rust/src/librustc/middle/const_eval.rs

484 lines
15 KiB
Rust

// Copyright 2012 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use syntax::{ast,ast_map,ast_util,visit};
use ast::*;
//
// This pass classifies expressions by their constant-ness.
//
// Constant-ness comes in 3 flavours:
//
// - Integer-constants: can be evaluated by the frontend all the way down
// to their actual value. They are used in a few places (enum
// discriminants, switch arms) and are a subset of
// general-constants. They cover all the integer and integer-ish
// literals (nil, bool, int, uint, char, iNN, uNN) and all integer
// operators and copies applied to them.
//
// - General-constants: can be evaluated by LLVM but not necessarily by
// the frontend; usually due to reliance on target-specific stuff such
// as "where in memory the value goes" or "what floating point mode the
// target uses". This _includes_ integer-constants, plus the following
// constructors:
//
// fixed-size vectors and strings: [] and ""/_
// vector and string slices: &[] and &""
// tuples: (,)
// records: {...}
// enums: foo(...)
// floating point literals and operators
// & and * pointers
// copies of general constants
//
// (in theory, probably not at first: if/alt on integer-const
// conditions / descriminants)
//
// - Non-constants: everything else.
//
enum constness {
integral_const,
general_const,
non_const
}
fn join(a: constness, b: constness) -> constness {
match (a, b) {
(integral_const, integral_const) => integral_const,
(integral_const, general_const)
| (general_const, integral_const)
| (general_const, general_const) => general_const,
_ => non_const
}
}
fn join_all(cs: &[constness]) -> constness {
vec::foldl(integral_const, cs, |a, b| join(a, *b))
}
fn classify(e: @expr,
def_map: resolve::DefMap,
tcx: ty::ctxt) -> constness {
let did = ast_util::local_def(e.id);
match tcx.ccache.find(did) {
Some(x) => x,
None => {
let cn =
match e.node {
ast::expr_lit(lit) => {
match lit.node {
ast::lit_str(*) |
ast::lit_float(*) => general_const,
_ => integral_const
}
}
ast::expr_copy(inner) |
ast::expr_unary(_, inner) |
ast::expr_paren(inner) => {
classify(inner, def_map, tcx)
}
ast::expr_binary(_, a, b) => {
join(classify(a, def_map, tcx),
classify(b, def_map, tcx))
}
ast::expr_tup(es) |
ast::expr_vec(es, ast::m_imm) => {
join_all(vec::map(es, |e| classify(*e, def_map, tcx)))
}
ast::expr_vstore(e, vstore) => {
match vstore {
ast::expr_vstore_fixed(_) |
ast::expr_vstore_slice => classify(e, def_map, tcx),
ast::expr_vstore_uniq |
ast::expr_vstore_box |
ast::expr_vstore_mut_box |
ast::expr_vstore_mut_slice => non_const
}
}
ast::expr_struct(_, ref fs, None) |
ast::expr_rec(ref fs, None) => {
let cs = do vec::map((*fs)) |f| {
if f.node.mutbl == ast::m_imm {
classify(f.node.expr, def_map, tcx)
} else {
non_const
}
};
join_all(cs)
}
ast::expr_cast(base, _) => {
let ty = ty::expr_ty(tcx, e);
let base = classify(base, def_map, tcx);
if ty::type_is_integral(ty) {
join(integral_const, base)
} else if ty::type_is_fp(ty) {
join(general_const, base)
} else {
non_const
}
}
ast::expr_field(base, _, _) => {
classify(base, def_map, tcx)
}
ast::expr_index(base, idx) => {
join(classify(base, def_map, tcx),
classify(idx, def_map, tcx))
}
ast::expr_addr_of(ast::m_imm, base) => {
classify(base, def_map, tcx)
}
// FIXME: (#3728) we can probably do something CCI-ish
// surrounding nonlocal constants. But we don't yet.
