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Make some float methods unstable const fn
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Some float methods are now `const fn` under the `const_float_methods` feature gate (except `f16` and `f128` versions, which I placed under `f16` and `f128` feature gates respectively).

In order to support `min` / `max`, the implementation of some intrinsics had to be moved from Miri to rustc_const_eval.
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@eduardosm
eduardosm committed Oct 4, 2024
1 parent 14f303b commit fa312ed
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Showing 9 changed files with 358 additions and 156 deletions.
43 changes: 43 additions & 0 deletions compiler/rustc_const_eval/src/interpret/intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -438,6 +438,23 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
self.write_scalar(Scalar::from_target_usize(align.bytes(), self), dest)?;
}

sym::minnumf16 | sym::maxnumf16 => {
let is_max = intrinsic_name == sym::maxnumf16;
self.float_min_max_intrinsic::<rustc_apfloat::ieee::Half>(is_max, args, dest)?;
}
sym::minnumf32 | sym::maxnumf32 => {
let is_max = intrinsic_name == sym::maxnumf32;
self.float_min_max_intrinsic::<rustc_apfloat::ieee::Single>(is_max, args, dest)?;
}
sym::minnumf64 | sym::maxnumf64 => {
let is_max = intrinsic_name == sym::maxnumf64;
self.float_min_max_intrinsic::<rustc_apfloat::ieee::Double>(is_max, args, dest)?;
}
sym::minnumf128 | sym::maxnumf128 => {
let is_max = intrinsic_name == sym::maxnumf128;
self.float_min_max_intrinsic::<rustc_apfloat::ieee::Quad>(is_max, args, dest)?;
}

// Unsupported intrinsic: skip the return_to_block below.
_ => return interp_ok(false),
}
Expand Down Expand Up @@ -697,4 +714,30 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
let rhs_bytes = get_bytes(self, rhs)?;
interp_ok(Scalar::from_bool(lhs_bytes == rhs_bytes))
}

fn float_min_max_intrinsic<F>(
&mut self,
is_max: bool,
args: &[OpTy<'tcx, M::Provenance>],
dest: &MPlaceTy<'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 res = if is_max { a.max(b) } else { a.min(b) };
self.write_scalar(adjust_nan(self, res, &[a, b]), dest)?;
interp_ok(())
}
}

// Performs appropriate non-deterministic adjustments of NaN results.
fn adjust_nan<'tcx, M, F1, F2>(this: &InterpCx<'tcx, M>, f: F2, inputs: &[F1]) -> F2
where
M: Machine<'tcx>,
F1: rustc_apfloat::Float + rustc_apfloat::FloatConvert<F2>,
F2: rustc_apfloat::Float,
{
if f.is_nan() { M::generate_nan(this, inputs) } else { f }
}
238 changes: 140 additions & 98 deletions library/core/src/intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1820,104 +1820,6 @@ extern "rust-intrinsic" {
#[rustc_nounwind]
pub fn fabsf128(x: f128) -> f128;

/// Returns the minimum of two `f16` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f16::min`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn minnumf16(x: f16, y: f16) -> f16;
/// Returns the minimum of two `f32` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f32::min`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn minnumf32(x: f32, y: f32) -> f32;
/// Returns the minimum of two `f64` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f64::min`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn minnumf64(x: f64, y: f64) -> f64;
/// Returns the minimum of two `f128` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f128::min`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn minnumf128(x: f128, y: f128) -> f128;

/// Returns the maximum of two `f16` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f16::max`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn maxnumf16(x: f16, y: f16) -> f16;
/// Returns the maximum of two `f32` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f32::max`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn maxnumf32(x: f32, y: f32) -> f32;
/// Returns the maximum of two `f64` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f64::max`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn maxnumf64(x: f64, y: f64) -> f64;
/// Returns the maximum of two `f128` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f128::max`]
#[rustc_safe_intrinsic]
#[rustc_nounwind]
pub fn maxnumf128(x: f128, y: f128) -> f128;

/// Copies the sign from `y` to `x` for `f16` values.
///
/// The stabilized version of this intrinsic is
Expand Down Expand Up @@ -3497,6 +3399,146 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
}
}

/// Returns the minimum of two `f16` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f16::min`]
#[rustc_nounwind]
// #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_const_unstable(feature = "f16", issue = "116909")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn minnumf16(_x: f16, _y: f16) -> f16 {
unimplemented!();
}

/// Returns the minimum of two `f32` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f32::min`]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn minnumf32(_x: f32, _y: f32) -> f32 {
unimplemented!();
}

/// Returns the minimum of two `f64` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f64::min`]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn minnumf64(_x: f64, _y: f64) -> f64 {
unimplemented!();
}

/// Returns the minimum of two `f128` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f128::min`]
#[rustc_nounwind]
// #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_const_unstable(feature = "f128", issue = "116909")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn minnumf128(_x: f128, _y: f128) -> f128 {
unimplemented!();
}

/// Returns the maximum of two `f16` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f16::max`]
#[rustc_nounwind]
// #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_const_unstable(feature = "f16", issue = "116909")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn maxnumf16(_x: f16, _y: f16) -> f16 {
unimplemented!();
}

/// Returns the maximum of two `f32` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f32::max`]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn maxnumf32(_x: f32, _y: f32) -> f32 {
unimplemented!();
}

/// Returns the maximum of two `f64` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f64::max`]
#[rustc_nounwind]
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn maxnumf64(_x: f64, _y: f64) -> f64 {
unimplemented!();
}

/// Returns the maximum of two `f128` values.
///
/// Note that, unlike most intrinsics, this is safe to call;
/// it does not require an `unsafe` block.
/// Therefore, implementations must not require the user to uphold
/// any safety invariants.
///
/// The stabilized version of this intrinsic is
/// [`f128::max`]
#[rustc_nounwind]
// #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[rustc_const_unstable(feature = "f128", issue = "116909")]
#[rustc_intrinsic]
#[rustc_intrinsic_must_be_overridden]
pub const fn maxnumf128(_x: f128, _y: f128) -> f128 {
unimplemented!();
}

/// Inform Miri that a given pointer definitely has a certain alignment.
#[cfg(miri)]
pub(crate) const fn miri_promise_symbolic_alignment(ptr: *const (), align: usize) {
Expand Down
1 change: 1 addition & 0 deletions library/core/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,7 @@
#![feature(const_char_encode_utf8)]
#![feature(const_eval_select)]
#![feature(const_exact_div)]
#![feature(const_float_methods)]
#![feature(const_fmt_arguments_new)]
#![feature(const_hash)]
#![feature(const_heap)]
Expand Down
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