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1 | // Copyright 2016 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 | //! A pass that qualifies constness of temporaries in constants, | |
12 | //! static initializers and functions and also drives promotion. | |
13 | //! | |
14 | //! The Qualif flags below can be used to also provide better | |
15 | //! diagnostics as to why a constant rvalue wasn't promoted. | |
16 | ||
17 | use rustc_data_structures::bitvec::BitVector; | |
3157f602 | 18 | use rustc_data_structures::indexed_vec::{IndexVec, Idx}; |
5bcae85e | 19 | use rustc::dep_graph::DepNode; |
a7813a04 XL |
20 | use rustc::hir; |
21 | use rustc::hir::def_id::DefId; | |
22 | use rustc::hir::intravisit::FnKind; | |
23 | use rustc::hir::map::blocks::FnLikeNode; | |
5bcae85e | 24 | use rustc::traits::{self, Reveal}; |
a7813a04 XL |
25 | use rustc::ty::{self, TyCtxt, Ty}; |
26 | use rustc::ty::cast::CastTy; | |
27 | use rustc::mir::repr::*; | |
28 | use rustc::mir::mir_map::MirMap; | |
3157f602 XL |
29 | use rustc::mir::traversal::{self, ReversePostorder}; |
30 | use rustc::mir::transform::{Pass, MirMapPass, MirPassHook, MirSource}; | |
a7813a04 XL |
31 | use rustc::mir::visit::{LvalueContext, Visitor}; |
32 | use rustc::util::nodemap::DefIdMap; | |
33 | use syntax::abi::Abi; | |
a7813a04 | 34 | use syntax::feature_gate::UnstableFeatures; |
3157f602 | 35 | use syntax_pos::Span; |
a7813a04 XL |
36 | |
37 | use std::collections::hash_map::Entry; | |
38 | use std::fmt; | |
39 | ||
40 | use build::Location; | |
a7813a04 XL |
41 | |
42 | use super::promote_consts::{self, Candidate, TempState}; | |
43 | ||
44 | bitflags! { | |
45 | flags Qualif: u8 { | |
46 | // Const item's qualification while recursing. | |
47 | // Recursive consts are an error. | |
48 | const RECURSIVE = 1 << 0, | |
49 | ||
50 | // Constant containing interior mutability (UnsafeCell). | |
51 | const MUTABLE_INTERIOR = 1 << 1, | |
52 | ||
53 | // Constant containing an ADT that implements Drop. | |
54 | const NEEDS_DROP = 1 << 2, | |
55 | ||
56 | // Function argument. | |
57 | const FN_ARGUMENT = 1 << 3, | |
58 | ||
59 | // Static lvalue or move from a static. | |
60 | const STATIC = 1 << 4, | |
61 | ||
62 | // Reference to a static. | |
63 | const STATIC_REF = 1 << 5, | |
64 | ||
65 | // Not constant at all - non-`const fn` calls, asm!, | |
66 | // pointer comparisons, ptr-to-int casts, etc. | |
67 | const NOT_CONST = 1 << 6, | |
68 | ||
69 | // Refers to temporaries which cannot be promoted as | |
70 | // promote_consts decided they weren't simple enough. | |
71 | const NOT_PROMOTABLE = 1 << 7, | |
72 | ||
73 | // Borrows of temporaries can be promoted only | |
74 | // if they have none of the above qualifications. | |
75 | const NEVER_PROMOTE = !0, | |
76 | ||
77 | // Const items can only have MUTABLE_INTERIOR | |
78 | // and NOT_PROMOTABLE without producing an error. | |
79 | const CONST_ERROR = !Qualif::MUTABLE_INTERIOR.bits & | |
80 | !Qualif::NOT_PROMOTABLE.bits | |
81 | } | |
82 | } | |
83 | ||
84 | impl<'a, 'tcx> Qualif { | |
85 | /// Remove flags which are impossible for the given type. | |
86 | fn restrict(&mut self, ty: Ty<'tcx>, | |
87 | tcx: TyCtxt<'a, 'tcx, 'tcx>, | |
88 | param_env: &ty::ParameterEnvironment<'tcx>) { | |
89 | if !ty.type_contents(tcx).interior_unsafe() { | |
90 | *self = *self - Qualif::MUTABLE_INTERIOR; | |
91 | } | |
92 | if !tcx.type_needs_drop_given_env(ty, param_env) { | |
93 | *self = *self - Qualif::NEEDS_DROP; | |
94 | } | |
95 | } | |
96 | } | |
97 | ||
98 | /// What kind of item we are in. | |
99 | #[derive(Copy, Clone, PartialEq, Eq)] | |
100 | enum Mode { | |
101 | Const, | |
102 | Static, | |
103 | StaticMut, | |
104 | ConstFn, | |
105 | Fn | |
106 | } | |
107 | ||
108 | impl fmt::Display for Mode { | |
109 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | |
110 | match *self { | |
111 | Mode::Const => write!(f, "constant"), | |
112 | Mode::Static | Mode::StaticMut => write!(f, "static"), | |
113 | Mode::ConstFn => write!(f, "constant function"), | |
114 | Mode::Fn => write!(f, "function") | |
115 | } | |
116 | } | |
117 | } | |
118 | ||
119 | fn is_const_fn(tcx: TyCtxt, def_id: DefId) -> bool { | |
120 | if let Some(node_id) = tcx.map.as_local_node_id(def_id) { | |
121 | let fn_like = FnLikeNode::from_node(tcx.map.get(node_id)); | |
122 | match fn_like.map(|f| f.kind()) { | |
123 | Some(FnKind::ItemFn(_, _, _, c, _, _, _)) => { | |
124 | c == hir::Constness::Const | |
125 | } | |
126 | Some(FnKind::Method(_, m, _, _)) => { | |
127 | m.constness == hir::Constness::Const | |
128 | } | |
129 | _ => false | |
130 | } | |
131 | } else { | |
132 | tcx.sess.cstore.is_const_fn(def_id) | |
133 | } | |
134 | } | |
135 | ||
