Expose algebraic floating point intrinsics

Author: calder

Diff for: library/core/src/intrinsics/mod.rs

@@ -2475,35 +2475,35 @@ pub unsafe fn float_to_int_unchecked<Float: Copy, Int: Copy>(value: Float) -> In
 
 /// Float addition that allows optimizations based on algebraic rules.
 ///
-/// This intrinsic does not have a stable counterpart.
+/// Stabilized as [`f16::algebraic_add`], [`f32::algebraic_add`], [`f64::algebraic_add`] and [`f128::algebraic_add`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
 pub fn fadd_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float subtraction that allows optimizations based on algebraic rules.
 ///
-/// This intrinsic does not have a stable counterpart.
+/// Stabilized as [`f16::algebraic_sub`], [`f32::algebraic_sub`], [`f64::algebraic_sub`] and [`f128::algebraic_sub`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
 pub fn fsub_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float multiplication that allows optimizations based on algebraic rules.
 ///
-/// This intrinsic does not have a stable counterpart.
+/// Stabilized as [`f16::algebraic_mul`], [`f32::algebraic_mul`], [`f64::algebraic_mul`] and [`f128::algebraic_mul`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
 pub fn fmul_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float division that allows optimizations based on algebraic rules.
 ///
-/// This intrinsic does not have a stable counterpart.
+/// Stabilized as [`f16::algebraic_div`], [`f32::algebraic_div`], [`f64::algebraic_div`] and [`f128::algebraic_div`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
 pub fn fdiv_algebraic<T: Copy>(a: T, b: T) -> T;
 
 /// Float remainder that allows optimizations based on algebraic rules.
 ///
-/// This intrinsic does not have a stable counterpart.
+/// Stabilized as [`f16::algebraic_rem`], [`f32::algebraic_rem`], [`f64::algebraic_rem`] and [`f128::algebraic_rem`].
 #[rustc_nounwind]
 #[rustc_intrinsic]
 pub fn frem_algebraic<T: Copy>(a: T, b: T) -> T;

Diff for: library/core/src/num/f128.rs

@@ -1362,4 +1362,54 @@ impl f128 {
         // SAFETY: this is actually a safe intrinsic
         unsafe { intrinsics::copysignf128(self, sign) }
     }
+
+    /// Float addition that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_add(self, rhs: f128) -> f128 {
+        intrinsics::fadd_algebraic(self, rhs)
+    }
+
+    /// Float subtraction that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_sub(self, rhs: f128) -> f128 {
+        intrinsics::fsub_algebraic(self, rhs)
+    }
+
+    /// Float multiplication that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_mul(self, rhs: f128) -> f128 {
+        intrinsics::fmul_algebraic(self, rhs)
+    }
+
+    /// Float division that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_div(self, rhs: f128) -> f128 {
+        intrinsics::fdiv_algebraic(self, rhs)
+    }
+
+    /// Float remainder that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_rem(self, rhs: f128) -> f128 {
+        intrinsics::frem_algebraic(self, rhs)
+    }
 }

Diff for: library/core/src/num/f16.rs

@@ -1338,4 +1338,54 @@ impl f16 {
         // SAFETY: this is actually a safe intrinsic
         unsafe { intrinsics::copysignf16(self, sign) }
     }
+
+    /// Float addition that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_add(self, rhs: f16) -> f16 {
+        intrinsics::fadd_algebraic(self, rhs)
+    }
+
+    /// Float subtraction that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_sub(self, rhs: f16) -> f16 {
+        intrinsics::fsub_algebraic(self, rhs)
+    }
+
+    /// Float multiplication that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_mul(self, rhs: f16) -> f16 {
+        intrinsics::fmul_algebraic(self, rhs)
+    }
+
+    /// Float division that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_div(self, rhs: f16) -> f16 {
+        intrinsics::fdiv_algebraic(self, rhs)
+    }
+
+    /// Float remainder that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_rem(self, rhs: f16) -> f16 {
+        intrinsics::frem_algebraic(self, rhs)
+    }
 }