ast::expr_path(_) => {
lookup_constness(tcx, e)
}
_ => non_const
};
tcx.ccache.insert(did, cn);
cn
}
}
}
fn lookup_const(tcx: ty::ctxt, e: @expr) -> Option<@expr> {
match tcx.def_map.find(e.id) {
Some(ast::def_const(def_id)) => lookup_const_by_id(tcx, def_id),
_ => None
}
}
fn lookup_const_by_id(tcx: ty::ctxt, def_id: ast::def_id) -> Option<@expr> {
if ast_util::is_local(def_id) {
match tcx.items.find(def_id.node) {
None => None,
Some(ast_map::node_item(it, _)) => match it.node {
item_const(_, const_expr) => Some(const_expr),
_ => None
},
Some(_) => None
}
} else {
None
}
}
fn lookup_constness(tcx: ty::ctxt, e: @expr) -> constness {
match lookup_const(tcx, e) {
Some(rhs) => {
let ty = ty::expr_ty(tcx, rhs);
if ty::type_is_integral(ty) {
integral_const
} else {
general_const
}
}
None => non_const
}
}
fn process_crate(crate: @ast::crate,
def_map: resolve::DefMap,
tcx: ty::ctxt) {
let v = visit::mk_simple_visitor(@{
visit_expr_post: |e| { classify(e, def_map, tcx); },
.. *visit::default_simple_visitor()
});
visit::visit_crate(*crate, (), v);
tcx.sess.abort_if_errors();
}
// FIXME (#33): this doesn't handle big integer/float literals correctly
// (nor does the rest of our literal handling).
enum const_val {
const_float(f64),
const_int(i64),
const_uint(u64),
const_str(~str),
const_bool(bool)
}
impl const_val : cmp::Eq {
pure fn eq(&self, other: &const_val) -> bool {
match ((*self), (*other)) {
(const_float(a), const_float(b)) => a == b,
(const_int(a), const_int(b)) => a == b,
(const_uint(a), const_uint(b)) => a == b,
(const_str(ref a), const_str(ref b)) => (*a) == (*b),
(const_bool(a), const_bool(b)) => a == b,
(const_float(_), _) | (const_int(_), _) | (const_uint(_), _) |
(const_str(_), _) | (const_bool(_), _) => false
}
}
pure fn ne(&self, other: &const_val) -> bool { !(*self).eq(other) }
}
fn eval_const_expr(tcx: middle::ty::ctxt, e: @expr) -> const_val {
match eval_const_expr_partial(tcx, e) {
Ok(ref r) => (*r),
Err(ref s) => fail (*s)
}
}
fn eval_const_expr_partial(tcx: middle::ty::ctxt, e: @expr)
-> Result<const_val, ~str> {
use middle::ty;
fn fromb(b: bool) -> Result<const_val, ~str> { Ok(const_int(b as i64)) }
match e.node {
expr_unary(neg, inner) => {
match eval_const_expr_partial(tcx, inner) {
Ok(const_float(f)) => Ok(const_float(-f)),
Ok(const_int(i)) => Ok(const_int(-i)),
Ok(const_uint(i)) => Ok(const_uint(-i)),
Ok(const_str(_)) => Err(~"Negate on string"),
Ok(const_bool(_)) => Err(~"Negate on boolean"),
ref err => (*err)
}
}
expr_unary(not, inner) => {
match eval_const_expr_partial(tcx, inner) {
Ok(const_int(i)) => Ok(const_int(!i)),
Ok(const_uint(i)) => Ok(const_uint(!i)),
Ok(const_bool(b)) => Ok(const_bool(!b)),
_ => Err(~"Not on float or string")
}
}
expr_binary(op, a, b) => {
match (eval_const_expr_partial(tcx, a),
eval_const_expr_partial(tcx, b)) {
(Ok(const_float(a)), Ok(const_float(b))) => {
match op {
add => Ok(const_float(a + b)),
subtract => Ok(const_float(a - b)),
mul => Ok(const_float(a * b)),
div => Ok(const_float(a / b)),
rem => Ok(const_float(a % b)),
eq => fromb(a == b),
lt => fromb(a < b),
le => fromb(a <= b),
ne => fromb(a != b),
ge => fromb(a >= b),
gt => fromb(a > b),
_ => Err(~"Can't do this op on floats")
}
}
(Ok(const_int(a)), Ok(const_int(b))) => {
match op {
add => Ok(const_int(a + b)),
subtract => Ok(const_int(a - b)),
mul => Ok(const_int(a * b)),
div => Ok(const_int(a / b)),
rem => Ok(const_int(a % b)),
and | bitand => Ok(const_int(a & b)),
or | bitor => Ok(const_int(a | b)),
bitxor => Ok(const_int(a ^ b)),
shl => Ok(const_int(a << b)),
shr => Ok(const_int(a >> b)),
eq => fromb(a == b),
lt => fromb(a < b),
le => fromb(a <= b),
ne => fromb(a != b),
ge => fromb(a >= b),
gt => fromb(a > b)
}
}
