1 // Copyright 2012-2014 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.
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.
11 #![allow(non_camel_case_types)]
12 #![allow(unsigned_negation)]
14 pub use self::const_val::*;
15 pub use self::constness::*;
17 use metadata::csearch;
18 use middle::{astencode, def};
19 use middle::pat_util::def_to_path;
20 use middle::ty::{self};
21 use middle::astconv_util::{ast_ty_to_prim_ty};
22 use util::nodemap::DefIdMap;
24 use syntax::ast::{self, Expr};
25 use syntax::parse::token::InternedString;
27 use syntax::visit::{self, Visitor};
28 use syntax::{ast_map, ast_util, codemap};
30 use std::collections::hash_map::Entry::Vacant;
34 // This pass classifies expressions by their constant-ness.
36 // Constant-ness comes in 3 flavours:
38 // - Integer-constants: can be evaluated by the frontend all the way down
39 // to their actual value. They are used in a few places (enum
40 // discriminants, switch arms) and are a subset of
41 // general-constants. They cover all the integer and integer-ish
42 // literals (nil, bool, int, uint, char, iNN, uNN) and all integer
43 // operators and copies applied to them.
45 // - General-constants: can be evaluated by LLVM but not necessarily by
46 // the frontend; usually due to reliance on target-specific stuff such
47 // as "where in memory the value goes" or "what floating point mode the
48 // target uses". This _includes_ integer-constants, plus the following
51 // fixed-size vectors and strings: [] and ""/_
52 // vector and string slices: &[] and &""
55 // floating point literals and operators
57 // copies of general constants
59 // (in theory, probably not at first: if/match on integer-const
60 // conditions / discriminants)
62 // - Non-constants: everything else.
72 type constness_cache = DefIdMap<constness>;
74 pub fn join(a: constness, b: constness) -> constness {
76 (integral_const, integral_const) => integral_const,
77 (integral_const, general_const)
78 | (general_const, integral_const)
79 | (general_const, general_const) => general_const,
84 pub fn join_all<It: Iterator<Item=constness>>(cs: It) -> constness {
85 cs.fold(integral_const, |a, b| join(a, b))
88 fn lookup_const<'a>(tcx: &'a ty::ctxt, e: &Expr) -> Option<&'a Expr> {
89 let opt_def = tcx.def_map.borrow().get(&e.id).cloned();
91 Some(def::DefConst(def_id)) => {
92 lookup_const_by_id(tcx, def_id)
94 Some(def::DefVariant(enum_def, variant_def, _)) => {
95 lookup_variant_by_id(tcx, enum_def, variant_def)
101 fn lookup_variant_by_id<'a>(tcx: &'a ty::ctxt,
102 enum_def: ast::DefId,
103 variant_def: ast::DefId)
104 -> Option<&'a Expr> {
105 fn variant_expr<'a>(variants: &'a [P<ast::Variant>], id: ast::NodeId)
106 -> Option<&'a Expr> {
107 for variant in variants.iter() {
108 if variant.node.id == id {
109 return variant.node.disr_expr.as_ref().map(|e| &**e);
115 if ast_util::is_local(enum_def) {
116 match tcx.map.find(enum_def.node) {
118 Some(ast_map::NodeItem(it)) => match it.node {
119 ast::ItemEnum(ast::EnumDef { ref variants }, _) => {
120 variant_expr(variants[], variant_def.node)
127 match tcx.extern_const_variants.borrow().get(&variant_def) {
128 Some(&ast::DUMMY_NODE_ID) => return None,
130 return Some(tcx.map.expect_expr(expr_id));
134 let expr_id = match csearch::maybe_get_item_ast(tcx, enum_def,
135 |a, b, c, d| astencode::decode_inlined_item(a, b, c, d)) {
136 csearch::found(&ast::IIItem(ref item)) => match item.node {
137 ast::ItemEnum(ast::EnumDef { ref variants }, _) => {
138 // NOTE this doesn't do the right thing, it compares inlined
139 // NodeId's to the original variant_def's NodeId, but they
140 // come from different crates, so they will likely never match.
