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Clarify specialization into two steps

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First is checking for constructor overlap, second is extracting the
resulting fields.
This commit is contained in:
Nadrieril 2020-10-25 22:42:43 +00:00
parent 7c4f94be48
commit 6ad9f44a50
1 changed files with 48 additions and 56 deletions
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104
compiler/rustc_mir_build/src/thir/pattern/_match.rs
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@ -2527,9 +2527,9 @@ fn pat_constructor<'tcx>(
fn specialize_one_pattern<'p, 'tcx>(
cx: &MatchCheckCtxt<'p, 'tcx>,
pat: &'p Pat<'tcx>,
constructor: &Constructor<'tcx>,
ctor: &Constructor<'tcx>,
ctor_wild_subpatterns: &Fields<'p, 'tcx>,
is_its_own_ctor: bool, // Whether `constructor` is known to be derived from `pat`
is_its_own_ctor: bool, // Whether `ctor` is known to be derived from `pat`
) -> Option<Fields<'p, 'tcx>> {
if pat.is_wildcard() {
return Some(ctor_wild_subpatterns.clone());
@ -2539,57 +2539,34 @@ fn specialize_one_pattern<'p, 'tcx>(
// `unwrap` is safe because `pat` is not a wildcard.
let pat_ctor = pat_constructor(cx.tcx, cx.param_env, pat).unwrap();
let result = match (constructor, &pat_ctor, pat.kind.as_ref()) {
(Single, Single, PatKind::Leaf { subpatterns }) => {
Some(ctor_wild_subpatterns.replace_with_fieldpats(subpatterns))
}
(Single, Single, PatKind::Deref { subpattern }) => {
Some(Fields::from_single_pattern(subpattern))
}
(Variant(_), Variant(_), _) if constructor != &pat_ctor => None,
(Variant(_), Variant(_), PatKind::Variant { subpatterns, .. }) => {
Some(ctor_wild_subpatterns.replace_with_fieldpats(subpatterns))
}
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), _) => {
ctor_range.intersection(cx.tcx, &pat_range)?;
// Constructor splitting should ensure that all intersections we encounter
// are actually inclusions.
assert!(ctor_range.is_subrange(&pat_range));
Some(Fields::empty())
(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
}
}
(FloatRange(ctor_from, ctor_to, ctor_end), FloatRange(pat_from, pat_to, pat_end), _) => {
(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)?;
let intersects = (from == Ordering::Greater || from == Ordering::Equal)
&& (to == Ordering::Less || (pat_end == ctor_end && to == Ordering::Equal));
if intersects { Some(Fields::empty()) } else { None }
(from == Ordering::Greater || from == Ordering::Equal)
&& (to == Ordering::Less || (pat_end == ctor_end && to == Ordering::Equal))
}
(Str(ctor_val), Str(pat_val), _) => {
(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)?;
if comparison == Ordering::Equal { Some(Fields::empty()) } else { None }
comparison == Ordering::Equal
}
(Slice(ctor_slice), Slice(pat_slice), _)
if !pat_slice.pattern_kind().covers_length(ctor_slice.arity()) =>
{
None
}
(
Slice(ctor_slice),
Slice(_),
PatKind::Array { prefix, suffix, .. } | PatKind::Slice { prefix, suffix, .. },
) => {
// Number of subpatterns for the constructor
let ctor_arity = ctor_slice.arity();
// 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 as usize - suffix.len() + i, p));
Some(ctor_wild_subpatterns.replace_fields_indexed(prefix.chain(suffix)))
(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
@ -2611,23 +2588,38 @@ fn specialize_one_pattern<'p, 'tcx>(
// (FOO, false) => {}
// }
// ```
(Opaque, Opaque, _) if is_its_own_ctor => Some(Fields::empty()),
(Opaque, Opaque) if is_its_own_ctor => true,
// We are trying to inspect an opaque constant. Thus we skip the row.
(Opaque, _, _) | (_, Opaque, _) => None,
(Opaque, _) | (_, Opaque) => false,
// Only a wildcard pattern can match the special extra constructor.
(NonExhaustive, _, _) => None,
(NonExhaustive, _) => false,
_ => bug!("trying to specialize pattern {:?} with constructor {:?}", pat, constructor),
_ => bug!("trying to specialize pattern {:?} with constructor {:?}", pat, ctor),
};
debug!(
"specialize({:#?}, {:#?}, {:#?}) = {:#?}",
pat, constructor, ctor_wild_subpatterns, result
);
if let Some(fields) = &result {
debug_assert_eq!(fields.len(), ctor_wild_subpatterns.len());
if !ctor_covered_by_pat {
return None;
}
result
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(),
};
debug!("specialize({:#?}, {:#?}, {:#?}) = {:#?}", pat, ctor, ctor_wild_subpatterns, fields);
Some(fields)
}