(Ok(const_uint(a)), Ok(const_uint(b))) => {
match op {
add => Ok(const_uint(a + b)),
subtract => Ok(const_uint(a - b)),
mul => Ok(const_uint(a * b)),
div => Ok(const_uint(a / b)),
rem => Ok(const_uint(a % b)),
and | bitand => Ok(const_uint(a & b)),
or | bitor => Ok(const_uint(a | b)),
bitxor => Ok(const_uint(a ^ b)),
shl => Ok(const_uint(a << b)),
shr => Ok(const_uint(a >> b)),
eq => fromb(a == b),
lt => fromb(a < b),
le => fromb(a <= b),
ne => fromb(a != b),
ge => fromb(a >= b),
gt => fromb(a > b),
}
}
// shifts can have any integral type as their rhs
(Ok(const_int(a)), Ok(const_uint(b))) => {
match op {
shl => Ok(const_int(a << b)),
shr => Ok(const_int(a >> b)),
_ => Err(~"Can't do this op on an int and uint")
}
}
(Ok(const_uint(a)), Ok(const_int(b))) => {
match op {
shl => Ok(const_uint(a << b)),
shr => Ok(const_uint(a >> b)),
_ => Err(~"Can't do this op on a uint and int")
}
}
(Ok(const_bool(a)), Ok(const_bool(b))) => {
Ok(const_bool(match op {
and => a && b,
or => a || b,
bitxor => a ^ b,
bitand => a & b,
bitor => a | b,
eq => a == b,
ne => a != b,
_ => return Err(~"Can't do this op on bools")
}))
}
_ => Err(~"Bad operands for binary")
}
}
expr_cast(base, _) => {
let ety = ty::expr_ty(tcx, e);
let base = eval_const_expr_partial(tcx, base);
match ty::get(ety).sty {
ty::ty_float(_) => {
match base {
Ok(const_uint(u)) => Ok(const_float(u as f64)),
Ok(const_int(i)) => Ok(const_float(i as f64)),
Ok(const_float(_)) => base,
_ => Err(~"Can't cast float to str")
}
}
ty::ty_uint(_) => {
match base {
Ok(const_uint(_)) => base,
Ok(const_int(i)) => Ok(const_uint(i as u64)),
Ok(const_float(f)) => Ok(const_uint(f as u64)),
_ => Err(~"Can't cast str to uint")
}
}
ty::ty_int(_) | ty::ty_bool => {
match base {
Ok(const_uint(u)) => Ok(const_int(u as i64)),
Ok(const_int(_)) => base,
Ok(const_float(f)) => Ok(const_int(f as i64)),
_ => Err(~"Can't cast str to int")
}
}
_ => Err(~"Can't cast this type")
}
}
expr_path(_) => {
match lookup_const(tcx, e) {
Some(actual_e) => eval_const_expr_partial(tcx, actual_e),
None => Err(~"Non-constant path in constant expr")
}
}
expr_lit(lit) => Ok(lit_to_const(lit)),
// If we have a vstore, just keep going; it has to be a string
expr_vstore(e, _) => eval_const_expr_partial(tcx, e),
expr_paren(e) => eval_const_expr_partial(tcx, e),
_ => Err(~"Unsupported constant expr")
}
}
fn lit_to_const(lit: @lit) -> const_val {
match lit.node {
lit_str(s) => const_str(*s),
lit_int(n, _) => const_int(n),
lit_uint(n, _) => const_uint(n),
lit_int_unsuffixed(n) => const_int(n),
lit_float(n, _) => const_float(float::from_str(*n).get() as f64),
lit_float_unsuffixed(n) =>
const_float(float::from_str(*n).get() as f64),
lit_nil => const_int(0i64),
lit_bool(b) => const_bool(b)
}
}
fn compare_const_vals(a: const_val, b: const_val) -> int {
match (a, b) {
(const_int(a), const_int(b)) => {
if a == b {
0
} else if a < b {
-1
} else {
1
}
}
(const_uint(a), const_uint(b)) => {
if a == b {
0
} else if a < b {
-1
} else {
1
}
}
(const_float(a), const_float(b)) => {
if a == b {
0
} else if a < b {
-1
} else {
1
}
}
(const_str(ref a), const_str(ref b)) => {
if (*a) == (*b) {
0
} else if (*a) < (*b) {
-1
} else {
1
}
}
(const_bool(a), const_bool(b)) => {
if a == b {
0
} else if a < b {
-1
} else {
1
}
}
_ => fail ~"compare_const_vals: ill-typed comparison"
}
}
fn compare_lit_exprs(tcx: middle::ty::ctxt, a: @expr, b: @expr) -> int {
compare_const_vals(eval_const_expr(tcx, a), eval_const_expr(tcx, b))
}
fn lit_expr_eq(tcx: middle::ty::ctxt, a: @expr, b: @expr) -> bool {
compare_lit_exprs(tcx, a, b) == 0
}
fn lit_eq(a: @lit, b: @lit) -> bool {
compare_const_vals(lit_to_const(a), lit_to_const(b)) == 0
}
// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End: