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// 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 std::cmp::Ordering;
use rustc_data_structures::fx::FxIndexMap;
use rustc_hir::{LangItem, RangeEnd};
use rustc_middle::mir::*;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::util::IntTypeExt;
use rustc_middle::ty::{self, GenericArg, Ty, TyCtxt};
use rustc_middle::{bug, span_bug};
use rustc_span::def_id::DefId;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{sym, Symbol};
use rustc_span::{Span, DUMMY_SP};
use tracing::{debug, instrument};
use crate::build::matches::{Candidate, MatchPairTree, Test, TestBranch, TestCase, TestKind};
use crate::build::Builder;
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 pick_test_for_match_pair<'pat>(
&mut self,
match_pair: &MatchPairTree<'pat, 'tcx>,
) -> Test<'tcx> {
let kind = match match_pair.test_case {
TestCase::Variant { adt_def, variant_index: _ } => TestKind::Switch { adt_def },
TestCase::Constant { .. } if match_pair.pattern.ty.is_bool() => TestKind::If,
TestCase::Constant { .. } if is_switch_ty(match_pair.pattern.ty) => TestKind::SwitchInt,
TestCase::Constant { value } => TestKind::Eq { value, ty: match_pair.pattern.ty },
TestCase::Range(range) => {
assert_eq!(range.ty, match_pair.pattern.ty);
TestKind::Range(Box::new(range.clone()))
}
TestCase::Slice { len, variable_length } => {
let op = if variable_length { BinOp::Ge } else { BinOp::Eq };
TestKind::Len { len: len as u64, op }
}
TestCase::Deref { temp, mutability } => TestKind::Deref { temp, mutability },
TestCase::Never => TestKind::Never,
// Or-patterns are not tested directly; instead they are expanded into subcandidates,
// which are then distinguished by testing whatever non-or patterns they contain.
TestCase::Or { .. } => bug!("or-patterns should have already been handled"),
TestCase::Irrefutable { .. } => span_bug!(
match_pair.pattern.span,
"simplifiable pattern found: {:?}",
match_pair.pattern
),
};
Test { span: match_pair.pattern.span, kind }
}
#[instrument(skip(self, target_blocks, place), level = "debug")]
pub(super) fn perform_test(
&mut self,
match_start_span: Span,
scrutinee_span: Span,
block: BasicBlock,
otherwise_block: BasicBlock,
place: Place<'tcx>,
test: &Test<'tcx>,
target_blocks: FxIndexMap<TestBranch<'tcx>, BasicBlock>,
) {
let place_ty = place.ty(&self.local_decls, self.tcx);
debug!(?place, ?place_ty);
let target_block = |branch| target_blocks.get(&branch).copied().unwrap_or(otherwise_block);
let source_info = self.source_info(test.span);
match test.kind {
TestKind::Switch { adt_def } => {
let otherwise_block = target_block(TestBranch::Failure);
let switch_targets = SwitchTargets::new(
adt_def.discriminants(self.tcx).filter_map(|(idx, discr)| {
if let Some(&block) = target_blocks.get(&TestBranch::Variant(idx)) {
Some((discr.val, block))
} else {
None
}
}),
otherwise_block,
);
debug!("num_enum_variants: {}", adt_def.variants().len());
let discr_ty = adt_def.repr().discr_type().to_ty(self.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 => {
// The switch may be inexhaustive so we have a catch-all block
let otherwise_block = target_block(TestBranch::Failure);
let switch_targets = SwitchTargets::new(
target_blocks.iter().filter_map(|(&branch, &block)| {
if let TestBranch::Constant(_, bits) = branch {
Some((bits, block))
} else {
None
}
}),
otherwise_block,
);
let terminator = TerminatorKind::SwitchInt {
discr: Operand::Copy(place),
targets: switch_targets,
};
self.cfg.terminate(block, self.source_info(match_start_span), terminator);
}
TestKind::If => {
let success_block = target_block(TestBranch::Success);
let fail_block = target_block(TestBranch::Failure);
let terminator =
TerminatorKind::if_(Operand::Copy(place), success_block, fail_block);
self.cfg.terminate(block, self.source_info(match_start_span), terminator);
}
TestKind::Eq { value, ty } => {
let tcx = self.tcx;
let success_block = target_block(TestBranch::Success);
let fail_block = target_block(TestBranch::Failure);
if let ty::Adt(def, _) = ty.kind()
&& tcx.is_lang_item(def.did(), LangItem::String)
{
if !tcx.features().string_deref_patterns {
span_bug!(
test.span,
"matching on `String` went through without enabling string_deref_patterns"
);
}
let re_erased = tcx.lifetimes.re_erased;
