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unchecked_{shl|shr} should use u32 as the RHS

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This commit is contained in:
Scott McMurray 2022-10-23 17:02:50 -07:00
parent 1ca6777c01
commit 3b16c04676
5 changed files with 87 additions and 12 deletions
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1
library/core/src/lib.rs
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@ -130,6 +130,7 @@
#![feature(const_pin)]
#![feature(const_ptr_sub_ptr)]
#![feature(const_replace)]
#![feature(const_result_drop)]
#![feature(const_ptr_as_ref)]
#![feature(const_ptr_is_null)]
#![feature(const_ptr_read)]

16
library/core/src/num/int_macros.rs
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@ -757,10 +757,11 @@ pub const fn checked_shl(self, rhs: u32) -> Option<Self> {
#[rustc_const_unstable(feature = "const_inherent_unchecked_arith", issue = "85122")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn unchecked_shl(self, rhs: Self) -> Self {
pub const unsafe fn unchecked_shl(self, rhs: u32) -> Self {
// SAFETY: the caller must uphold the safety contract for
// `unchecked_shl`.
unsafe { intrinsics::unchecked_shl(self, rhs) }
// Any legal shift amount is losslessly representable in the self type.
unsafe { intrinsics::unchecked_shl(self, rhs.try_into().ok().unwrap_unchecked()) }
}
/// Checked shift right. Computes `self >> rhs`, returning `None` if `rhs` is
@ -804,10 +805,11 @@ pub const fn checked_shr(self, rhs: u32) -> Option<Self> {
#[rustc_const_unstable(feature = "const_inherent_unchecked_arith", issue = "85122")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn unchecked_shr(self, rhs: Self) -> Self {
pub const unsafe fn unchecked_shr(self, rhs: u32) -> Self {
// SAFETY: the caller must uphold the safety contract for
// `unchecked_shr`.
unsafe { intrinsics::unchecked_shr(self, rhs) }
// Any legal shift amount is losslessly representable in the self type.
unsafe { intrinsics::unchecked_shr(self, rhs.try_into().ok().unwrap_unchecked()) }
}
/// Checked absolute value. Computes `self.abs()`, returning `None` if
@ -1354,11 +1356,12 @@ pub const fn wrapping_neg(self) -> Self {
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline(always)]
#[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]
pub const fn wrapping_shl(self, rhs: u32) -> Self {
// SAFETY: the masking by the bitsize of the type ensures that we do not shift
// out of bounds
unsafe {
intrinsics::unchecked_shl(self, (rhs & ($BITS - 1)) as $SelfT)
self.unchecked_shl(rhs & ($BITS - 1))
}
}
@ -1383,11 +1386,12 @@ pub const fn wrapping_shl(self, rhs: u32) -> Self {
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline(always)]
#[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]
pub const fn wrapping_shr(self, rhs: u32) -> Self {
// SAFETY: the masking by the bitsize of the type ensures that we do not shift
// out of bounds
unsafe {
intrinsics::unchecked_shr(self, (rhs & ($BITS - 1)) as $SelfT)
self.unchecked_shr(rhs & ($BITS - 1))
}
}

1
library/core/src/num/mod.rs
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@ -3,6 +3,7 @@
#![stable(feature = "rust1", since = "1.0.0")]
use crate::ascii;
use crate::convert::TryInto;
use crate::error::Error;
use crate::intrinsics;
use crate::mem;

