is a compact encoding of a type that is used by interpreted glue.
// This substitutes for the runtime tags used by e.g. MLs.

import lib::llvm::True;
import lib::llvm::llvm::ModuleRef;
import lib::llvm::llvm::TypeRef;
import lib::llvm::llvm::ValueRef;
import middle::trans;
import middle::trans_common::crate_ctxt;
import middle::trans::llsize_of;
import middle::trans_common::val_ty;
import middle::trans_common;
import middle::trans_common::C_bytes;
import middle::trans_common::C_int;
import middle::trans_common::C_named_struct;
import middle::trans_common::C_struct;
import middle::trans_common::C_uint;
import middle::trans_common::T_i8;
import middle::trans_common::T_ptr;
import middle::ty;
import middle::ty::field;
import middle::ty::mt;
import syntax::ast;
import syntax::codemap::span;
import syntax::util::interner;
import util::common;

import std::ivec;
import std::map::hashmap;
import std::option::none;
import std::option::some;
import std::str;

import ty_ctxt = middle::ty::ctxt;

type res_info = { did: ast::def_id, t: ty::t };

type ctxt = {
    mutable next_tag_id: u16,
    pad: u16,
    tag_id_to_index: hashmap[ast::def_id,u16],
    mutable tag_order: [ast::def_id],
    resources: interner::interner[res_info],
    llshapetablesty: TypeRef,
    llshapetables: ValueRef
};

const shape_u8 : u8 = 0u8;
const shape_u16 : u8 = 1u8;
const shape_u32 : u8 = 2u8;
const shape_u64 : u8 = 3u8;
const shape_i8 : u8 = 4u8;
const shape_i16 : u8 = 5u8;
const shape_i32 : u8 = 6u8;
const shape_i64 : u8 = 7u8;
const shape_f32 : u8 = 8u8;
const shape_f64 : u8 = 9u8;
const shape_evec : u8 = 10u8;
const shape_ivec : u8 = 11u8;
const shape_tag : u8 = 12u8;
const shape_box : u8 = 13u8;
const shape_port : u8 = 14u8;
const shape_chan : u8 = 15u8;
const shape_task : u8 = 16u8;
const shape_struct : u8 = 17u8;
const shape_fn : u8 = 18u8;
const shape_obj : u8 = 19u8;
const shape_res : u8 = 20u8;
const shape_var : u8 = 21u8;
const shape_uniq : u8 = 22u8;

// FIXME: This is a bad API in trans_common.
fn C_u8(n : u8) -> ValueRef { ret trans_common::C_u8(n as uint); }

fn fake_span() -> span { ret { lo: 0u, hi: 0u }; }

fn hash_res_info(ri : &res_info) -> uint {
    let h = 5381u;
    h *= 33u; h += (ri.did.crate as uint);
    h *= 33u; h += (ri.did.node as uint);
    h *= 33u; h += (ri.t as uint);
    ret h;
}

fn eq_res_info(a : &res_info, b : &res_info) -> bool {
    ret a.did.crate == b.did.crate && a.did.node == b.did.node && a.t == b.t;
}

fn mk_global(ccx : &@crate_ctxt, name : &str, llval : ValueRef) -> ValueRef {
    let llglobal = lib::llvm::llvm::LLVMAddGlobal(ccx.llmod, val_ty(llval),
                                                   str::buf(name));
    lib::llvm::llvm::LLVMSetInitializer(llglobal, llval);
    lib::llvm::llvm::LLVMSetGlobalConstant(llglobal, True);
    lib::llvm::llvm::LLVMSetLinkage(llglobal, lib::llvm::LLVMInternalLinkage
                                    as lib::llvm::llvm::Linkage);
    ret llglobal;
}


// Computes a set of variants of a tag that are guaranteed to have size and
// alignment at least as large as any other variant of the tag. This is an
// important performance optimization.
//
// TODO: Use this in dynamic_size_of() as well.

