unstably constify float mul_add methods

Qelxiros · Qelxiros · commit e45ce83fba1e · 2025-09-18T17:03:34.000-04:00
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -636,6 +636,14 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 dest,
                 rustc_apfloat::Round::NearestTiesToEven,
             )?,
+            sym::fmaf16 => self.fma_intrinsic::<Half>(args, dest)?,
+            sym::fmaf32 => self.fma_intrinsic::<Single>(args, dest)?,
+            sym::fmaf64 => self.fma_intrinsic::<Double>(args, dest)?,
+            sym::fmaf128 => self.fma_intrinsic::<Quad>(args, dest)?,
+            sym::fmuladdf16 => self.float_muladd_intrinsic::<Half>(args, dest)?,
+            sym::fmuladdf32 => self.float_muladd_intrinsic::<Single>(args, dest)?,
+            sym::fmuladdf64 => self.float_muladd_intrinsic::<Double>(args, dest)?,
+            sym::fmuladdf128 => self.float_muladd_intrinsic::<Quad>(args, dest)?,
 
             // Unsupported intrinsic: skip the return_to_block below.
             _ => return interp_ok(false),
@@ -1035,4 +1043,42 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         self.write_scalar(res, dest)?;
         interp_ok(())
     }
+
+    fn fma_intrinsic<F>(
+        &mut self,
+        args: &[OpTy<'tcx, M::Provenance>],
+        dest: &PlaceTy<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx, ()>
+    where
+        F: rustc_apfloat::Float + rustc_apfloat::FloatConvert<F> + Into<Scalar<M::Provenance>>,
+    {
+        let a: F = self.read_scalar(&args[0])?.to_float()?;
+        let b: F = self.read_scalar(&args[1])?.to_float()?;
+        let c: F = self.read_scalar(&args[2])?.to_float()?;
+
+        let res = a.mul_add(b, c).value;
+        let res = self.adjust_nan(res, &[a, b, c]);
+        self.write_scalar(res, dest)?;
+        interp_ok(())
+    }
+
+    fn float_muladd_intrinsic<F>(
+        &mut self,
+        args: &[OpTy<'tcx, M::Provenance>],
+        dest: &PlaceTy<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx, ()>
+    where
+        F: rustc_apfloat::Float + rustc_apfloat::FloatConvert<F> + Into<Scalar<M::Provenance>>,
+    {
+        let a: F = self.read_scalar(&args[0])?.to_float()?;
+        let b: F = self.read_scalar(&args[1])?.to_float()?;
+        let c: F = self.read_scalar(&args[2])?.to_float()?;
+
+        let fuse = M::float_nondet(&self.machine);
+
+        let res = if fuse { a.mul_add(b, c).value } else { ((a * b).value + c).value };
+        let res = self.adjust_nan(res, &[a, b, c]);
+        self.write_scalar(res, dest)?;
+        interp_ok(())
+    }
 }
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -301,6 +301,9 @@ pub trait Machine<'tcx>: Sized {
     /// Determines the result of a `NullaryOp::ContractChecks` invocation.
     fn contract_checks(_ecx: &InterpCx<'tcx, Self>) -> InterpResult<'tcx, bool>;
 
+    /// Determines whether floating-point operations can behave non-deterministically.
+    fn float_nondet(_machine: &Self) -> bool;
+
     /// Called when the interpreter encounters a `StatementKind::ConstEvalCounter` instruction.
     /// You can use this to detect long or endlessly running programs.
     #[inline]
@@ -686,6 +689,11 @@ pub macro compile_time_machine(<$tcx: lifetime>) {
         interp_ok(true)
     }
 
