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nikicnikic
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Use LLVM intrinsics for saturating add/sub
1 parent d8a0dd7 commit 4a4186e

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5 files changed

+101
-3
lines changed

5 files changed

+101
-3
lines changed

‎src/libcore/intrinsics.rs

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1493,6 +1493,19 @@ extern "rust-intrinsic" {
14931493
/// [`std::u32::wrapping_mul`](../../std/primitive.u32.html#method.wrapping_mul)
14941494
pub fn overflowing_mul<T>(a: T, b: T) -> T;
14951495

1496+
/// Computes `a + b`, while saturating at numeric bounds.
1497+
/// The stabilized versions of this intrinsic are available on the integer
1498+
/// primitives via the `saturating_add` method. For example,
1499+
/// [`std::u32::saturating_add`](../../std/primitive.u32.html#method.saturating_add)
1500+
#[cfg(not(stage0))]
1501+
pub fn saturating_add<T>(a: T, b: T) -> T;
1502+
/// Computes `a - b`, while saturating at numeric bounds.
1503+
/// The stabilized versions of this intrinsic are available on the integer
1504+
/// primitives via the `saturating_sub` method. For example,
1505+
/// [`std::u32::saturating_sub`](../../std/primitive.u32.html#method.saturating_sub)
1506+
#[cfg(not(stage0))]
1507+
pub fn saturating_sub<T>(a: T, b: T) -> T;
1508+
14961509
/// Returns the value of the discriminant for the variant in 'v',
14971510
/// cast to a `u64`; if `T` has no discriminant, returns 0.
14981511
pub fn discriminant_value<T>(v: &T) -> u64;

‎src/libcore/num/mod.rs

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -883,11 +883,16 @@ $EndFeature, "
883883
#[stable(feature = "rust1", since = "1.0.0")]
884884
#[inline]
885885
pub fn saturating_add(self, rhs: Self) -> Self {
886+
#[cfg(stage0)]
886887
match self.checked_add(rhs) {
887888
Some(x) => x,
888889
None if rhs >= 0 => Self::max_value(),
889890
None => Self::min_value(),
890891
}
892+
#[cfg(not(stage0))]
893+
{
894+
intrinsics::saturating_add(self, rhs)
895+
}
891896
}
892897
}
893898

@@ -908,11 +913,16 @@ $EndFeature, "
908913
#[stable(feature = "rust1", since = "1.0.0")]
909914
#[inline]
910915
pub fn saturating_sub(self, rhs: Self) -> Self {
916+
#[cfg(stage0)]
911917
match self.checked_sub(rhs) {
912918
Some(x) => x,
913919
None if rhs >= 0 => Self::min_value(),
914920
None => Self::max_value(),
915921
}
922+
#[cfg(not(stage0))]
923+
{
924+
intrinsics::saturating_sub(self, rhs)
925+
}
916926
}
917927
}
918928

@@ -2744,10 +2754,15 @@ assert_eq!(200u8.saturating_add(127), 255);", $EndFeature, "
27442754
#[stable(feature = "rust1", since = "1.0.0")]
27452755
#[inline]
27462756
pub fn saturating_add(self, rhs: Self) -> Self {
2757+
#[cfg(stage0)]
27472758
match self.checked_add(rhs) {
27482759
Some(x) => x,
27492760
None => Self::max_value(),
27502761
}
2762+
#[cfg(not(stage0))]
2763+
{
2764+
intrinsics::saturating_add(self, rhs)
2765+
}
27512766
}
27522767
}
27532768

@@ -2766,10 +2781,15 @@ assert_eq!(13", stringify!($SelfT), ".saturating_sub(127), 0);", $EndFeature, "
27662781
#[stable(feature = "rust1", since = "1.0.0")]
27672782
#[inline]
27682783
pub fn saturating_sub(self, rhs: Self) -> Self {
2784+
#[cfg(stage0)]
27692785
match self.checked_sub(rhs) {
27702786
Some(x) => x,
27712787
None => Self::min_value(),
27722788
}
2789+
#[cfg(not(stage0))]
2790+
{
2791+
intrinsics::saturating_sub(self, rhs)
2792+
}
27732793
}
27742794
}
27752795

