1 // Copyright 2015 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.
13 // After candidates have been simplified, the only match pairs that
14 // remain are those that require some sort of test. The functions here
15 // identify what tests are needed, perform the tests, and then filter
16 // the candidates based on the result.
19 use build::matches::{Candidate, MatchPair, Test, TestKind};
21 use rustc_data_structures::fx::FxHashMap;
22 use rustc_data_structures::bitvec::BitVector;
23 use rustc::ty::{self, Ty};
24 use rustc::ty::util::IntTypeExt;
26 use rustc::hir::{RangeEnd, Mutability};
28 use std::cmp::Ordering;
30 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
31 /// Identifies what test is needed to decide if `match_pair` is applicable.
33 /// It is a bug to call this with a simplifyable pattern.
34 pub fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> {
35 match *match_pair.pattern.kind {
36 PatternKind::Variant { ref adt_def, substs: _, variant_index: _, subpatterns: _ } => {
38 span: match_pair.pattern.span,
39 kind: TestKind::Switch {
40 adt_def: adt_def.clone(),
41 variants: BitVector::new(adt_def.variants.len()),
46 PatternKind::Constant { .. }
47 if is_switch_ty(match_pair.pattern.ty) => {
48 // for integers, we use a SwitchInt match, which allows
49 // us to handle more cases
51 span: match_pair.pattern.span,
52 kind: TestKind::SwitchInt {
53 switch_ty: match_pair.pattern.ty,
55 // these maps are empty to start; cases are
56 // added below in add_cases_to_switch
63 PatternKind::Constant { value } => {
65 span: match_pair.pattern.span,
68 ty: match_pair.pattern.ty.clone()
73 PatternKind::Range { lo, hi, end } => {
75 span: match_pair.pattern.span,
76 kind: TestKind::Range {
77 lo: Literal::Value { value: lo },
78 hi: Literal::Value { value: hi },
79 ty: match_pair.pattern.ty.clone(),
85 PatternKind::Slice { ref prefix, ref slice, ref suffix }
86 if !match_pair.slice_len_checked => {
87 let len = prefix.len() + suffix.len();
88 let op = if slice.is_some() {
94 span: match_pair.pattern.span,
95 kind: TestKind::Len { len: len as u64, op: op },
99 PatternKind::Array { .. } |
100 PatternKind::Slice { .. } |
102 PatternKind::Binding { .. } |
103 PatternKind::Leaf { .. } |
104 PatternKind::Deref { .. } => {
105 self.error_simplifyable(match_pair)
110 pub fn add_cases_to_switch<'pat>(&mut self,
111 test_place: &Place<'tcx>,
112 candidate: &Candidate<'pat, 'tcx>,
114 options: &mut Vec<u128>,
115 indices: &mut FxHashMap<&'tcx ty::Const<'tcx>, usize>)
118 let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
119 Some(match_pair) => match_pair,
120 _ => { return false; }
123 match *match_pair.pattern.kind {
124 PatternKind::Constant { value } => {
127 options.push(value.unwrap_bits(switch_ty));
132 PatternKind::Variant { .. } => {
133 panic!("you should have called add_variants_to_switch instead!");
135 PatternKind::Range { .. } |
136 PatternKind::Slice { .. } |
137 PatternKind::Array { .. } |
139 PatternKind::Binding { .. } |
140 PatternKind::Leaf { .. } |
141 PatternKind::Deref { .. } => {
142 // don't know how to add these patterns to a switch
148 pub fn add_variants_to_switch<'pat>(&mut self,
149 test_place: &Place<'tcx>,
150 candidate: &Candidate<'pat, 'tcx>,
151 variants: &mut BitVector)
154 let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
155 Some(match_pair) => match_pair,
156 _ => { return false; }
159 match *match_pair.pattern.kind {
160 PatternKind::Variant { adt_def: _ , variant_index, .. } => {
161 // We have a pattern testing for variant `variant_index`
162 // set the corresponding index to true
163 variants.insert(variant_index);
167 // don't know how to add these patterns to a switch
173 /// Generates the code to perform a test.
174 pub fn perform_test(&mut self,
179 debug!("perform_test({:?}, {:?}: {:?}, {:?})",
182 place.ty(&self.local_decls, self.hir.tcx()),
184 let source_info = self.source_info(test.span);
186 TestKind::Switch { adt_def, ref variants } => {
187 // Variants is a BitVec of indexes into adt_def.variants.
