src/librustc/middle/const_eval.rs

   1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use core::prelude::*;
  12
  13 use metadata::csearch;
  14 use middle::astencode;
  15 use middle::ty;
  16 use middle;
  17
  18 use core::float;
  19 use core::vec;
  20 use syntax::{ast, ast_map, ast_util, visit};
  21 use syntax::ast::*;
  22
  23 use core::hashmap::linear::{LinearMap, LinearSet};
  24
  25 //
  26 // This pass classifies expressions by their constant-ness.
  27 //
  28 // Constant-ness comes in 3 flavours:
  29 //
  30 //   - Integer-constants: can be evaluated by the frontend all the way down
  31 //     to their actual value. They are used in a few places (enum
  32 //     discriminants, switch arms) and are a subset of
  33 //     general-constants. They cover all the integer and integer-ish
  34 //     literals (nil, bool, int, uint, char, iNN, uNN) and all integer
  35 //     operators and copies applied to them.
  36 //
  37 //   - General-constants: can be evaluated by LLVM but not necessarily by
  38 //     the frontend; usually due to reliance on target-specific stuff such
  39 //     as "where in memory the value goes" or "what floating point mode the
  40 //     target uses". This _includes_ integer-constants, plus the following
  41 //     constructors:
  42 //
  43 //        fixed-size vectors and strings: [] and ""/_
  44 //        vector and string slices: &[] and &""
  45 //        tuples: (,)
  46 //        records: {...}
  47 //        enums: foo(...)
  48 //        floating point literals and operators
  49 //        & and * pointers
  50 //        copies of general constants
  51 //
  52 //        (in theory, probably not at first: if/match on integer-const
  53 //         conditions / descriminants)
  54 //
  55 //   - Non-constants: everything else.
  56 //
  57
  58 pub enum constness {
  59     integral_const,
  60     general_const,
  61     non_const
  62 }
  63
  64 pub fn join(a: constness, b: constness) -> constness {
  65     match (a, b) {
  66       (integral_const, integral_const) => integral_const,
  67       (integral_const, general_const)
  68       | (general_const, integral_const)
  69       | (general_const, general_const) => general_const,
  70       _ => non_const
  71     }
  72 }
  73
  74 pub fn join_all(cs: &[constness]) -> constness {
  75     vec::foldl(integral_const, cs, |a, b| join(a, *b))
  76 }
  77
  78 pub fn classify(e: @expr,
  79                 tcx: ty::ctxt)
  80              -> constness {
  81     let did = ast_util::local_def(e.id);
  82     match tcx.ccache.find(&did) {
  83       Some(&x) => x,
  84       None => {
  85         let cn =
  86             match e.node {
  87               ast::expr_lit(lit) => {
  88                 match lit.node {
  89                   ast::lit_str(*) |
  90                   ast::lit_float(*) => general_const,
  91                   _ => integral_const
  92                 }
  93               }
  94
  95               ast::expr_copy(inner) |
  96               ast::expr_unary(_, inner) |
  97               ast::expr_paren(inner) => {
  98                 classify(inner, tcx)
  99               }
 100
 101               ast::expr_binary(_, a, b) => {
 102                 join(classify(a, tcx),
 103                      classify(b, tcx))
 104               }
 105
 106               ast::expr_tup(ref es) |
 107               ast::expr_vec(ref es, ast::m_imm) => {
 108                 join_all(vec::map(*es, |e| classify(*e, tcx)))
 109               }
 110
 111               ast::expr_vstore(e, vstore) => {
 112                   match vstore {
 113                       ast::expr_vstore_slice => classify(e, tcx),
 114                       ast::expr_vstore_uniq |
 115                       ast::expr_vstore_box |
 116                       ast::expr_vstore_mut_box |
 117                       ast::expr_vstore_mut_slice => non_const
 118                   }
 119               }
 120
 121               ast::expr_struct(_, ref fs, None) => {
 122                 let cs = do vec::map((*fs)) |f| {
 123                     if f.node.mutbl == ast::m_imm {
 124                         classify(f.node.expr, tcx)
 125                     } else {
 126                         non_const
 127                     }
 128                 };
 129                 join_all(cs)
 130               }
 131
 132               ast::expr_cast(base, _) => {
 133                 let ty = ty::expr_ty(tcx, e);
 134                 let base = classify(base, tcx);
 135                 if ty::type_is_integral(ty) {
 136                     join(integral_const, base)
 137                 } else if ty::type_is_fp(ty) {
 138                     join(general_const, base)
 139                 } else {
 140                     non_const
 141                 }
 142               }
 143
 144               ast::expr_field(base, _, _) => {
 145                 classify(base, tcx)
 146               }
 147
 148               ast::expr_index(base, idx) => {
 149                 join(classify(base, tcx),
 150                      classify(idx, tcx))
 151               }
 152
 153               ast::expr_addr_of(ast::m_imm, base) => {
 154                 classify(base, tcx)
 155               }
 156
 157               // FIXME: (#3728) we can probably do something CCI-ish
 158               // surrounding nonlocal constants. But we don't yet.
