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 } => {
125 let switch_ty = ty::ParamEnv::empty().and(switch_ty);
128 options.push(value.unwrap_bits(self.hir.tcx(), switch_ty));
133 PatternKind::Variant { .. } => {
134 panic!("you should have called add_variants_to_switch instead!");
136 PatternKind::Range { .. } |
137 PatternKind::Slice { .. } |
138 PatternKind::Array { .. } |
140 PatternKind::Binding { .. } |
141 PatternKind::Leaf { .. } |
142 PatternKind::Deref { .. } => {
143 // don't know how to add these patterns to a switch
149 pub fn add_variants_to_switch<'pat>(&mut self,
150 test_place: &Place<'tcx>,
151 candidate: &Candidate<'pat, 'tcx>,
152 variants: &mut BitVector)
155 let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
156 Some(match_pair) => match_pair,
157 _ => { return false; }
160 match *match_pair.pattern.kind {
161 PatternKind::Variant { adt_def: _ , variant_index, .. } => {
162 // We have a pattern testing for variant `variant_index`
163 // set the corresponding index to true
164 variants.insert(variant_index);
168 // don't know how to add these patterns to a switch
174 /// Generates the code to perform a test.
175 pub fn perform_test(&mut self,
180 debug!("perform_test({:?}, {:?}: {:?}, {:?})",
183 place.ty(&self.local_decls, self.hir.tcx()),
185 let source_info = self.source_info(test.span);
187 TestKind::Switch { adt_def, ref variants } => {
188 // Variants is a BitVec of indexes into adt_def.variants.
189 let num_enum_variants = adt_def.variants.len();
190 let used_variants = variants.count();
191 let mut otherwise_block = None;
192 let mut target_blocks = Vec::with_capacity(num_enum_variants);
193 let mut targets = Vec::with_capacity(used_variants + 1);
194 let mut values = Vec::with_capacity(used_variants);
195 let tcx = self.hir.tcx();
196 for (idx, discr) in adt_def.discriminants(tcx).enumerate() {
197 target_blocks.push(if variants.contains(idx) {
198 values.push(discr.val);
199 targets.push(self.cfg.start_new_block());
200 *targets.last().unwrap()
202 if otherwise_block.is_none() {
203 otherwise_block = Some(self.cfg.start_new_block());
205 otherwise_block.unwrap()
208 if let Some(otherwise_block) = otherwise_block {
209 targets.push(otherwise_block);
211 targets.push(self.unreachable_block());
213 debug!("num_enum_variants: {}, tested variants: {:?}, variants: {:?}",
214 num_enum_variants, values, variants);
215 let discr_ty = adt_def.repr.discr_type().to_ty(tcx);
216 let discr = self.temp(discr_ty, test.span);
217 self.cfg.push_assign(block, source_info, &discr,
218 Rvalue::Discriminant(place.clone()));
219 assert_eq!(values.len() + 1, targets.len());
220 self.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
221 discr: Operand::Move(discr),
223 values: From::from(values),
229 TestKind::SwitchInt { switch_ty, ref options, indices: _ } => {
230 let (ret, terminator) = if switch_ty.sty == ty::TyBool {
231 assert!(options.len() > 0 && options.len() <= 2);
232 let (true_bb, false_bb) = (self.cfg.start_new_block(),
233 self.cfg.start_new_block());
234 let ret = match options[0] {
235 1 => vec![true_bb, false_bb],
236 0 => vec![false_bb, true_bb],
237 v => span_bug!(test.span, "expected boolean value but got {:?}", v)
239 (ret, TerminatorKind::if_(self.hir.tcx(), Operand::Copy(place.clone()),
242 // The switch may be inexhaustive so we
243 // add a catch all block
244 let otherwise = self.cfg.start_new_block();
245 let targets: Vec<_> =
247 .map(|_| self.cfg.start_new_block())
248 .chain(Some(otherwise))
250 (targets.clone(), TerminatorKind::SwitchInt {
251 discr: Operand::Copy(place.clone()),
253 values: options.clone().into(),
257 self.cfg.terminate(block, source_info, terminator);
261 TestKind::Eq { value, mut ty } => {
262 let mut val = Operand::Copy(place.clone());
263 let mut expect = self.literal_operand(test.span, ty, Literal::Value {
266 // Use PartialEq::eq instead of BinOp::Eq
267 // (the binop can only handle primitives)
268 let fail = self.cfg.start_new_block();
270 // If we're using b"..." as a pattern, we need to insert an
271 // unsizing coercion, as the byte string has the type &[u8; N].
273 // We want to do this even when the scrutinee is a reference to an
274 // array, so we can call `<[u8]>::eq` rather than having to find an
276 let unsize = |ty: Ty<'tcx>| match ty.sty {
277 ty::TyRef(region, rty, _) => match rty.sty {
278 ty::TyArray(inner_ty, n) => Some((region, inner_ty, n)),
283 let opt_ref_ty = unsize(ty);
284 let opt_ref_test_ty = unsize(value.ty);
285 let mut place = place.clone();
286 match (opt_ref_ty, opt_ref_test_ty) {
287 // nothing to do, neither is an array
289 (Some((region, elem_ty, _)), _) |
290 (None, Some((region, elem_ty, _))) => {
291 let tcx = self.hir.tcx();
293 ty = tcx.mk_imm_ref(region, tcx.mk_slice(elem_ty));
294 if opt_ref_ty.is_some() {
295 place = self.temp(ty, test.span);
296 self.cfg.push_assign(block, source_info, &place,
297 Rvalue::Cast(CastKind::Unsize, val, ty));
299 if opt_ref_test_ty.is_some() {
300 let array = self.literal_operand(
308 let slice = self.temp(ty, test.span);
309 self.cfg.push_assign(block, source_info, &slice,
310 Rvalue::Cast(CastKind::Unsize, array, ty));
311 expect = Operand::Move(slice);
315 let eq_def_id = self.hir.tcx().lang_items().eq_trait().unwrap();
316 let (mty, method) = self.hir.trait_method(eq_def_id, "eq", ty, &[ty.into()]);
318 // take the argument by reference
319 let region_scope = self.topmost_scope();
320 let region = self.hir.tcx().mk_region(ty::ReScope(region_scope));
321 let tam = ty::TypeAndMut {
323 mutbl: Mutability::MutImmutable,
325 let ref_ty = self.hir.tcx().mk_ref(region, tam);
327 // let lhs_ref_place = &lhs;
328 let ref_rvalue = Rvalue::Ref(region, BorrowKind::Shared, place.clone());
329 let lhs_ref_place = self.temp(ref_ty, test.span);
330 self.cfg.push_assign(block, source_info, &lhs_ref_place, ref_rvalue);
331 let val = Operand::Move(lhs_ref_place);
333 // let rhs_place = rhs;
334 let rhs_place = self.temp(ty, test.span);
335 self.cfg.push_assign(block, source_info, &rhs_place, Rvalue::Use(expect));
337 // let rhs_ref_place = &rhs_place;
338 let ref_rvalue = Rvalue::Ref(region, BorrowKind::Shared, rhs_place);
339 let rhs_ref_place = self.temp(ref_ty, test.span);
340 self.cfg.push_assign(block, source_info, &rhs_ref_place, ref_rvalue);
341 let expect = Operand::Move(rhs_ref_place);
343 let bool_ty = self.hir.bool_ty();
344 let eq_result = self.temp(bool_ty, test.span);
345 let eq_block = self.cfg.start_new_block();
346 let cleanup = self.diverge_cleanup();
347 self.cfg.terminate(block, source_info, TerminatorKind::Call {
348 func: Operand::Constant(box Constant {
353 args: vec![val, expect],
354 destination: Some((eq_result.clone(), eq_block)),
355 cleanup: Some(cleanup),
359 let block = self.cfg.start_new_block();
360 self.cfg.terminate(eq_block, source_info,
361 TerminatorKind::if_(self.hir.tcx(),
362 Operand::Move(eq_result),
366 let block = self.compare(block, fail, test.span, BinOp::Eq, expect, val);
371 TestKind::Range { ref lo, ref hi, ty, ref end } => {
372 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
373 let lo = self.literal_operand(test.span, ty.clone(), lo.clone());
374 let hi = self.literal_operand(test.span, ty.clone(), hi.clone());
375 let val = Operand::Copy(place.clone());
377 let fail = self.cfg.start_new_block();
378 let block = self.compare(block, fail, test.span, BinOp::Le, lo, val.clone());
379 let block = match *end {
380 RangeEnd::Included => self.compare(block, fail, test.span, BinOp::Le, val, hi),
381 RangeEnd::Excluded => self.compare(block, fail, test.span, BinOp::Lt, val, hi),
387 TestKind::Len { len, op } => {
388 let (usize_ty, bool_ty) = (self.hir.usize_ty(), self.hir.bool_ty());
389 let (actual, result) = (self.temp(usize_ty, test.span),
390 self.temp(bool_ty, test.span));
392 // actual = len(place)
393 self.cfg.push_assign(block, source_info,
394 &actual, Rvalue::Len(place.clone()));
397 let expected = self.push_usize(block, source_info, len);
399 // result = actual == expected OR result = actual < expected
400 self.cfg.push_assign(block, source_info, &result,
402 Operand::Move(actual),
403 Operand::Move(expected)));
405 // branch based on result
406 let (false_bb, true_bb) = (self.cfg.start_new_block(),
407 self.cfg.start_new_block());
408 self.cfg.terminate(block, source_info,
409 TerminatorKind::if_(self.hir.tcx(), Operand::Move(result),
411 vec![true_bb, false_bb]
416 fn compare(&mut self,
418 fail_block: BasicBlock,
422 right: Operand<'tcx>) -> BasicBlock {
423 let bool_ty = self.hir.bool_ty();
424 let result = self.temp(bool_ty, span);
426 // result = op(left, right)
427 let source_info = self.source_info(span);
428 self.cfg.push_assign(block, source_info, &result,
429 Rvalue::BinaryOp(op, left, right));
431 // branch based on result
432 let target_block = self.cfg.start_new_block();
433 self.cfg.terminate(block, source_info,
434 TerminatorKind::if_(self.hir.tcx(), Operand::Move(result),
435 target_block, fail_block));
439 /// Given that we are performing `test` against `test_place`,
440 /// this job sorts out what the status of `candidate` will be
441 /// after the test. The `resulting_candidates` vector stores, for
442 /// each possible outcome of `test`, a vector of the candidates
443 /// that will result. This fn should add a (possibly modified)
444 /// clone of candidate into `resulting_candidates` wherever
447 /// So, for example, if this candidate is `x @ Some(P0)` and the
448 /// test is a variant test, then we would add `(x as Option).0 @
449 /// P0` to the `resulting_candidates` entry corresponding to the
452 /// However, in some cases, the test may just not be relevant to
453 /// candidate. For example, suppose we are testing whether `foo.x == 22`,
454 /// but in one match arm we have `Foo { x: _, ... }`... in that case,
455 /// the test for what value `x` has has no particular relevance
456 /// to this candidate. In such cases, this function just returns false
457 /// without doing anything. This is used by the overall `match_candidates`
458 /// algorithm to structure the match as a whole. See `match_candidates` for
461 /// FIXME(#29623). In some cases, we have some tricky choices to
462 /// make. for example, if we are testing that `x == 22`, but the
463 /// candidate is `x @ 13..55`, what should we do? In the event
464 /// that the test is true, we know that the candidate applies, but
465 /// in the event of false, we don't know that it *doesn't*
466 /// apply. For now, we return false, indicate that the test does
467 /// not apply to this candidate, but it might be we can get
468 /// tighter match code if we do something a bit different.
469 pub fn sort_candidate<'pat>(&mut self,
470 test_place: &Place<'tcx>,
472 candidate: &Candidate<'pat, 'tcx>,
473 resulting_candidates: &mut [Vec<Candidate<'pat, 'tcx>>])
475 // Find the match_pair for this place (if any). At present,
476 // afaik, there can be at most one. (In the future, if we
477 // adopted a more general `@` operator, there might be more
478 // than one, but it'd be very unusual to have two sides that
479 // both require tests; you'd expect one side to be simplified
481 let tested_match_pair = candidate.match_pairs.iter()
483 .filter(|&(_, mp)| mp.place == *test_place)
485 let (match_pair_index, match_pair) = match tested_match_pair {
488 // We are not testing this place. Therefore, this
489 // candidate applies to ALL outcomes.
494 match (&test.kind, &*match_pair.pattern.kind) {
495 // If we are performing a variant switch, then this
496 // informs variant patterns, but nothing else.
497 (&TestKind::Switch { adt_def: tested_adt_def, .. },
498 &PatternKind::Variant { adt_def, variant_index, ref subpatterns, .. }) => {
499 assert_eq!(adt_def, tested_adt_def);
501 self.candidate_after_variant_switch(match_pair_index,
506 resulting_candidates[variant_index].push(new_candidate);
509 (&TestKind::Switch { .. }, _) => false,
511 // If we are performing a switch over integers, then this informs integer
512 // equality, but nothing else.
514 // FIXME(#29623) we could use PatternKind::Range to rule
515 // things out here, in some cases.
516 (&TestKind::SwitchInt { switch_ty: _, options: _, ref indices },
517 &PatternKind::Constant { ref value })
518 if is_switch_ty(match_pair.pattern.ty) => {
519 let index = indices[value];
520 let new_candidate = self.candidate_without_match_pair(match_pair_index,
522 resulting_candidates[index].push(new_candidate);
525 (&TestKind::SwitchInt { .. }, _) => false,
528 (&TestKind::Len { len: test_len, op: BinOp::Eq },
529 &PatternKind::Slice { ref prefix, ref slice, ref suffix }) => {
530 let pat_len = (prefix.len() + suffix.len()) as u64;
531 match (test_len.cmp(&pat_len), slice) {
532 (Ordering::Equal, &None) => {
533 // on true, min_len = len = $actual_length,
534 // on false, len != $actual_length
535 resulting_candidates[0].push(
536 self.candidate_after_slice_test(match_pair_index,
544 (Ordering::Less, _) => {
545 // test_len < pat_len. If $actual_len = test_len,
546 // then $actual_len < pat_len and we don't have
548 resulting_candidates[1].push(candidate.clone());
551 (Ordering::Equal, &Some(_)) | (Ordering::Greater, &Some(_)) => {
552 // This can match both if $actual_len = test_len >= pat_len,
553 // and if $actual_len > test_len. We can't advance.
556 (Ordering::Greater, &None) => {
557 // test_len != pat_len, so if $actual_len = test_len, then
558 // $actual_len != pat_len.
559 resulting_candidates[1].push(candidate.clone());
565 (&TestKind::Len { len: test_len, op: BinOp::Ge },
566 &PatternKind::Slice { ref prefix, ref slice, ref suffix }) => {
567 // the test is `$actual_len >= test_len`
568 let pat_len = (prefix.len() + suffix.len()) as u64;
569 match (test_len.cmp(&pat_len), slice) {
570 (Ordering::Equal, &Some(_)) => {
571 // $actual_len >= test_len = pat_len,
573 resulting_candidates[0].push(
574 self.candidate_after_slice_test(match_pair_index,
582 (Ordering::Less, _) | (Ordering::Equal, &None) => {
583 // test_len <= pat_len. If $actual_len < test_len,
584 // then it is also < pat_len, so the test passing is
585 // necessary (but insufficient).
586 resulting_candidates[0].push(candidate.clone());
589 (Ordering::Greater, &None) => {
590 // test_len > pat_len. If $actual_len >= test_len > pat_len,
591 // then we know we won't have a match.
592 resulting_candidates[1].push(candidate.clone());
595 (Ordering::Greater, &Some(_)) => {
596 // test_len < pat_len, and is therefore less
597 // strict. This can still go both ways.
603 (&TestKind::Eq { .. }, _) |
604 (&TestKind::Range { .. }, _) |
605 (&TestKind::Len { .. }, _) => {
606 // These are all binary tests.
608 // FIXME(#29623) we can be more clever here
609 let pattern_test = self.test(&match_pair);
610 if pattern_test.kind == test.kind {
611 let new_candidate = self.candidate_without_match_pair(match_pair_index,
613 resulting_candidates[0].push(new_candidate);
622 fn candidate_without_match_pair<'pat>(&mut self,
623 match_pair_index: usize,
624 candidate: &Candidate<'pat, 'tcx>)
625 -> Candidate<'pat, 'tcx> {
626 let other_match_pairs =
627 candidate.match_pairs.iter()
629 .filter(|&(index, _)| index != match_pair_index)
630 .map(|(_, mp)| mp.clone())
633 span: candidate.span,
634 match_pairs: other_match_pairs,
635 bindings: candidate.bindings.clone(),
636 guard: candidate.guard.clone(),
637 arm_index: candidate.arm_index,
638 pre_binding_block: candidate.pre_binding_block,
639 next_candidate_pre_binding_block: candidate.next_candidate_pre_binding_block,
643 fn candidate_after_slice_test<'pat>(&mut self,
644 match_pair_index: usize,
645 candidate: &Candidate<'pat, 'tcx>,
646 prefix: &'pat [Pattern<'tcx>],
647 opt_slice: Option<&'pat Pattern<'tcx>>,
648 suffix: &'pat [Pattern<'tcx>])
649 -> Candidate<'pat, 'tcx> {
650 let mut new_candidate =
651 self.candidate_without_match_pair(match_pair_index, candidate);
652 self.prefix_slice_suffix(
653 &mut new_candidate.match_pairs,
654 &candidate.match_pairs[match_pair_index].place,
662 fn candidate_after_variant_switch<'pat>(&mut self,
663 match_pair_index: usize,
664 adt_def: &'tcx ty::AdtDef,
665 variant_index: usize,
666 subpatterns: &'pat [FieldPattern<'tcx>],
667 candidate: &Candidate<'pat, 'tcx>)
668 -> Candidate<'pat, 'tcx> {
669 let match_pair = &candidate.match_pairs[match_pair_index];
671 // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
672 // we want to create a set of derived match-patterns like
673 // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
674 let elem = ProjectionElem::Downcast(adt_def, variant_index);
675 let downcast_place = match_pair.place.clone().elem(elem); // `(x as Variant)`
676 let consequent_match_pairs =
679 // e.g., `(x as Variant).0`
680 let place = downcast_place.clone().field(subpattern.field,
681 subpattern.pattern.ty);
682 // e.g., `(x as Variant).0 @ P1`
683 MatchPair::new(place, &subpattern.pattern)
686 // In addition, we need all the other match pairs from the old candidate.
687 let other_match_pairs =
688 candidate.match_pairs.iter()
690 .filter(|&(index, _)| index != match_pair_index)
691 .map(|(_, mp)| mp.clone());
693 let all_match_pairs = consequent_match_pairs.chain(other_match_pairs).collect();
696 span: candidate.span,
697 match_pairs: all_match_pairs,
698 bindings: candidate.bindings.clone(),
699 guard: candidate.guard.clone(),
700 arm_index: candidate.arm_index,
701 pre_binding_block: candidate.pre_binding_block,
702 next_candidate_pre_binding_block: candidate.next_candidate_pre_binding_block,
706 fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
707 span_bug!(match_pair.pattern.span,
708 "simplifyable pattern found: {:?}",
713 fn is_switch_ty<'tcx>(ty: Ty<'tcx>) -> bool {
714 ty.is_integral() || ty.is_char() || ty.is_bool()