fn largest_variants(ccx : &@crate_ctxt, tag_id : &ast::def_id) -> [uint] {
    // Compute the minimum and maximum size and alignment for each variant.
    //
    // TODO: We could do better here; e.g. we know that any variant that
    // contains (T,T) must be as least as large as any variant that contains
    // just T.
    let ranges = ~[];
    let variants = ty::tag_variants(ccx.tcx, tag_id);
    for variant : ty::variant_info in variants {
        let bounded = true;
        let { a: min_size, b: min_align } = { a: 0u, b: 0u };
        for elem_t : ty::t in variant.args {
            if ty::type_contains_params(ccx.tcx, elem_t) {
                // TODO: We could do better here; this causes us to
                // conservatively assume that (int, T) has minimum size 0,
                // when in fact it has minimum size sizeof(int).
                bounded = false;
            } else {
                let llty = trans::type_of(ccx, fake_span(), elem_t);
                min_size += trans::llsize_of_real(ccx, llty);
                min_align += trans::llalign_of_real(ccx, llty);
            }
        }

        ranges += ~[{ size:  { min: min_size,  bounded: bounded },
                      align: { min: min_align, bounded: bounded } }];
    }

    // Initialize the candidate set to contain all variants.
    let candidates = ~[mutable];
    for variant in variants { candidates += ~[mutable true]; }

    // Do a pairwise comparison among all variants still in the candidate set.
    // Throw out any variant that we know has size and alignment at least as
    // small as some other variant.
    let i = 0u;
    while i < ivec::len(ranges) - 1u {
        if candidates.(i) {
            let j = i + 1u;
            while (j < ivec::len(ranges)) {
                if candidates.(j) {
                    if ranges.(i).size.bounded && ranges.(i).align.bounded &&
                            ranges.(j).size.bounded &&
                            ranges.(j).align.bounded {
                        if ranges.(i).size >= ranges.(j).size &&
                                ranges.(i).align >= ranges.(j).align {
                            // Throw out j.
                            candidates.(j) = false;
                        } else if ranges.(j).size >= ranges.(i).size &&
                                ranges.(j).align >= ranges.(j).align {
                            // Throw out i.
                            candidates.(i) = false;
                        }
                    }
                }
                j += 1u;
            }
        }
        i += 1u;
    }

    // Return the resulting set.
    let result = ~[];
    i = 0u;
    while i < ivec::len(candidates) {
        if candidates.(i) { result += ~[i]; }
        i += 1u;
    }
    ret result;
}

// Computes the static size of a tag, without using mk_imm_tup(), which is
// bad for performance.
//
// TODO: Migrate trans over to use this.

fn round_up(size : u16, align : u8) -> u16 {
    assert align >= 1u8;
    let alignment = align as u16;
    ret ((size-1u16) + alignment) & !(alignment-1u16);
}

type size_align = { size: u16, align: u8 };

fn compute_static_tag_size(ccx : &@crate_ctxt, largest_variants : &[uint],
                           did : &ast::def_id) -> size_align {
    let max_size = 0u16; let max_align = 1u8;
    let variants = ty::tag_variants(ccx.tcx, did);
    for vid : uint in largest_variants {
        // We increment a "virtual data pointer" to compute the size.
        let lltys = ~[];
        for typ : ty::t in variants.(vid).args {
            lltys += ~[trans::type_of(ccx, fake_span(), typ)];
        }

        let llty = trans_common::T_struct(lltys);
        let dp = trans::llsize_of_real(ccx, llty) as u16;
        let variant_align = trans::llalign_of_real(ccx, llty) as u8;

        if max_size < dp { max_size = dp; }
        if max_align < variant_align { max_align = variant_align; }
    }

    // Add space for the tag if applicable.
    // FIXME (issue #792): This is wrong. If the tag starts with an 8 byte
    // aligned quantity, we don't align it.
    if ivec::len(variants) > 1u {
        max_size += 4u16;
        max_align = 4u8;
    }

    ret { size: max_size, align: max_align };
}

tag tag_kind {
    tk_unit;
    tk_enum;
    tk_complex;
}

fn tag_kind(ccx : &@crate_ctxt, did : &ast::def_id) -> tag_kind {
    let variants = ty::tag_variants(ccx.tcx, did);
    if ivec::len(variants) == 0u { ret tk_complex; }
    for v : ty::variant_info in variants {
        if ivec::len(v.args) > 0u { ret tk_complex; }
    }
    if ivec::len(variants) == 1u { ret tk_unit; }
    ret tk_enum;
}