 159               ast::expr_path(_) => {
 160                 lookup_constness(tcx, e)
 161               }
 162
 163               _ => non_const
 164             };
 165         tcx.ccache.insert(did, cn);
 166         cn
 167       }
 168     }
 169 }
 170
 171 pub fn lookup_const(tcx: ty::ctxt, e: @expr) -> Option<@expr> {
 172     match tcx.def_map.find(&e.id) {
 173         Some(&ast::def_const(def_id)) => lookup_const_by_id(tcx, def_id),
 174         _ => None
 175     }
 176 }
 177
 178 pub fn lookup_const_by_id(tcx: ty::ctxt,
 179                           def_id: ast::def_id)
 180                        -> Option<@expr> {
 181     if ast_util::is_local(def_id) {
 182         match tcx.items.find(&def_id.node) {
 183             None => None,
 184             Some(&ast_map::node_item(it, _)) => match it.node {
 185                 item_const(_, const_expr) => Some(const_expr),
 186                 _ => None
 187             },
 188             Some(_) => None
 189         }
 190     } else {
 191         let maps = astencode::Maps {
 192             mutbl_map: @mut LinearSet::new(),
 193             root_map: @mut LinearMap::new(),
 194             last_use_map: @mut LinearMap::new(),
 195             method_map: @mut LinearMap::new(),
 196             vtable_map: @mut LinearMap::new(),
 197             write_guard_map: @mut LinearSet::new(),
 198             moves_map: @mut LinearSet::new(),
 199             capture_map: @mut LinearMap::new()
 200         };
 201         match csearch::maybe_get_item_ast(tcx, def_id,
 202             |a, b, c, d| astencode::decode_inlined_item(a, b, maps, /*bar*/ copy c, d)) {
 203             csearch::found(ast::ii_item(item)) => match item.node {
 204                 item_const(_, const_expr) => Some(const_expr),
 205                 _ => None
 206             },
 207             _ => None
 208         }
 209     }
 210 }
 211
 212 pub fn lookup_constness(tcx: ty::ctxt, e: @expr) -> constness {
 213     match lookup_const(tcx, e) {
 214         Some(rhs) => {
 215             let ty = ty::expr_ty(tcx, rhs);
 216             if ty::type_is_integral(ty) {
 217                 integral_const
 218             } else {
 219                 general_const
 220             }
 221         }
 222         None => non_const
 223     }
 224 }
 225
 226 pub fn process_crate(crate: @ast::crate,
 227                      tcx: ty::ctxt) {
 228     let v = visit::mk_simple_visitor(@visit::SimpleVisitor {
 229         visit_expr_post: |e| { classify(e, tcx); },
 230         .. *visit::default_simple_visitor()
 231     });
 232     visit::visit_crate(*crate, (), v);
 233     tcx.sess.abort_if_errors();
 234 }
 235
 236
 237 // FIXME (#33): this doesn't handle big integer/float literals correctly
 238 // (nor does the rest of our literal handling).