+    #[inline(always)]
+    fn float_nondet(_machine: &Self) -> bool {
+        true
+    }
+
     #[inline(always)]
     fn adjust_global_allocation<'b>(
         _ecx: &InterpCx<$tcx, Self>,
diff --git a/library/core/src/intrinsics/mod.rs b/library/core/src/intrinsics/mod.rs
@@ -1312,28 +1312,28 @@ pub unsafe fn log2f128(x: f128) -> f128;
 /// [`f16::mul_add`](../../std/primitive.f16.html#method.mul_add)
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmaf16(a: f16, b: f16, c: f16) -> f16;
+pub const unsafe fn fmaf16(a: f16, b: f16, c: f16) -> f16;
 /// Returns `a * b + c` for `f32` values.
 ///
 /// The stabilized version of this intrinsic is
 /// [`f32::mul_add`](../../std/primitive.f32.html#method.mul_add)
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmaf32(a: f32, b: f32, c: f32) -> f32;
+pub const unsafe fn fmaf32(a: f32, b: f32, c: f32) -> f32;
 /// Returns `a * b + c` for `f64` values.
 ///
 /// The stabilized version of this intrinsic is
 /// [`f64::mul_add`](../../std/primitive.f64.html#method.mul_add)
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmaf64(a: f64, b: f64, c: f64) -> f64;
+pub const unsafe fn fmaf64(a: f64, b: f64, c: f64) -> f64;
 /// Returns `a * b + c` for `f128` values.
 ///
 /// The stabilized version of this intrinsic is
 /// [`f128::mul_add`](../../std/primitive.f128.html#method.mul_add)
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmaf128(a: f128, b: f128, c: f128) -> f128;
+pub const unsafe fn fmaf128(a: f128, b: f128, c: f128) -> f128;
 
 /// Returns `a * b + c` for `f16` values, non-deterministically executing
 /// either a fused multiply-add or two operations with rounding of the
@@ -1347,7 +1347,7 @@ pub unsafe fn fmaf128(a: f128, b: f128, c: f128) -> f128;
 /// example.
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmuladdf16(a: f16, b: f16, c: f16) -> f16;
+pub const unsafe fn fmuladdf16(a: f16, b: f16, c: f16) -> f16;
 /// Returns `a * b + c` for `f32` values, non-deterministically executing
 /// either a fused multiply-add or two operations with rounding of the
 /// intermediate result.
@@ -1360,7 +1360,7 @@ pub unsafe fn fmuladdf16(a: f16, b: f16, c: f16) -> f16;
 /// example.
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmuladdf32(a: f32, b: f32, c: f32) -> f32;
+pub const unsafe fn fmuladdf32(a: f32, b: f32, c: f32) -> f32;
 /// Returns `a * b + c` for `f64` values, non-deterministically executing
 /// either a fused multiply-add or two operations with rounding of the
 /// intermediate result.
@@ -1373,7 +1373,7 @@ pub unsafe fn fmuladdf32(a: f32, b: f32, c: f32) -> f32;
 /// example.
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmuladdf64(a: f64, b: f64, c: f64) -> f64;
+pub const unsafe fn fmuladdf64(a: f64, b: f64, c: f64) -> f64;
 /// Returns `a * b + c` for `f128` values, non-deterministically executing
 /// either a fused multiply-add or two operations with rounding of the
 /// intermediate result.
@@ -1386,7 +1386,7 @@ pub unsafe fn fmuladdf64(a: f64, b: f64, c: f64) -> f64;
 /// example.
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn fmuladdf128(a: f128, b: f128, c: f128) -> f128;
+pub const unsafe fn fmuladdf128(a: f128, b: f128, c: f128) -> f128;
 