188 let num_enum_variants = adt_def.variants.len();
189 let used_variants = variants.count();
190 let mut otherwise_block = None;
191 let mut target_blocks = Vec::with_capacity(num_enum_variants);
192 let mut targets = Vec::with_capacity(used_variants + 1);
193 let mut values = Vec::with_capacity(used_variants);
194 let tcx = self.hir.tcx();
195 for (idx, discr) in adt_def.discriminants(tcx).enumerate() {
196 target_blocks.push(if variants.contains(idx) {
197 values.push(discr.val);
198 targets.push(self.cfg.start_new_block());
199 *targets.last().unwrap()
201 if otherwise_block.is_none() {
202 otherwise_block = Some(self.cfg.start_new_block());
204 otherwise_block.unwrap()
207 if let Some(otherwise_block) = otherwise_block {
208 targets.push(otherwise_block);
210 targets.push(self.unreachable_block());
212 debug!("num_enum_variants: {}, tested variants: {:?}, variants: {:?}",
213 num_enum_variants, values, variants);
214 let discr_ty = adt_def.repr.discr_type().to_ty(tcx);
215 let discr = self.temp(discr_ty, test.span);
216 self.cfg.push_assign(block, source_info, &discr,
217 Rvalue::Discriminant(place.clone()));
218 assert_eq!(values.len() + 1, targets.len());
219 self.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
220 discr: Operand::Move(discr),
222 values: From::from(values),
228 TestKind::SwitchInt { switch_ty, ref options, indices: _ } => {
229 let (ret, terminator) = if switch_ty.sty == ty::TyBool {
230 assert!(options.len() > 0 && options.len() <= 2);
231 let (true_bb, false_bb) = (self.cfg.start_new_block(),
232 self.cfg.start_new_block());
233 let ret = match options[0] {
234 1 => vec![true_bb, false_bb],
235 0 => vec![false_bb, true_bb],
236 v => span_bug!(test.span, "expected boolean value but got {:?}", v)
238 (ret, TerminatorKind::if_(self.hir.tcx(), Operand::Copy(place.clone()),
241 // The switch may be inexhaustive so we
242 // add a catch all block
243 let otherwise = self.cfg.start_new_block();
244 let targets: Vec<_> =
246 .map(|_| self.cfg.start_new_block())
247 .chain(Some(otherwise))
249 (targets.clone(), TerminatorKind::SwitchInt {
250 discr: Operand::Copy(place.clone()),
252 values: options.clone().into(),
256 self.cfg.terminate(block, source_info, terminator);
260 TestKind::Eq { value, mut ty } => {
261 let mut val = Operand::Copy(place.clone());
262 let mut expect = self.literal_operand(test.span, ty, Literal::Value {
265 // Use PartialEq::eq instead of BinOp::Eq
266 // (the binop can only handle primitives)
267 let fail = self.cfg.start_new_block();
269 // If we're using b"..." as a pattern, we need to insert an
270 // unsizing coercion, as the byte string has the type &[u8; N].
272 // We want to do this even when the scrutinee is a reference to an
273 // array, so we can call `<[u8]>::eq` rather than having to find an
275 let unsize = |ty: Ty<'tcx>| match ty.sty {
276 ty::TyRef(region, rty, _) => match rty.sty {
277 ty::TyArray(inner_ty, n) => Some((region, inner_ty, n)),
282 let opt_ref_ty = unsize(ty);
283 let opt_ref_test_ty = unsize(value.ty);
284 let mut place = place.clone();
285 match (opt_ref_ty, opt_ref_test_ty) {
286 // nothing to do, neither is an array
288 (Some((region, elem_ty, _)), _) |
289 (None, Some((region, elem_ty, _))) => {
290 let tcx = self.hir.tcx();
292 ty = tcx.mk_imm_ref(region, tcx.mk_slice(elem_ty));
293 if opt_ref_ty.is_some() {
294 place = self.temp(ty, test.span);
295 self.cfg.push_assign(block, source_info, &place,
296 Rvalue::Cast(CastKind::Unsize, val, ty));
298 if opt_ref_test_ty.is_some() {
299 let array = self.literal_operand(
307 let slice = self.temp(ty, test.span);
308 self.cfg.push_assign(block, source_info, &slice,
309 Rvalue::Cast(CastKind::Unsize, array, ty));
310 expect = Operand::Move(slice);
314 let eq_def_id = self.hir.tcx().lang_items().eq_trait().unwrap();
315 let (mty, method) = self.hir.trait_method(eq_def_id, "eq", ty, &[ty]);
317 // take the argument by reference
318 let region_scope = self.topmost_scope();
319 let region = self.hir.tcx().mk_region(ty::ReScope(region_scope));
320 let tam = ty::TypeAndMut {
322 mutbl: Mutability::MutImmutable,
324 let ref_ty = self.hir.tcx().mk_ref(region, tam);
326 // let lhs_ref_place = &lhs;
327 let ref_rvalue = Rvalue::Ref(region, BorrowKind::Shared, place.clone());
328 let lhs_ref_place = self.temp(ref_ty, test.span);
329 self.cfg.push_assign(block, source_info, &lhs_ref_place, ref_rvalue);
330 let val = Operand::Move(lhs_ref_place);
332 // let rhs_place = rhs;
333 let rhs_place = self.temp(ty, test.span);
334 self.cfg.push_assign(block, source_info, &rhs_place, Rvalue::Use(expect));
