bjoernager/rust
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miri: make float min/max non-deterministic

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This commit is contained in:
Ralf Jung 2025-01-31 11:53:32 +01:00
parent 25a16572a3
commit d98270b07a
5 changed files with 64 additions and 6 deletions
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16
compiler/rustc_const_eval/src/interpret/intrinsics.rs
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@ -747,7 +747,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
{
let a: F = self.read_scalar(&args[0])?.to_float()?;
let b: F = self.read_scalar(&args[1])?.to_float()?;
let res = self.adjust_nan(a.min(b), &[a, b]);
let res = if a == b {
// They are definitely not NaN (those are never equal), but they could be `+0` and `-0`.
// Let the machine decide which one to return.
M::equal_float_min_max(self, a, b)
} else {
self.adjust_nan(a.min(b), &[a, b])
};
self.write_scalar(res, dest)?;
interp_ok(())
}
@ -762,7 +768,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
{
let a: F = self.read_scalar(&args[0])?.to_float()?;
let b: F = self.read_scalar(&args[1])?.to_float()?;
let res = self.adjust_nan(a.max(b), &[a, b]);
let res = if a == b {
// They are definitely not NaN (those are never equal), but they could be `+0` and `-0`.
// Let the machine decide which one to return.
M::equal_float_min_max(self, a, b)
} else {
self.adjust_nan(a.max(b), &[a, b])
};
self.write_scalar(res, dest)?;
interp_ok(())
}

6
compiler/rustc_const_eval/src/interpret/machine.rs
View file

@ -278,6 +278,12 @@ pub trait Machine<'tcx>: Sized {
F2::NAN
}
/// 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.
a
}
/// Called before a basic block terminator is executed.
#[inline]
fn before_terminator(_ecx: &mut InterpCx<'tcx, Self>) -> InterpResult<'tcx> {