 /// Returns the largest integer less than or equal to an `f16`.
 ///
diff --git a/library/core/src/num/f128.rs b/library/core/src/num/f128.rs
@@ -1663,7 +1663,8 @@ impl f128 {
     #[doc(alias = "fmaf128", alias = "fusedMultiplyAdd")]
     #[unstable(feature = "f128", issue = "116909")]
     #[must_use = "method returns a new number and does not mutate the original value"]
-    pub fn mul_add(self, a: f128, b: f128) -> f128 {
+    #[rustc_const_unstable(feature = "const_mul_add", issue = "146724")]
+    pub const fn mul_add(self, a: f128, b: f128) -> f128 {
         // SAFETY: intrinsic with no preconditions
         unsafe { intrinsics::fmaf128(self, a, b) }
     }
diff --git a/library/core/src/num/f16.rs b/library/core/src/num/f16.rs
@@ -1638,7 +1638,8 @@ impl f16 {
     #[unstable(feature = "f16", issue = "116909")]
     #[doc(alias = "fmaf16", alias = "fusedMultiplyAdd")]
     #[must_use = "method returns a new number and does not mutate the original value"]
-    pub fn mul_add(self, a: f16, b: f16) -> f16 {
+    #[rustc_const_unstable(feature = "const_mul_add", issue = "146724")]
+    pub const fn mul_add(self, a: f16, b: f16) -> f16 {
         // SAFETY: intrinsic with no preconditions
         unsafe { intrinsics::fmaf16(self, a, b) }
     }
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
@@ -1803,7 +1803,8 @@ pub mod math {
     #[doc(alias = "fmaf", alias = "fusedMultiplyAdd")]
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[unstable(feature = "core_float_math", issue = "137578")]
-    pub fn mul_add(x: f32, y: f32, z: f32) -> f32 {
+    #[rustc_const_unstable(feature = "const_mul_add", issue = "146724")]
+    pub const fn mul_add(x: f32, y: f32, z: f32) -> f32 {
         // SAFETY: intrinsic with no preconditions
         unsafe { intrinsics::fmaf32(x, y, z) }
     }
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
@@ -1801,7 +1801,8 @@ pub mod math {
     #[doc(alias = "fma", alias = "fusedMultiplyAdd")]
     #[unstable(feature = "core_float_math", issue = "137578")]
     #[must_use = "method returns a new number and does not mutate the original value"]
-    pub fn mul_add(x: f64, a: f64, b: f64) -> f64 {
+    #[rustc_const_unstable(feature = "const_mul_add", issue = "146724")]
+    pub const fn mul_add(x: f64, a: f64, b: f64) -> f64 {
         // SAFETY: intrinsic with no preconditions
         unsafe { intrinsics::fmaf64(x, a, b) }
     }
diff --git a/library/coretests/tests/floats/f128.rs b/library/coretests/tests/floats/f128.rs
@@ -20,24 +20,6 @@ const TOL_PRECISE: f128 = 1e-28;
 // FIXME(f16_f128,miri): many of these have to be disabled since miri does not yet support
 // the intrinsics.
 
-#[test]
-#[cfg(not(miri))]
-#[cfg(target_has_reliable_f128_math)]
-fn test_mul_add() {
-    let nan: f128 = f128::NAN;
-    let inf: f128 = f128::INFINITY;
-    let neg_inf: f128 = f128::NEG_INFINITY;
-    assert_biteq!(12.3f128.mul_add(4.5, 6.7), 62.0500000000000000000000000000000037);
-    assert_biteq!((-12.3f128).mul_add(-4.5, -6.7), 48.6500000000000000000000000000000049);
-    assert_biteq!(0.0f128.mul_add(8.9, 1.2), 1.2);
-    assert_biteq!(3.4f128.mul_add(-0.0, 5.6), 5.6);
-    assert!(nan.mul_add(7.8, 9.0).is_nan());
-    assert_biteq!(inf.mul_add(7.8, 9.0), inf);
-    assert_biteq!(neg_inf.mul_add(7.8, 9.0), neg_inf);
-    assert_biteq!(8.9f128.mul_add(inf, 3.2), inf);
-    assert_biteq!((-3.2f128).mul_add(2.4, neg_inf), neg_inf);
-}
-
 #[test]
 #[cfg(any(miri, target_has_reliable_f128_math))]
 fn test_max_recip() {
diff --git a/library/coretests/tests/floats/f16.rs b/library/coretests/tests/floats/f16.rs
@@ -22,24 +22,6 @@ const TOL_P4: f16 = 10.0;
 // FIXME(f16_f128,miri): many of these have to be disabled since miri does not yet support
 // the intrinsics.
 
