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miri: algebraic intrinsics: bring back float non-determinism #140439

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Merged
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Apr 30, 2025
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miri: algebraic intrinsics: bring back float non-determinism #140439

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3 changes: 1 addition & 2 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 @@ -178,8 +178,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {

let res = self.binary_op(op, &a, &b)?;
// `binary_op` already called `generate_nan` if needed.

// FIXME: Miri should add some non-determinism to the result here to catch any dependences on exact computations. This has previously been done, but the behaviour was removed as part of constification.
let res = M::apply_float_nondet(self, res)?;
self.write_immediate(*res, dest)?;
}

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8 changes: 8 additions & 0 deletions compiler/rustc_const_eval/src/interpret/machine.rs
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Expand Up @@ -276,6 +276,14 @@ pub trait Machine<'tcx>: Sized {
F2::NAN
}

/// Apply non-determinism to float operations that do not return a precise result.
fn apply_float_nondet(
_ecx: &mut InterpCx<'tcx, Self>,
val: ImmTy<'tcx, Self::Provenance>,
) -> InterpResult<'tcx, ImmTy<'tcx, Self::Provenance>> {
interp_ok(val)
}

/// Determines the result of `min`/`max` on floats when the arguments are equal.
fn equal_float_min_max<F: Float>(_ecx: &InterpCx<'tcx, Self>, a: F, _b: F) -> F {
// By default, we pick the left argument.
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27 changes: 2 additions & 25 deletions src/tools/miri/src/intrinsics/mod.rs
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Expand Up @@ -7,13 +7,13 @@ use rand::Rng;
use rustc_abi::Size;
use rustc_apfloat::{Float, Round};
use rustc_middle::mir;
use rustc_middle::ty::{self, FloatTy, ScalarInt};
use rustc_middle::ty::{self, FloatTy};
use rustc_span::{Symbol, sym};

use self::atomic::EvalContextExt as _;
use self::helpers::{ToHost, ToSoft, check_intrinsic_arg_count};
use self::simd::EvalContextExt as _;
use crate::math::apply_random_float_error_ulp;
use crate::math::apply_random_float_error_to_imm;
use crate::*;

impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
Expand Down Expand Up @@ -473,26 +473,3 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
interp_ok(EmulateItemResult::NeedsReturn)
}
}

/// Applies a random 16ULP floating point error to `val` and returns the new value.
/// Will fail if `val` is not a floating point number.
fn apply_random_float_error_to_imm<'tcx>(
ecx: &mut MiriInterpCx<'tcx>,
val: ImmTy<'tcx>,
ulp_exponent: u32,
) -> InterpResult<'tcx, ImmTy<'tcx>> {
let scalar = val.to_scalar_int()?;
let res: ScalarInt = match val.layout.ty.kind() {
ty::Float(FloatTy::F16) =>
apply_random_float_error_ulp(ecx, scalar.to_f16(), ulp_exponent).into(),
ty::Float(FloatTy::F32) =>
apply_random_float_error_ulp(ecx, scalar.to_f32(), ulp_exponent).into(),
ty::Float(FloatTy::F64) =>
apply_random_float_error_ulp(ecx, scalar.to_f64(), ulp_exponent).into(),
ty::Float(FloatTy::F128) =>
apply_random_float_error_ulp(ecx, scalar.to_f128(), ulp_exponent).into(),
_ => bug!("intrinsic called with non-float input type"),
};

interp_ok(ImmTy::from_scalar_int(res, val.layout))
}
10 changes: 10 additions & 0 deletions src/tools/miri/src/machine.rs
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Expand Up @@ -1199,6 +1199,16 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
ecx.generate_nan(inputs)
}

#[inline(always)]
fn apply_float_nondet(
ecx: &mut InterpCx<'tcx, Self>,
val: ImmTy<'tcx>,
) -> InterpResult<'tcx, ImmTy<'tcx>> {
crate::math::apply_random_float_error_to_imm(
ecx, val, 2 /* log2(4) */
)
}

#[inline(always)]
fn equal_float_min_max<F: Float>(ecx: &MiriInterpCx<'tcx>, a: F, b: F) -> F {
ecx.equal_float_min_max(a, b)
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26 changes: 26 additions & 0 deletions src/tools/miri/src/math.rs
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@@ -1,6 +1,9 @@
use rand::Rng as _;
use rustc_apfloat::Float as _;
use rustc_apfloat::ieee::IeeeFloat;
use rustc_middle::ty::{self, FloatTy, ScalarInt};

use crate::*;

