// Testing candidates // // After candidates have been simplified, the only match pairs that // remain are those that require some sort of test. The functions here // identify what tests are needed, perform the tests, and then filter // the candidates based on the result. use crate::build::expr::as_place::PlaceBuilder; use crate::build::matches::{Candidate, MatchPair, Test, TestKind}; use crate::build::Builder; use crate::thir::pattern::compare_const_vals; use rustc_data_structures::fx::FxIndexMap; use rustc_hir::{LangItem, RangeEnd}; use rustc_index::bit_set::BitSet; use rustc_middle::mir::*; use rustc_middle::thir::*; use rustc_middle::ty::util::IntTypeExt; use rustc_middle::ty::GenericArg; use rustc_middle::ty::{self, adjustment::PointerCast, Ty, TyCtxt}; use rustc_span::def_id::DefId; use rustc_span::symbol::{sym, Symbol}; use rustc_span::Span; use rustc_target::abi::VariantIdx; use std::cmp::Ordering; impl<'a, 'tcx> Builder<'a, 'tcx> { /// Identifies what test is needed to decide if `match_pair` is applicable. /// /// It is a bug to call this with a not-fully-simplified pattern. pub(super) fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> { match match_pair.pattern.kind { PatKind::Variant { adt_def, substs: _, variant_index: _, subpatterns: _ } => Test { span: match_pair.pattern.span, kind: TestKind::Switch { adt_def, variants: BitSet::new_empty(adt_def.variants().len()), }, }, PatKind::Constant { .. } if is_switch_ty(match_pair.pattern.ty) => { // For integers, we use a `SwitchInt` match, which allows // us to handle more cases. Test { span: match_pair.pattern.span, kind: TestKind::SwitchInt { switch_ty: match_pair.pattern.ty, // these maps are empty to start; cases are // added below in add_cases_to_switch options: Default::default(), }, } } PatKind::Constant { value } => Test { span: match_pair.pattern.span, kind: TestKind::Eq { value, ty: match_pair.pattern.ty }, }, PatKind::Range(ref range) => { assert_eq!(range.lo.ty(), match_pair.pattern.ty); assert_eq!(range.hi.ty(), match_pair.pattern.ty); Test { span: match_pair.pattern.span, kind: TestKind::Range(range.clone()) } } PatKind::Slice { ref prefix, ref slice, ref suffix } => { let len = prefix.len() + suffix.len(); let op = if slice.is_some() { BinOp::Ge } else { BinOp::Eq }; Test { span: match_pair.pattern.span, kind: TestKind::Len { len: len as u64, op } } } PatKind::Or { .. } => bug!("or-patterns should have already been handled"), PatKind::AscribeUserType { .. } | PatKind::Array { .. } | PatKind::Wild | PatKind::Binding { .. } | PatKind::Leaf { .. } | PatKind::Deref { .. } => self.error_simplifyable(match_pair), } } pub(super) fn add_cases_to_switch<'pat>( &mut self, test_place: &PlaceBuilder<'tcx>, candidate: &Candidate<'pat, 'tcx>, switch_ty: Ty<'tcx>, options: &mut FxIndexMap, u128>, ) -> bool { let Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else { return false; }; match match_pair.pattern.kind { PatKind::Constant { value } => { options .entry(value) .or_insert_with(|| value.eval_bits(self.tcx, self.param_env, switch_ty)); true } PatKind::Variant { .. } => { panic!("you should have called add_variants_to_switch instead!"); } PatKind::Range(ref range) => { // Check that none of the switch values are in the range. self.values_not_contained_in_range(&*range, options).unwrap_or(false) } PatKind::Slice { .. } | PatKind::Array { .. } | PatKind::Wild | PatKind::Or { .. } | PatKind::Binding { .. } | PatKind::AscribeUserType { .. } | PatKind::Leaf { .. } | PatKind::Deref { .. } => { // don't know how to add these patterns to a switch false } } } pub(super) fn add_variants_to_switch<'pat>( &mut self, test_place: &PlaceBuilder<'tcx>, candidate: &Candidate<'pat, 'tcx>, variants: &mut BitSet, ) -> bool { let Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else { return false; }; match match_pair.pattern.kind { PatKind::Variant { adt_def: _, variant_index, .. } => { // We have a pattern testing for variant `variant_index` // set the corresponding index to true variants.insert(variant_index); true } _ => { // don't know how to add these patterns to a switch false } } } #[instrument(skip(self, make_target_blocks, place_builder), level = "debug")] pub(super) fn perform_test( &mut self, match_start_span: Span, scrutinee_span: Span, block: BasicBlock, place_builder: &PlaceBuilder<'tcx>, test: &Test<'tcx>, make_target_blocks: impl FnOnce(&mut Self) -> Vec, ) { let place = place_builder.to_place(self); let place_ty = place.ty(&self.local_decls, self.tcx); debug!