136 | struct Qualifier<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { | |
137 | mode: Mode, | |
138 | span: Span, | |
139 | def_id: DefId, | |
140 | mir: &'a Mir<'tcx>, | |
141 | rpo: ReversePostorder<'a, 'tcx>, | |
142 | tcx: TyCtxt<'a, 'gcx, 'tcx>, | |
143 | param_env: ty::ParameterEnvironment<'tcx>, | |
144 | qualif_map: &'a mut DefIdMap<Qualif>, | |
145 | mir_map: Option<&'a MirMap<'tcx>>, | |
3157f602 | 146 | temp_qualif: IndexVec<Temp, Option<Qualif>>, |
a7813a04 XL |
147 | return_qualif: Option<Qualif>, |
148 | qualif: Qualif, | |
149 | const_fn_arg_vars: BitVector, | |
150 | location: Location, | |
3157f602 | 151 | temp_promotion_state: IndexVec<Temp, TempState>, |
a7813a04 XL |
152 | promotion_candidates: Vec<Candidate> |
153 | } | |
154 | ||
155 | impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> { | |
156 | fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>, | |
157 | param_env: ty::ParameterEnvironment<'tcx>, | |
158 | qualif_map: &'a mut DefIdMap<Qualif>, | |
159 | mir_map: Option<&'a MirMap<'tcx>>, | |
160 | def_id: DefId, | |
161 | mir: &'a Mir<'tcx>, | |
162 | mode: Mode) | |
163 | -> Qualifier<'a, 'tcx, 'tcx> { | |
164 | let mut rpo = traversal::reverse_postorder(mir); | |
165 | let temps = promote_consts::collect_temps(mir, &mut rpo); | |
166 | rpo.reset(); | |
167 | Qualifier { | |
168 | mode: mode, | |
169 | span: mir.span, | |
170 | def_id: def_id, | |
171 | mir: mir, | |
172 | rpo: rpo, | |
173 | tcx: tcx, | |
174 | param_env: param_env, | |
175 | qualif_map: qualif_map, | |
176 | mir_map: mir_map, | |
3157f602 | 177 | temp_qualif: IndexVec::from_elem(None, &mir.temp_decls), |
a7813a04 XL |
178 | return_qualif: None, |
179 | qualif: Qualif::empty(), | |
180 | const_fn_arg_vars: BitVector::new(mir.var_decls.len()), | |
181 | location: Location { | |
182 | block: START_BLOCK, | |
183 | statement_index: 0 | |
184 | }, | |
185 | temp_promotion_state: temps, | |
186 | promotion_candidates: vec![] | |
187 | } | |
188 | } | |
189 | ||
190 | // FIXME(eddyb) we could split the errors into meaningful | |
191 | // categories, but enabling full miri would make that | |
192 | // slightly pointless (even with feature-gating). | |
193 | fn not_const(&mut self) { | |
194 | self.add(Qualif::NOT_CONST); | |
195 | if self.mode != Mode::Fn { | |
196 | span_err!(self.tcx.sess, self.span, E0019, | |
197 | "{} contains unimplemented expression type", self.mode); | |
198 | } | |
199 | } | |
200 | ||
201 | /// Error about extra statements in a constant. | |
202 | fn statement_like(&mut self) { | |
203 | self.add(Qualif::NOT_CONST); | |
204 | if self.mode != Mode::Fn { | |
205 | span_err!(self.tcx.sess, self.span, E0016, | |
206 | "blocks in {}s are limited to items and tail expressions", | |
207 | self.mode); | |
208 | } | |
209 | } | |
210 | ||
211 | /// Add the given qualification to self.qualif. | |
212 | fn add(&mut self, qualif: Qualif) { | |
213 | self.qualif = self.qualif | qualif; | |
214 | } | |
215 | ||
216 | /// Add the given type's qualification to self.qualif. | |
217 | fn add_type(&mut self, ty: Ty<'tcx>) { | |
218 | self.add(Qualif::MUTABLE_INTERIOR | Qualif::NEEDS_DROP); | |
219 | self.qualif.restrict(ty, self.tcx, &self.param_env); | |
220 | } | |
221 | ||
222 | /// Within the provided closure, self.qualif will start | |
223 | /// out empty, and its value after the closure returns will | |
224 | /// be combined with the value before the call to nest. | |
225 | fn nest<F: FnOnce(&mut Self)>(&mut self, f: F) { | |
226 | let original = self.qualif; | |
227 | self.qualif = Qualif::empty(); | |
228 | f(self); | |
229 | self.add(original); | |
230 | } | |
231 | ||
232 | /// Check for NEEDS_DROP (from an ADT or const fn call) and | |
233 | /// error, unless we're in a function, or the feature-gate | |
234 | /// for globals with destructors is enabled. | |
235 | fn deny_drop(&self) { | |
236 | if self.mode == Mode::Fn || !self.qualif.intersects(Qualif::NEEDS_DROP) { | |
237 | return; | |
238 | } | |
239 | ||
240 | // Static and const fn's allow destructors, but they're feature-gated. | |
241 | let msg = if self.mode != Mode::Const { | |
242 | // Feature-gate for globals with destructors is enabled. | |
243 | if self.tcx.sess.features.borrow().drop_types_in_const { | |
244 | return; | |
245 | } | |
246 | ||
247 | // This comes from a macro that has #[allow_internal_unstable]. | |
248 | if self.tcx.sess.codemap().span_allows_unstable(self.span) { | |
249 | return; | |
250 | } | |
251 | ||
252 | format!("destructors in {}s are an unstable feature", | |
253 | self.mode) | |
254 | } else { | |
255 | format!("{}s are not allowed to have destructors", | |
256 | self.mode) | |
257 | }; | |
258 | ||
259 | let mut err = | |
260 | struct_span_err!(self.tcx.sess, self.span, E0493, "{}", msg); | |