/// Disturbes a floating-point result by a relative error in the range (-2^scale, 2^scale).
///
Expand Down Expand Up @@ -43,6 +46,29 @@ pub(crate) fn apply_random_float_error_ulp<F: rustc_apfloat::Float>(
apply_random_float_error(ecx, val, err_scale)
}

/// Applies a random 16ULP floating point error to `val` and returns the new value.
/// Will fail if `val` is not a floating point number.
pub(crate) fn apply_random_float_error_to_imm<'tcx>(
ecx: &mut MiriInterpCx<'tcx>,
val: ImmTy<'tcx>,
ulp_exponent: u32,
) -> InterpResult<'tcx, ImmTy<'tcx>> {
let scalar = val.to_scalar_int()?;
let res: ScalarInt = match val.layout.ty.kind() {
ty::Float(FloatTy::F16) =>
apply_random_float_error_ulp(ecx, scalar.to_f16(), ulp_exponent).into(),
ty::Float(FloatTy::F32) =>
apply_random_float_error_ulp(ecx, scalar.to_f32(), ulp_exponent).into(),
ty::Float(FloatTy::F64) =>
apply_random_float_error_ulp(ecx, scalar.to_f64(), ulp_exponent).into(),
ty::Float(FloatTy::F128) =>
apply_random_float_error_ulp(ecx, scalar.to_f128(), ulp_exponent).into(),
_ => bug!("intrinsic called with non-float input type"),
};

interp_ok(ImmTy::from_scalar_int(res, val.layout))
}

pub(crate) fn sqrt<S: rustc_apfloat::ieee::Semantics>(x: IeeeFloat<S>) -> IeeeFloat<S> {
match x.category() {
// preserve zero sign
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119 changes: 60 additions & 59 deletions src/tools/miri/tests/pass/float.rs
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Expand Up @@ -1292,8 +1292,7 @@ fn test_non_determinism() {
}
}
// We saw the same thing N times.
// FIXME: temporarily disabled as it breaks std tests.
//panic!("expected non-determinism, got {rounds} times the same result: {first:?}");
panic!("expected non-determinism, got {rounds} times the same result: {first:?}");
}