(?place, ?place_ty,); let source_info = self.source_info(test.span); match test.kind { TestKind::Switch { adt_def, ref variants } => { let target_blocks = make_target_blocks(self); // Variants is a BitVec of indexes into adt_def.variants. let num_enum_variants = adt_def.variants().len(); debug_assert_eq!(target_blocks.len(), num_enum_variants + 1); let otherwise_block = *target_blocks.last().unwrap(); let tcx = self.tcx; let switch_targets = SwitchTargets::new( adt_def.discriminants(tcx).filter_map(|(idx, discr)| { if variants.contains(idx) { debug_assert_ne!( target_blocks[idx.index()], otherwise_block, "no canididates for tested discriminant: {:?}", discr, ); Some((discr.val, target_blocks[idx.index()])) } else { debug_assert_eq!( target_blocks[idx.index()], otherwise_block, "found canididates for untested discriminant: {:?}", discr, ); None } }), otherwise_block, ); debug!("num_enum_variants: {}, variants: {:?}", num_enum_variants, variants); let discr_ty = adt_def.repr().discr_type().to_ty(tcx); let discr = self.temp(discr_ty, test.span); self.cfg.push_assign( block, self.source_info(scrutinee_span), discr, Rvalue::Discriminant(place), ); self.cfg.terminate( block, self.source_info(match_start_span), TerminatorKind::SwitchInt { discr: Operand::Move(discr), targets: switch_targets, }, ); } TestKind::SwitchInt { switch_ty, ref options } => { let target_blocks = make_target_blocks(self); let terminator = if *switch_ty.kind() == ty::Bool { assert!(!options.is_empty() && options.len() <= 2); let [first_bb, second_bb] = *target_blocks else { bug!("`TestKind::SwitchInt` on `bool` should have two targets") }; let (true_bb, false_bb) = match options[0] { 1 => (first_bb, second_bb), 0 => (second_bb, first_bb), v => span_bug!(test.span, "expected boolean value but got {:?}", v), }; TerminatorKind::if_(Operand::Copy(place), true_bb, false_bb) } else { // The switch may be inexhaustive so we have a catch all block debug_assert_eq!(options.len() + 1, target_blocks.len()); let otherwise_block = *target_blocks.last().unwrap(); let switch_targets = SwitchTargets::new( options.values().copied().zip(target_blocks), otherwise_block, ); TerminatorKind::SwitchInt { discr: Operand::Copy(place), targets: switch_targets, } }; self.cfg.terminate(block, self.source_info(match_start_span), terminator); } TestKind::Eq { value, ty } => { let tcx = self.tcx; if let ty::Adt(def, _) = ty.kind() && Some(def.did()) == tcx.lang_items().string() { if !tcx.features().string_deref_patterns { bug!("matching on `String` went through without enabling string_deref_patterns"); } let re_erased = tcx.lifetimes.re_erased; let ref_string = self.temp(tcx.mk_imm_ref(re_erased, ty), test.span); let ref_str_ty = tcx.mk_imm_ref(re_erased, tcx.types.str_); let ref_str = self.temp(ref_str_ty, test.span); let deref = tcx.require_lang_item(LangItem::Deref, None); let method = trait_method(tcx, deref, sym::deref, [ty]); let eq_block = self.cfg.start_new_block(); self.cfg.push_assign(block, source_info, ref_string, Rvalue::Ref(re_erased, BorrowKind::Shared, place)); self.cfg.terminate( block, source_info, TerminatorKind::Call { func: Operand::Constant(Box::new(Constant { span: test.span, user_ty: None, literal: method, })), args: vec![Operand::Move(ref_string)], destination: ref_str, target: Some(eq_block), cleanup: None, from_hir_call: false, fn_span: source_info.span } ); self.non_scalar_compare(eq_block, make_target_blocks, source_info, value, ref_str, ref_str_ty); return; } if !ty.is_scalar() { // Use `PartialEq::eq` instead of `BinOp::Eq` // (the binop can only handle primitives) self.non_scalar_compare( block, make_target_blocks, source_info, value, place, ty, ); } else if let [success, fail] = *make_target_blocks(self) { assert_eq!