261 | if self.mode != Mode::Const { | |
262 | help!(&mut err, | |
263 | "in Nightly builds, add `#![feature(drop_types_in_const)]` \ | |
264 | to the crate attributes to enable"); | |
265 | } | |
266 | err.emit(); | |
267 | } | |
268 | ||
269 | /// Check if an Lvalue with the current qualifications could | |
270 | /// be consumed, by either an operand or a Deref projection. | |
271 | fn try_consume(&mut self) -> bool { | |
272 | if self.qualif.intersects(Qualif::STATIC) && self.mode != Mode::Fn { | |
273 | let msg = if self.mode == Mode::Static || | |
274 | self.mode == Mode::StaticMut { | |
275 | "cannot refer to other statics by value, use the \ | |
276 | address-of operator or a constant instead" | |
277 | } else { | |
278 | "cannot refer to statics by value, use a constant instead" | |
279 | }; | |
280 | span_err!(self.tcx.sess, self.span, E0394, "{}", msg); | |
281 | ||
282 | // Replace STATIC with NOT_CONST to avoid further errors. | |
283 | self.qualif = self.qualif - Qualif::STATIC; | |
284 | self.add(Qualif::NOT_CONST); | |
285 | ||
286 | false | |
287 | } else { | |
288 | true | |
289 | } | |
290 | } | |
291 | ||
292 | /// Assign the current qualification to the given destination. | |
293 | fn assign(&mut self, dest: &Lvalue<'tcx>) { | |
294 | let qualif = self.qualif; | |
295 | let span = self.span; | |
296 | let store = |slot: &mut Option<Qualif>| { | |
297 | if slot.is_some() { | |
298 | span_bug!(span, "multiple assignments to {:?}", dest); | |
299 | } | |
300 | *slot = Some(qualif); | |
301 | }; | |
302 | ||
303 | // Only handle promotable temps in non-const functions. | |
304 | if self.mode == Mode::Fn { | |
305 | if let Lvalue::Temp(index) = *dest { | |
3157f602 XL |
306 | if self.temp_promotion_state[index].is_promotable() { |
307 | store(&mut self.temp_qualif[index]); | |
a7813a04 XL |
308 | } |
309 | } | |
310 | return; | |
311 | } | |
312 | ||
313 | match *dest { | |
3157f602 | 314 | Lvalue::Temp(index) => store(&mut self.temp_qualif[index]), |
a7813a04 XL |
315 | Lvalue::ReturnPointer => store(&mut self.return_qualif), |
316 | ||
317 | Lvalue::Projection(box Projection { | |
318 | base: Lvalue::Temp(index), | |
319 | elem: ProjectionElem::Deref | |
3157f602 XL |
320 | }) if self.mir.temp_decls[index].ty.is_unique() |
321 | && self.temp_qualif[index].map_or(false, |qualif| { | |
a7813a04 XL |
322 | qualif.intersects(Qualif::NOT_CONST) |
323 | }) => { | |
324 | // Part of `box expr`, we should've errored | |
325 | // already for the Box allocation Rvalue. | |
326 | } | |
327 | ||
328 | // This must be an explicit assignment. | |
329 | _ => { | |
330 | // Catch more errors in the destination. | |
331 | self.visit_lvalue(dest, LvalueContext::Store); | |
332 | self.statement_like(); | |
333 | } | |
334 | } | |
335 | } | |
336 | ||
a7813a04 XL |
337 | /// Qualify a whole const, static initializer or const fn. |
338 | fn qualify_const(&mut self) -> Qualif { | |
339 | let mir = self.mir; | |
340 | ||
3157f602 | 341 | let mut seen_blocks = BitVector::new(mir.basic_blocks().len()); |
a7813a04 XL |
342 | let mut bb = START_BLOCK; |
343 | loop { | |
344 | seen_blocks.insert(bb.index()); | |
345 | ||
346 | self.visit_basic_block_data(bb, &mir[bb]); | |
347 | ||
348 | let target = match mir[bb].terminator().kind { | |
349 | TerminatorKind::Goto { target } | | |
350 | // Drops are considered noops. | |
351 | TerminatorKind::Drop { target, .. } | | |
3157f602 | 352 | TerminatorKind::Assert { target, .. } | |
a7813a04 XL |
353 | TerminatorKind::Call { destination: Some((_, target)), .. } => { |
354 | Some(target) | |
355 | } | |
356 | ||
357 | // Non-terminating calls cannot produce any value. | |
358 | TerminatorKind::Call { destination: None, .. } => { | |
359 | return Qualif::empty(); | |
360 | } | |
361 | ||
3157f602 | 362 | TerminatorKind::If {..} | |
a7813a04 XL |
363 | TerminatorKind::Switch {..} | |
364 | TerminatorKind::SwitchInt {..} | | |
3157f602 XL |
365 | TerminatorKind::DropAndReplace { .. } | |
366 | TerminatorKind::Resume | | |
367 | TerminatorKind::Unreachable => None, | |
a7813a04 XL |
368 | |
369 | TerminatorKind::Return => { | |
370 | // Check for unused values. This usually means | |
371 | // there are extra statements in the AST. | |
3157f602 XL |
372 | for temp in mir.temp_decls.indices() { |
373 | if self.temp_qualif[temp].is_none() { | |
a7813a04 XL |
374 | continue; |
375 | } | |
376 | ||
3157f602 | 377 | let state = self.temp_promotion_state[temp]; |
a7813a04 XL |
378 | if let TempState::Defined { location, uses: 0 } = state { |
379 | let data = &mir[location.block]; | |
380 | let stmt_idx = location.statement_index; | |
381 | ||
382 | // Get the span for the initialization. | |
3157f602 XL |
383 | let source_info = if stmt_idx < data.statements.len() { |