macro_rules! test_operations_f {
Expand All @@ -1319,66 +1318,68 @@ fn test_non_determinism() {
}
pub fn test_operations_f32(a: f32, b: f32) {
test_operations_f!(a, b);
ensure_nondet(|| a.log(b));
ensure_nondet(|| a.exp());
ensure_nondet(|| 10f32.exp2());
ensure_nondet(|| f32::consts::E.ln());
ensure_nondet(|| 1f32.ln_1p());
ensure_nondet(|| 10f32.log10());
ensure_nondet(|| 8f32.log2());
ensure_nondet(|| 27.0f32.cbrt());
ensure_nondet(|| 3.0f32.hypot(4.0f32));
ensure_nondet(|| 1f32.sin());
ensure_nondet(|| 0f32.cos());
// On i686-pc-windows-msvc , these functions are implemented by calling the `f64` version,
// which means the little rounding errors Miri introduces are discard by the cast down to `f32`.
// Just skip the test for them.
if !cfg!(all(target_os = "windows", target_env = "msvc", target_arch = "x86")) {
ensure_nondet(|| 1.0f32.tan());
ensure_nondet(|| 1.0f32.asin());
ensure_nondet(|| 5.0f32.acos());
ensure_nondet(|| 1.0f32.atan());
ensure_nondet(|| 1.0f32.atan2(2.0f32));
ensure_nondet(|| 1.0f32.sinh());
ensure_nondet(|| 1.0f32.cosh());
ensure_nondet(|| 1.0f32.tanh());
}
ensure_nondet(|| 1.0f32.asinh());
ensure_nondet(|| 2.0f32.acosh());
ensure_nondet(|| 0.5f32.atanh());
ensure_nondet(|| 5.0f32.gamma());
ensure_nondet(|| 5.0f32.ln_gamma());
ensure_nondet(|| 5.0f32.erf());
ensure_nondet(|| 5.0f32.erfc());
// FIXME: temporarily disabled as it breaks std tests.
// ensure_nondet(|| a.log(b));
// ensure_nondet(|| a.exp());
// ensure_nondet(|| 10f32.exp2());
// ensure_nondet(|| f32::consts::E.ln());
// ensure_nondet(|| 1f32.ln_1p());
// ensure_nondet(|| 10f32.log10());
// ensure_nondet(|| 8f32.log2());
// ensure_nondet(|| 27.0f32.cbrt());
// ensure_nondet(|| 3.0f32.hypot(4.0f32));
// ensure_nondet(|| 1f32.sin());
// ensure_nondet(|| 0f32.cos());
// // On i686-pc-windows-msvc , these functions are implemented by calling the `f64` version,
// // which means the little rounding errors Miri introduces are discard by the cast down to `f32`.
// // Just skip the test for them.
// if !cfg!(all(target_os = "windows", target_env = "msvc", target_arch = "x86")) {
// ensure_nondet(|| 1.0f32.tan());
// ensure_nondet(|| 1.0f32.asin());
// ensure_nondet(|| 5.0f32.acos());
// ensure_nondet(|| 1.0f32.atan());
// ensure_nondet(|| 1.0f32.atan2(2.0f32));
// ensure_nondet(|| 1.0f32.sinh());
// ensure_nondet(|| 1.0f32.cosh());
// ensure_nondet(|| 1.0f32.tanh());
// }
// ensure_nondet(|| 1.0f32.asinh());
// ensure_nondet(|| 2.0f32.acosh());
// ensure_nondet(|| 0.5f32.atanh());
// ensure_nondet(|| 5.0f32.gamma());
// ensure_nondet(|| 5.0f32.ln_gamma());
// ensure_nondet(|| 5.0f32.erf());
// ensure_nondet(|| 5.0f32.erfc());
}
pub fn test_operations_f64(a: f64, b: f64) {
test_operations_f!(a, b);
ensure_nondet(|| a.log(b));
ensure_nondet(|| a.exp());
ensure_nondet(|| 50f64.exp2());
ensure_nondet(|| 3f64.ln());
ensure_nondet(|| 1f64.ln_1p());
ensure_nondet(|| f64::consts::E.log10());
ensure_nondet(|| f64::consts::E.log2());
ensure_nondet(|| 27.0f64.cbrt());
ensure_nondet(|| 3.0f64.hypot(4.0f64));
ensure_nondet(|| 1f64.sin());
ensure_nondet(|| 0f64.cos());
ensure_nondet(|| 1.0f64.tan());
ensure_nondet(|| 1.0f64.asin());
ensure_nondet(|| 5.0f64.acos());
ensure_nondet(|| 1.0f64.atan());
ensure_nondet(|| 1.0f64.atan2(2.0f64));
ensure_nondet(|| 1.0f64.sinh());
ensure_nondet(|| 1.0f64.cosh());
ensure_nondet(|| 1.0f64.tanh());
ensure_nondet(|| 1.0f64.asinh());
ensure_nondet(|| 3.0f64.acosh());
ensure_nondet(|| 0.5f64.atanh());
ensure_nondet(|| 5.0f64.gamma());
ensure_nondet(|| 5.0f64.ln_gamma());
ensure_nondet(|| 5.0f64.erf());
ensure_nondet(|| 5.0f64.erfc());
// FIXME: temporarily disabled as it breaks std tests.
// ensure_nondet(|| a.log(b));
// ensure_nondet(|| a.exp());
// ensure_nondet(|| 50f64.exp2());
// ensure_nondet(|| 3f64.ln());
// ensure_nondet(|| 1f64.ln_1p());
// ensure_nondet(|| f64::consts::E.log10());
// ensure_nondet(|| f64::consts::E.log2());
// ensure_nondet(|| 27.0f64.cbrt());
// ensure_nondet(|| 3.0f64.hypot(4.0f64));
// ensure_nondet(|| 1f64.sin());
// ensure_nondet(|| 0f64.cos());
// ensure_nondet(|| 1.0f64.tan());
// ensure_nondet(|| 1.0f64.asin());
// ensure_nondet(|| 5.0f64.acos());
// ensure_nondet(|| 1.0f64.atan());
// ensure_nondet(|| 1.0f64.atan2(2.0f64));
// ensure_nondet(|| 1.0f64.sinh());
// ensure_nondet(|| 1.0f64.cosh());
// ensure_nondet(|| 1.0f64.tanh());
// ensure_nondet(|| 1.0f64.asinh());
// ensure_nondet(|| 3.0f64.acosh());
// ensure_nondet(|| 0.5f64.atanh());
// ensure_nondet(|| 5.0f64.gamma());
// ensure_nondet(|| 5.0f64.ln_gamma());
// ensure_nondet(|| 5.0f64.erf());
// ensure_nondet(|| 5.0f64.erfc());
}
pub fn test_operations_f128(a: f128, b: f128) {
test_operations_f!(a, b);
Expand Down
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