(value.ty(), ty); let expect = self.literal_operand(test.span, value); let val = Operand::Copy(place); self.compare(block, success, fail, source_info, BinOp::Eq, expect, val); } else { bug!("`TestKind::Eq` should have two target blocks"); } } TestKind::Range(box PatRange { lo, hi, ref end }) => { let lower_bound_success = self.cfg.start_new_block(); let target_blocks = make_target_blocks(self); // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons. let lo = self.literal_operand(test.span, lo); let hi = self.literal_operand(test.span, hi); let val = Operand::Copy(place); let [success, fail] = *target_blocks else { bug!("`TestKind::Range` should have two target blocks"); }; self.compare( block, lower_bound_success, fail, source_info, BinOp::Le, lo, val.clone(), ); let op = match *end { RangeEnd::Included => BinOp::Le, RangeEnd::Excluded => BinOp::Lt, }; self.compare(lower_bound_success, success, fail, source_info, op, val, hi); } TestKind::Len { len, op } => { let target_blocks = make_target_blocks(self); let usize_ty = self.tcx.types.usize; let actual = self.temp(usize_ty, test.span); // actual = len(place) self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place)); // expected = let expected = self.push_usize(block, source_info, len); let [true_bb, false_bb] = *target_blocks else { bug!("`TestKind::Len` should have two target blocks"); }; // result = actual == expected OR result = actual < expected // branch based on result self.compare( block, true_bb, false_bb, source_info, op, Operand::Move(actual), Operand::Move(expected), ); } } } /// Compare using the provided built-in comparison operator fn compare( &mut self, block: BasicBlock, success_block: BasicBlock, fail_block: BasicBlock, source_info: SourceInfo, op: BinOp, left: Operand<'tcx>, right: Operand<'tcx>, ) { let bool_ty = self.tcx.types.bool; let result = self.temp(bool_ty, source_info.span); // result = op(left, right) self.cfg.push_assign( block, source_info, result, Rvalue::BinaryOp(op, Box::new((left, right))), ); // branch based on result self.cfg.terminate( block, source_info, TerminatorKind::if_(Operand::Move(result), success_block, fail_block), ); } /// Compare two `&T` values using `::eq` fn non_scalar_compare( &mut self, block: BasicBlock, make_target_blocks: impl FnOnce(&mut Self) -> Vec, source_info: SourceInfo, value: ConstantKind<'tcx>, place: Place<'tcx>, mut ty: Ty<'tcx>, ) { let mut expect = self.literal_operand(source_info.span, value); let mut val = Operand::Copy(place); // If we're using `b"..."` as a pattern, we need to insert an // unsizing coercion, as the byte string has the type `&[u8; N]`. // // We want to do this even when the scrutinee is a reference to an // array, so we can call `<[u8]>::eq` rather than having to find an // `<[u8; N]>::eq`. let unsize = |ty: Ty<'tcx>| match ty.kind() { ty::Ref(region, rty, _) => match rty.kind() { ty::Array(inner_ty, n) => Some((region, inner_ty, n)), _ => None, }, _ => None, }; let opt_ref_ty = unsize(ty); let opt_ref_test_ty = unsize(value.ty()); match (opt_ref_ty, opt_ref_test_ty) { // nothing to do, neither is an array (None, None) => {} (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => { let tcx = self.tcx; // make both a slice ty = tcx.mk_imm_ref(*region, tcx.mk_slice(*elem_ty)); if opt_ref_ty.is_some() { let temp = self.temp(ty, source_info.span); self.cfg.push_assign( block, source_info, temp, Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty), ); val = Operand::Move(temp); } if opt_ref_test_ty.is_some() { let slice = self.temp(ty, source_info.span); self.cfg.push_assign( block, source_info, slice, Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty), ); expect = Operand::Move(slice); } } } let ty::Ref(_, deref_ty, _) = *ty.kind() else { bug!