let ref_str_ty = Ty::new_imm_ref(tcx, re_erased, tcx.types.str_);
let ref_str = self.temp(ref_str_ty, test.span);
let eq_block = self.cfg.start_new_block();
// `let ref_str: &str = <String as Deref>::deref(&place);`
self.call_deref(
block,
eq_block,
place,
Mutability::Not,
ty,
ref_str,
test.span,
);
self.non_scalar_compare(
eq_block,
success_block,
fail_block,
source_info,
value,
ref_str,
ref_str_ty,
);
} else if !ty.is_scalar() {
// Use `PartialEq::eq` instead of `BinOp::Eq`
// (the binop can only handle primitives)
self.non_scalar_compare(
block,
success_block,
fail_block,
source_info,
value,
place,
ty,
);
} else {
assert_eq!(value.ty(), ty);
let expect = self.literal_operand(test.span, value);
let val = Operand::Copy(place);
self.compare(
block,
success_block,
fail_block,
source_info,
BinOp::Eq,
expect,
val,
);
}
}
TestKind::Range(ref range) => {
let success = target_block(TestBranch::Success);
let fail = target_block(TestBranch::Failure);
// Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
let val = Operand::Copy(place);
let intermediate_block = if !range.lo.is_finite() {
block
} else if !range.hi.is_finite() {
success
} else {
self.cfg.start_new_block()
};
if let Some(lo) = range.lo.as_finite() {
let lo = self.literal_operand(test.span, lo);
self.compare(
block,
intermediate_block,
fail,
source_info,
BinOp::Le,
lo,
val.clone(),
);
};
if let Some(hi) = range.hi.as_finite() {
let hi = self.literal_operand(test.span, hi);
let op = match range.end {
RangeEnd::Included => BinOp::Le,
RangeEnd::Excluded => BinOp::Lt,
};
self.compare(intermediate_block, success, fail, source_info, op, val, hi);
}
}
TestKind::Len { len, op } => {
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 = <N>
let expected = self.push_usize(block, source_info, len);
let success_block = target_block(TestBranch::Success);
let fail_block = target_block(TestBranch::Failure);
// result = actual == expected OR result = actual < expected
// branch based on result
self.compare(
block,
success_block,
fail_block,
source_info,
op,
Operand::Move(actual),
Operand::Move(expected),
);
}
TestKind::Deref { temp, mutability } => {
let ty = place_ty.ty;
let target = target_block(TestBranch::Success);
self.call_deref(block, target, place, mutability, ty, temp, test.span);
}
TestKind::Never => {
// Check that the place is initialized.
// FIXME(never_patterns): Also assert validity of the data at `place`.
self.cfg.push_fake_read(
block,
source_info,
FakeReadCause::ForMatchedPlace(None),
place,
);
// A never pattern is only allowed on an uninhabited type, so validity of the data
// implies unreachability.
self.cfg.terminate(block, source_info, TerminatorKind::Unreachable);
}
}
}
/// Perform `let temp = <ty as Deref>::deref(&place)`.
/// or `let temp = <ty as DerefMut>::deref_mut(&mut place)`.
pub(super) fn call_deref(
&mut self,
block: BasicBlock,
target_block: BasicBlock,
place: Place<'tcx>,
mutability: Mutability,
ty: Ty<'tcx>,
temp: Place<'tcx>,
span: Span,
) {
let (trait_item, method) = match mutability {
Mutability::Not => (LangItem::Deref, sym::deref),
Mutability::Mut => (LangItem::DerefMut, sym::deref_mut),
};
let borrow_kind = super::util::ref_pat_borrow_kind(mutability);
let source_info = self.source_info(span);
let re_erased = self.tcx.lifetimes.re_erased;
let trait_item = self.tcx.require_lang_item(trait_item, None);
let method = trait_method(self.tcx, trait_item, method, [ty]);
let ref_src = self.temp(Ty::new_ref(self.tcx, re_erased, ty, mutability), span);
// `let ref_src = &src_place;`
// or `let ref_src = &mut src_place;`
self.cfg.push_assign(
block,
source_info,
ref_src,
Rvalue::Ref(re_erased, borrow_kind, place),
);
// `let temp = <Ty as Deref>::deref(ref_src);`
// or `let temp = <Ty as DerefMut>::deref_mut(ref_src);`
self.cfg.terminate(
block,
source_info,
TerminatorKind::Call {
func: Operand::Constant(Box::new(ConstOperand {
span,
user_ty: None,
const_: method,
})),
args: [Spanned { node: Operand::Move(ref_src), span }].into(),
destination: temp,
target: Some(target_block),
unwind: UnwindAction::Continue,
call_source: CallSource::Misc,
fn_span: source_info.span,
},
);
}
/// 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 values using `<T as std::compare::PartialEq>::eq`.