// Returns the code corresponding to the pointer size on this architecture.
fn s_int(tcx : &ty_ctxt) -> u8 {
    ret shape_i32;      // TODO: x86-64
}

fn s_uint(tcx : &ty_ctxt) -> u8 {
    ret shape_u32;      // TODO: x86-64
}

fn s_float(tcx : &ty_ctxt) -> u8 {
    ret shape_f64;      // TODO: x86-64
}

fn mk_ctxt(llmod : ModuleRef) -> ctxt {
    let llshapetablesty = trans_common::T_named_struct("shapes");
    let llshapetables =
        lib::llvm::llvm::LLVMAddGlobal(llmod, llshapetablesty,
                                       str::buf("shapes"));

    ret {
        mutable next_tag_id: 0u16,
        pad: 0u16,
        tag_id_to_index: common::new_def_hash(),
        mutable tag_order: ~[],
        resources: interner::mk(hash_res_info, eq_res_info),
        llshapetablesty: llshapetablesty,
        llshapetables: llshapetables
    };
}

fn add_bool(dest : &mutable [u8], val : bool) {
    dest += ~[if val { 1u8 } else { 0u8 }];
}

fn add_u16(dest : &mutable [u8], val : u16) {
    dest += ~[(val & 0xffu16) as u8, (val >> 8u16) as u8];
}

fn add_substr(dest : &mutable [u8], src : &[u8]) {
    add_u16(dest, ivec::len(src) as u16);
    dest += src;
}

fn shape_of(ccx : &@crate_ctxt, t : ty::t) -> [u8] {
    let s = ~[];

    alt ty::struct(ccx.tcx, t) {
      ty::ty_nil. | ty::ty_bool. | ty::ty_machine(ast::ty_u8.) | ty::ty_bot. {
        s += ~[shape_u8];
      }

      ty::ty_int. { s += ~[s_int(ccx.tcx)]; }
      ty::ty_float. { s += ~[s_float(ccx.tcx)]; }

      ty::ty_uint. | ty::ty_ptr(_) | ty::ty_type. | ty::ty_native(_) {
        s += ~[s_uint(ccx.tcx)];
      }

      ty::ty_machine(ast::ty_i8.) { s += ~[shape_i8]; }
      ty::ty_machine(ast::ty_u16.) { s += ~[shape_u16]; }
      ty::ty_machine(ast::ty_i16.) { s += ~[shape_i16]; }
      ty::ty_machine(ast::ty_u32.) | ty::ty_char. { s += ~[shape_u32]; }
      ty::ty_machine(ast::ty_i32.) { s += ~[shape_i32]; }
      ty::ty_machine(ast::ty_u64.) { s += ~[shape_u64]; }
      ty::ty_machine(ast::ty_i64.) { s += ~[shape_i64]; }

      ty::ty_str. { s += ~[shape_evec, 1u8, 1u8, 0u8, shape_u8]; }
      ty::ty_istr. { s += ~[shape_ivec, 1u8, 1u8, 0u8, shape_u8]; }

      ty::ty_tag(did, tps) {
        alt tag_kind(ccx, did) {
          tk_unit. {
            // FIXME: For now we do this.
            s += ~[shape_u32];
          }
          tk_enum. { s += ~[shape_u32]; }
          tk_complex. {
            s += ~[shape_tag];

            let sub = ~[];

            let id;
            alt ccx.shape_cx.tag_id_to_index.find(did) {
              none. {
                id = ccx.shape_cx.next_tag_id;
                ccx.shape_cx.tag_id_to_index.insert(did, id);
                ccx.shape_cx.tag_order += ~[did];
                ccx.shape_cx.next_tag_id += 1u16;
              }
              some(existing_id) { id = existing_id; }
            }
            add_u16(sub, id as u16);