141 variant_expr(variants[], variant_def.node).map(|e| e.id)
147 tcx.extern_const_variants.borrow_mut().insert(variant_def,
148 expr_id.unwrap_or(ast::DUMMY_NODE_ID));
149 expr_id.map(|id| tcx.map.expect_expr(id))
153 pub fn lookup_const_by_id<'a>(tcx: &'a ty::ctxt, def_id: ast::DefId)
154 -> Option<&'a Expr> {
155 if ast_util::is_local(def_id) {
156 match tcx.map.find(def_id.node) {
158 Some(ast_map::NodeItem(it)) => match it.node {
159 ast::ItemConst(_, ref const_expr) => {
167 match tcx.extern_const_statics.borrow().get(&def_id) {
168 Some(&ast::DUMMY_NODE_ID) => return None,
170 return Some(tcx.map.expect_expr(expr_id));
174 let expr_id = match csearch::maybe_get_item_ast(tcx, def_id,
175 |a, b, c, d| astencode::decode_inlined_item(a, b, c, d)) {
176 csearch::found(&ast::IIItem(ref item)) => match item.node {
177 ast::ItemConst(_, ref const_expr) => Some(const_expr.id),
182 tcx.extern_const_statics.borrow_mut().insert(def_id,
183 expr_id.unwrap_or(ast::DUMMY_NODE_ID));
184 expr_id.map(|id| tcx.map.expect_expr(id))
188 struct ConstEvalVisitor<'a, 'tcx: 'a> {
189 tcx: &'a ty::ctxt<'tcx>,
190 ccache: constness_cache,
193 impl<'a, 'tcx> ConstEvalVisitor<'a, 'tcx> {
194 fn classify(&mut self, e: &Expr) -> constness {
195 let did = ast_util::local_def(e.id);
196 match self.ccache.get(&did) {
197 Some(&x) => return x,
200 let cn = match e.node {
201 ast::ExprLit(ref lit) => {
203 ast::LitStr(..) | ast::LitFloat(..) => general_const,
208 ast::ExprUnary(_, ref inner) | ast::ExprParen(ref inner) =>
209 self.classify(&**inner),
211 ast::ExprBinary(_, ref a, ref b) =>
212 join(self.classify(&**a), self.classify(&**b)),
214 ast::ExprTup(ref es) |
215 ast::ExprVec(ref es) =>
216 join_all(es.iter().map(|e| self.classify(&**e))),
218 ast::ExprStruct(_, ref fs, None) => {
219 let cs = fs.iter().map(|f| self.classify(&*f.expr));
223 ast::ExprCast(ref base, _) => {
224 let ty = ty::expr_ty(self.tcx, e);
225 let base = self.classify(&**base);
226 if ty::type_is_integral(ty) {
227 join(integral_const, base)
228 } else if ty::type_is_fp(ty) {
229 join(general_const, base)
235 ast::ExprField(ref base, _) => self.classify(&**base),
237 ast::ExprTupField(ref base, _) => self.classify(&**base),
239 ast::ExprIndex(ref base, ref idx) =>
240 join(self.classify(&**base), self.classify(&**idx)),
242 ast::ExprAddrOf(ast::MutImmutable, ref base) =>
243 self.classify(&**base),
245 // FIXME: (#3728) we can probably do something CCI-ish
246 // surrounding nonlocal constants. But we don't yet.
247 ast::ExprPath(_) => self.lookup_constness(e),
249 ast::ExprRepeat(..) => general_const,
251 ast::ExprBlock(ref block) => {
253 Some(ref e) => self.classify(&**e),
254 None => integral_const
260 self.ccache.insert(did, cn);
264 fn lookup_constness(&self, e: &Expr) -> constness {
265 match lookup_const(self.tcx, e) {
267 let ty = ty::expr_ty(self.tcx, &*rhs);
268 if ty::type_is_integral(ty) {
280 impl<'a, 'tcx, 'v> Visitor<'v> for ConstEvalVisitor<'a, 'tcx> {
281 fn visit_expr_post(&mut self, e: &Expr) {
286 pub fn process_crate(tcx: &ty::ctxt) {
287 visit::walk_crate(&mut ConstEvalVisitor {
289 ccache: DefIdMap::new(),
291 tcx.sess.abort_if_errors();
295 // FIXME (#33): this doesn't handle big integer/float literals correctly
296 // (nor does the rest of our literal handling).