("non_scalar_compare called on non-reference type: {}", ty); }; let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, Some(source_info.span)); let method = trait_method(self.tcx, eq_def_id, sym::eq, [deref_ty, deref_ty]); let bool_ty = self.tcx.types.bool; let eq_result = self.temp(bool_ty, source_info.span); let eq_block = self.cfg.start_new_block(); self.cfg.terminate( block, source_info, TerminatorKind::Call { func: Operand::Constant(Box::new(Constant { span: source_info.span, // FIXME(#54571): This constant comes from user input (a // constant in a pattern). Are there forms where users can add // type annotations here? For example, an associated constant? // Need to experiment. user_ty: None, literal: method, })), args: vec![val, expect], destination: eq_result, target: Some(eq_block), cleanup: None, from_hir_call: false, fn_span: source_info.span, }, ); self.diverge_from(block); let [success_block, fail_block] = *make_target_blocks(self) else { bug!("`TestKind::Eq` should have two target blocks") }; // check the result self.cfg.terminate( eq_block, source_info, TerminatorKind::if_(Operand::Move(eq_result), success_block, fail_block), ); } /// Given that we are performing `test` against `test_place`, this job /// sorts out what the status of `candidate` will be after the test. See /// `test_candidates` for the usage of this function. The returned index is /// the index that this candidate should be placed in the /// `target_candidates` vec. The candidate may be modified to update its /// `match_pairs`. /// /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is /// a variant test, then we would modify the candidate to be `(x as /// Option).0 @ P0` and return the index corresponding to the variant /// `Some`. /// /// However, in some cases, the test may just not be relevant to candidate. /// For example, suppose we are testing whether `foo.x == 22`, but in one /// match arm we have `Foo { x: _, ... }`... in that case, the test for /// what value `x` has has no particular relevance to this candidate. In /// such cases, this function just returns None without doing anything. /// This is used by the overall `match_candidates` algorithm to structure /// the match as a whole. See `match_candidates` for more details. /// /// FIXME(#29623). In some cases, we have some tricky choices to make. for /// example, if we are testing that `x == 22`, but the candidate is `x @ /// 13..55`, what should we do? In the event that the test is true, we know /// that the candidate applies, but in the event of false, we don't know /// that it *doesn't* apply. For now, we return false, indicate that the /// test does not apply to this candidate, but it might be we can get /// tighter match code if we do something a bit different. pub(super) fn sort_candidate<'pat>( &mut self, test_place: &PlaceBuilder<'tcx>, test: &Test<'tcx>, candidate: &mut Candidate<'pat, 'tcx>, ) -> Option { // Find the match_pair for this place (if any). At present, // afaik, there can be at most one. (In the future, if we // adopted a more general `@` operator, there might be more // than one, but it'd be very unusual to have two sides that // both require tests; you'd expect one side to be simplified // away.) let (match_pair_index, match_pair) = candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?; match (&test.kind, &match_pair.pattern.kind) { // If we are performing a variant switch, then this // informs variant patterns, but nothing else. ( &TestKind::Switch { adt_def: tested_adt_def, .. }, &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. }, ) => { assert_eq!