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Factor out the two specialization steps

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Nadrieril 2020-10-25 22:51:50 +00:00
parent 6ad9f44a50
commit c511955a9f
1 changed files with 107 additions and 80 deletions
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187
compiler/rustc_mir_build/src/thir/pattern/_match.rs
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@ -1132,6 +1132,66 @@ impl<'tcx> Constructor<'tcx> {
}
}
/// Returns whether `self` is covered by `other`, ie whether `self` is a subset of `other`. For
/// the simple cases, this is simply checking for equality. For the "grouped" constructors,
/// this checks for inclusion.
fn is_covered_by<'p>(
&self,
cx: &MatchCheckCtxt<'p, 'tcx>,
other: &Constructor<'tcx>,
ty: Ty<'tcx>,
) -> bool {
match (self, other) {
(Single, Single) => true,
(Variant(self_id), Variant(other_id)) => self_id == other_id,
(IntRange(self_range), IntRange(other_range)) => {
if self_range.intersection(cx.tcx, other_range).is_some() {
// Constructor splitting should ensure that all intersections we encounter
// are actually inclusions.
assert!(self_range.is_subrange(other_range));
true
} else {
false
}
}
(
FloatRange(self_from, self_to, self_end),
FloatRange(other_from, other_to, other_end),
) => {
match (
compare_const_vals(cx.tcx, self_to, other_to, cx.param_env, ty),
compare_const_vals(cx.tcx, self_from, other_from, cx.param_env, ty),
) {
(Some(to), Some(from)) => {
(from == Ordering::Greater || from == Ordering::Equal)
&& (to == Ordering::Less
|| (other_end == self_end && to == Ordering::Equal))
}
_ => false,
}
}
(Str(self_val), Str(other_val)) => {
// FIXME: there's probably a more direct way of comparing for equality
match compare_const_vals(cx.tcx, self_val, other_val, cx.param_env, ty) {
Some(comparison) => comparison == Ordering::Equal,
None => false,
}
}
(Slice(self_slice), Slice(other_slice)) => {
other_slice.pattern_kind().covers_length(self_slice.arity())
}
// We are trying to inspect an opaque constant. Thus we skip the row.
(Opaque, _) | (_, Opaque) => false,
// Only a wildcard pattern can match the special extra constructor.
(NonExhaustive, _) => false,
_ => bug!("trying to compare incompatible constructors {:?} and {:?}", self, other),
}
}
/// Apply a constructor to a list of patterns, yielding a new pattern. `pats`
/// must have as many elements as this constructor's arity.
///
@ -1461,6 +1521,41 @@ impl<'p, 'tcx> Fields<'p, 'tcx> {
}
}
/// Replaces contained fields with the arguments of the given pattern. Only use on a pattern
/// that is compatible with the constructor used to build `self`.
/// This is meant to be used on the result of `Fields::wildcards()`. The idea is that
/// `wildcards` constructs a list of fields where all entries are wildcards, and the pattern
/// provided to this function fills some of the fields with non-wildcards.
/// In the following example `Fields::wildcards` would return `[_, _, _, _]`. If we call
/// `replace_with_pattern_arguments` on it with the pattern, the result will be `[Some(0), _,
/// _, _]`.
/// ```rust
/// let x: [Option<u8>; 4] = foo();
/// match x {
/// [Some(0), ..] => {}
/// }
/// ```
fn replace_with_pattern_arguments(&self, pat: &'p Pat<'tcx>) -> Self {
match pat.kind.as_ref() {
PatKind::Deref { subpattern } => Self::from_single_pattern(subpattern),
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
self.replace_with_fieldpats(subpatterns)
}
PatKind::Array { prefix, suffix, .. } | PatKind::Slice { prefix, suffix, .. } => {
// Number of subpatterns for the constructor
let ctor_arity = self.len();
// Replace the prefix and the suffix with the given patterns, leaving wildcards in
// the middle if there was a subslice pattern `..`.
let prefix = prefix.iter().enumerate();
let suffix =
suffix.iter().enumerate().map(|(i, p)| (ctor_arity - suffix.len() + i, p));
self.replace_fields_indexed(prefix.chain(suffix))
}
_ => self.clone(),
}
}
fn push_on_patstack(self, stack: &[&'p Pat<'tcx>]) -> PatStack<'p, 'tcx> {
let pats: SmallVec<_> = match self {
Fields::Slice(pats) => pats.iter().chain(stack.iter().copied()).collect(),
@ -2535,89 +2630,21 @@ fn specialize_one_pattern<'p, 'tcx>(
return Some(ctor_wild_subpatterns.clone());
}
let ty = pat.ty;
// `unwrap` is safe because `pat` is not a wildcard.
let pat_ctor = pat_constructor(cx.tcx, cx.param_env, pat).unwrap();
let ctor_covered_by_pat = match (ctor, &pat_ctor) {
(Single, Single) => true,
(Variant(ctor_id), Variant(pat_id)) => ctor_id == pat_id,
(IntRange(ctor_range), IntRange(pat_range)) => {
if ctor_range.intersection(cx.tcx, pat_range).is_some() {
// Constructor splitting should ensure that all intersections we encounter
// are actually inclusions.
assert!(ctor_range.is_subrange(pat_range));
true
} else {
false
}
// We return `None` if `ctor` is not covered by `pat`. If `ctor` is known to be derived from
// `pat` then we don't need to check; otherwise, we compute the constructor of `pat` and check
// for constructor inclusion.
// Note that this shortcut is also necessary for correctness: a pattern should always be
// specializable with its own constructor, even in cases where we refuse to inspect values like
// opaque constants.
if !is_its_own_ctor {
// `unwrap` is safe because `pat` is not a wildcard.
let pat_ctor = pat_constructor(cx.tcx, cx.param_env, pat).unwrap();
if !ctor.is_covered_by(cx, &pat_ctor, pat.ty) {
return None;
}
(FloatRange(ctor_from, ctor_to, ctor_end), FloatRange(pat_from, pat_to, pat_end)) => {
let to = compare_const_vals(cx.tcx, ctor_to, pat_to, cx.param_env, ty)?;
let from = compare_const_vals(cx.tcx, ctor_from, pat_from, cx.param_env, ty)?;
(from == Ordering::Greater || from == Ordering::Equal)
&& (to == Ordering::Less || (pat_end == ctor_end && to == Ordering::Equal))
}
(Str(ctor_val), Str(pat_val)) => {
// FIXME: there's probably a more direct way of comparing for equality
let comparison = compare_const_vals(cx.tcx, ctor_val, pat_val, cx.param_env, ty)?;
comparison == Ordering::Equal
}
(Slice(ctor_slice), Slice(pat_slice)) => {
pat_slice.pattern_kind().covers_length(ctor_slice.arity())
}
// Only a wildcard pattern can match an opaque constant, unless we're specializing the
// value against its own constructor. That happens when we call
// `v.specialize_constructor(ctor)` with `ctor` obtained from `pat_constructor(v.head())`.
// For example, in the following match, when we are dealing with the third branch, we will
// specialize with an `Opaque` ctor. We want to ignore the second branch because opaque
// constants should not be inspected, but we don't want to ignore the current (third)
// branch, as that would cause us to always conclude that such a branch is unreachable.
// ```rust
// #[derive(PartialEq)]
// struct Foo(i32);
// impl Eq for Foo {}
// const FOO: Foo = Foo(42);
//
// match (Foo(0), true) {
// (_, true) => {}
// (FOO, true) => {}
// (FOO, false) => {}
// }
// ```
(Opaque, Opaque) if is_its_own_ctor => true,
// We are trying to inspect an opaque constant. Thus we skip the row.
(Opaque, _) | (_, Opaque) => false,
// Only a wildcard pattern can match the special extra constructor.
(NonExhaustive, _) => false,
_ => bug!("trying to specialize pattern {:?} with constructor {:?}", pat, ctor),
};
if !ctor_covered_by_pat {
return None;
}
let fields = match pat.kind.as_ref() {
PatKind::Deref { subpattern } => Fields::from_single_pattern(subpattern),
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
ctor_wild_subpatterns.replace_with_fieldpats(subpatterns)
}
PatKind::Array { prefix, suffix, .. } | PatKind::Slice { prefix, suffix, .. } => {
// Number of subpatterns for the constructor
let ctor_arity = ctor_wild_subpatterns.len();
// Replace the prefix and the suffix with the given patterns, leaving wildcards in
// the middle if there was a subslice pattern `..`.
let prefix = prefix.iter().enumerate();
let suffix = suffix.iter().enumerate().map(|(i, p)| (ctor_arity - suffix.len() + i, p));
ctor_wild_subpatterns.replace_fields_indexed(prefix.chain(suffix))
}
_ => ctor_wild_subpatterns.clone(),
};
let fields = ctor_wild_subpatterns.replace_with_pattern_arguments(pat);
debug!("specialize({:#?}, {:#?}, {:#?}) = {:#?}", pat, ctor, ctor_wild_subpatterns, fields);