/// If the values are already references, just call it directly, otherwise
/// take a reference to the values first and then call it.
fn non_scalar_compare(
&mut self,
block: BasicBlock,
success_block: BasicBlock,
fail_block: BasicBlock,
source_info: SourceInfo,
value: Const<'tcx>,
mut val: Place<'tcx>,
mut ty: Ty<'tcx>,
) {
let mut expect = self.literal_operand(source_info.span, value);
// 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 = Ty::new_imm_ref(tcx, *region, Ty::new_slice(tcx, *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::PointerCoercion(PointerCoercion::Unsize),
Operand::Copy(val),
ty,
),
);
val = 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::PointerCoercion(PointerCoercion::Unsize),
expect,
ty,
),
);
expect = Operand::Move(slice);
}
}
}
// Figure out the type on which we are calling `PartialEq`. This involves an extra wrapping
// reference: we can only compare two `&T`, and then compare_ty will be `T`.
// Make sure that we do *not* call any user-defined code here.
// The only types that can end up here are string and byte literals,
// which have their comparison defined in `core`.
// (Interestingly this means that exhaustiveness analysis relies, for soundness,
// on the `PartialEq` impls for `str` and `[u8]` to b correct!)
let compare_ty = match *ty.kind() {
ty::Ref(_, deref_ty, _)
if deref_ty == self.tcx.types.str_ || deref_ty != self.tcx.types.u8 =>
{
deref_ty
}
_ => span_bug!(source_info.span, "invalid type for non-scalar compare: {}", 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,
self.tcx.with_opt_host_effect_param(self.def_id, eq_def_id, [compare_ty, compare_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(ConstOperand {
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,
const_: method,
})),
args: [
Spanned { node: Operand::Copy(val), span: DUMMY_SP },
Spanned { node: expect, span: DUMMY_SP },
]
.into(),
destination: eq_result,
target: Some(eq_block),
unwind: UnwindAction::Continue,
call_source: CallSource::MatchCmp,
fn_span: source_info.span,
},
);
self.diverge_from(block);
// 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 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
/// the value of `x` 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(
&mut self,
test_place: Place<'tcx>,
test: &Test<'tcx>,
candidate: &mut Candidate<'_, 'tcx>,
sorted_candidates: &FxIndexMap<TestBranch<'tcx>, Vec<&mut Candidate<'_, 'tcx>>>,
) -> Option<TestBranch<'tcx>> {
// 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 == Some(test_place))?;
// If true, the match pair is completely entailed by its corresponding test
// branch, so it can be removed. If false, the match pair is _compatible_
// with its test branch, but still needs a more specific test.
let fully_matched;
let ret = match (&test.kind, &match_pair.test_case) {
// If we are performing a variant switch, then this
// informs variant patterns, but nothing else.
(
&TestKind::Switch { adt_def: tested_adt_def },
&TestCase::Variant { adt_def, variant_index },
) => {
assert_eq!(adt_def, tested_adt_def);
fully_matched = true;
Some(TestBranch::Variant(variant_index))
}
// 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, &TestCase::Constant { value })
if is_switch_ty(match_pair.pattern.ty) =>
{
// An important invariant of candidate sorting is that a candidate
// must not match in multiple branches. For `SwitchInt` tests, adding
// a new value might invalidate that property for range patterns that
// have already been sorted into the failure arm, so we must take care
// not to add such values here.
let is_covering_range = |test_case: &TestCase<'_, 'tcx>| {
test_case.as_range().is_some_and(|range| {
matches!(range.contains(value, self.tcx, self.param_env), None | Some(true))
})
};
let is_conflicting_candidate = |candidate: &&mut Candidate<'_, 'tcx>| {
candidate
.match_pairs
.iter()
.any(|mp| mp.place == Some(test_place) && is_covering_range(&mp.test_case))
};
if sorted_candidates
.get(&TestBranch::Failure)
.is_some_and(|candidates| candidates.iter().any(is_conflicting_candidate))
{
fully_matched = false;
None
} else {
fully_matched = true;
let bits = value.eval_bits(self.tcx, self.param_env);
Some(TestBranch::Constant(value, bits))
}
}
(TestKind::SwitchInt, TestCase::Range(range)) => {
// When performing a `SwitchInt` test, a range pattern can be
// sorted into the failure arm if it doesn't contain _any_ of
// the values being tested. (This restricts what values can be
// added to the test by subsequent candidates.)
fully_matched = false;
let not_contained =
sorted_candidates.keys().filter_map(|br| br.as_constant()).copied().all(
|val| matches!(range.contains(val, self.tcx, self.param_env), Some(false)),
);
not_contained.then(|| {
// No switch values are contained in the pattern range,
// so the pattern can be matched only if this test fails.
TestBranch::Failure
})
}
(TestKind::If, TestCase::Constant { value }) => {
fully_matched = true;
let value = value.try_eval_bool(self.tcx, self.param_env).unwrap_or_else(|| {
span_bug!(test.span, "expected boolean value but got {value:?}")
});
Some(if value { TestBranch::Success } else { TestBranch::Failure })
}
(
&TestKind::Len { len: test_len, op: BinOp::Eq },
&TestCase::Slice { len, variable_length },
) => {
match (test_len.cmp(&(len as u64)), variable_length) {
(Ordering::Equal, false) => {
// on true, min_len = len = $actual_length,
// on false, len != $actual_length
fully_matched = true;
Some(TestBranch::Success)
}
(Ordering::Less, _) => {
// test_len < pat_len. If $actual_len = test_len,
// then $actual_len < pat_len and we don't have
// enough elements.
fully_matched = false;
Some(TestBranch::Failure)
}
(Ordering::Equal | Ordering::Greater, true) => {
// This can match both if $actual_len = test_len >= pat_len,
// and if $actual_len > test_len. We can't advance.
fully_matched = false;
None
}
(Ordering::Greater, false) => {
// test_len != pat_len, so if $actual_len = test_len, then
// $actual_len != pat_len.
fully_matched = false;
Some(TestBranch::Failure)
}
}
}
(
&TestKind::Len { len: test_len, op: BinOp::Ge },
&TestCase::Slice { len, variable_length },
) => {
// the test is `$actual_len >= test_len`
match (test_len.cmp(&(len as u64)), variable_length) {
(Ordering::Equal, true) => {
// $actual_len >= test_len = pat_len,
// so we can match.
fully_matched = true;
Some(TestBranch::Success)
}
(Ordering::Less, _) | (Ordering::Equal, false) => {
// test_len <= pat_len. If $actual_len < test_len,
// then it is also < pat_len, so the test passing is
// necessary (but insufficient).
fully_matched = false;
Some(TestBranch::Success)
}
(Ordering::Greater, false) => {
// test_len > pat_len. If $actual_len >= test_len > pat_len,
// then we know we won't have a match.
fully_matched = false;
Some(TestBranch::Failure)
}
(Ordering::Greater, true) => {
// test_len < pat_len, and is therefore less
// strict. This can still go both ways.
fully_matched = false;
None
}
}
}
(TestKind::Range(test), &TestCase::Range(pat)) => {
if test.as_ref() == pat {
fully_matched = true;
Some(TestBranch::Success)
} else {
fully_matched = false;
// If the testing range does not overlap with pattern range,
// the pattern can be matched only if this test fails.
if !test.overlaps(pat, self.tcx, self.param_env)? {
Some(TestBranch::Failure)
} else {
None
}
}
}
(TestKind::Range(range), &TestCase::Constant { value }) => {
fully_matched = false;
if !range.contains(value, self.tcx, self.param_env)? {
// `value` is not contained in the testing range,
// so `value` can be matched only if this test fails.
Some(TestBranch::Failure)
} else {
None
}
}
(TestKind::Eq { value: test_val, .. }, TestCase::Constant { value: case_val }) => {
if test_val == case_val {
fully_matched = true;
Some(TestBranch::Success)
} else {
fully_matched = false;
Some(TestBranch::Failure)
}
}
(TestKind::Deref { temp: test_temp, .. }, TestCase::Deref { temp, .. })
if test_temp == temp =>
{
fully_matched = true;
Some(TestBranch::Success)
}
(TestKind::Never, _) => {
fully_matched = true;
Some(TestBranch::Success)
}
(
TestKind::Switch { .. }
| TestKind::SwitchInt { .. }
| TestKind::If
| TestKind::Len { .. }
| TestKind::Range { .. }
| TestKind::Eq { .. }
| TestKind::Deref { .. },
_,
) => {
fully_matched = false;
None
}
};
if fully_matched {
// Replace the match pair by its sub-pairs.
let match_pair = candidate.match_pairs.remove(match_pair_index);
candidate.match_pairs.extend(match_pair.subpairs);
// Move or-patterns to the end.
candidate.match_pairs.sort_by_key(|pair| matches!(pair.test_case, TestCase::Or { .. }));
}
ret
}
}
fn is_switch_ty(ty: Ty<'_>) -> bool {
ty.is_integral() || ty.is_char()
}
fn trait_method<'tcx>(
tcx: TyCtxt<'tcx>,
trait_def_id: DefId,
method_name: Symbol,
args: impl IntoIterator<Item: Into<GenericArg<'tcx>>>,
) -> Const<'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 = Ty::new_fn_def(tcx, item.def_id, args);
Const::zero_sized(method_ty)
}