384 | data.statements[stmt_idx].source_info | |
a7813a04 | 385 | } else { |
3157f602 XL |
386 | data.terminator().source_info |
387 | }; | |
388 | self.span = source_info.span; | |
a7813a04 XL |
389 | |
390 | // Treat this as a statement in the AST. | |
391 | self.statement_like(); | |
392 | } | |
393 | } | |
394 | ||
395 | // Make sure there are no extra unassigned variables. | |
396 | self.qualif = Qualif::NOT_CONST; | |
397 | for index in 0..mir.var_decls.len() { | |
398 | if !self.const_fn_arg_vars.contains(index) { | |
3157f602 | 399 | self.assign(&Lvalue::Var(Var::new(index))); |
a7813a04 XL |
400 | } |
401 | } | |
402 | ||
403 | break; | |
404 | } | |
405 | }; | |
406 | ||
407 | match target { | |
408 | // No loops allowed. | |
409 | Some(target) if !seen_blocks.contains(target.index()) => { | |
410 | bb = target; | |
411 | } | |
412 | _ => { | |
413 | self.not_const(); | |
414 | break; | |
415 | } | |
416 | } | |
417 | } | |
418 | ||
5bcae85e | 419 | let return_ty = mir.return_ty; |
a7813a04 XL |
420 | self.qualif = self.return_qualif.unwrap_or(Qualif::NOT_CONST); |
421 | ||
422 | match self.mode { | |
423 | Mode::StaticMut => { | |
424 | // Check for destructors in static mut. | |
425 | self.add_type(return_ty); | |
426 | self.deny_drop(); | |
427 | } | |
428 | _ => { | |
429 | // Account for errors in consts by using the | |
430 | // conservative type qualification instead. | |
431 | if self.qualif.intersects(Qualif::CONST_ERROR) { | |
432 | self.qualif = Qualif::empty(); | |
433 | self.add_type(return_ty); | |
434 | } | |
435 | } | |
436 | } | |
437 | self.qualif | |
438 | } | |
439 | } | |
440 | ||
441 | /// Accumulates an Rvalue or Call's effects in self.qualif. | |
442 | /// For functions (constant or not), it also records | |
443 | /// candidates for promotion in promotion_candidates. | |
444 | impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> { | |
445 | fn visit_lvalue(&mut self, lvalue: &Lvalue<'tcx>, context: LvalueContext) { | |
446 | match *lvalue { | |
447 | Lvalue::Arg(_) => { | |
448 | self.add(Qualif::FN_ARGUMENT); | |
449 | } | |
450 | Lvalue::Var(_) => { | |
451 | self.add(Qualif::NOT_CONST); | |
452 | } | |
453 | Lvalue::Temp(index) => { | |
3157f602 | 454 | if !self.temp_promotion_state[index].is_promotable() { |
a7813a04 XL |
455 | self.add(Qualif::NOT_PROMOTABLE); |
456 | } | |
457 | ||
3157f602 | 458 | if let Some(qualif) = self.temp_qualif[index] { |
a7813a04 XL |
459 | self.add(qualif); |
460 | } else { | |
461 | self.not_const(); | |
462 | } | |
463 | } | |
464 | Lvalue::Static(_) => { | |
465 | self.add(Qualif::STATIC); | |
466 | if self.mode == Mode::Const || self.mode == Mode::ConstFn { | |
467 | span_err!(self.tcx.sess, self.span, E0013, | |
468 | "{}s cannot refer to statics, use \ | |
469 | a constant instead", self.mode); | |
470 | } | |
471 | } | |
472 | Lvalue::ReturnPointer => { | |
473 | self.not_const(); | |
474 | } | |
475 | Lvalue::Projection(ref proj) => { | |
476 | self.nest(|this| { | |
477 | this.super_lvalue(lvalue, context); | |
478 | match proj.elem { | |
479 | ProjectionElem::Deref => { | |
480 | if !this.try_consume() { | |
481 | return; | |
482 | } | |
483 | ||
484 | if this.qualif.intersects(Qualif::STATIC_REF) { | |
485 | this.qualif = this.qualif - Qualif::STATIC_REF; | |
486 | this.add(Qualif::STATIC); | |
487 | } | |
488 | ||
5bcae85e | 489 | let base_ty = proj.base.ty(this.mir, this.tcx).to_ty(this.tcx); |
a7813a04 XL |
490 | if let ty::TyRawPtr(_) = base_ty.sty { |
491 | this.add(Qualif::NOT_CONST); | |
492 | if this.mode != Mode::Fn { | |
493 | span_err!(this.tcx.sess, this.span, E0396, | |
494 | "raw pointers cannot be dereferenced in {}s", | |
495 | this.mode); | |
496 | } | |
497 | } | |
498 | } | |
499 | ||
500 | ProjectionElem::Field(..) | | |
501 | ProjectionElem::Index(_) => { | |
502 | if this.mode != Mode::Fn && | |
503 | this.qualif.intersects(Qualif::STATIC) { | |
504 | span_err!(this.tcx.sess, this.span, E0494, | |
505 | "cannot refer to the interior of another \ | |
506 | static, use a constant instead"); | |
507 | } | |
5bcae85e | 508 | let ty = lvalue.ty(this.mir, this.tcx).to_ty(this.tcx); |
a7813a04 XL |
509 | this.qualif.restrict(ty, this.tcx, &this.param_env); |
510 | } | |
511 | ||
512 | ProjectionElem::ConstantIndex {..} | | |
3157f602 | 513 | ProjectionElem::Subslice {..} | |
a7813a04 XL |
514 | ProjectionElem::Downcast(..) => { |
515 | this.not_const() | |
516 | } | |
517 | } | |
518 | }); | |
519 | } | |
520 | } | |
521 | } | |
522 | ||
523 | fn visit_operand(&mut self, operand: &Operand<'tcx>) { | |
524 | match *operand { | |
525 | Operand::Consume(_) => { | |
526 | self.nest(|this| { | |
527 | this.super_operand(operand); | |
528 | this.try_consume(); | |