Diff for: library/core/src/num/f32.rs

@@ -1504,4 +1504,54 @@ impl f32 {
         // SAFETY: this is actually a safe intrinsic
         unsafe { intrinsics::copysignf32(self, sign) }
     }
+
+    /// Float addition that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_add(self, rhs: f32) -> f32 {
+        intrinsics::fadd_algebraic(self, rhs)
+    }
+
+    /// Float subtraction that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_sub(self, rhs: f32) -> f32 {
+        intrinsics::fsub_algebraic(self, rhs)
+    }
+
+    /// Float multiplication that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_mul(self, rhs: f32) -> f32 {
+        intrinsics::fmul_algebraic(self, rhs)
+    }
+
+    /// Float division that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_div(self, rhs: f32) -> f32 {
+        intrinsics::fdiv_algebraic(self, rhs)
+    }
+
+    /// Float remainder that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_rem(self, rhs: f32) -> f32 {
+        intrinsics::frem_algebraic(self, rhs)
+    }
 }

Diff for: library/core/src/num/f64.rs

@@ -1503,4 +1503,54 @@ impl f64 {
         // SAFETY: this is actually a safe intrinsic
         unsafe { intrinsics::copysignf64(self, sign) }
     }
+
+    /// Float addition that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_add(self, rhs: f64) -> f64 {
+        intrinsics::fadd_algebraic(self, rhs)
+    }
+
+    /// Float subtraction that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_sub(self, rhs: f64) -> f64 {
+        intrinsics::fsub_algebraic(self, rhs)
+    }
+
+    /// Float multiplication that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_mul(self, rhs: f64) -> f64 {
+        intrinsics::fmul_algebraic(self, rhs)
+    }
+
+    /// Float division that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_div(self, rhs: f64) -> f64 {
+        intrinsics::fdiv_algebraic(self, rhs)
+    }
+
+    /// Float remainder that allows optimizations based on algebraic rules.
+    ///
+    /// See [algebraic operators](primitive@f32#algebraic-operators) for more info.
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    #[unstable(feature = "float_algebraic", issue = "136469")]
+    #[inline]
+    pub fn algebraic_rem(self, rhs: f64) -> f64 {
+        intrinsics::frem_algebraic(self, rhs)
+    }
 }

Diff for: library/core/src/primitive_docs.rs

@@ -1315,6 +1315,51 @@ mod prim_f16 {}
 /// | `wasm32`, `wasm64` | If all input NaNs are quiet with all-zero payload: None.<br> Otherwise: all possible payloads. |
 ///
 /// For targets not in this table, all payloads are possible.
+///
+/// # Algebraic operators
+///
+/// Algebraic operators of the form `a.algebraic_*(b)` allow the compiler to optimize
+/// floating point operations using all the usual algebraic properties of real numbers --
+/// despite the fact that those properties do *not* hold on floating point numbers.
+/// This can give a great performance boost since it may unlock vectorization.
+///
+/// The exact set of optimizations is unspecified but typically allows combining operations,
+/// rearranging series of operations based on mathematical properties, converting between division
+/// and reciprocal multiplication, and disregarding the sign of zero. This means that the results of
+/// elementary operations may have undefined precision, and "non-mathematical" values
+/// such as NaN, +/-Inf, or -0.0 may behave in unexpected ways, but these operations
+/// will never cause undefined behavior.
+///
+/// Because of the unpredictable nature of compiler optimizations, the same inputs may produce
+/// different results even within a single program run. **Unsafe code must not rely on any property
+/// of the return value for soundness.** However, implementations will generally do their best to
+/// pick a reasonable tradeoff between performance and accuracy of the result.
+///
+/// For example:
+///
+/// ```
+/// # #![feature(float_algebraic)]
+/// # #![allow(unused_assignments)]
+/// # let mut x: f32 = 0.0;
+/// # let a: f32 = 1.0;
+/// # let b: f32 = 2.0;
+/// # let c: f32 = 3.0;
+/// # let d: f32 = 4.0;
+/// x = a.algebraic_add(b).algebraic_add(c).algebraic_add(d);
+/// ```
+///
+/// May be rewritten as:
+///
+/// ```
+/// # #![allow(unused_assignments)]
+/// # let mut x: f32 = 0.0;
+/// # let a: f32 = 1.0;
+/// # let b: f32 = 2.0;
+/// # let c: f32 = 3.0;
+/// # let d: f32 = 4.0;
+/// x = a + b + c + d; // As written
+/// x = (a + c) + (b + d); // Reordered to shorten critical path and enable vectorization
+/// ```
 
