radiance · commit

Fix wrapped integer casts in constant expressions

b9457de15f59cd99c5bfb16f713459f65ec664e5a4ba02ea4f0a03fddc2f1dff

Constant evaluation of integer casts only changed the recorded width
and signedness. It neither truncated values to the destination width
nor reinterpreted the destination sign bit, so narrowing followed by
widening produced incorrect constants.

Mask constant values to the target width and sign-extend them when the
target is signed before recording the cast result.

Assisted-by: Codex:gpt-5.6-sol

Alexis Sellier committed 1 month ago 1 parent f061b302

lib/std/lang/resolver.rad +25 -10

/// Construct an integer constant descriptor.
fn constInt(magnitude: u64, bits: u8, signed: bool, negative: bool) -> ConstValue {
    return ConstValue::Int(ConstInt { magnitude, bits, signed, negative });
}

/// Apply an integer cast to a constant value, including target-width
/// truncation and signed interpretation.
fn castConstInt(value: ConstInt, target: Type) -> ConstValue {
    // Convert sign-magnitude metadata to its two's-complement bit pattern.
    let raw = (0 - value.magnitude) if value.negative else value.magnitude;
    let range = integerRange(target)
        else panic "castConstInt: expected integer type";

    match range {
        case IntegerRange::Unsigned { bits, max } =>
            return constInt(raw & max, bits, false, false),
        case IntegerRange::Signed { bits, max, lim, .. } => {
            let mask = (max as u64) | lim;
            let truncated = raw & mask;
            if (truncated & lim) <> 0 {
                return constInt((0 - truncated) & mask, bits, true, true);
            }
            return constInt(truncated, bits, true, false);
        }
    }
}

/// Return the constant `u32` value for a slice bound when known.
fn constSliceIndex(self: *mut Resolver, node: *ast::Node) -> ?u32 {
    let value = constValueEntry(self, node)
        else return nil;
    let case ConstValue::Int(int) = value


    assert sourceTy <> Type::Unknown;
    assert targetTy <> Type::Unknown;

    if isValidCast(sourceTy, targetTy) {
        // Propagate constant value through the cast, adjusting integer
        // metadata to match the target type.
        // Propagate the constant value after applying the cast's target-width
        // truncation and signed interpretation.
        if let value = constValueEntry(self, expr.value) {
            if let case ConstValue::Int(i) = value {
                if let range = integerRange(targetTy) {
                    match range {
                        case IntegerRange::Signed { bits, .. } =>
                            setNodeConstValue(self, node, constInt(i.magnitude, bits, true, i.negative)),
                        case IntegerRange::Unsigned { bits, .. } =>
                            setNodeConstValue(self, node, constInt(i.magnitude, bits, false, false)),
                    }
                }
                setNodeConstValue(self, node, castConstInt(i, targetTy));
            }
        }
        return setNodeType(self, node, targetTy);
    }
    throw emitError(self, node, ErrorKind::InvalidAsCast(InvalidAsCast {

test/tests/const-cast-wrap.rad added +14 -0

1	+	//! returns: 0
2	+
3	+	/// Integer casts in constant expressions must apply target-width wrapping
4	+	/// before their values participate in subsequent casts or arithmetic.
5	+	constant NEG_ONE_WIDE: u16 = ((-1) as u8) as u16;
6	+	constant TRUNCATED_WIDE: u16 = (257 as u8) as u16;
7	+	constant SIGNED_WIDE: i16 = (255 as i8) as i16;
8	+
9	+	@default fn main() -> i32 {
10	+	assert NEG_ONE_WIDE == 255;
11	+	assert TRUNCATED_WIDE == 1;
12	+	assert SIGNED_WIDE == -1;
13	+	return 0;
14	+	}

2908	2908		/// Construct an integer constant descriptor.
2909	2909		fn constInt(magnitude: u64, bits: u8, signed: bool, negative: bool) -> ConstValue {
2910	2910		return ConstValue::Int(ConstInt { magnitude, bits, signed, negative });
2911	2911		}
2912	2912
	2913	+	/// Apply an integer cast to a constant value, including target-width
	2914	+	/// truncation and signed interpretation.
	2915	+	fn castConstInt(value: ConstInt, target: Type) -> ConstValue {
	2916	+	// Convert sign-magnitude metadata to its two's-complement bit pattern.
	2917	+	let raw = (0 - value.magnitude) if value.negative else value.magnitude;
	2918	+	let range = integerRange(target)
	2919	+	else panic "castConstInt: expected integer type";
	2920	+
	2921	+	match range {
	2922	+	case IntegerRange::Unsigned { bits, max } =>
	2923	+	return constInt(raw & max, bits, false, false),
	2924	+	case IntegerRange::Signed { bits, max, lim, .. } => {
	2925	+	let mask = (max as u64) \| lim;
	2926	+	let truncated = raw & mask;
	2927	+	if (truncated & lim) <> 0 {
	2928	+	return constInt((0 - truncated) & mask, bits, true, true);
	2929	+	}
	2930	+	return constInt(truncated, bits, true, false);
	2931	+	}
	2932	+	}
	2933	+	}
	2934	+
2913	2935		/// Return the constant `u32` value for a slice bound when known.
2914	2936		fn constSliceIndex(self: mut Resolver, node: ast::Node) -> ?u32 {
2915	2937		let value = constValueEntry(self, node)
2916	2938		else return nil;
2917	2939		let case ConstValue::Int(int) = value

5952	5974
5953	5975		assert sourceTy <> Type::Unknown;
5954	5976		assert targetTy <> Type::Unknown;
5955	5977
5956	5978		if isValidCast(sourceTy, targetTy) {
5957		-	// Propagate constant value through the cast, adjusting integer
5958		-	// metadata to match the target type.
	5979	+	// Propagate the constant value after applying the cast's target-width
	5980	+	// truncation and signed interpretation.
5959	5981		if let value = constValueEntry(self, expr.value) {
5960	5982		if let case ConstValue::Int(i) = value {
5961		-	if let range = integerRange(targetTy) {
5962		-	match range {
5963		-	case IntegerRange::Signed { bits, .. } =>
5964		-	setNodeConstValue(self, node, constInt(i.magnitude, bits, true, i.negative)),
5965		-	case IntegerRange::Unsigned { bits, .. } =>
5966		-	setNodeConstValue(self, node, constInt(i.magnitude, bits, false, false)),
5967		-	}
5968		-	}
	5983	+	setNodeConstValue(self, node, castConstInt(i, targetTy));
5969	5984		}
5970	5985		}
5971	5986		return setNodeType(self, node, targetTy);
5972	5987		}
5973	5988		throw emitError(self, node, ErrorKind::InvalidAsCast(InvalidAsCast {