-#[test]
-#[cfg(not(miri))]
-#[cfg(target_has_reliable_f16_math)]
-fn test_mul_add() {
-    let nan: f16 = f16::NAN;
-    let inf: f16 = f16::INFINITY;
-    let neg_inf: f16 = f16::NEG_INFINITY;
-    assert_biteq!(12.3f16.mul_add(4.5, 6.7), 62.031);
-    assert_biteq!((-12.3f16).mul_add(-4.5, -6.7), 48.625);
-    assert_biteq!(0.0f16.mul_add(8.9, 1.2), 1.2);
-    assert_biteq!(3.4f16.mul_add(-0.0, 5.6), 5.6);
-    assert!(nan.mul_add(7.8, 9.0).is_nan());
-    assert_biteq!(inf.mul_add(7.8, 9.0), inf);
-    assert_biteq!(neg_inf.mul_add(7.8, 9.0), neg_inf);
-    assert_biteq!(8.9f16.mul_add(inf, 3.2), inf);
-    assert_biteq!((-3.2f16).mul_add(2.4, neg_inf), neg_inf);
-}
-
 #[test]
 #[cfg(any(miri, target_has_reliable_f16_math))]
 fn test_max_recip() {
diff --git a/library/coretests/tests/floats/f32.rs b/library/coretests/tests/floats/f32.rs
diff --git a/library/coretests/tests/floats/f64.rs b/library/coretests/tests/floats/f64.rs
diff --git a/library/coretests/tests/floats/mod.rs b/library/coretests/tests/floats/mod.rs
@@ -34,6 +34,8 @@ trait TestableFloat: Sized {
     const RAW_12_DOT_5: Self;
     const RAW_1337: Self;
     const RAW_MINUS_14_DOT_25: Self;
+    const MUL_ADD_RESULT: Self;
+    const NEG_MUL_ADD_RESULT: Self;
 }
 
 impl TestableFloat for f16 {
@@ -58,6 +60,8 @@ impl TestableFloat for f16 {
     const RAW_12_DOT_5: Self = Self::from_bits(0x4a40);
     const RAW_1337: Self = Self::from_bits(0x6539);
     const RAW_MINUS_14_DOT_25: Self = Self::from_bits(0xcb20);
+    const MUL_ADD_RESULT: Self = 62.031;
+    const NEG_MUL_ADD_RESULT: Self = 48.625;
 }
 
 impl TestableFloat for f32 {
@@ -84,6 +88,8 @@ impl TestableFloat for f32 {
     const RAW_12_DOT_5: Self = Self::from_bits(0x41480000);
     const RAW_1337: Self = Self::from_bits(0x44a72000);
     const RAW_MINUS_14_DOT_25: Self = Self::from_bits(0xc1640000);
+    const MUL_ADD_RESULT: Self = 62.05;
+    const NEG_MUL_ADD_RESULT: Self = 48.65;
 }
 
 impl TestableFloat for f64 {
@@ -106,6 +112,8 @@ impl TestableFloat for f64 {
     const RAW_12_DOT_5: Self = Self::from_bits(0x4029000000000000);
     const RAW_1337: Self = Self::from_bits(0x4094e40000000000);
     const RAW_MINUS_14_DOT_25: Self = Self::from_bits(0xc02c800000000000);
+    const MUL_ADD_RESULT: Self = 62.050000000000004;
+    const NEG_MUL_ADD_RESULT: Self = 48.650000000000006;
 }
 
 impl TestableFloat for f128 {
@@ -128,6 +136,8 @@ impl TestableFloat for f128 {
     const RAW_12_DOT_5: Self = Self::from_bits(0x40029000000000000000000000000000);
     const RAW_1337: Self = Self::from_bits(0x40094e40000000000000000000000000);
     const RAW_MINUS_14_DOT_25: Self = Self::from_bits(0xc002c800000000000000000000000000);
+    const MUL_ADD_RESULT: Self = 62.0500000000000000000000000000000037;
+    const NEG_MUL_ADD_RESULT: Self = 48.6500000000000000000000000000000049;
 }
 
