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Optimise fast path of checked_ops with unlikely #73938

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Jul 2, 2020
+43 −27
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Optimise fast path of checked_ops with unlikely #73938

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70 changes: 43 additions & 27 deletions src/libcore/num/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,21 @@ macro_rules! try_opt {
};
}

#[cfg(bootstrap)]
macro_rules! unlikely {
($e: expr) => {
$e
};
}

#[cfg(not(bootstrap))]
#[allow_internal_unstable(const_likely)]
macro_rules! unlikely {
($e: expr) => {
intrinsics::unlikely($e)
};
}

macro_rules! impl_nonzero_fmt {
( #[$stability: meta] ( $( $Trait: ident ),+ ) for $Ty: ident ) => {
$(
Expand Down Expand Up @@ -745,7 +760,7 @@ $EndFeature, "
#[inline]
pub const fn checked_add(self, rhs: Self) -> Option<Self> {
let (a, b) = self.overflowing_add(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
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Will it have the same effect by flipping the case?

if !b { Some(a) } else { None }

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Rearranging the code gives no hint to LLVM that one branch has more weight than another.

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I tried it. The code is better for only this method alone, not at callsite. But at callsite, things are not improved.

}
}

Expand Down Expand Up @@ -787,7 +802,7 @@ $EndFeature, "
#[inline]
pub const fn checked_sub(self, rhs: Self) -> Option<Self> {
let (a, b) = self.overflowing_sub(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down Expand Up @@ -829,7 +844,7 @@ $EndFeature, "
#[inline]
pub const fn checked_mul(self, rhs: Self) -> Option<Self> {
let (a, b) = self.overflowing_mul(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down Expand Up @@ -871,7 +886,7 @@ $EndFeature, "
without modifying the original"]
#[inline]
pub const fn checked_div(self, rhs: Self) -> Option<Self> {
if rhs == 0 || (self == Self::MIN && rhs == -1) {
if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
None
} else {
// SAFETY: div by zero and by INT_MIN have been checked above
Expand Down Expand Up @@ -900,7 +915,7 @@ assert_eq!((1", stringify!($SelfT), ").checked_div_euclid(0), None);
without modifying the original"]
#[inline]
pub const fn checked_div_euclid(self, rhs: Self) -> Option<Self> {
if rhs == 0 || (self == Self::MIN && rhs == -1) {
if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
None
} else {
Some(self.div_euclid(rhs))
Expand Down Expand Up @@ -929,7 +944,7 @@ $EndFeature, "
without modifying the original"]
#[inline]
pub const fn checked_rem(self, rhs: Self) -> Option<Self> {
if rhs == 0 || (self == Self::MIN && rhs == -1) {
if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
None
} else {
// SAFETY: div by zero and by INT_MIN have been checked above
Expand Down Expand Up @@ -957,7 +972,7 @@ assert_eq!(", stringify!($SelfT), "::MIN.checked_rem_euclid(-1), None);
without modifying the original"]
#[inline]
pub const fn checked_rem_euclid(self, rhs: Self) -> Option<Self> {
if rhs == 0 || (self == Self::MIN && rhs == -1) {
if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
None
} else {
Some(self.rem_euclid(rhs))
Expand All @@ -983,7 +998,7 @@ $EndFeature, "
#[inline]
pub const fn checked_neg(self) -> Option<Self> {
let (a, b) = self.overflowing_neg();
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand All @@ -1007,7 +1022,7 @@ $EndFeature, "
#[inline]
pub const fn checked_shl(self, rhs: u32) -> Option<Self> {
let (a, b) = self.overflowing_shl(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand All @@ -1031,7 +1046,7 @@ $EndFeature, "
#[inline]
pub const fn checked_shr(self, rhs: u32) -> Option<Self> {
let (a, b) = self.overflowing_shr(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down Expand Up @@ -1738,7 +1753,7 @@ $EndFeature, "
#[must_use = "this returns the result of the operation, \
without modifying the original"]
pub const fn overflowing_div(self, rhs: Self) -> (Self, bool) {
if self == Self::MIN && rhs == -1 {
if unlikely!(self == Self::MIN && rhs == -1) {
(self, true)
} else {
(self / rhs, false)
Expand Down Expand Up @@ -1771,7 +1786,7 @@ assert_eq!(", stringify!($SelfT), "::MIN.overflowing_div_euclid(-1), (", stringi
#[must_use = "this returns the result of the operation, \