16
library/core/src/num/uint_macros.rs
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@ -901,10 +901,11 @@ pub const fn checked_shl(self, rhs: u32) -> Option<Self> {
#[rustc_const_unstable(feature = "const_inherent_unchecked_arith", issue = "85122")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn unchecked_shl(self, rhs: Self) -> Self {
pub const unsafe fn unchecked_shl(self, rhs: u32) -> Self {
// SAFETY: the caller must uphold the safety contract for
// `unchecked_shl`.
unsafe { intrinsics::unchecked_shl(self, rhs) }
// Any legal shift amount is losslessly representable in the self type.
unsafe { intrinsics::unchecked_shl(self, rhs.try_into().ok().unwrap_unchecked()) }
}
/// Checked shift right. Computes `self >> rhs`, returning `None`
@ -948,10 +949,11 @@ pub const fn checked_shr(self, rhs: u32) -> Option<Self> {
#[rustc_const_unstable(feature = "const_inherent_unchecked_arith", issue = "85122")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub const unsafe fn unchecked_shr(self, rhs: Self) -> Self {
pub const unsafe fn unchecked_shr(self, rhs: u32) -> Self {
// SAFETY: the caller must uphold the safety contract for
// `unchecked_shr`.
unsafe { intrinsics::unchecked_shr(self, rhs) }
// Any legal shift amount is losslessly representable in the self type.
unsafe { intrinsics::unchecked_shr(self, rhs.try_into().ok().unwrap_unchecked()) }
}
/// Checked exponentiation. Computes `self.pow(exp)`, returning `None` if
@ -1367,11 +1369,12 @@ pub const fn wrapping_neg(self) -> Self {
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline(always)]
#[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]
pub const fn wrapping_shl(self, rhs: u32) -> Self {
// SAFETY: the masking by the bitsize of the type ensures that we do not shift
// out of bounds
unsafe {
intrinsics::unchecked_shl(self, (rhs & ($BITS - 1)) as $SelfT)
self.unchecked_shl(rhs & ($BITS - 1))
}
}
@ -1399,11 +1402,12 @@ pub const fn wrapping_shl(self, rhs: u32) -> Self {
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline(always)]
#[rustc_allow_const_fn_unstable(const_inherent_unchecked_arith)]
pub const fn wrapping_shr(self, rhs: u32) -> Self {
// SAFETY: the masking by the bitsize of the type ensures that we do not shift
// out of bounds
unsafe {
intrinsics::unchecked_shr(self, (rhs & ($BITS - 1)) as $SelfT)
self.unchecked_shr(rhs & ($BITS - 1))
}
}

65
src/test/codegen/unchecked_shifts.rs Normal file
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@ -0,0 +1,65 @@
// compile-flags: -O
// min-llvm-version: 15.0 (LLVM 13 in CI does this differently from submodule LLVM)
#![crate_type = "lib"]
#![feature(unchecked_math)]
// CHECK-LABEL: @unchecked_shl_unsigned_same
#[no_mangle]
pub unsafe fn unchecked_shl_unsigned_same(a: u32, b: u32) -> u32 {
// CHECK-NOT: and i32
// CHECK: shl i32 %a, %b
// CHECK-NOT: and i32
a.unchecked_shl(b)
}
// CHECK-LABEL: @unchecked_shl_unsigned_smaller
#[no_mangle]
pub unsafe fn unchecked_shl_unsigned_smaller(a: u16, b: u32) -> u16 {
// This uses -DAG to avoid failing on irrelevant reorderings,
// like emitting the truncation earlier.
// CHECK-DAG: %[[INRANGE:.+]] = icmp ult i32 %b, 65536
// CHECK-DAG: tail call void @llvm.assume(i1 %[[INRANGE]])
// CHECK-DAG: %[[TRUNC:.+]] = trunc i32 %b to i16
// CHECK-DAG: shl i16 %a, %[[TRUNC]]
a.unchecked_shl(b)
}
// CHECK-LABEL: @unchecked_shl_unsigned_bigger
#[no_mangle]
pub unsafe fn unchecked_shl_unsigned_bigger(a: u64, b: u32) -> u64 {
// CHECK: %[[EXT:.+]] = zext i32 %b to i64
// CHECK: shl i64 %a, %[[EXT]]
a.unchecked_shl(b)
}
// CHECK-LABEL: @unchecked_shr_signed_same
#[no_mangle]
pub unsafe fn unchecked_shr_signed_same(a: i32, b: u32) -> i32 {
// CHECK-NOT: and i32
// CHECK: ashr i32 %a, %b
// CHECK-NOT: and i32
a.unchecked_shr(b)
}
// CHECK-LABEL: @unchecked_shr_signed_smaller
#[no_mangle]
pub unsafe fn unchecked_shr_signed_smaller(a: i16, b: u32) -> i16 {
// This uses -DAG to avoid failing on irrelevant reorderings,
// like emitting the truncation earlier.
// CHECK-DAG: %[[INRANGE:.+]] = icmp ult i32 %b, 32768
// CHECK-DAG: tail call void @llvm.assume(i1 %[[INRANGE]])
// CHECK-DAG: %[[TRUNC:.+]] = trunc i32 %b to i16
// CHECK-DAG: ashr i16 %a, %[[TRUNC]]
a.unchecked_shr(b)
}
// CHECK-LABEL: @unchecked_shr_signed_bigger
#[no_mangle]
pub unsafe fn unchecked_shr_signed_bigger(a: i64, b: u32) -> i64 {
// CHECK: %[[EXT:.+]] = zext i32 %b to i64
// CHECK: ashr i64 %a, %[[EXT]]
a.unchecked_shr(b)
}