 /// Determine the tolerance for values of the argument type.
@@ -359,8 +369,6 @@ macro_rules! float_test {
 
 mod f128;
 mod f16;
-mod f32;
-mod f64;
 
 float_test! {
     name: num,
@@ -1542,3 +1550,25 @@ float_test! {
         assert_biteq!(Float::from_bits(masked_nan2), Float::from_bits(masked_nan2));
     }
 }
+
+float_test! {
+    name: mul_add,
+    attrs: {
+        f16: #[cfg(any(miri, target_has_reliable_f16))],
+        f128: #[cfg(any(miri, target_has_reliable_f128))],
+    },
+    test<Float> {
+        let nan: Float = Float::NAN;
+        let inf: Float = Float::INFINITY;
+        let neg_inf: Float = Float::NEG_INFINITY;
+        assert_biteq!(flt(12.3).mul_add(4.5, 6.7), Float::MUL_ADD_RESULT);
+        assert_biteq!((flt(-12.3)).mul_add(-4.5, -6.7), Float::NEG_MUL_ADD_RESULT);
+        assert_biteq!(flt(0.0).mul_add(8.9, 1.2), 1.2);
+        assert_biteq!(flt(3.4).mul_add(-0.0, 5.6), 5.6);
+        assert!(nan.mul_add(7.8, 9.0).is_nan());
+        assert_biteq!(inf.mul_add(7.8, 9.0), inf);
+        assert_biteq!(neg_inf.mul_add(7.8, 9.0), neg_inf);
+        assert_biteq!(flt(8.9).mul_add(inf, 3.2), inf);
+        assert_biteq!((flt(-3.2)).mul_add(2.4, neg_inf), neg_inf);
+    }
+}
diff --git a/library/coretests/tests/lib.rs b/library/coretests/tests/lib.rs
@@ -20,6 +20,7 @@
 #![feature(const_convert)]
 #![feature(const_destruct)]
 #![feature(const_eval_select)]
+#![feature(const_mul_add)]
 #![feature(const_ops)]
 #![feature(const_option_ops)]
 #![feature(const_ref_cell)]
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
@@ -332,6 +332,7 @@
 #![feature(char_internals)]
 #![feature(clone_to_uninit)]
 #![feature(const_convert)]
+#![feature(const_mul_add)]
 #![feature(core_intrinsics)]
 #![feature(core_io_borrowed_buf)]
 #![feature(drop_guard)]
diff --git a/library/std/src/num/f32.rs b/library/std/src/num/f32.rs
@@ -217,7 +217,8 @@ impl f32 {
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
-    pub fn mul_add(self, a: f32, b: f32) -> f32 {
+    #[rustc_const_unstable(feature = "const_mul_add", issue = "146724")]
+    pub const fn mul_add(self, a: f32, b: f32) -> f32 {
         core::f32::math::mul_add(self, a, b)
     }
 
diff --git a/library/std/src/num/f64.rs b/library/std/src/num/f64.rs
@@ -217,7 +217,8 @@ impl f64 {
     #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
-    pub fn mul_add(self, a: f64, b: f64) -> f64 {
+    #[rustc_const_unstable(feature = "const_mul_add", issue = "146724")]
+    pub const fn mul_add(self, a: f64, b: f64) -> f64 {
         core::f64::math::mul_add(self, a, b)
     }
 
diff --git a/src/tools/miri/src/intrinsics/mod.rs b/src/tools/miri/src/intrinsics/mod.rs
diff --git a/src/tools/miri/src/machine.rs b/src/tools/miri/src/machine.rs