297 #[derive(Clone, PartialEq)]
302 const_str(InternedString),
303 const_binary(Rc<Vec<u8> >),
307 pub fn const_expr_to_pat(tcx: &ty::ctxt, expr: &Expr) -> P<ast::Pat> {
308 let pat = match expr.node {
309 ast::ExprTup(ref exprs) =>
310 ast::PatTup(exprs.iter().map(|expr| const_expr_to_pat(tcx, &**expr)).collect()),
312 ast::ExprCall(ref callee, ref args) => {
313 let def = tcx.def_map.borrow()[callee.id].clone();
314 if let Vacant(entry) = tcx.def_map.borrow_mut().entry(expr.id) {
317 let path = match def {
318 def::DefStruct(def_id) => def_to_path(tcx, def_id),
319 def::DefVariant(_, variant_did, _) => def_to_path(tcx, variant_did),
322 let pats = args.iter().map(|expr| const_expr_to_pat(tcx, &**expr)).collect();
323 ast::PatEnum(path, Some(pats))
326 ast::ExprStruct(ref path, ref fields, None) => {
327 let field_pats = fields.iter().map(|field| codemap::Spanned {
328 span: codemap::DUMMY_SP,
329 node: ast::FieldPat {
330 ident: field.ident.node,
331 pat: const_expr_to_pat(tcx, &*field.expr),
335 ast::PatStruct(path.clone(), field_pats, false)
338 ast::ExprVec(ref exprs) => {
339 let pats = exprs.iter().map(|expr| const_expr_to_pat(tcx, &**expr)).collect();
340 ast::PatVec(pats, None, vec![])
343 ast::ExprPath(ref path) => {
344 let opt_def = tcx.def_map.borrow().get(&expr.id).cloned();
346 Some(def::DefStruct(..)) =>
347 ast::PatStruct(path.clone(), vec![], false),
348 Some(def::DefVariant(..)) =>
349 ast::PatEnum(path.clone(), None),
351 match lookup_const(tcx, expr) {
352 Some(actual) => return const_expr_to_pat(tcx, actual),
359 _ => ast::PatLit(P(expr.clone()))
361 P(ast::Pat { id: expr.id, node: pat, span: expr.span })
364 pub fn eval_const_expr(tcx: &ty::ctxt, e: &Expr) -> const_val {
365 match eval_const_expr_partial(tcx, e) {
367 Err(s) => tcx.sess.span_fatal(e.span, s[])
371 pub fn eval_const_expr_partial(tcx: &ty::ctxt, e: &Expr) -> Result<const_val, String> {
372 fn fromb(b: bool) -> Result<const_val, String> { Ok(const_int(b as i64)) }
374 ast::ExprUnary(ast::UnNeg, ref inner) => {
375 match eval_const_expr_partial(tcx, &**inner) {
376 Ok(const_float(f)) => Ok(const_float(-f)),
377 Ok(const_int(i)) => Ok(const_int(-i)),
378 Ok(const_uint(i)) => Ok(const_uint(-i)),
379 Ok(const_str(_)) => Err("negate on string".to_string()),
380 Ok(const_bool(_)) => Err("negate on boolean".to_string()),
381 ref err => ((*err).clone())
384 ast::ExprUnary(ast::UnNot, ref inner) => {
385 match eval_const_expr_partial(tcx, &**inner) {
386 Ok(const_int(i)) => Ok(const_int(!i)),
387 Ok(const_uint(i)) => Ok(const_uint(!i)),
388 Ok(const_bool(b)) => Ok(const_bool(!b)),
389 _ => Err("not on float or string".to_string())
392 ast::ExprBinary(op, ref a, ref b) => {
393 match (eval_const_expr_partial(tcx, &**a),
394 eval_const_expr_partial(tcx, &**b)) {
395 (Ok(const_float(a)), Ok(const_float(b))) => {
397 ast::BiAdd => Ok(const_float(a + b)),
398 ast::BiSub => Ok(const_float(a - b)),
399 ast::BiMul => Ok(const_float(a * b)),
400 ast::BiDiv => Ok(const_float(a / b)),