529 | }); | |
530 | } | |
531 | Operand::Constant(ref constant) => { | |
532 | // Only functions and methods can have these types. | |
533 | if let ty::TyFnDef(..) = constant.ty.sty { | |
534 | return; | |
535 | } | |
536 | ||
537 | if let Literal::Item { def_id, substs } = constant.literal { | |
538 | // Don't peek inside generic (associated) constants. | |
539 | if !substs.types.is_empty() { | |
540 | self.add_type(constant.ty); | |
541 | } else { | |
542 | let qualif = qualify_const_item_cached(self.tcx, | |
543 | self.qualif_map, | |
544 | self.mir_map, | |
545 | def_id); | |
546 | self.add(qualif); | |
547 | } | |
548 | ||
549 | // FIXME(eddyb) check recursive constants here, | |
550 | // instead of rustc_passes::static_recursion. | |
551 | if self.qualif.intersects(Qualif::RECURSIVE) { | |
552 | span_bug!(constant.span, | |
553 | "recursive constant wasn't caught earlier"); | |
554 | } | |
555 | ||
556 | // Let `const fn` transitively have destructors, | |
557 | // but they do get stopped in `const` or `static`. | |
558 | if self.mode != Mode::ConstFn { | |
559 | self.deny_drop(); | |
560 | } | |
561 | } | |
562 | } | |
563 | } | |
564 | } | |
565 | ||
566 | fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>) { | |
567 | // Recurse through operands and lvalues. | |
568 | self.super_rvalue(rvalue); | |
569 | ||
570 | match *rvalue { | |
571 | Rvalue::Use(_) | | |
572 | Rvalue::Repeat(..) | | |
573 | Rvalue::UnaryOp(..) | | |
3157f602 | 574 | Rvalue::CheckedBinaryOp(..) | |
a7813a04 XL |
575 | Rvalue::Cast(CastKind::ReifyFnPointer, _, _) | |
576 | Rvalue::Cast(CastKind::UnsafeFnPointer, _, _) | | |
577 | Rvalue::Cast(CastKind::Unsize, _, _) => {} | |
578 | ||
579 | Rvalue::Len(_) => { | |
580 | // Static lvalues in consts would have errored already, | |
581 | // don't treat length checks as reads from statics. | |
582 | self.qualif = self.qualif - Qualif::STATIC; | |
583 | } | |
584 | ||
585 | Rvalue::Ref(_, kind, ref lvalue) => { | |
586 | // Static lvalues in consts would have errored already, | |
587 | // only keep track of references to them here. | |
588 | if self.qualif.intersects(Qualif::STATIC) { | |
589 | self.qualif = self.qualif - Qualif::STATIC; | |
590 | self.add(Qualif::STATIC_REF); | |
591 | } | |
592 | ||
5bcae85e | 593 | let ty = lvalue.ty(self.mir, self.tcx).to_ty(self.tcx); |
a7813a04 XL |
594 | if kind == BorrowKind::Mut { |
595 | // In theory, any zero-sized value could be borrowed | |
596 | // mutably without consequences. However, only &mut [] | |
597 | // is allowed right now, and only in functions. | |
598 | let allow = if self.mode == Mode::StaticMut { | |
599 | // Inside a `static mut`, &mut [...] is also allowed. | |
600 | match ty.sty { | |
601 | ty::TyArray(..) | ty::TySlice(_) => { | |
602 | // Mutating can expose drops, be conservative. | |
603 | self.add_type(ty); | |
604 | self.deny_drop(); | |
605 | true | |
606 | } | |
607 | _ => false | |
608 | } | |
609 | } else if let ty::TyArray(_, 0) = ty.sty { | |
610 | self.mode == Mode::Fn | |
611 | } else { | |
612 | false | |
613 | }; | |
614 | ||
615 | if !allow { | |
616 | self.add(Qualif::NOT_CONST); | |
617 | if self.mode != Mode::Fn { | |
5bcae85e SL |
618 | struct_span_err!(self.tcx.sess, self.span, E0017, |
619 | "references in {}s may only refer \ | |
620 | to immutable values", self.mode) | |
621 | .span_label(self.span, &format!("{}s require immutable values", | |
622 | self.mode)) | |
623 | .emit(); | |
a7813a04 XL |
624 | } |
625 | } | |
626 | } else { | |
627 | // Constants cannot be borrowed if they contain interior mutability as | |
628 | // it means that our "silent insertion of statics" could change | |
629 | // initializer values (very bad). | |
630 | if self.qualif.intersects(Qualif::MUTABLE_INTERIOR) { | |
631 | // Replace MUTABLE_INTERIOR with NOT_CONST to avoid | |
632 | // duplicate errors (from reborrowing, for example). | |
633 | self.qualif = self.qualif - Qualif::MUTABLE_INTERIOR; | |
634 | self.add(Qualif::NOT_CONST); | |
635 | if self.mode != Mode::Fn { | |
636 | span_err!(self.tcx.sess, self.span, E0492, | |
637 | "cannot borrow a constant which contains \ | |
638 | interior mutability, create a static instead"); | |
639 | } | |
640 | } | |
641 | } | |
642 | ||
643 | // We might have a candidate for promotion. | |
644 | let candidate = Candidate::Ref(self.location); | |
645 | if self.mode == Mode::Fn || self.mode == Mode::ConstFn { | |
646 | if !self.qualif.intersects(Qualif::NEVER_PROMOTE) { | |
647 | // We can only promote direct borrows of temps. | |
648 | if let Lvalue::Temp(_) = *lvalue { | |
649 | self.promotion_candidates.push(candidate); | |
650 | } | |
651 | } | |
652 | } | |
653 | } | |
654 | ||
655 | Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => { | |
5bcae85e | 656 | let operand_ty = operand.ty(self.mir, self.tcx); |
a7813a04 XL |
657 | let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast"); |
658 | let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast"); | |
659 | match (cast_in, cast_out) { | |
660 | (CastTy::Ptr(_), CastTy::Int(_)) | | |
661 | (CastTy::FnPtr, CastTy::Int(_)) => { | |
662 | self.add(Qualif::NOT_CONST); | |
663 | if self.mode != Mode::Fn { | |
664 | span_err!(self.tcx.sess, self.span, E0018, | |
665 | "raw pointers cannot be cast to integers in {}s", | |
666 | self.mode); | |
667 | } | |
668 | } | |
669 | _ => {} | |
670 | } | |
671 | } | |
672 | ||
673 | Rvalue::BinaryOp(op, ref lhs, _) => { | |
5bcae85e | 674 | if let ty::TyRawPtr(_) = lhs.ty(self.mir, self.tcx).sty { |
a7813a04 XL |
675 | assert!(op == BinOp::Eq || op == BinOp::Ne || |
676 | op == BinOp::Le || op == BinOp::Lt || | |
677 | op == BinOp::Ge || op == BinOp::Gt); | |
678 | ||
679 | self.add(Qualif::NOT_CONST); | |
680 | if self.mode != Mode::Fn { | |
681 | span_err!(self.tcx.sess, self.span, E0395, | |
682 | "raw pointers cannot be compared in {}s", | |
683 | self.mode); | |
684 | } | |
685 | } | |
686 | } | |
687 | ||
688 | Rvalue::Box(_) => { | |
689 | self.add(Qualif::NOT_CONST); | |
690 | if self.mode != Mode::Fn { | |
5bcae85e SL |
691 | struct_span_err!(self.tcx.sess, self.span, E0010, |
692 | "allocations are not allowed in {}s", self.mode) | |
693 | .span_label(self.span, &format!("allocation not allowed in {}s", self.mode)) | |
694 | .emit(); | |
a7813a04 XL |
695 | } |
696 | } | |
697 | ||
698 | Rvalue::Aggregate(ref kind, _) => { | |
699 | if let AggregateKind::Adt(def, _, _) = *kind { | |
700 | if def.has_dtor() { | |
701 | self.add(Qualif::NEEDS_DROP); | |
702 | self.deny_drop(); | |
703 | } | |
704 | ||
705 | if Some(def.did) == self.tcx.lang_items.unsafe_cell_type() { | |
5bcae85e | 706 | let ty = rvalue.ty(self.mir, self.tcx).unwrap(); |
a7813a04 XL |
707 | self.add_type(ty); |
708 | assert!(self.qualif.intersects(Qualif::MUTABLE_INTERIOR)); | |
709 | // Even if the value inside may not need dropping, | |
710 | // mutating it would change that. | |
711 | if !self.qualif.intersects(Qualif::NOT_CONST) { | |
712 | self.deny_drop(); | |
713 | } | |
714 | } | |
715 | } | |
716 | } | |
717 | ||
a7813a04 XL |
718 | Rvalue::InlineAsm {..} => { |
719 | self.not_const(); | |
720 | } | |
721 | } | |
722 | } | |
723 | ||
724 | fn visit_terminator_kind(&mut self, bb: BasicBlock, kind: &TerminatorKind<'tcx>) { | |
725 | if let TerminatorKind::Call { ref func, ref args, ref destination, .. } = *kind { | |
726 | self.visit_operand(func); | |
727 | ||
5bcae85e | 728 | let fn_ty = func.ty(self.mir, self.tcx); |
a7813a04 XL |
729 | let (is_shuffle, is_const_fn) = match fn_ty.sty { |
730 | ty::TyFnDef(def_id, _, f) => { | |
731 | (f.abi == Abi::PlatformIntrinsic && | |
732 | self.tcx.item_name(def_id).as_str().starts_with("simd_shuffle"), | |
733 | is_const_fn(self.tcx, def_id)) | |
734 | } | |
735 | _ => (false, false) | |
736 | }; | |
737 | ||
738 | for (i, arg) in args.iter().enumerate() { | |
739 | self.nest(|this| { | |
740 | this.visit_operand(arg); | |
741 | if is_shuffle && i == 2 && this.mode == Mode::Fn { | |
742 | let candidate = Candidate::ShuffleIndices(bb); | |
743 | if !this.qualif.intersects(Qualif::NEVER_PROMOTE) { | |
744 | this.promotion_candidates.push(candidate); | |
745 | } else { | |
746 | span_err!(this.tcx.sess, this.span, E0526, | |
747 | "shuffle indices are not constant"); | |
748 | } | |
749 | } | |
750 | }); | |
751 | } | |
752 | ||
753 | // Const fn calls. | |
754 | if is_const_fn { | |
755 | // We are in a const or static initializer, | |
756 | if self.mode != Mode::Fn && | |
757 | ||
758 | // feature-gate is not enabled, | |
759 | !self.tcx.sess.features.borrow().const_fn && | |
760 | ||
761 | // this doesn't come from a crate with the feature-gate enabled, | |
762 | self.def_id.is_local() && | |
763 | ||
764 | // this doesn't come from a macro that has #[allow_internal_unstable] | |
765 | !self.tcx.sess.codemap().span_allows_unstable(self.span) | |
766 | { | |
767 | let mut err = self.tcx.sess.struct_span_err(self.span, | |
768 | "const fns are an unstable feature"); | |
769 | help!(&mut err, | |
770 | "in Nightly builds, add `#![feature(const_fn)]` \ | |
771 | to the crate attributes to enable"); | |
772 | err.emit(); | |
773 | } | |
774 | } else { | |
775 | self.qualif = Qualif::NOT_CONST; | |
776 | if self.mode != Mode::Fn { | |
777 | // FIXME(#24111) Remove this check when const fn stabilizes | |
778 | let (msg, note) = if let UnstableFeatures::Disallow = | |
779 | self.tcx.sess.opts.unstable_features { | |
780 | (format!("calls in {}s are limited to \ | |