 239 #[deriving(Eq)]
 240 pub enum const_val {
 241     const_float(f64),
 242     const_int(i64),
 243     const_uint(u64),
 244     const_str(~str),
 245     const_bool(bool)
 246 }
 247
 248 pub fn eval_const_expr(tcx: middle::ty::ctxt, e: @expr) -> const_val {
 249     match eval_const_expr_partial(tcx, e) {
 250         Ok(ref r) => (/*bad*/copy *r),
 251         Err(ref s) => fail!(/*bad*/copy *s)
 252     }
 253 }
 254
 255 pub fn eval_const_expr_partial(tcx: middle::ty::ctxt, e: @expr)
 256                             -> Result<const_val, ~str> {
 257     use middle::ty;
 258     fn fromb(b: bool) -> Result<const_val, ~str> { Ok(const_int(b as i64)) }
 259     match e.node {
 260       expr_unary(neg, inner) => {
 261         match eval_const_expr_partial(tcx, inner) {
 262           Ok(const_float(f)) => Ok(const_float(-f)),
 263           Ok(const_int(i)) => Ok(const_int(-i)),
 264           Ok(const_uint(i)) => Ok(const_uint(-i)),
 265           Ok(const_str(_)) => Err(~"Negate on string"),
 266           Ok(const_bool(_)) => Err(~"Negate on boolean"),
 267           ref err => (/*bad*/copy *err)
 268         }
 269       }
 270       expr_unary(not, inner) => {
 271         match eval_const_expr_partial(tcx, inner) {
 272           Ok(const_int(i)) => Ok(const_int(!i)),
 273           Ok(const_uint(i)) => Ok(const_uint(!i)),
 274           Ok(const_bool(b)) => Ok(const_bool(!b)),
 275           _ => Err(~"Not on float or string")
 276         }
 277       }
 278       expr_binary(op, a, b) => {
 279         match (eval_const_expr_partial(tcx, a),
 280                eval_const_expr_partial(tcx, b)) {
 281           (Ok(const_float(a)), Ok(const_float(b))) => {
 282             match op {
 283               add => Ok(const_float(a + b)),
 284               subtract => Ok(const_float(a - b)),
 285               mul => Ok(const_float(a * b)),
 286               div => Ok(const_float(a / b)),
 287               rem => Ok(const_float(a % b)),
 288               eq => fromb(a == b),
 289               lt => fromb(a < b),
 290               le => fromb(a <= b),
 291               ne => fromb(a != b),
 292               ge => fromb(a >= b),
 293               gt => fromb(a > b),
 294               _ => Err(~"Can't do this op on floats")
 295             }
 296           }
 297           (Ok(const_int(a)), Ok(const_int(b))) => {
 298             match op {
 299               add => Ok(const_int(a + b)),
 300               subtract => Ok(const_int(a - b)),
 301               mul => Ok(const_int(a * b)),
 302               div if b == 0 => Err(~"divide by zero"),
 303               div => Ok(const_int(a / b)),
 304               rem if b == 0 => Err(~"modulo zero"),
 305               rem => Ok(const_int(a % b)),
 306               and | bitand => Ok(const_int(a & b)),
 307               or | bitor => Ok(const_int(a | b)),
 308               bitxor => Ok(const_int(a ^ b)),
 309               shl => Ok(const_int(a << b)),
 310               shr => Ok(const_int(a >> b)),
 311               eq => fromb(a == b),
 312               lt => fromb(a < b),
 313               le => fromb(a <= b),
 314               ne => fromb(a != b),
 315               ge => fromb(a >= b),
 316               gt => fromb(a > b)
 317             }
 318           }
 319           (Ok(const_uint(a)), Ok(const_uint(b))) => {
 320             match op {
 321               add => Ok(const_uint(a + b)),
 322               subtract => Ok(const_uint(a - b)),
 323               mul => Ok(const_uint(a * b)),
 324               div if b == 0 => Err(~"divide by zero"),
 325               div => Ok(const_uint(a / b)),
 326               rem if b == 0 => Err(~"modulo zero"),
 327               rem => Ok(const_uint(a % b)),
 328               and | bitand => Ok(const_uint(a & b)),
 329               or | bitor => Ok(const_uint(a | b)),
 330               bitxor => Ok(const_uint(a ^ b)),
 331               shl => Ok(const_uint(a << b)),
 332               shr => Ok(const_uint(a >> b)),
 333               eq => fromb(a == b),
 334               lt => fromb(a < b),
 335               le => fromb(a <= b),
 336               ne => fromb(a != b),
 337               ge => fromb(a >= b),
 338               gt => fromb(a > b),
 339             }
 340           }
 341           // shifts can have any integral type as their rhs
 342           (Ok(const_int(a)), Ok(const_uint(b))) => {
 343             match op {
 344               shl => Ok(const_int(a << b)),
 345               shr => Ok(const_int(a >> b)),
 346               _ => Err(~"Can't do this op on an int and uint")
 347             }
 348           }
 349           (Ok(const_uint(a)), Ok(const_int(b))) => {
 350             match op {
 351               shl => Ok(const_uint(a << b)),
 352               shr => Ok(const_uint(a >> b)),
