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Add checked float-to-int helper function #3025

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Aug 11, 2023
Merged

Add checked float-to-int helper function #3025

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b57bc6d
Add checked float-to-int helper function
eduardosm Aug 11, 2023
5141436
Remove `float_to_int_unchecked` and inline it into its call sites
eduardosm Aug 11, 2023
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65 changes: 62 additions & 3 deletions src/helpers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,11 @@ use rustc_index::IndexVec;
use rustc_middle::mir;
use rustc_middle::ty::{
self,
layout::{LayoutOf, TyAndLayout},
List, TyCtxt,
layout::{IntegerExt as _, LayoutOf, TyAndLayout},
List, Ty, TyCtxt,
};
use rustc_span::{def_id::CrateNum, sym, Span, Symbol};
use rustc_target::abi::{Align, FieldIdx, FieldsShape, Size, Variants};
use rustc_target::abi::{Align, FieldIdx, FieldsShape, Integer, Size, Variants};
use rustc_target::spec::abi::Abi;

use rand::RngCore;
Expand Down Expand Up @@ -1011,6 +1011,65 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
None => tcx.item_name(def_id),
}
}

/// Converts `f` to integer type `dest_ty` after rounding with mode `round`.
/// Returns `None` if `f` is NaN or out of range.
fn float_to_int_checked<F>(
&self,
f: F,
dest_ty: Ty<'tcx>,
round: rustc_apfloat::Round,
) -> Option<Scalar<Provenance>>
where
F: rustc_apfloat::Float + Into<Scalar<Provenance>>,
{
let this = self.eval_context_ref();

match dest_ty.kind() {
// Unsigned
ty::Uint(t) => {
let size = Integer::from_uint_ty(this, *t).size();
let res = f.to_u128_r(size.bits_usize(), round, &mut false);
if res.status.intersects(
rustc_apfloat::Status::INVALID_OP
| rustc_apfloat::Status::OVERFLOW
| rustc_apfloat::Status::UNDERFLOW,
) {
// Floating point value is NaN (flagged with INVALID_OP) or outside the range
// of values of the integer type (flagged with OVERFLOW or UNDERFLOW).
None
} else {
// Floating point value can be represented by the integer type after rounding.
// The INEXACT flag is ignored on purpose to allow rounding.
Some(Scalar::from_uint(res.value, size))
}
}
// Signed
ty::Int(t) => {
let size = Integer::from_int_ty(this, *t).size();
let res = f.to_i128_r(size.bits_usize(), round, &mut false);
if res.status.intersects(
rustc_apfloat::Status::INVALID_OP
| rustc_apfloat::Status::OVERFLOW
| rustc_apfloat::Status::UNDERFLOW,
) {
// Floating point value is NaN (flagged with INVALID_OP) or outside the range
// of values of the integer type (flagged with OVERFLOW or UNDERFLOW).
None
} else {
// Floating point value can be represented by the integer type after rounding.
// The INEXACT flag is ignored on purpose to allow rounding.
Some(Scalar::from_int(res.value, size))
}
}
// Nothing else
_ =>
span_bug!(
this.cur_span(),
"attempted float-to-int conversion with non-int output type {dest_ty:?}"
),
}
}
}

impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
Expand Down
85 changes: 25 additions & 60 deletions src/shims/intrinsics/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,12 +6,12 @@ use std::iter;
use log::trace;

use rustc_apfloat::{Float, Round};
use rustc_middle::ty::layout::{IntegerExt, LayoutOf};
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::{
mir,
ty::{self, FloatTy, Ty},
ty::{self, FloatTy},
};
use rustc_target::abi::{Integer, Size};
use rustc_target::abi::Size;

use crate::*;
use atomic::EvalContextExt as _;
Expand Down Expand Up @@ -356,10 +356,28 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
let val = this.read_immediate(val)?;

let res = match val.layout.ty.kind() {
ty::Float(FloatTy::F32) =>
this.float_to_int_unchecked(val.to_scalar().to_f32()?, dest.layout.ty)?,
ty::Float(FloatTy::F64) =>
this.float_to_int_unchecked(val.to_scalar().to_f64()?, dest.layout.ty)?,
ty::Float(FloatTy::F32) => {
let f = val.to_scalar().to_f32()?;
this
.float_to_int_checked(f, dest.layout.ty, Round::TowardZero)
.ok_or_else(|| {
err_ub_format!(
"`float_to_int_unchecked` intrinsic called on {f} which cannot be represented in target type `{:?}`",
dest.layout.ty
)
})?
}
ty::Float(FloatTy::F64) => {
let f = val.to_scalar().to_f64()?;
this
.float_to_int_checked(f, dest.layout.ty, Round::TowardZero)
.ok_or_else(|| {
err_ub_format!(
"`float_to_int_unchecked` intrinsic called on {f} which cannot be represented in target type `{:?}`",
dest.layout.ty
)
})?
}
_ =>
span_bug!(
this.cur_span(),
Expand All @@ -383,57 +401,4 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {

Ok(())
}

fn float_to_int_unchecked<F>(
&self,
f: F,
dest_ty: Ty<'tcx>,
) -> InterpResult<'tcx, Scalar<Provenance>>
where
F: Float + Into<Scalar<Provenance>>,
{
let this = self.eval_context_ref();

// Step 1: cut off the fractional part of `f`. The result of this is
// guaranteed to be precisely representable in IEEE floats.
let f = f.round_to_integral(Round::TowardZero).value;

// Step 2: Cast the truncated float to the target integer type and see if we lose any information in this step.
Ok(match dest_ty.kind() {
// Unsigned
ty::Uint(t) => {
let size = Integer::from_uint_ty(this, *t).size();
let res = f.to_u128(size.bits_usize());
if res.status.is_empty() {
// No status flags means there was no further rounding or other loss of precision.
Scalar::from_uint(res.value, size)
} else {
// `f` was not representable in this integer type.
throw_ub_format!(
"`float_to_int_unchecked` intrinsic called on {f} which cannot be represented in target type `{dest_ty:?}`",
);
}
}
// Signed
ty::Int(t) => {
let size = Integer::from_int_ty(this, *t).size();
let res = f.to_i128(size.bits_usize());
if res.status.is_empty() {
// No status flags means there was no further rounding or other loss of precision.
Scalar::from_int(res.value, size)
} else {
// `f` was not representable in this integer type.
throw_ub_format!(
"`float_to_int_unchecked` intrinsic called on {f} which cannot be represented in target type `{dest_ty:?}`",
);
}
}
// Nothing else
_ =>
span_bug!(
this.cur_span(),
"`float_to_int_unchecked` called with non-int output type {dest_ty:?}"
),
})
}
}
47 changes: 31 additions & 16 deletions src/shims/intrinsics/simd.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use rustc_apfloat::Float;
use rustc_apfloat::{Float, Round};
use rustc_middle::ty::layout::{HasParamEnv, LayoutOf};
use rustc_middle::{mir, ty, ty::FloatTy};
use rustc_target::abi::{Endian, HasDataLayout, Size};
Expand Down Expand Up @@ -420,7 +420,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
}
}
}
#[rustfmt::skip]
RalfJung marked this conversation as resolved.
Show resolved Hide resolved
"cast" | "as" | "cast_ptr" | "expose_addr" | "from_exposed_addr" => {
let [op] = check_arg_count(args)?;
let (op, op_len) = this.operand_to_simd(op)?;
Expand All @@ -440,7 +439,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {

let val = match (op.layout.ty.kind(), dest.layout.ty.kind()) {
// Int-to-(int|float): always safe
(ty::Int(_) | ty::Uint(_), ty::Int(_) | ty::Uint(_) | ty::Float(_)) if safe_cast || unsafe_cast =>
(ty::Int(_) | ty::Uint(_), ty::Int(_) | ty::Uint(_) | ty::Float(_))
if safe_cast || unsafe_cast =>
this.int_to_int_or_float(&op, dest.layout.ty)?,
// Float-to-float: always safe
(ty::Float(_), ty::Float(_)) if safe_cast || unsafe_cast =>
Expand All @@ -449,21 +449,36 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
(ty::Float(_), ty::Int(_) | ty::Uint(_)) if safe_cast =>
this.float_to_float_or_int(&op, dest.layout.ty)?,
// Float-to-int in unchecked mode
(ty::Float(FloatTy::F32), ty::Int(_) | ty::Uint(_)) if unsafe_cast =>
this.float_to_int_unchecked(op.to_scalar().to_f32()?, dest.layout.ty)?.into(),
(ty::Float(FloatTy::F64), ty::Int(_) | ty::Uint(_)) if unsafe_cast =>
this.float_to_int_unchecked(op.to_scalar().to_f64()?, dest.layout.ty)?.into(),
// Ptr-to-ptr cast
(ty::RawPtr(..), ty::RawPtr(..)) if ptr_cast => {
this.ptr_to_ptr(&op, dest.layout.ty)?
}
// Ptr/Int casts
(ty::RawPtr(..), ty::Int(_) | ty::Uint(_)) if expose_cast => {
this.pointer_expose_address_cast(&op, dest.layout.ty)?
(ty::Float(FloatTy::F32), ty::Int(_) | ty::Uint(_)) if unsafe_cast => {
let f = op.to_scalar().to_f32()?;
this.float_to_int_checked(f, dest.layout.ty, Round::TowardZero)
.ok_or_else(|| {
err_ub_format!(
"`simd_cast` intrinsic called on {f} which cannot be represented in target type `{:?}`",
dest.layout.ty
)
})?
.into()
}
(ty::Int(_) | ty::Uint(_), ty::RawPtr(..)) if from_exposed_cast => {
this.pointer_from_exposed_address_cast(&op, dest.layout.ty)?
(ty::Float(FloatTy::F64), ty::Int(_) | ty::Uint(_)) if unsafe_cast => {
let f = op.to_scalar().to_f64()?;
this.float_to_int_checked(f, dest.layout.ty, Round::TowardZero)
.ok_or_else(|| {
err_ub_format!(
"`simd_cast` intrinsic called on {f} which cannot be represented in target type `{:?}`",
dest.layout.ty
)
})?
.into()
}
// Ptr-to-ptr cast
(ty::RawPtr(..), ty::RawPtr(..)) if ptr_cast =>
this.ptr_to_ptr(&op, dest.layout.ty)?,
// Ptr/Int casts
(ty::RawPtr(..), ty::Int(_) | ty::Uint(_)) if expose_cast =>
this.pointer_expose_address_cast(&op, dest.layout.ty)?,
(ty::Int(_) | ty::Uint(_), ty::RawPtr(..)) if from_exposed_cast =>
this.pointer_from_exposed_address_cast(&op, dest.layout.ty)?,
// Error otherwise
_ =>
throw_unsup_format!(
Expand Down
44 changes: 10 additions & 34 deletions src/shims/x86/sse.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -195,24 +195,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
_ => unreachable!(),
};