336 // let rhs_ref_place = &rhs_place;
337 let ref_rvalue = Rvalue::Ref(region, BorrowKind::Shared, rhs_place);
338 let rhs_ref_place = self.temp(ref_ty, test.span);
339 self.cfg.push_assign(block, source_info, &rhs_ref_place, ref_rvalue);
340 let expect = Operand::Move(rhs_ref_place);
342 let bool_ty = self.hir.bool_ty();
343 let eq_result = self.temp(bool_ty, test.span);
344 let eq_block = self.cfg.start_new_block();
345 let cleanup = self.diverge_cleanup();
346 self.cfg.terminate(block, source_info, TerminatorKind::Call {
347 func: Operand::Constant(box Constant {
352 args: vec![val, expect],
353 destination: Some((eq_result.clone(), eq_block)),
354 cleanup: Some(cleanup),
358 let block = self.cfg.start_new_block();
359 self.cfg.terminate(eq_block, source_info,
360 TerminatorKind::if_(self.hir.tcx(),
361 Operand::Move(eq_result),
365 let block = self.compare(block, fail, test.span, BinOp::Eq, expect, val);
370 TestKind::Range { ref lo, ref hi, ty, ref end } => {
371 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
372 let lo = self.literal_operand(test.span, ty.clone(), lo.clone());
373 let hi = self.literal_operand(test.span, ty.clone(), hi.clone());
374 let val = Operand::Copy(place.clone());
376 let fail = self.cfg.start_new_block();
377 let block = self.compare(block, fail, test.span, BinOp::Le, lo, val.clone());
378 let block = match *end {
379 RangeEnd::Included => self.compare(block, fail, test.span, BinOp::Le, val, hi),
380 RangeEnd::Excluded => self.compare(block, fail, test.span, BinOp::Lt, val, hi),
386 TestKind::Len { len, op } => {
387 let (usize_ty, bool_ty) = (self.hir.usize_ty(), self.hir.bool_ty());
388 let (actual, result) = (self.temp(usize_ty, test.span),
389 self.temp(bool_ty, test.span));
391 // actual = len(place)
392 self.cfg.push_assign(block, source_info,
393 &actual, Rvalue::Len(place.clone()));
396 let expected = self.push_usize(block, source_info, len);
398 // result = actual == expected OR result = actual < expected
399 self.cfg.push_assign(block, source_info, &result,
401 Operand::Move(actual),
402 Operand::Move(expected)));
404 // branch based on result
405 let (false_bb, true_bb) = (self.cfg.start_new_block(),
406 self.cfg.start_new_block());
407 self.cfg.terminate(block, source_info,
408 TerminatorKind::if_(self.hir.tcx(), Operand::Move(result),
410 vec![true_bb, false_bb]
415 fn compare(&mut self,
417 fail_block: BasicBlock,
421 right: Operand<'tcx>) -> BasicBlock {
422 let bool_ty = self.hir.bool_ty();
423 let result = self.temp(bool_ty, span);
425 // result = op(left, right)
426 let source_info = self.source_info(span);
427 self.cfg.push_assign(block, source_info, &result,
428 Rvalue::BinaryOp(op, left, right));
430 // branch based on result
431 let target_block = self.cfg.start_new_block();
432 self.cfg.terminate(block, source_info,
433 TerminatorKind::if_(self.hir.tcx(), Operand::Move(result),
434 target_block, fail_block));
438 /// Given that we are performing `test` against `test_place`,
439 /// this job sorts out what the status of `candidate` will be
440 /// after the test. The `resulting_candidates` vector stores, for
441 /// each possible outcome of `test`, a vector of the candidates
442 /// that will result. This fn should add a (possibly modified)
443 /// clone of candidate into `resulting_candidates` wherever
446 /// So, for example, if this candidate is `x @ Some(P0)` and the
447 /// test is a variant test, then we would add `(x as Option).0 @
448 /// P0` to the `resulting_candidates` entry corresponding to the
451 /// However, in some cases, the test may just not be relevant to
452 /// candidate. For example, suppose we are testing whether `foo.x == 22`,
453 /// but in one match arm we have `Foo { x: _, ... }`... in that case,
454 /// the test for what value `x` has has no particular relevance
455 /// to this candidate. In such cases, this function just returns false
456 /// without doing anything. This is used by the overall `match_candidates`
457 /// algorithm to structure the match as a whole. See `match_candidates` for
460 /// FIXME(#29623). In some cases, we have some tricky choices to
461 /// make. for example, if we are testing that `x == 22`, but the
462 /// candidate is `x @ 13..55`, what should we do? In the event
463 /// that the test is true, we know that the candidate applies, but
464 /// in the event of false, we don't know that it *doesn't*
465 /// apply. For now, we return false, indicate that the test does
466 /// not apply to this candidate, but it might be we can get
467 /// tighter match code if we do something a bit different.