‎src/librustc_codegen_llvm/context.rs

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -757,6 +757,30 @@ impl CodegenCx<'b, 'tcx> {
757757
ifn!("llvm.umul.with.overflow.i64", fn(t_i64, t_i64) -> mk_struct!{t_i64, i1});
758758
ifn!("llvm.umul.with.overflow.i128", fn(t_i128, t_i128) -> mk_struct!{t_i128, i1});
759759

760+
ifn!("llvm.sadd.sat.i8", fn(t_i8, t_i8) -> t_i8);
761+
ifn!("llvm.sadd.sat.i16", fn(t_i16, t_i16) -> t_i16);
762+
ifn!("llvm.sadd.sat.i32", fn(t_i32, t_i32) -> t_i32);
763+
ifn!("llvm.sadd.sat.i64", fn(t_i64, t_i64) -> t_i64);
764+
ifn!("llvm.sadd.sat.i128", fn(t_i128, t_i128) -> t_i128);
765+
766+
ifn!("llvm.uadd.sat.i8", fn(t_i8, t_i8) -> t_i8);
767+
ifn!("llvm.uadd.sat.i16", fn(t_i16, t_i16) -> t_i16);
768+
ifn!("llvm.uadd.sat.i32", fn(t_i32, t_i32) -> t_i32);
769+
ifn!("llvm.uadd.sat.i64", fn(t_i64, t_i64) -> t_i64);
770+
ifn!("llvm.uadd.sat.i128", fn(t_i128, t_i128) -> t_i128);
771+
772+
ifn!("llvm.ssub.sat.i8", fn(t_i8, t_i8) -> t_i8);
773+
ifn!("llvm.ssub.sat.i16", fn(t_i16, t_i16) -> t_i16);
774+
ifn!("llvm.ssub.sat.i32", fn(t_i32, t_i32) -> t_i32);
775+
ifn!("llvm.ssub.sat.i64", fn(t_i64, t_i64) -> t_i64);
776+
ifn!("llvm.ssub.sat.i128", fn(t_i128, t_i128) -> t_i128);
777+
778+
ifn!("llvm.usub.sat.i8", fn(t_i8, t_i8) -> t_i8);
779+
ifn!("llvm.usub.sat.i16", fn(t_i16, t_i16) -> t_i16);
780+
ifn!("llvm.usub.sat.i32", fn(t_i32, t_i32) -> t_i32);
781+
ifn!("llvm.usub.sat.i64", fn(t_i64, t_i64) -> t_i64);
782+
ifn!("llvm.usub.sat.i128", fn(t_i128, t_i128) -> t_i128);
783+
760784
ifn!("llvm.lifetime.start", fn(t_i64,i8p) -> void);
761785
ifn!("llvm.lifetime.end", fn(t_i64, i8p) -> void);
762786

‎src/librustc_codegen_llvm/intrinsic.rs

Lines changed: 41 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@ use type_::Type;
1414
use type_of::LayoutLlvmExt;
1515
use rustc::ty::{self, Ty};
1616
use rustc::ty::layout::{self, LayoutOf, HasTyCtxt, Primitive};
17-
use rustc_codegen_ssa::common::TypeKind;
17+
use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
1818
use rustc::hir;
1919
use syntax::ast::{self, FloatTy};
2020
use syntax::symbol::Symbol;
@@ -28,7 +28,7 @@ use rustc::session::Session;
2828
use syntax_pos::Span;
2929

3030
use std::cmp::Ordering;
31-
use std::iter;
31+
use std::{iter, i128, u128};
3232

3333
fn get_simple_intrinsic(cx: &CodegenCx<'ll, '_>, name: &str) -> Option<&'ll Value> {
3434
let llvm_name = match name {
@@ -342,7 +342,7 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
342342
"bitreverse" | "add_with_overflow" | "sub_with_overflow" |
343343
"mul_with_overflow" | "overflowing_add" | "overflowing_sub" | "overflowing_mul" |
344344
"unchecked_div" | "unchecked_rem" | "unchecked_shl" | "unchecked_shr" | "exact_div" |
345-
"rotate_left" | "rotate_right" => {
345+
"rotate_left" | "rotate_right" | "saturating_add" | "saturating_sub" => {
346346
let ty = arg_tys[0];
347347
match int_type_width_signed(ty, self) {
348348
Some((width, signed)) =>
@@ -468,6 +468,44 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
468468
self.or(shift1, shift2)
469469
}
470470
},
471+
"saturating_add" | "saturating_sub" => {
472+
let is_add = name == "saturating_add";
473+
let lhs = args[0].immediate();
474+
let rhs = args[1].immediate();
475+
if llvm_util::get_major_version() >= 8 {
476+
let llvm_name = &format!("llvm.{}{}.sat.i{}",
477+
if signed { 's' } else { 'u' },
478+
if is_add { "add" } else { "sub" },
479+
width);
480+
let llfn = self.get_intrinsic(llvm_name);
481+
self.call(llfn, &[lhs, rhs], None)
482+
} else {
483+
let llvm_name = &format!("llvm.{}{}.with.overflow.i{}",
484+
if signed { 's' } else { 'u' },
485+
if is_add { "add" } else { "sub" },
486+
width);
487+
let llfn = self.get_intrinsic(llvm_name);
488+
let pair = self.call(llfn, &[lhs, rhs], None);
489+
let val = self.extract_value(pair, 0);
490+
let overflow = self.extract_value(pair, 1);
491+
let llty = self.type_ix(width);
492+
493+
let limit = if signed {
494+
let limit_lo = self.const_uint_big(
495+
llty, (i128::MIN >> (128 - width)) as u128);
496+
let limit_hi = self.const_uint_big(
497+
llty, (i128::MAX >> (128 - width)) as u128);
498+
let neg = self.icmp(
499+
IntPredicate::IntSLT, val, self.const_uint(llty, 0));
500+
self.select(neg, limit_hi, limit_lo)
501+
} else if is_add {
502+
self.const_uint_big(llty, u128::MAX >> (128 - width))
503+
} else {
504+
self.const_uint(llty, 0)
505+
};
506+
self.select(overflow, limit, val)
507+
}
508+
},
471509
_ => bug!(),
472510
},
473511
None => {

‎src/librustc_typeck/check/intrinsic.rs

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -68,6 +68,7 @@ pub fn intrisic_operation_unsafety(intrinsic: &str) -> hir::Unsafety {
6868
"size_of" | "min_align_of" | "needs_drop" |
6969
"add_with_overflow" | "sub_with_overflow" | "mul_with_overflow" |
7070
"overflowing_add" | "overflowing_sub" | "overflowing_mul" |
71+
"saturating_add" | "saturating_sub" |
7172
"rotate_left" | "rotate_right" |
7273
"ctpop" | "ctlz" | "cttz" | "bswap" | "bitreverse"
7374
=> hir::Unsafety::Normal,
@@ -307,6 +308,8 @@ pub fn check_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
307308

308309
"overflowing_add" | "overflowing_sub" | "overflowing_mul" =>
309310
(1, vec![param(0), param(0)], param(0)),
311+
"saturating_add" | "saturating_sub" =>
312+
(1, vec![param(0), param(0)], param(0)),
310313
"fadd_fast" | "fsub_fast" | "fmul_fast" | "fdiv_fast" | "frem_fast" =>
311314
(1, vec![param(0), param(0)], param(0)),
312315

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