(adt_def, tested_adt_def); self.candidate_after_variant_switch( match_pair_index, adt_def, variant_index, subpatterns, candidate, ); Some(variant_index.as_usize()) } (&TestKind::Switch { .. }, _) => None, // If we are performing a switch over integers, then this informs integer // equality, but nothing else. // // FIXME(#29623) we could use PatKind::Range to rule // things out here, in some cases. (TestKind::SwitchInt { switch_ty: _, options }, PatKind::Constant { value }) if is_switch_ty(match_pair.pattern.ty) => { let index = options.get_index_of(value).unwrap(); self.candidate_without_match_pair(match_pair_index, candidate); Some(index) } (TestKind::SwitchInt { switch_ty: _, options }, PatKind::Range(range)) => { let not_contained = self.values_not_contained_in_range(&*range, options).unwrap_or(false); not_contained.then(|| { // No switch values are contained in the pattern range, // so the pattern can be matched only if this test fails. options.len() }) } (&TestKind::SwitchInt { .. }, _) => None, ( &TestKind::Len { len: test_len, op: BinOp::Eq }, PatKind::Slice { prefix, slice, suffix }, ) => { let pat_len = (prefix.len() + suffix.len()) as u64; match (test_len.cmp(&pat_len), slice) { (Ordering::Equal, &None) => { // on true, min_len = len = $actual_length, // on false, len != $actual_length self.candidate_after_slice_test( match_pair_index, candidate, prefix, slice, suffix, ); Some(0) } (Ordering::Less, _) => { // test_len < pat_len. If $actual_len = test_len, // then $actual_len < pat_len and we don't have // enough elements. Some(1) } (Ordering::Equal | Ordering::Greater, &Some(_)) => { // This can match both if $actual_len = test_len >= pat_len, // and if $actual_len > test_len. We can't advance. None } (Ordering::Greater, &None) => { // test_len != pat_len, so if $actual_len = test_len, then // $actual_len != pat_len. Some(1) } } } ( &TestKind::Len { len: test_len, op: BinOp::Ge }, PatKind::Slice { prefix, slice, suffix }, ) => { // the test is `$actual_len >= test_len` let pat_len = (prefix.len() + suffix.len()) as u64; match (test_len.cmp(&pat_len), slice) { (Ordering::Equal, &Some(_)) => { // $actual_len >= test_len = pat_len, // so we can match. self.candidate_after_slice_test( match_pair_index, candidate, prefix, slice, suffix, ); Some(0) } (Ordering::Less, _) | (Ordering::Equal, &None) => { // test_len <= pat_len. If $actual_len < test_len, // then it is also < pat_len, so the test passing is // necessary (but insufficient). Some(0) } (Ordering::Greater, &None) => { // test_len > pat_len. If $actual_len >= test_len > pat_len, // then we know we won't have a match. Some(1) } (Ordering::Greater, &Some(_)) => { // test_len < pat_len, and is therefore less // strict. This can still go both ways. None } } } (TestKind::Range(test), PatKind::Range(pat)) => { use std::cmp::Ordering::*; if test == pat { self.candidate_without_match_pair(match_pair_index, candidate); return Some(0); } // For performance, it's important to only do the second // `compare_const_vals` if necessary. let no_overlap = if matches!( (compare_const_vals(self.tcx, test.hi, pat.lo, self.param_env)?, test.end), (Less, _) | (Equal, RangeEnd::Excluded) // test < pat ) || matches!( (compare_const_vals(self.tcx, test.lo, pat.hi, self.param_env)?, pat.end), (Greater, _) | (Equal, RangeEnd::Excluded) // test > pat ) { Some(1) } else { None }; // If the testing range does not overlap with pattern range, // the pattern can be matched only if this test fails. no_overlap } (TestKind::Range(range), &PatKind::Constant { value }) => { if let Some(false) = self.const_range_contains(&*range, value) { // `value` is not contained in the testing range, // so `value` can be matched only if this test fails. Some(1) } else { None } } (&TestKind::Range { .. }, _) => None, (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => { // The call to `self.test(&match_pair)` below is not actually used to generate any // MIR. Instead, we just want to compare with `test` (the parameter of the method) // to see if it is the same. // // However, at this point we can still encounter or-patterns that were extracted // from previous calls to `sort_candidate`, so we need to manually address that // case to avoid panicking in `self.test()`. if let PatKind::Or { .. } = &match_pair.pattern.kind { return None; } // These are all binary tests. // // FIXME(#29623) we can be more clever here let pattern_test = self.test(&match_pair); if pattern_test.kind == test.kind { self.candidate_without_match_pair(match_pair_index, candidate); Some(0) } else { None } } } } fn candidate_without_match_pair( &mut self, match_pair_index: usize, candidate: &mut Candidate<'_, 'tcx>, ) { candidate.match_pairs.remove(match_pair_index); } fn candidate_after_slice_test<'pat>( &mut self, match_pair_index: usize, candidate: &mut Candidate<'pat, 'tcx>, prefix: &'pat [Box>], opt_slice: &'pat Option>>, suffix: &'pat [Box>], ) { let removed_place = candidate.match_pairs.remove(match_pair_index).place; self.prefix_slice_suffix( &mut candidate.match_pairs, &removed_place, prefix, opt_slice, suffix, ); } fn candidate_after_variant_switch<'pat>( &mut self, match_pair_index: usize, adt_def: ty::AdtDef<'tcx>, variant_index: VariantIdx, subpatterns: &'pat [FieldPat<'tcx>], candidate: &mut Candidate<'pat, 'tcx>, ) { let match_pair = candidate.match_pairs.remove(match_pair_index); // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`, // we want to create a set of derived match-patterns like // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`. let downcast_place = match_pair.place.downcast(adt_def, variant_index); // `(x as Variant)` let consequent_match_pairs = subpatterns.iter().map(|subpattern| { // e.g., `(x as Variant).0` let place = downcast_place .clone_project(PlaceElem::Field(subpattern.field, subpattern.pattern.ty)); // e.g., `(x as Variant).0 @ P1` MatchPair::new(place, &subpattern.pattern, self) }); candidate.match_pairs.extend(consequent_match_pairs); } fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! { span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern) } fn const_range_contains( &self, range: &PatRange<'tcx>, value: ConstantKind<'tcx>, ) -> Option { use std::cmp::Ordering::*; // For performance, it's important to only do the second // `compare_const_vals` if necessary. Some( matches!(compare_const_vals(self.tcx, range.lo, value, self.param_env)?, Less | Equal) && matches!( (compare_const_vals(self.tcx, value, range.hi, self.param_env)?, range.end), (Less, _) | (Equal, RangeEnd::Included) ), ) } fn values_not_contained_in_range( &self, range: &PatRange<'tcx>, options: &FxIndexMap, u128>, ) -> Option { for &val in options.keys() { if self.const_range_contains(range, val)? { return Some(false); } } Some(true) } } impl Test<'_> { pub(super) fn targets(&self) -> usize { match self.kind { TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2, TestKind::Switch { adt_def, .. } => { // While the switch that we generate doesn't test for all // variants, we have a target for each variant and the // otherwise case, and we make sure that all of the cases not // specified have the same block. adt_def.variants().len() + 1 } TestKind::SwitchInt { switch_ty, ref options, .. } => { if switch_ty.is_bool() { // `bool` is special cased in `perform_test` to always // branch to two blocks. 2 } else { options.len() + 1 } } } } } fn is_switch_ty(ty: Ty<'_>) -> bool { ty.is_integral() || ty.is_char() || ty.is_bool() } fn trait_method<'tcx>( tcx: TyCtxt<'tcx>, trait_def_id: DefId, method_name: Symbol, substs: impl IntoIterator>>, ) -> ConstantKind<'tcx> { // The unhygienic comparison here is acceptable because this is only // used on known traits. let item = tcx .associated_items(trait_def_id) .filter_by_name_unhygienic(method_name) .find(|item| item.kind == ty::AssocKind::Fn) .expect("trait method not found"); let method_ty = tcx.mk_fn_def(item.def_id, substs); ConstantKind::zero_sized(method_ty) }