401 ast::BiRem => Ok(const_float(a % b)),
402 ast::BiEq => fromb(a == b),
403 ast::BiLt => fromb(a < b),
404 ast::BiLe => fromb(a <= b),
405 ast::BiNe => fromb(a != b),
406 ast::BiGe => fromb(a >= b),
407 ast::BiGt => fromb(a > b),
408 _ => Err("can't do this op on floats".to_string())
411 (Ok(const_int(a)), Ok(const_int(b))) => {
413 ast::BiAdd => Ok(const_int(a + b)),
414 ast::BiSub => Ok(const_int(a - b)),
415 ast::BiMul => Ok(const_int(a * b)),
416 ast::BiDiv if b == 0 => {
417 Err("attempted to divide by zero".to_string())
419 ast::BiDiv => Ok(const_int(a / b)),
420 ast::BiRem if b == 0 => {
421 Err("attempted remainder with a divisor of \
424 ast::BiRem => Ok(const_int(a % b)),
425 ast::BiAnd | ast::BiBitAnd => Ok(const_int(a & b)),
426 ast::BiOr | ast::BiBitOr => Ok(const_int(a | b)),
427 ast::BiBitXor => Ok(const_int(a ^ b)),
428 ast::BiShl => Ok(const_int(a << b as uint)),
429 ast::BiShr => Ok(const_int(a >> b as uint)),
430 ast::BiEq => fromb(a == b),
431 ast::BiLt => fromb(a < b),
432 ast::BiLe => fromb(a <= b),
433 ast::BiNe => fromb(a != b),
434 ast::BiGe => fromb(a >= b),
435 ast::BiGt => fromb(a > b)
438 (Ok(const_uint(a)), Ok(const_uint(b))) => {
440 ast::BiAdd => Ok(const_uint(a + b)),
441 ast::BiSub => Ok(const_uint(a - b)),
442 ast::BiMul => Ok(const_uint(a * b)),
443 ast::BiDiv if b == 0 => {
444 Err("attempted to divide by zero".to_string())
446 ast::BiDiv => Ok(const_uint(a / b)),
447 ast::BiRem if b == 0 => {
448 Err("attempted remainder with a divisor of \
451 ast::BiRem => Ok(const_uint(a % b)),
452 ast::BiAnd | ast::BiBitAnd => Ok(const_uint(a & b)),
453 ast::BiOr | ast::BiBitOr => Ok(const_uint(a | b)),
454 ast::BiBitXor => Ok(const_uint(a ^ b)),
455 ast::BiShl => Ok(const_uint(a << b as uint)),
456 ast::BiShr => Ok(const_uint(a >> b as uint)),
457 ast::BiEq => fromb(a == b),
458 ast::BiLt => fromb(a < b),
459 ast::BiLe => fromb(a <= b),
460 ast::BiNe => fromb(a != b),
461 ast::BiGe => fromb(a >= b),
462 ast::BiGt => fromb(a > b),
465 // shifts can have any integral type as their rhs
466 (Ok(const_int(a)), Ok(const_uint(b))) => {
468 ast::BiShl => Ok(const_int(a << b as uint)),
469 ast::BiShr => Ok(const_int(a >> b as uint)),
470 _ => Err("can't do this op on an int and uint".to_string())
473 (Ok(const_uint(a)), Ok(const_int(b))) => {
475 ast::BiShl => Ok(const_uint(a << b as uint)),
476 ast::BiShr => Ok(const_uint(a >> b as uint)),
477 _ => Err("can't do this op on a uint and int".to_string())
480 (Ok(const_bool(a)), Ok(const_bool(b))) => {
481 Ok(const_bool(match op {
482 ast::BiAnd => a && b,
484 ast::BiBitXor => a ^ b,
485 ast::BiBitAnd => a & b,
486 ast::BiBitOr => a | b,
489 _ => return Err("can't do this op on bools".to_string())
492 _ => Err("bad operands for binary".to_string())
495 ast::ExprCast(ref base, ref target_ty) => {
496 // This tends to get called w/o the type actually having been
497 // populated in the ctxt, which was causing things to blow up
498 // (#5900). Fall back to doing a limited lookup to get past it.