 353               _ => Err(~"Can't do this op on a uint and int")
 354             }
 355           }
 356           (Ok(const_bool(a)), Ok(const_bool(b))) => {
 357             Ok(const_bool(match op {
 358               and => a && b,
 359               or => a || b,
 360               bitxor => a ^ b,
 361               bitand => a & b,
 362               bitor => a | b,
 363               eq => a == b,
 364               ne => a != b,
 365               _ => return Err(~"Can't do this op on bools")
 366              }))
 367           }
 368           _ => Err(~"Bad operands for binary")
 369         }
 370       }
 371       expr_cast(base, _) => {
 372         let ety = ty::expr_ty(tcx, e);
 373         let base = eval_const_expr_partial(tcx, base);
 374         match ty::get(ety).sty {
 375           ty::ty_float(_) => {
 376             match base {
 377               Ok(const_uint(u)) => Ok(const_float(u as f64)),
 378               Ok(const_int(i)) => Ok(const_float(i as f64)),
 379               Ok(const_float(_)) => base,
 380               _ => Err(~"Can't cast float to str")
 381             }
 382           }
 383           ty::ty_uint(_) => {
 384             match base {
 385               Ok(const_uint(_)) => base,
 386               Ok(const_int(i)) => Ok(const_uint(i as u64)),
 387               Ok(const_float(f)) => Ok(const_uint(f as u64)),
 388               _ => Err(~"Can't cast str to uint")
 389             }
 390           }
 391           ty::ty_int(_) | ty::ty_bool => {
 392             match base {
 393               Ok(const_uint(u)) => Ok(const_int(u as i64)),
 394               Ok(const_int(_)) => base,
 395               Ok(const_float(f)) => Ok(const_int(f as i64)),
 396               _ => Err(~"Can't cast str to int")
 397             }
 398           }
 399           _ => Err(~"Can't cast this type")
 400         }
 401       }
 402       expr_path(_) => {
 403           match lookup_const(tcx, e) {
 404               Some(actual_e) => eval_const_expr_partial(tcx, actual_e),
 405               None => Err(~"Non-constant path in constant expr")
 406           }
 407       }
 408       expr_lit(lit) => Ok(lit_to_const(lit)),
 409       // If we have a vstore, just keep going; it has to be a string
 410       expr_vstore(e, _) => eval_const_expr_partial(tcx, e),
 411       expr_paren(e)     => eval_const_expr_partial(tcx, e),
 412       _ => Err(~"Unsupported constant expr")
 413     }
 414 }
 415
 416 pub fn lit_to_const(lit: @lit) -> const_val {
 417     match lit.node {
 418       lit_str(s) => const_str(/*bad*/copy *s),
 419       lit_int(n, _) => const_int(n),
 420       lit_uint(n, _) => const_uint(n),
 421       lit_int_unsuffixed(n) => const_int(n),
 422       lit_float(n, _) => const_float(float::from_str(*n).get() as f64),
 423       lit_float_unsuffixed(n) =>
 424         const_float(float::from_str(*n).get() as f64),
 425       lit_nil => const_int(0i64),
 426       lit_bool(b) => const_bool(b)
 427     }
 428 }
 429
 430 pub fn compare_const_vals(a: const_val, b: const_val) -> int {
 431   match (&a, &b) {
 432     (&const_int(a), &const_int(b)) => {
 433         if a == b {
 434             0
 435         } else if a < b {
 436             -1
 437         } else {
 438             1
 439         }
 440     }
 441     (&const_uint(a), &const_uint(b)) => {
 442         if a == b {
 443             0
 444         } else if a < b {
 445             -1
 446         } else {
 447             1
 448         }
 449     }
 450     (&const_float(a), &const_float(b)) => {
 451         if a == b {
 452             0
 453         } else if a < b {
 454             -1
 455         } else {
 456             1
 457         }
 458     }
 459     (&const_str(ref a), &const_str(ref b)) => {
 460         if (*a) == (*b) {
 461             0
 462         } else if (*a) < (*b) {
 463             -1
 464         } else {
 465             1
 466         }
 467     }
 468     (&const_bool(a), &const_bool(b)) => {
 469         if a == b {
 470             0
 471         } else if a < b {
 472             -1
 473         } else {
 474             1
 475         }
 476     }
 477     _ => fail!(~"compare_const_vals: ill-typed comparison")
 478   }
 479 }
 480
 481 pub fn compare_lit_exprs(tcx: middle::ty::ctxt, a: @expr, b: @expr) -> int {
 482   compare_const_vals(eval_const_expr(tcx, a), eval_const_expr(tcx, b))
 483 }
 484
 485 pub fn lit_expr_eq(tcx: middle::ty::ctxt, a: @expr, b: @expr) -> bool {
 486     compare_lit_exprs(tcx, a, b) == 0
 487 }
 488
 489 pub fn lit_eq(a: @lit, b: @lit) -> bool {
 490     compare_const_vals(lit_to_const(a), lit_to_const(b)) == 0
 491 }
 492
 493
 494 // Local Variables:
 495 // mode: rust
 496 // fill-column: 78;
 497 // indent-tabs-mode: nil
 498 // c-basic-offset: 4
 499 // buffer-file-coding-system: utf-8-unix
 500 // End: