Add ctlz_nonzero & cttz_nonzero intrinsics

LLVM currently doesn't remove the "bypass if argument is zero" assembly inside branches where the value is known to be non-zero, pessimizing code that uses uN::leading_zeros
This commit is contained in:
Scott McMurray 2017-05-27 20:56:25 -07:00
parent 9454dd5d2d
commit 13e2400347
4 changed files with 80 additions and 2 deletions

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@ -1229,6 +1229,23 @@ extern "rust-intrinsic" {
/// ```
pub fn ctlz<T>(x: T) -> T;
/// Like `ctlz`, but extra-unsafe as it returns `undef` when
/// given an `x` with value `0`.
///
/// # Examples
///
/// ```
/// #![feature(core_intrinsics)]
///
/// use std::intrinsics::ctlz_nonzero;
///
/// let x = 0b0001_1100_u8;
/// let num_leading = unsafe { ctlz_nonzero(x) };
/// assert_eq!(num_leading, 3);
/// ```
#[cfg(not(stage0))]
pub fn ctlz_nonzero<T>(x: T) -> T;
/// Returns the number of trailing unset bits (zeroes) in an integer type `T`.
///
/// # Examples
@ -1256,6 +1273,23 @@ extern "rust-intrinsic" {
/// ```
pub fn cttz<T>(x: T) -> T;
/// Like `cttz`, but extra-unsafe as it returns `undef` when
/// given an `x` with value `0`.
///
/// # Examples
///
/// ```
/// #![feature(core_intrinsics)]
///
/// use std::intrinsics::cttz_nonzero;
///
/// let x = 0b0011_1000_u8;
/// let num_trailing = unsafe { cttz_nonzero(x) };
/// assert_eq!(num_trailing, 3);
/// ```
#[cfg(not(stage0))]
pub fn cttz_nonzero<T>(x: T) -> T;
/// Reverses the bytes in an integer type `T`.
pub fn bswap<T>(x: T) -> T;

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@ -267,7 +267,7 @@ pub fn trans_intrinsic_call<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
};
bcx.call(expect, &[llargs[0], C_i32(ccx, rw), llargs[1], C_i32(ccx, cache_type)], None)
},
"ctlz" | "cttz" | "ctpop" | "bswap" |
"ctlz" | "ctlz_nonzero" | "cttz" | "cttz_nonzero" | "ctpop" | "bswap" |
"add_with_overflow" | "sub_with_overflow" | "mul_with_overflow" |
"overflowing_add" | "overflowing_sub" | "overflowing_mul" |
"unchecked_div" | "unchecked_rem" | "unchecked_shl" | "unchecked_shr" => {
@ -280,6 +280,12 @@ pub fn trans_intrinsic_call<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
let llfn = ccx.get_intrinsic(&format!("llvm.{}.i{}", name, width));
bcx.call(llfn, &[llargs[0], y], None)
}
"ctlz_nonzero" | "cttz_nonzero" => {
let y = C_bool(bcx.ccx, true);
let llvm_name = &format!("llvm.{}.i{}", &name[..4], width);
let llfn = ccx.get_intrinsic(llvm_name);
bcx.call(llfn, &[llargs[0], y], None)
}
"ctpop" => bcx.call(ccx.get_intrinsic(&format!("llvm.ctpop.i{}", width)),
&llargs, None),
"bswap" => {

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@ -272,7 +272,8 @@ pub fn check_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
"volatile_store" =>
(1, vec![ tcx.mk_mut_ptr(param(0)), param(0) ], tcx.mk_nil()),
"ctpop" | "ctlz" | "cttz" | "bswap" => (1, vec![param(0)], param(0)),
"ctpop" | "ctlz" | "ctlz_nonzero" | "cttz" | "cttz_nonzero" | "bswap" =>
(1, vec![param(0)], param(0)),
"add_with_overflow" | "sub_with_overflow" | "mul_with_overflow" =>
(1, vec![param(0), param(0)],

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@ -14,7 +14,9 @@ mod rusti {
extern "rust-intrinsic" {
pub fn ctpop<T>(x: T) -> T;
pub fn ctlz<T>(x: T) -> T;
pub fn ctlz_nonzero<T>(x: T) -> T;
pub fn cttz<T>(x: T) -> T;
pub fn cttz_nonzero<T>(x: T) -> T;
pub fn bswap<T>(x: T) -> T;
}
}
@ -68,6 +70,21 @@ pub fn main() {
assert_eq!(ctlz(100u32), 25); assert_eq!(ctlz(100i32), 25);
assert_eq!(ctlz(100u64), 57); assert_eq!(ctlz(100i64), 57);
assert_eq!(ctlz_nonzero(1u8), 7); assert_eq!(ctlz_nonzero(1i8), 7);
assert_eq!(ctlz_nonzero(1u16), 15); assert_eq!(ctlz_nonzero(1i16), 15);
assert_eq!(ctlz_nonzero(1u32), 31); assert_eq!(ctlz_nonzero(1i32), 31);
assert_eq!(ctlz_nonzero(1u64), 63); assert_eq!(ctlz_nonzero(1i64), 63);
assert_eq!(ctlz_nonzero(10u8), 4); assert_eq!(ctlz_nonzero(10i8), 4);
assert_eq!(ctlz_nonzero(10u16), 12); assert_eq!(ctlz_nonzero(10i16), 12);
assert_eq!(ctlz_nonzero(10u32), 28); assert_eq!(ctlz_nonzero(10i32), 28);
assert_eq!(ctlz_nonzero(10u64), 60); assert_eq!(ctlz_nonzero(10i64), 60);
assert_eq!(ctlz_nonzero(100u8), 1); assert_eq!(ctlz_nonzero(100i8), 1);
assert_eq!(ctlz_nonzero(100u16), 9); assert_eq!(ctlz_nonzero(100i16), 9);
assert_eq!(ctlz_nonzero(100u32), 25); assert_eq!(ctlz_nonzero(100i32), 25);
assert_eq!(ctlz_nonzero(100u64), 57); assert_eq!(ctlz_nonzero(100i64), 57);
assert_eq!(cttz(-1i8 as u8), 0); assert_eq!(cttz(-1i8), 0);
assert_eq!(cttz(-1i16 as u16), 0); assert_eq!(cttz(-1i16), 0);
assert_eq!(cttz(-1i32 as u32), 0); assert_eq!(cttz(-1i32), 0);
@ -93,6 +110,26 @@ pub fn main() {
assert_eq!(cttz(100u32), 2); assert_eq!(cttz(100i32), 2);
assert_eq!(cttz(100u64), 2); assert_eq!(cttz(100i64), 2);
assert_eq!(cttz_nonzero(-1i8 as u8), 0); assert_eq!(cttz_nonzero(-1i8), 0);
assert_eq!(cttz_nonzero(-1i16 as u16), 0); assert_eq!(cttz_nonzero(-1i16), 0);
assert_eq!(cttz_nonzero(-1i32 as u32), 0); assert_eq!(cttz_nonzero(-1i32), 0);
assert_eq!(cttz_nonzero(-1i64 as u64), 0); assert_eq!(cttz_nonzero(-1i64), 0);
assert_eq!(cttz_nonzero(1u8), 0); assert_eq!(cttz_nonzero(1i8), 0);
assert_eq!(cttz_nonzero(1u16), 0); assert_eq!(cttz_nonzero(1i16), 0);
assert_eq!(cttz_nonzero(1u32), 0); assert_eq!(cttz_nonzero(1i32), 0);
assert_eq!(cttz_nonzero(1u64), 0); assert_eq!(cttz_nonzero(1i64), 0);
assert_eq!(cttz_nonzero(10u8), 1); assert_eq!(cttz_nonzero(10i8), 1);
assert_eq!(cttz_nonzero(10u16), 1); assert_eq!(cttz_nonzero(10i16), 1);
assert_eq!(cttz_nonzero(10u32), 1); assert_eq!(cttz_nonzero(10i32), 1);
assert_eq!(cttz_nonzero(10u64), 1); assert_eq!(cttz_nonzero(10i64), 1);
assert_eq!(cttz_nonzero(100u8), 2); assert_eq!(cttz_nonzero(100i8), 2);
assert_eq!(cttz_nonzero(100u16), 2); assert_eq!(cttz_nonzero(100i16), 2);
assert_eq!(cttz_nonzero(100u32), 2); assert_eq!(cttz_nonzero(100i32), 2);
assert_eq!(cttz_nonzero(100u64), 2); assert_eq!(cttz_nonzero(100i64), 2);
assert_eq!(bswap(0x0Au8), 0x0A); // no-op
assert_eq!(bswap(0x0Ai8), 0x0A); // no-op
assert_eq!(bswap(0x0A0Bu16), 0x0B0A);