781 | struct and enum constructors", | |
782 | self.mode), | |
783 | Some("a limited form of compile-time function \ | |
784 | evaluation is available on a nightly \ | |
785 | compiler via `const fn`")) | |
786 | } else { | |
787 | (format!("calls in {}s are limited \ | |
788 | to constant functions, \ | |
789 | struct and enum constructors", | |
790 | self.mode), | |
791 | None) | |
792 | }; | |
793 | let mut err = struct_span_err!(self.tcx.sess, self.span, E0015, "{}", msg); | |
794 | if let Some(note) = note { | |
795 | err.span_note(self.span, note); | |
796 | } | |
797 | err.emit(); | |
798 | } | |
799 | } | |
800 | ||
801 | if let Some((ref dest, _)) = *destination { | |
802 | // Avoid propagating irrelevant callee/argument qualifications. | |
803 | if self.qualif.intersects(Qualif::CONST_ERROR) { | |
804 | self.qualif = Qualif::NOT_CONST; | |
805 | } else { | |
806 | // Be conservative about the returned value of a const fn. | |
807 | let tcx = self.tcx; | |
5bcae85e | 808 | let ty = dest.ty(self.mir, tcx).to_ty(tcx); |
a7813a04 XL |
809 | self.qualif = Qualif::empty(); |
810 | self.add_type(ty); | |
811 | ||
812 | // Let `const fn` transitively have destructors, | |
813 | // but they do get stopped in `const` or `static`. | |
814 | if self.mode != Mode::ConstFn { | |
815 | self.deny_drop(); | |
816 | } | |
817 | } | |
818 | self.assign(dest); | |
819 | } | |
820 | } else { | |
821 | // Qualify any operands inside other terminators. | |
822 | self.super_terminator_kind(bb, kind); | |
823 | } | |
824 | } | |
825 | ||
826 | fn visit_assign(&mut self, _: BasicBlock, dest: &Lvalue<'tcx>, rvalue: &Rvalue<'tcx>) { | |
827 | self.visit_rvalue(rvalue); | |
828 | ||
829 | // Check the allowed const fn argument forms. | |
830 | if let (Mode::ConstFn, &Lvalue::Var(index)) = (self.mode, dest) { | |
3157f602 | 831 | if self.const_fn_arg_vars.insert(index.index()) { |
a7813a04 XL |
832 | // Direct use of an argument is permitted. |
833 | if let Rvalue::Use(Operand::Consume(Lvalue::Arg(_))) = *rvalue { | |
834 | return; | |
835 | } | |
836 | ||
837 | // Avoid a generic error for other uses of arguments. | |
838 | if self.qualif.intersects(Qualif::FN_ARGUMENT) { | |
3157f602 XL |
839 | let decl = &self.mir.var_decls[index]; |
840 | span_err!(self.tcx.sess, decl.source_info.span, E0022, | |
a7813a04 XL |
841 | "arguments of constant functions can only \ |
842 | be immutable by-value bindings"); | |
843 | return; | |
844 | } | |
845 | } | |
846 | } | |
847 | ||
848 | self.assign(dest); | |
849 | } | |
850 | ||
3157f602 XL |
851 | fn visit_source_info(&mut self, source_info: &SourceInfo) { |
852 | self.span = source_info.span; | |
853 | } | |
854 | ||
a7813a04 XL |
855 | fn visit_statement(&mut self, bb: BasicBlock, statement: &Statement<'tcx>) { |
856 | assert_eq!(self.location.block, bb); | |
5bcae85e SL |
857 | self.nest(|this| { |
858 | this.visit_source_info(&statement.source_info); | |
859 | match statement.kind { | |
860 | StatementKind::Assign(ref lvalue, ref rvalue) => { | |
861 | this.visit_assign(bb, lvalue, rvalue); | |
862 | } | |
863 | StatementKind::SetDiscriminant { .. } | | |
864 | StatementKind::StorageLive(_) | | |
865 | StatementKind::StorageDead(_) => {} | |
866 | } | |
867 | }); | |
a7813a04 XL |
868 | self.location.statement_index += 1; |
869 | } | |
870 | ||
871 | fn visit_terminator(&mut self, bb: BasicBlock, terminator: &Terminator<'tcx>) { | |
872 | assert_eq!(self.location.block, bb); | |
a7813a04 XL |
873 | self.nest(|this| this.super_terminator(bb, terminator)); |
874 | } | |
875 | ||
876 | fn visit_basic_block_data(&mut self, bb: BasicBlock, data: &BasicBlockData<'tcx>) { | |
877 | self.location.statement_index = 0; | |
878 | self.location.block = bb; | |
879 | self.super_basic_block_data(bb, data); | |
880 | } | |
881 | } | |
882 | ||
883 | fn qualify_const_item_cached<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, | |
884 | qualif_map: &mut DefIdMap<Qualif>, | |
885 | mir_map: Option<&MirMap<'tcx>>, | |
886 | def_id: DefId) | |
887 | -> Qualif { | |
888 | match qualif_map.entry(def_id) { | |
889 | Entry::Occupied(entry) => return *entry.get(), | |
890 | Entry::Vacant(entry) => { | |
891 | // Guard against `const` recursion. | |
892 | entry.insert(Qualif::RECURSIVE); | |
893 | } | |
894 | } | |
895 | ||
896 | let extern_mir; | |
897 | let param_env_and_mir = if def_id.is_local() { | |
5bcae85e SL |
898 | mir_map.and_then(|map| map.map.get(&def_id)).map(|mir| { |
899 | let node_id = tcx.map.as_local_node_id(def_id).unwrap(); | |
a7813a04 XL |
900 | (ty::ParameterEnvironment::for_item(tcx, node_id), mir) |
901 | }) | |
902 | } else if let Some(mir) = tcx.sess.cstore.maybe_get_item_mir(tcx, def_id) { | |
903 | // These should only be monomorphic constants. | |