            add_u16(sub, ivec::len(tps) as u16);
            for tp : ty::t in tps {
                let subshape = shape_of(ccx, tp);
                add_u16(sub, ivec::len(subshape) as u16);
                sub += subshape;
            }

            s += sub;
          }
        }
      }

      ty::ty_box(mt) {
        s += ~[shape_box];
        add_substr(s, shape_of(ccx, mt.ty));
      }
      ty::ty_uniq(subt) {
        s += ~[shape_uniq];
        add_substr(s, shape_of(ccx, subt));
      }
      ty::ty_vec(mt) {
        s += ~[shape_evec];
        add_bool(s, ty::type_is_pod(ccx.tcx, mt.ty));
        add_substr(s, shape_of(ccx, mt.ty));
      }
      ty::ty_ivec(mt) {
        s += ~[shape_ivec];
        add_bool(s, ty::type_is_pod(ccx.tcx, mt.ty));
        add_size_hint(ccx, s, mt.ty);
        add_substr(s, shape_of(ccx, mt.ty));
      }
      ty::ty_port(t) {
        s += ~[shape_port];
        add_substr(s, shape_of(ccx, t));
      }
      ty::ty_chan(t) { s += ~[shape_chan]; }
      ty::ty_task. { s += ~[shape_task]; }

      ty::ty_rec(fields) {
        s += ~[shape_struct];
        let sub = ~[];
        for f : field in fields { sub += shape_of(ccx, f.mt.ty); }
        add_substr(s, sub);
      }
      ty::ty_tup(elts) {
        s += ~[shape_struct];
        let sub = ~[];
        for elt in elts { sub += shape_of(ccx, elt.ty); }
        add_substr(s, sub);
      }

      ty::ty_fn(_,_,_,_,_) { s += ~[shape_fn]; }
      ty::ty_native_fn(_,_,_) { s += ~[shape_u32]; }
      ty::ty_obj(_) { s += ~[shape_obj]; }

      ty::ty_res(did, raw_subt, tps) {
        let subt = ty::substitute_type_params(ccx.tcx, tps, raw_subt);
        let ri = { did: did, t: subt };
        let id = interner::intern(ccx.shape_cx.resources, ri);

        s += ~[shape_res];
        add_u16(s, id as u16);
        add_u16(s, ivec::len(tps) as u16);

        let sub = ~[];
        for tp : ty::t in tps { add_substr(s, sub); }
        add_substr(s, sub);

        add_substr(s, shape_of(ccx, subt));

      }

      ty::ty_var(n) { fail "shape_of ty_var"; }
      ty::ty_param(n,_) { s += ~[shape_var, n as u8]; }
    }

    ret s;
}

fn add_size_hint(ccx : &@crate_ctxt, s : &mutable [u8], typ : ty::t) {
    if (ty::type_has_dynamic_size(ccx.tcx, typ)) {
        s += ~[ 0u8, 0u8, 0u8 ];
        ret;
    }

    let llty = trans::type_of(ccx, fake_span(), typ);
    add_u16(s, trans::llsize_of_real(ccx, llty) as u16);
    s += ~[ trans::llalign_of_real(ccx, llty) as u8 ];
}

// FIXME: We might discover other variants as we traverse these. Handle this.
fn shape_of_variant(ccx : &@crate_ctxt, v : &ty::variant_info) -> [u8] {
    let s = ~[];
    for t : ty::t in v.args { s += shape_of(ccx, t); }
    ret s;
}

fn gen_tag_shapes(ccx : &@crate_ctxt) -> ValueRef {
    // Loop over all the tag variants and write their shapes into a data
    // buffer. As we do this, it's possible for us to discover new tags, so we
    // must do this first.
    let i = 0u;
    let data = ~[]; let offsets = ~[];
    while (i < ivec::len(ccx.shape_cx.tag_order)) {
        let did = ccx.shape_cx.tag_order.(i);
        let variants = ty::tag_variants(ccx.tcx, did);

        for v : ty::variant_info in variants {
            offsets += ~[ivec::len(data) as u16];

            let variant_shape = shape_of_variant(ccx, v);
            add_substr(data, variant_shape);
        }

        i += 1u;
    }

    // Now calculate the sizes of the header space (which contains offsets to
    // info records for each tag) and the info space (which contains offsets
    // to each variant shape). As we do so, build up the header.