499 let ety = ty::expr_ty_opt(tcx, e)
500 .or_else(|| ast_ty_to_prim_ty(tcx, &**target_ty))
502 tcx.sess.span_fatal(target_ty.span,
503 "target type not found for const cast")
506 macro_rules! define_casts(
513 }) => (match ety.sty {
516 const_bool(b) => Ok($const_type(b as $intermediate_ty as $target_ty)),
517 const_uint(u) => Ok($const_type(u as $intermediate_ty as $target_ty)),
518 const_int(i) => Ok($const_type(i as $intermediate_ty as $target_ty)),
519 const_float(f) => Ok($const_type(f as $intermediate_ty as $target_ty)),
521 "can't cast this type to ", stringify!($const_type)
525 _ => Err("can't cast this type".to_string())
529 eval_const_expr_partial(tcx, &**base)
530 .and_then(|val| define_casts!(val, {
531 ty::ty_int(ast::TyI) => (int, const_int, i64),
532 ty::ty_int(ast::TyI8) => (i8, const_int, i64),
533 ty::ty_int(ast::TyI16) => (i16, const_int, i64),
534 ty::ty_int(ast::TyI32) => (i32, const_int, i64),
535 ty::ty_int(ast::TyI64) => (i64, const_int, i64),
536 ty::ty_uint(ast::TyU) => (uint, const_uint, u64),
537 ty::ty_uint(ast::TyU8) => (u8, const_uint, u64),
538 ty::ty_uint(ast::TyU16) => (u16, const_uint, u64),
539 ty::ty_uint(ast::TyU32) => (u32, const_uint, u64),
540 ty::ty_uint(ast::TyU64) => (u64, const_uint, u64),
541 ty::ty_float(ast::TyF32) => (f32, const_float, f64),
542 ty::ty_float(ast::TyF64) => (f64, const_float, f64)
545 ast::ExprPath(_) => {
546 match lookup_const(tcx, e) {
547 Some(actual_e) => eval_const_expr_partial(tcx, &*actual_e),
548 None => Err("non-constant path in constant expr".to_string())
551 ast::ExprLit(ref lit) => Ok(lit_to_const(&**lit)),
552 ast::ExprParen(ref e) => eval_const_expr_partial(tcx, &**e),
553 ast::ExprBlock(ref block) => {
555 Some(ref expr) => eval_const_expr_partial(tcx, &**expr),
556 None => Ok(const_int(0i64))
559 ast::ExprTupField(ref base, index) => {
560 // Get the base tuple if it is constant
561 if let Some(&ast::ExprTup(ref fields)) = lookup_const(tcx, &**base).map(|s| &s.node) {
562 // Check that the given index is within bounds and evaluate its value
563 if fields.len() > index.node {
564 return eval_const_expr_partial(tcx, &*fields[index.node])
566 return Err("tuple index out of bounds".to_string())
570 Err("non-constant struct in constant expr".to_string())
572 ast::ExprField(ref base, field_name) => {
573 // Get the base expression if it is a struct and it is constant
574 if let Some(&ast::ExprStruct(_, ref fields, _)) = lookup_const(tcx, &**base)
576 // Check that the given field exists and evaluate it
577 if let Some(f) = fields.iter().find(|f|
578 f.ident.node.as_str() == field_name.node.as_str()) {
579 return eval_const_expr_partial(tcx, &*f.expr)
581 return Err("nonexistent struct field".to_string())
585 Err("non-constant struct in constant expr".to_string())
587 _ => Err("unsupported constant expr".to_string())
591 pub fn lit_to_const(lit: &ast::Lit) -> const_val {
593 ast::LitStr(ref s, _) => const_str((*s).clone()),
594 ast::LitBinary(ref data) => {
595 const_binary(Rc::new(data.iter().map(|x| *x).collect()))
597 ast::LitByte(n) => const_uint(n as u64),
598 ast::LitChar(n) => const_uint(n as u64),
599 ast::LitInt(n, ast::SignedIntLit(_, ast::Plus)) |
600 ast::LitInt(n, ast::UnsuffixedIntLit(ast::Plus)) => const_int(n as i64),
601 ast::LitInt(n, ast::SignedIntLit(_, ast::Minus)) |
602 ast::LitInt(n, ast::UnsuffixedIntLit(ast::Minus)) => const_int(-(n as i64)),
603 ast::LitInt(n, ast::UnsignedIntLit(_)) => const_uint(n),
604 ast::LitFloat(ref n, _) |
605 ast::LitFloatUnsuffixed(ref n) => {
606 const_float(n.get().parse::<f64>().unwrap() as f64)
608 ast::LitBool(b) => const_bool(b)
612 fn compare_vals<T: PartialOrd>(a: T, b: T) -> Option<int> {
613 Some(if a == b { 0 } else if a < b { -1 } else { 1 })
615 pub fn compare_const_vals(a: &const_val, b: &const_val) -> Option<int> {
617 (&const_int(a), &const_int(b)) => compare_vals(a, b),
618 (&const_uint(a), &const_uint(b)) => compare_vals(a, b),
619 (&const_float(a), &const_float(b)) => compare_vals(a, b),
620 (&const_str(ref a), &const_str(ref b)) => compare_vals(a, b),
621 (&const_bool(a), &const_bool(b)) => compare_vals(a, b),
622 (&const_binary(ref a), &const_binary(ref b)) => compare_vals(a, b),
627 pub fn compare_lit_exprs(tcx: &ty::ctxt, a: &Expr, b: &Expr) -> Option<int> {
628 compare_const_vals(&eval_const_expr(tcx, a), &eval_const_expr(tcx, b))