468 pub fn sort_candidate<'pat>(&mut self,
469 test_place: &Place<'tcx>,
471 candidate: &Candidate<'pat, 'tcx>,
472 resulting_candidates: &mut [Vec<Candidate<'pat, 'tcx>>])
474 // Find the match_pair for this place (if any). At present,
475 // afaik, there can be at most one. (In the future, if we
476 // adopted a more general `@` operator, there might be more
477 // than one, but it'd be very unusual to have two sides that
478 // both require tests; you'd expect one side to be simplified
480 let tested_match_pair = candidate.match_pairs.iter()
482 .filter(|&(_, mp)| mp.place == *test_place)
484 let (match_pair_index, match_pair) = match tested_match_pair {
487 // We are not testing this place. Therefore, this
488 // candidate applies to ALL outcomes.
493 match (&test.kind, &*match_pair.pattern.kind) {
494 // If we are performing a variant switch, then this
495 // informs variant patterns, but nothing else.
496 (&TestKind::Switch { adt_def: tested_adt_def, .. },
497 &PatternKind::Variant { adt_def, variant_index, ref subpatterns, .. }) => {
498 assert_eq!(adt_def, tested_adt_def);
500 self.candidate_after_variant_switch(match_pair_index,
505 resulting_candidates[variant_index].push(new_candidate);
508 (&TestKind::Switch { .. }, _) => false,
510 // If we are performing a switch over integers, then this informs integer
511 // equality, but nothing else.
513 // FIXME(#29623) we could use PatternKind::Range to rule
514 // things out here, in some cases.
515 (&TestKind::SwitchInt { switch_ty: _, options: _, ref indices },
516 &PatternKind::Constant { ref value })
517 if is_switch_ty(match_pair.pattern.ty) => {
518 let index = indices[value];
519 let new_candidate = self.candidate_without_match_pair(match_pair_index,
521 resulting_candidates[index].push(new_candidate);
524 (&TestKind::SwitchInt { .. }, _) => false,
527 (&TestKind::Len { len: test_len, op: BinOp::Eq },
528 &PatternKind::Slice { ref prefix, ref slice, ref suffix }) => {
529 let pat_len = (prefix.len() + suffix.len()) as u64;
530 match (test_len.cmp(&pat_len), slice) {
531 (Ordering::Equal, &None) => {
532 // on true, min_len = len = $actual_length,
533 // on false, len != $actual_length
534 resulting_candidates[0].push(
535 self.candidate_after_slice_test(match_pair_index,
543 (Ordering::Less, _) => {
544 // test_len < pat_len. If $actual_len = test_len,
545 // then $actual_len < pat_len and we don't have
547 resulting_candidates[1].push(candidate.clone());
550 (Ordering::Equal, &Some(_)) | (Ordering::Greater, &Some(_)) => {
551 // This can match both if $actual_len = test_len >= pat_len,
552 // and if $actual_len > test_len. We can't advance.
555 (Ordering::Greater, &None) => {
556 // test_len != pat_len, so if $actual_len = test_len, then
557 // $actual_len != pat_len.
558 resulting_candidates[1].push(candidate.clone());
564 (&TestKind::Len { len: test_len, op: BinOp::Ge },
565 &PatternKind::Slice { ref prefix, ref slice, ref suffix }) => {
566 // the test is `$actual_len >= test_len`
567 let pat_len = (prefix.len() + suffix.len()) as u64;
568 match (test_len.cmp(&pat_len), slice) {
569 (Ordering::Equal, &Some(_)) => {
570 // $actual_len >= test_len = pat_len,
572 resulting_candidates[0].push(
573 self.candidate_after_slice_test(match_pair_index,
581 (Ordering::Less, _) | (Ordering::Equal, &None) => {
582 // test_len <= pat_len. If $actual_len < test_len,
583 // then it is also < pat_len, so the test passing is
584 // necessary (but insufficient).
585 resulting_candidates[0].push(candidate.clone());
588 (Ordering::Greater, &None) => {
589 // test_len > pat_len. If $actual_len >= test_len > pat_len,
590 // then we know we won't have a match.
591 resulting_candidates[1].push(candidate.clone());
594 (Ordering::Greater, &Some(_)) => {
595 // test_len < pat_len, and is therefore less
596 // strict. This can still go both ways.
602 (&TestKind::Eq { .. }, _) |
603 (&TestKind::Range { .. }, _) |
604 (&TestKind::Len { .. }, _) => {
605 // These are all binary tests.
607 // FIXME(#29623) we can be more clever here
608 let pattern_test = self.test(&match_pair);
609 if pattern_test.kind == test.kind {
610 let new_candidate = self.candidate_without_match_pair(match_pair_index,
612 resulting_candidates[0].push(new_candidate);
621 fn candidate_without_match_pair<'pat>(&mut self,
622 match_pair_index: usize,
623 candidate: &Candidate<'pat, 'tcx>)
624 -> Candidate<'pat, 'tcx> {
625 let other_match_pairs =
626 candidate.match_pairs.iter()
628 .filter(|&(index, _)| index != match_pair_index)
629 .map(|(_, mp)| mp.clone())
632 span: candidate.span,
633 match_pairs: other_match_pairs,
634 bindings: candidate.bindings.clone(),
635 guard: candidate.guard.clone(),
636 arm_index: candidate.arm_index,
637 pre_binding_block: candidate.pre_binding_block,
638 next_candidate_pre_binding_block: candidate.next_candidate_pre_binding_block,
642 fn candidate_after_slice_test<'pat>(&mut self,
643 match_pair_index: usize,
644 candidate: &Candidate<'pat, 'tcx>,
645 prefix: &'pat [Pattern<'tcx>],
646 opt_slice: Option<&'pat Pattern<'tcx>>,
647 suffix: &'pat [Pattern<'tcx>])
648 -> Candidate<'pat, 'tcx> {
649 let mut new_candidate =
650 self.candidate_without_match_pair(match_pair_index, candidate);
651 self.prefix_slice_suffix(
652 &mut new_candidate.match_pairs,
653 &candidate.match_pairs[match_pair_index].place,
661 fn candidate_after_variant_switch<'pat>(&mut self,
662 match_pair_index: usize,
663 adt_def: &'tcx ty::AdtDef,
664 variant_index: usize,
665 subpatterns: &'pat [FieldPattern<'tcx>],
666 candidate: &Candidate<'pat, 'tcx>)
667 -> Candidate<'pat, 'tcx> {
668 let match_pair = &candidate.match_pairs[match_pair_index];
670 // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
671 // we want to create a set of derived match-patterns like
672 // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
673 let elem = ProjectionElem::Downcast(adt_def, variant_index);
674 let downcast_place = match_pair.place.clone().elem(elem); // `(x as Variant)`
675 let consequent_match_pairs =
678 // e.g., `(x as Variant).0`
679 let place = downcast_place.clone().field(subpattern.field,
680 subpattern.pattern.ty);
681 // e.g., `(x as Variant).0 @ P1`
682 MatchPair::new(place, &subpattern.pattern)
685 // In addition, we need all the other match pairs from the old candidate.
686 let other_match_pairs =
687 candidate.match_pairs.iter()
689 .filter(|&(index, _)| index != match_pair_index)
690 .map(|(_, mp)| mp.clone());
692 let all_match_pairs = consequent_match_pairs.chain(other_match_pairs).collect();
695 span: candidate.span,
696 match_pairs: all_match_pairs,
697 bindings: candidate.bindings.clone(),
698 guard: candidate.guard.clone(),
699 arm_index: candidate.arm_index,
700 pre_binding_block: candidate.pre_binding_block,
701 next_candidate_pre_binding_block: candidate.next_candidate_pre_binding_block,
705 fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
706 span_bug!(match_pair.pattern.span,
707 "simplifyable pattern found: {:?}",
712 fn is_switch_ty<'tcx>(ty: Ty<'tcx>) -> bool {
713 ty.is_integral() || ty.is_char() || ty.is_bool()