without modifying the original"]
pub const fn overflowing_div_euclid(self, rhs: Self) -> (Self, bool) {
if self == Self::MIN && rhs == -1 {
if unlikely!(self == Self::MIN && rhs == -1) {
(self, true)
} else {
(self.div_euclid(rhs), false)
Expand Down Expand Up @@ -1805,7 +1820,7 @@ $EndFeature, "
#[must_use = "this returns the result of the operation, \
without modifying the original"]
pub const fn overflowing_rem(self, rhs: Self) -> (Self, bool) {
if self == Self::MIN && rhs == -1 {
if unlikely!(self == Self::MIN && rhs == -1) {
(0, true)
} else {
(self % rhs, false)
Expand Down Expand Up @@ -1838,7 +1853,7 @@ assert_eq!(", stringify!($SelfT), "::MIN.overflowing_rem_euclid(-1), (0, true));
without modifying the original"]
#[inline]
pub const fn overflowing_rem_euclid(self, rhs: Self) -> (Self, bool) {
if self == Self::MIN && rhs == -1 {
if unlikely!(self == Self::MIN && rhs == -1) {
(0, true)
} else {
(self.rem_euclid(rhs), false)
Expand Down Expand Up @@ -1869,7 +1884,7 @@ assert_eq!(", stringify!($SelfT), "::MIN.overflowing_neg(), (", stringify!($Self
#[allow(unused_attributes)]
#[cfg_attr(bootstrap, allow_internal_unstable(const_if_match))]
pub const fn overflowing_neg(self) -> (Self, bool) {
if self == Self::MIN {
if unlikely!(self == Self::MIN) {
(Self::MIN, true)
} else {
(-self, false)
Expand Down Expand Up @@ -2981,7 +2996,7 @@ assert_eq!((", stringify!($SelfT), "::MAX - 2).checked_add(3), None);", $EndFeat
#[inline]
pub const fn checked_add(self, rhs: Self) -> Option<Self> {
let (a, b) = self.overflowing_add(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down Expand Up @@ -3021,7 +3036,7 @@ assert_eq!(0", stringify!($SelfT), ".checked_sub(1), None);", $EndFeature, "
#[inline]
pub const fn checked_sub(self, rhs: Self) -> Option<Self> {
let (a, b) = self.overflowing_sub(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down Expand Up @@ -3061,7 +3076,7 @@ assert_eq!(", stringify!($SelfT), "::MAX.checked_mul(2), None);", $EndFeature, "
#[inline]
pub const fn checked_mul(self, rhs: Self) -> Option<Self> {
let (a, b) = self.overflowing_mul(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down Expand Up @@ -3100,11 +3115,12 @@ assert_eq!(1", stringify!($SelfT), ".checked_div(0), None);", $EndFeature, "
without modifying the original"]
#[inline]
pub const fn checked_div(self, rhs: Self) -> Option<Self> {
match rhs {
0 => None,
if unlikely!(rhs == 0) {
None
} else {
// SAFETY: div by zero has been checked above and unsigned types have no other
// failure modes for division
rhs => Some(unsafe { intrinsics::unchecked_div(self, rhs) }),
Some(unsafe { intrinsics::unchecked_div(self, rhs) })
}
}
}
Expand All @@ -3127,7 +3143,7 @@ assert_eq!(1", stringify!($SelfT), ".checked_div_euclid(0), None);
without modifying the original"]
#[inline]
pub const fn checked_div_euclid(self, rhs: Self) -> Option<Self> {
if rhs == 0 {
if unlikely!(rhs == 0) {
None
} else {
Some(self.div_euclid(rhs))
Expand All @@ -3154,7 +3170,7 @@ assert_eq!(5", stringify!($SelfT), ".checked_rem(0), None);", $EndFeature, "
without modifying the original"]
#[inline]
pub const fn checked_rem(self, rhs: Self) -> Option<Self> {
if rhs == 0 {
if unlikely!(rhs == 0) {
None
} else {
// SAFETY: div by zero has been checked above and unsigned types have no other
Expand Down Expand Up @@ -3182,7 +3198,7 @@ assert_eq!(5", stringify!($SelfT), ".checked_rem_euclid(0), None);
without modifying the original"]
#[inline]
pub const fn checked_rem_euclid(self, rhs: Self) -> Option<Self> {
if rhs == 0 {
if unlikely!(rhs == 0) {
None
} else {
Some(self.rem_euclid(rhs))
Expand All @@ -3209,7 +3225,7 @@ assert_eq!(1", stringify!($SelfT), ".checked_neg(), None);", $EndFeature, "
#[inline]
pub const fn checked_neg(self) -> Option<Self> {
let (a, b) = self.overflowing_neg();
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand All @@ -3232,7 +3248,7 @@ assert_eq!(0x10", stringify!($SelfT), ".checked_shl(129), None);", $EndFeature,
#[inline]
pub const fn checked_shl(self, rhs: u32) -> Option<Self> {
let (a, b) = self.overflowing_shl(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand All @@ -3255,7 +3271,7 @@ assert_eq!(0x10", stringify!($SelfT), ".checked_shr(129), None);", $EndFeature,
#[inline]
pub const fn checked_shr(self, rhs: u32) -> Option<Self> {
let (a, b) = self.overflowing_shr(rhs);
if b {None} else {Some(a)}
if unlikely!(b) {None} else {Some(a)}
}
}

Expand Down