bjoernager/rust
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Auto merge of #88242 - bonega:allocation_range, r=oli-obk

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Use custom wrap-around type instead of RangeInclusive

Two reasons:

1. More memory is allocated than necessary for `valid_range` in `Scalar`. The range is not used as an iterator and `exhausted` is never used.
2. `contains`, `count` etc. methods in `RangeInclusive` are doing very unhelpful(and dangerous!) things when used as a wrap-around range. - In general this PR wants to limit potentially confusing methods, that have a low probability of working.

Doing a local perf run, every metric shows improvement except for instructions.
Max-rss seem to have a very consistent improvement.

Sorry - newbie here, probably doing something wrong.
This commit is contained in:
bors 2021-08-25 02:17:41 +00:00
commit e5484cec0e
8 changed files with 115 additions and 81 deletions
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103
compiler/rustc_target/src/abi/mod.rs
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@ -677,32 +677,80 @@ impl Primitive {
}
}
/// Inclusive wrap-around range of valid values, that is, if
/// start > end, it represents `start..=MAX`,
/// followed by `0..=end`.
///
/// That is, for an i8 primitive, a range of `254..=2` means following
/// sequence:
///
/// 254 (-2), 255 (-1), 0, 1, 2
///
/// This is intended specifically to mirror LLVM’s `!range` metadata,
/// semantics.
#[derive(Clone, PartialEq, Eq, Hash)]
#[derive(HashStable_Generic)]
pub struct WrappingRange {
pub start: u128,
pub end: u128,
}
impl WrappingRange {
/// Returns `true` if `v` is contained in the range.
#[inline(always)]
pub fn contains(&self, v: u128) -> bool {
if self.start <= self.end {
self.start <= v && v <= self.end
} else {
self.start <= v || v <= self.end
}
}
/// Returns `true` if zero is contained in the range.
/// Equal to `range.contains(0)` but should be faster.
#[inline(always)]
pub fn contains_zero(&self) -> bool {
self.start > self.end || self.start == 0
}
/// Returns `self` with replaced `start`
#[inline(always)]
pub fn with_start(mut self, start: u128) -> Self {
self.start = start;
self
}
/// Returns `self` with replaced `end`
#[inline(always)]
pub fn with_end(mut self, end: u128) -> Self {
self.end = end;
self
}
}
impl fmt::Debug for WrappingRange {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(fmt, "{}..={}", self.start, self.end)?;
Ok(())
}
}
/// Information about one scalar component of a Rust type.
#[derive(Clone, PartialEq, Eq, Hash, Debug)]
#[derive(HashStable_Generic)]
pub struct Scalar {
pub value: Primitive,
/// Inclusive wrap-around range of valid values, that is, if
/// start > end, it represents `start..=MAX`,
/// followed by `0..=end`.
///
/// That is, for an i8 primitive, a range of `254..=2` means following
/// sequence:
///
/// 254 (-2), 255 (-1), 0, 1, 2
///
/// This is intended specifically to mirror LLVM’s `!range` metadata,
/// semantics.
// FIXME(eddyb) always use the shortest range, e.g., by finding
// the largest space between two consecutive valid values and
// taking everything else as the (shortest) valid range.
pub valid_range: RangeInclusive<u128>,
pub valid_range: WrappingRange,
}
impl Scalar {
pub fn is_bool(&self) -> bool {
matches!(self.value, Int(I8, false)) && self.valid_range == (0..=1)
matches!(self.value, Int(I8, false))
&& matches!(self.valid_range, WrappingRange { start: 0, end: 1 })
}
/// Returns the valid range as a `x..y` range.
@ -715,8 +763,8 @@ impl Scalar {
let bits = self.value.size(cx).bits();
assert!(bits <= 128);
let mask = !0u128 >> (128 - bits);
let start = *self.valid_range.start();
let end = *self.valid_range.end();
let start = self.valid_range.start;
let end = self.valid_range.end;
assert_eq!(start, start & mask);
assert_eq!(end, end & mask);
start..(end.wrapping_add(1) & mask)
@ -971,14 +1019,14 @@ impl Niche {
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();
let niche = v.end.wrapping_add(1)..v.start;
niche.end.wrapping_sub(niche.start) & max_value
}
pub 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 Scalar { value, valid_range: v } = self.scalar.clone();
let bits = value.size(cx).bits();
assert!(bits <= 128);
let max_value = !0u128 >> (128 - bits);
@ -988,24 +1036,14 @@ impl Niche {
}
// 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;
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) {
if v.contains(end) {
return None;
}
Some((start, Scalar { value, valid_range: *v.start()..=end }))
Some((start, Scalar { value, valid_range: v.with_end(end) }))
}
}
@ -1212,9 +1250,8 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
{
let scalar_allows_raw_init = move |s: &Scalar| -> bool {
if zero {
let range = &s.valid_range;
// The range must contain 0.
range.contains(&0) || (*range.start() > *range.end()) // wrap-around allows 0
s.valid_range.contains_zero()
} else {
// The range must include all values. `valid_range_exclusive` handles
// the wrap-around using target arithmetic; with wrap-around then the full