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rustc: compute ty::layout::Niche's available on the fly.

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This commit is contained in:
Eduard-Mihai Burtescu 2019-07-11 20:01:29 +03:00
parent 5480b47d7f
commit 8c050fc805
1 changed files with 43 additions and 29 deletions
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72
src/librustc/ty/layout.rs
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@ -2225,24 +2225,50 @@ where
struct Niche {
offset: Size,
scalar: Scalar,
available: u128,
}
impl Niche {
fn reserve<'tcx>(
&self,
cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
count: u128,
) -> Option<(u128, Scalar)> {
if count > self.available {
return None;
}
fn available<C: HasDataLayout>(&self, cx: &C) -> u128 {
let Scalar { value, valid_range: ref v } = self.scalar;
let bits = value.size(cx).bits();
assert!(bits <= 128);
let max_value = !0u128 >> (128 - bits);
// Find out how many values are outside the valid range.
let niche = v.end().wrapping_add(1)..*v.start();
niche.end.wrapping_sub(niche.start) & max_value
}
fn reserve<C: HasDataLayout>(&self, cx: &C, count: u128) -> Option<(u128, Scalar)> {
assert!(count > 0);
let Scalar { value, valid_range: ref v } = self.scalar;
let bits = value.size(cx).bits();
assert!(bits <= 128);
let max_value = !0u128 >> (128 - bits);
if count > max_value {
return None;
}
// Compute the range of invalid values being reserved.
let start = v.end().wrapping_add(1) & max_value;
let end = v.end().wrapping_add(count) & max_value;
// If the `end` of our range is inside the valid range,
// then we ran out of invalid values.
// FIXME(eddyb) abstract this with a wraparound range type.
let valid_range_contains = |x| {
if v.start() <= v.end() {
*v.start() <= x && x <= *v.end()
} else {
*v.start() <= x || x <= *v.end()
}
};
if valid_range_contains(end) {
return None;
}
Some((start, Scalar { value, valid_range: *v.start()..=end }))
}
}
@ -2253,25 +2279,12 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
// FIXME(eddyb) traverse already optimized enums.
fn find_niche(&self, layout: TyLayout<'tcx>) -> Result<Option<Niche>, LayoutError<'tcx>> {
let scalar_niche = |scalar: &Scalar, offset| {
let Scalar { value, valid_range: ref v } = *scalar;
let bits = value.size(self).bits();
assert!(bits <= 128);
let max_value = !0u128 >> (128 - bits);
// Find out how many values are outside the valid range.
let available = if v.start() <= v.end() {
v.start() + (max_value - v.end())
let niche = Niche { offset, scalar: scalar.clone() };
if niche.available(self) > 0 {
Some(niche)
} else {
v.start() - v.end() - 1
};
// Give up if there is no niche value available.
if available == 0 {
return None;
None
}
Some(Niche { offset, scalar: scalar.clone(), available })
};
// Locals variables which live across yields are stored
@ -2293,7 +2306,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
)
.chain(iter::once((a, Size::ZERO)))
.filter_map(|(scalar, offset)| scalar_niche(scalar, offset))
.max_by_key(|niche| niche.available);
.max_by_key(|niche| niche.available(self));
return Ok(niche);
}
Abi::Vector { ref element, .. } => {
@ -2325,8 +2338,9 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let mut available = 0;
for i in 0..layout.fields.count() {
if let Some(mut c) = self.find_niche(layout.field(self, i)?)? {
if c.available > available {
available = c.available;
let c_available = c.available(self);
if c_available > available {
available = c_available;
c.offset += layout.fields.offset(i);
niche = Some(c);
}