 #[stable(feature = "rust1", since = "1.0.0")]
 mod prim_f32 {}

Diff for: library/std/src/lib.rs

@@ -340,6 +340,7 @@
 #![feature(exact_size_is_empty)]
 #![feature(exclusive_wrapper)]
 #![feature(extend_one)]
+#![feature(float_algebraic)]
 #![feature(float_gamma)]
 #![feature(float_minimum_maximum)]
 #![feature(fmt_internals)]

Diff for: library/std/tests/floats/f128.rs

@@ -984,6 +984,25 @@ fn test_total_cmp() {
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&s_nan()));
 }
 
+#[test]
+fn test_algebraic() {
+    let a: f128 = 123.0;
+    let b: f128 = 456.0;
+
+    // Check that individual operations match their primitive counterparts.
+    //
+    // This is a check of current implementations and does NOT imply any form of
+    // guarantee about future behavior. The compiler reserves the right to make
+    // these operations inexact matches in the future.
+    let eps = if cfg!(miri) { 1e-6 } else { 0.0 };
+
+    assert_approx_eq!(a.algebraic_add(b), a + b, eps);
+    assert_approx_eq!(a.algebraic_sub(b), a - b, eps);
+    assert_approx_eq!(a.algebraic_mul(b), a * b, eps);
+    assert_approx_eq!(a.algebraic_div(b), a / b, eps);
+    assert_approx_eq!(a.algebraic_rem(b), a % b, eps);
+}
+
 #[test]
 fn test_from() {
     assert_eq!(f128::from(false), 0.0);

Diff for: library/std/tests/floats/f16.rs

@@ -954,6 +954,27 @@ fn test_total_cmp() {
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&s_nan()));
 }
 
+#[test]
+fn test_algebraic() {
+    let a: f16 = 123.0;
+    let b: f16 = 456.0;
+
+    // Check that individual operations match their primitive counterparts.
+    //
+    // This is a check of current implementations and does NOT imply any form of
+    // guarantee about future behavior. The compiler reserves the right to make
+    // these operations inexact matches in the future.
+    let eps_add = if cfg!(miri) { 1e1 } else { 0.0 };
+    let eps_mul = if cfg!(miri) { 1e3 } else { 0.0 };
+    let eps_div = if cfg!(miri) { 1e0 } else { 0.0 };
+
+    assert_approx_eq!(a.algebraic_add(b), a + b, eps_add);
+    assert_approx_eq!(a.algebraic_sub(b), a - b, eps_add);
+    assert_approx_eq!(a.algebraic_mul(b), a * b, eps_mul);
+    assert_approx_eq!(a.algebraic_div(b), a / b, eps_div);
+    assert_approx_eq!(a.algebraic_rem(b), a % b, eps_div);
+}
+
 #[test]
 fn test_from() {
     assert_eq!(f16::from(false), 0.0);

Diff for: library/std/tests/floats/f32.rs

@@ -915,3 +915,24 @@ fn test_total_cmp() {
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&f32::INFINITY));
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&s_nan()));
 }
+
+#[test]
+fn test_algebraic() {
+    let a: f32 = 123.0;
+    let b: f32 = 456.0;
+
+    // Check that individual operations match their primitive counterparts.
+    //
+    // This is a check of current implementations and does NOT imply any form of
+    // guarantee about future behavior. The compiler reserves the right to make
+    // these operations inexact matches in the future.
+    let eps_add = if cfg!(miri) { 1e-3 } else { 0.0 };
+    let eps_mul = if cfg!(miri) { 1e-1 } else { 0.0 };
+    let eps_div = if cfg!(miri) { 1e-4 } else { 0.0 };
+
+    assert_approx_eq!(a.algebraic_add(b), a + b, eps_add);
+    assert_approx_eq!(a.algebraic_sub(b), a - b, eps_add);
+    assert_approx_eq!(a.algebraic_mul(b), a * b, eps_mul);
+    assert_approx_eq!(a.algebraic_div(b), a / b, eps_div);
+    assert_approx_eq!(a.algebraic_rem(b), a % b, eps_div);
+}