let mut exact = false;
let cvt = op.to_i128_r(32, rnd, &mut exact);
let res = if cvt.status.intersects(
rustc_apfloat::Status::INVALID_OP
| rustc_apfloat::Status::OVERFLOW
| rustc_apfloat::Status::UNDERFLOW,
) {
// Input is NaN (flagged with INVALID_OP) or does not fit
// in an i32 (flagged with OVERFLOW or UNDERFLOW), fallback
// to minimum acording to SSE semantics. The INEXACT flag
// is ignored on purpose because rounding can happen during
// float-to-int conversion.
i32::MIN
} else {
i32::try_from(cvt.value).unwrap()
};
let res = this.float_to_int_checked(op, dest.layout.ty, rnd).unwrap_or_else(|| {
// Fallback to minimum acording to SSE semantics.
Scalar::from_i32(i32::MIN)
});

this.write_scalar(Scalar::from_i32(res), dest)?;
this.write_scalar(res, dest)?;
}
// Use to implement _mm_cvtss_si64 and _mm_cvttss_si64.
// Converts the first component of `op` from f32 to i64.
Expand All @@ -232,24 +220,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
_ => unreachable!(),
};

let mut exact = false;
let cvt = op.to_i128_r(64, rnd, &mut exact);
let res = if cvt.status.intersects(
rustc_apfloat::Status::INVALID_OP
| rustc_apfloat::Status::OVERFLOW
| rustc_apfloat::Status::UNDERFLOW,
) {
// Input is NaN (flagged with INVALID_OP) or does not fit
// in an i64 (flagged with OVERFLOW or UNDERFLOW), fallback
// to minimum acording to SSE semantics. The INEXACT flag
// is ignored on purpose because rounding can happen during
// float-to-int conversion.
i64::MIN
} else {
i64::try_from(cvt.value).unwrap()
};
let res = this.float_to_int_checked(op, dest.layout.ty, rnd).unwrap_or_else(|| {
// Fallback to minimum acording to SSE semantics.
Scalar::from_i64(i64::MIN)
});

this.write_scalar(Scalar::from_i64(res), dest)?;
this.write_scalar(res, dest)?;
}
// Used to implement the _mm_cvtsi32_ss function.
// Converts `right` from i32 to f32. Returns a SIMD vector with
Expand Down
4 changes: 2 additions & 2 deletions tests/fail/intrinsics/float_to_int_64_neg.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
error: Undefined Behavior: `float_to_int_unchecked` intrinsic called on -1 which cannot be represented in target type `u128`
error: Undefined Behavior: `float_to_int_unchecked` intrinsic called on -1.0000000000000999 which cannot be represented in target type `u128`
--> $DIR/float_to_int_64_neg.rs:LL:CC
|
LL | float_to_int_unchecked::<f64, u128>(-1.0000000000001f64);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `float_to_int_unchecked` intrinsic called on -1 which cannot be represented in target type `u128`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `float_to_int_unchecked` intrinsic called on -1.0000000000000999 which cannot be represented in target type `u128`
|
= help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
= help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
Expand Down
4 changes: 2 additions & 2 deletions tests/fail/intrinsics/simd-float-to-int.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
error: Undefined Behavior: `float_to_int_unchecked` intrinsic called on 3.40282347E+38 which cannot be represented in target type `i32`
error: Undefined Behavior: `simd_cast` intrinsic called on 3.40282347E+38 which cannot be represented in target type `i32`
--> $DIR/simd-float-to-int.rs:LL:CC
|
LL | let _x: i32x2 = f32x2::from_array([f32::MAX, f32::MIN]).to_int_unchecked();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `float_to_int_unchecked` intrinsic called on 3.40282347E+38 which cannot be represented in target type `i32`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `simd_cast` intrinsic called on 3.40282347E+38 which cannot be represented in target type `i32`
|
= help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
= help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
Expand Down