904 | extern_mir = mir; | |
905 | Some((tcx.empty_parameter_environment(), &extern_mir)) | |
906 | } else { | |
907 | None | |
908 | }; | |
909 | ||
910 | let (param_env, mir) = param_env_and_mir.unwrap_or_else(|| { | |
911 | bug!("missing constant MIR for {}", tcx.item_path_str(def_id)) | |
912 | }); | |
913 | ||
914 | let mut qualifier = Qualifier::new(tcx, param_env, qualif_map, mir_map, | |
915 | def_id, mir, Mode::Const); | |
916 | let qualif = qualifier.qualify_const(); | |
917 | qualifier.qualif_map.insert(def_id, qualif); | |
918 | qualif | |
919 | } | |
920 | ||
921 | pub struct QualifyAndPromoteConstants; | |
922 | ||
923 | impl Pass for QualifyAndPromoteConstants {} | |
924 | ||
925 | impl<'tcx> MirMapPass<'tcx> for QualifyAndPromoteConstants { | |
3157f602 XL |
926 | fn run_pass<'a>(&mut self, |
927 | tcx: TyCtxt<'a, 'tcx, 'tcx>, | |
928 | map: &mut MirMap<'tcx>, | |
929 | hooks: &mut [Box<for<'s> MirPassHook<'s>>]) { | |
a7813a04 XL |
930 | let mut qualif_map = DefIdMap(); |
931 | ||
932 | // First, visit `const` items, potentially recursing, to get | |
933 | // accurate MUTABLE_INTERIOR and NEEDS_DROP qualifications. | |
5bcae85e SL |
934 | let keys = map.map.keys(); |
935 | for &def_id in &keys { | |
936 | let _task = tcx.dep_graph.in_task(DepNode::Mir(def_id)); | |
937 | let id = tcx.map.as_local_node_id(def_id).unwrap(); | |
a7813a04 XL |
938 | let src = MirSource::from_node(tcx, id); |
939 | if let MirSource::Const(_) = src { | |
940 | qualify_const_item_cached(tcx, &mut qualif_map, Some(map), def_id); | |
941 | } | |
942 | } | |
943 | ||
944 | // Then, handle everything else, without recursing, | |
945 | // as the MIR map is not shared, since promotion | |
946 | // in functions (including `const fn`) mutates it. | |
5bcae85e SL |
947 | for &def_id in &keys { |
948 | let _task = tcx.dep_graph.in_task(DepNode::Mir(def_id)); | |
949 | let id = tcx.map.as_local_node_id(def_id).unwrap(); | |
a7813a04 XL |
950 | let src = MirSource::from_node(tcx, id); |
951 | let mode = match src { | |
952 | MirSource::Fn(_) => { | |
953 | if is_const_fn(tcx, def_id) { | |
954 | Mode::ConstFn | |
955 | } else { | |
956 | Mode::Fn | |
957 | } | |
958 | } | |
959 | MirSource::Const(_) => continue, | |
960 | MirSource::Static(_, hir::MutImmutable) => Mode::Static, | |
961 | MirSource::Static(_, hir::MutMutable) => Mode::StaticMut, | |
962 | MirSource::Promoted(..) => bug!() | |
963 | }; | |
964 | let param_env = ty::ParameterEnvironment::for_item(tcx, id); | |
965 | ||
5bcae85e | 966 | let mir = map.map.get_mut(&def_id).unwrap(); |
3157f602 XL |
967 | for hook in &mut *hooks { |
968 | hook.on_mir_pass(tcx, src, mir, self, false); | |
969 | } | |
970 | ||
a7813a04 XL |
971 | if mode == Mode::Fn || mode == Mode::ConstFn { |
972 | // This is ugly because Qualifier holds onto mir, | |
973 | // which can't be mutated until its scope ends. | |
974 | let (temps, candidates) = { | |
975 | let mut qualifier = Qualifier::new(tcx, param_env, &mut qualif_map, | |
976 | None, def_id, mir, mode); | |
977 | if mode == Mode::ConstFn { | |
978 | // Enforce a constant-like CFG for `const fn`. | |
979 | qualifier.qualify_const(); | |
980 | } else { | |
981 | while let Some((bb, data)) = qualifier.rpo.next() { | |
982 | qualifier.visit_basic_block_data(bb, data); | |
983 | } | |
984 | } | |
985 | ||
986 | (qualifier.temp_promotion_state, | |
987 | qualifier.promotion_candidates) | |
988 | }; | |
989 | ||
990 | // Do the actual promotion, now that we know what's viable. | |
991 | promote_consts::promote_candidates(mir, tcx, temps, candidates); | |
992 | } else { | |
993 | let mut qualifier = Qualifier::new(tcx, param_env, &mut qualif_map, | |
994 | None, def_id, mir, mode); | |
995 | qualifier.qualify_const(); | |
996 | } | |
997 | ||
3157f602 XL |
998 | for hook in &mut *hooks { |
999 | hook.on_mir_pass(tcx, src, mir, self, true); | |
1000 | } | |
1001 | ||
a7813a04 XL |
1002 | // Statics must be Sync. |
1003 | if mode == Mode::Static { | |
5bcae85e SL |
1004 | let ty = mir.return_ty; |
1005 | tcx.infer_ctxt(None, None, Reveal::NotSpecializable).enter(|infcx| { | |
a7813a04 XL |
1006 | let cause = traits::ObligationCause::new(mir.span, id, traits::SharedStatic); |
1007 | let mut fulfillment_cx = traits::FulfillmentContext::new(); | |
1008 | fulfillment_cx.register_builtin_bound(&infcx, ty, ty::BoundSync, cause); | |
1009 | if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) { | |
1010 | infcx.report_fulfillment_errors(&err); | |
1011 | } | |
1012 | ||
1013 | if let Err(errors) = fulfillment_cx.select_rfc1592_obligations(&infcx) { | |
1014 | infcx.report_fulfillment_errors_as_warnings(&errors, id); | |
1015 | } | |
1016 | }); | |
1017 | } | |
1018 | } | |
1019 | } | |
1020 | } |