    let header = ~[]; let info = ~[];
    let header_sz = 2u16 * ccx.shape_cx.next_tag_id;
    let data_sz = ivec::len(data) as u16;

    let info_sz = 0u16;
    for did_ : ast::def_id in ccx.shape_cx.tag_order {
        let did = did_;    // Satisfy alias checker.
        let variants = ty::tag_variants(ccx.tcx, did);
        add_u16(header, header_sz + info_sz);
        info_sz += 2u16 * ((ivec::len(variants) as u16) + 2u16) + 3u16;
    }

    // Construct the info tables, which contain offsets to the shape of each
    // variant. Also construct the largest-variant table for each tag, which
    // contains the variants that the size-of operation needs to look at.

    let lv_table = ~[];
    i = 0u;
    for did_ : ast::def_id in ccx.shape_cx.tag_order {
        let did = did_;    // Satisfy alias checker.
        let variants = ty::tag_variants(ccx.tcx, did);
        add_u16(info, ivec::len(variants) as u16);

        // Construct the largest-variants table.
        add_u16(info, header_sz + info_sz + data_sz +
                (ivec::len(lv_table) as u16));

        let lv = largest_variants(ccx, did);
        add_u16(lv_table, ivec::len(lv) as u16);
        for v : uint in lv { add_u16(lv_table, v as u16); }

        // Determine whether the tag has dynamic size.
        let dynamic = false;
        for variant : ty::variant_info in variants {
            for typ : ty::t in variant.args {
                if ty::type_has_dynamic_size(ccx.tcx, typ) { dynamic = true; }
            }
        }

        // If we can, write in the static size and alignment of the tag.
        // Otherwise, write a placeholder.
        let size_align;
        if dynamic {
            size_align = { size: 0u16, align: 0u8 };
        } else {
            size_align = compute_static_tag_size(ccx, lv, did);
        }
        add_u16(info, size_align.size);
        info += ~[size_align.align];

        // Now write in the offset of each variant.
        for v : ty::variant_info in variants {
            add_u16(info, header_sz + info_sz + offsets.(i));
            i += 1u;
        }
    }

    assert (i == ivec::len(offsets));
    assert (header_sz == (ivec::len(header) as u16));
    assert (info_sz == (ivec::len(info) as u16));
    assert (data_sz == (ivec::len(data) as u16));

    header += info;
    header += data;
    header += lv_table;

    ret mk_global(ccx, "tag_shapes", C_bytes(header));
}

fn gen_resource_shapes(ccx : &@crate_ctxt) -> ValueRef {
    let dtors = ~[];
    let i = 0u;
    let len = interner::len(ccx.shape_cx.resources);
    while i < len {
        let ri = interner::get(ccx.shape_cx.resources, i);
        dtors += ~[trans_common::get_res_dtor(ccx, fake_span(), ri.did,
                                              ri.t)];
        i += 1u;
    }

    ret mk_global(ccx, "resource_shapes", C_struct(dtors));
}

fn gen_shape_tables(ccx : &@crate_ctxt) {
    let lltagstable = gen_tag_shapes(ccx);
    let llresourcestable = gen_resource_shapes(ccx);
    trans_common::set_struct_body(ccx.shape_cx.llshapetablesty,
                                  ~[val_ty(lltagstable),
                                    val_ty(llresourcestable)]);

    let lltables = C_named_struct(ccx.shape_cx.llshapetablesty,
                                  ~[lltagstable, llresourcestable]);
    lib::llvm::llvm::LLVMSetInitializer(ccx.shape_cx.llshapetables, lltables);
    lib::llvm::llvm::LLVMSetGlobalConstant(ccx.shape_cx.llshapetables, True);
    lib::llvm::llvm::LLVMSetLinkage(ccx.shape_cx.llshapetables,
                                    lib::llvm::LLVMInternalLinkage as
                                    lib::llvm::llvm::Linkage);
}