radiance · commit

lang: Mask folded shift counts by width

1361514f621f67b88a853c1f9cbf1354b4f18c45fccf263a349037b2557ac2d9

Constant declarations retained untyped integer metadata, and folded
left shifts used the host word count without truncating to the operand
width. Typed constant shifts therefore diverged from runtime shifts.

Preserve a constant binding’s declared integer representation and
fold left shifts from width-truncated bit patterns with masked counts.

Assisted-by: Codex:gpt-5.6-sol

Alexis Sellier committed 1 month ago 1 parent 85cc0364

lib/std/lang/resolver.rad +30 -5

    let attrs = resolveAttributes(self, attrList);
    let bindingTy = try infer(self, typeNode);
    let valueTy = try checkAssignable(self, valueNode, bindingTy);

    if isConst {
        let constVal = constValueEntry(self, valueNode);
        let mut constVal = constValueEntry(self, valueNode);
        if constVal == nil and not isConstExpr(self, valueNode) {
            throw emitError(self, valueNode, ErrorKind::ConstExprRequired);
        }
        if let val = constVal {
            if let case ConstValue::Int(int) = val; isNumericType(bindingTy) {
                set constVal = castConstInt(int, bindingTy);
            }
        }
        try bindConstIdent(self, ident, node, bindingTy, constVal, attrs);
    } else {
        if not isConstExpr(self, valueNode) {
            throw emitError(self, valueNode, ErrorKind::ConstExprRequired);
        }

        signed,
        negative: false,
    };
}

/// Build a [`ConstInt`] from a two's-complement bit pattern.
fn constIntFromBits(raw: u64, bits: u8, signed: bool) -> ConstInt {
    let mask = parser::U64_MAX if bits == 64 else parser::U64_MAX >> (64 - bits) as u64;
    let truncated = raw & mask;

    if signed {
        let signBit = (mask >> 1) + 1;
        if (truncated & signBit) <> 0 {
            return ConstInt {
                magnitude: (0 - truncated) & mask,
                bits,
                signed,
                negative: true,
            };
        }
    }
    return ConstInt { magnitude: truncated, bits, signed, negative: false };
}

/// Try to fold a binary operation on two integer constants.
/// Returns the resulting constant value if successful.
fn foldIntBinOp(op: ast::BinaryOp, left: ConstInt, right: ConstInt) -> ?ConstValue {
    // Use the wider bit width and propagate signedness.
    let mut bits = left.bits;

    let signed = left.signed or right.signed;
    let l = constIntToSigned(left);
    let r = constIntToSigned(right);

    match op {
        // Shifts operate on unsigned magnitudes directly.
        // Shift counts are masked to the left operand's width, matching
        // the runtime word instructions.
        case ast::BinaryOp::Shl => {
            return ConstValue::Int(ConstInt {
                magnitude: left.magnitude << right.magnitude, bits, signed, negative: left.negative,
            });
            let raw = (0 - left.magnitude) if left.negative else left.magnitude;
            let shamt = right.magnitude % left.bits as u64;
            return ConstValue::Int(constIntFromBits(raw << shamt, left.bits, left.signed));
        },
        case ast::BinaryOp::Shr => {
            return ConstValue::Int(ConstInt {
                magnitude: left.magnitude >> right.magnitude, bits, signed, negative: left.negative,
            });

test/tests/const.u32.shift.mask.rad added +12 -0

1	+	//! returns: 0
2	+	//! Constant shifts must mask the count to the operand width like runtime shifts.
3	+
4	+	constant ONE: u32 = 1;
5	+	constant SHIFTED: u32 = ONE << 40;
6	+
7	+	@default fn main() -> i32 {
8	+	if SHIFTED == 256 {
9	+	return 0;
10	+	}
11	+	return 1;
12	+	}

3020	3020		let attrs = resolveAttributes(self, attrList);
3021	3021		let bindingTy = try infer(self, typeNode);
3022	3022		let valueTy = try checkAssignable(self, valueNode, bindingTy);
3023	3023
3024	3024		if isConst {
3025		-	let constVal = constValueEntry(self, valueNode);
	3025	+	let mut constVal = constValueEntry(self, valueNode);
3026	3026		if constVal == nil and not isConstExpr(self, valueNode) {
3027	3027		throw emitError(self, valueNode, ErrorKind::ConstExprRequired);
3028	3028		}
	3029	+	if let val = constVal {
	3030	+	if let case ConstValue::Int(int) = val; isNumericType(bindingTy) {
	3031	+	set constVal = castConstInt(int, bindingTy);
	3032	+	}
	3033	+	}
3029	3034		try bindConstIdent(self, ident, node, bindingTy, constVal, attrs);
3030	3035		} else {
3031	3036		if not isConstExpr(self, valueNode) {
3032	3037		throw emitError(self, valueNode, ErrorKind::ConstExprRequired);
3033	3038		}

6300	6305		signed,
6301	6306		negative: false,
6302	6307		};
6303	6308		}
6304	6309
	6310	+	/// Build a [`ConstInt`] from a two's-complement bit pattern.
	6311	+	fn constIntFromBits(raw: u64, bits: u8, signed: bool) -> ConstInt {
	6312	+	let mask = parser::U64_MAX if bits == 64 else parser::U64_MAX >> (64 - bits) as u64;
	6313	+	let truncated = raw & mask;
	6314	+
	6315	+	if signed {
	6316	+	let signBit = (mask >> 1) + 1;
	6317	+	if (truncated & signBit) <> 0 {
	6318	+	return ConstInt {
	6319	+	magnitude: (0 - truncated) & mask,
	6320	+	bits,
	6321	+	signed,
	6322	+	negative: true,
	6323	+	};
	6324	+	}
	6325	+	}
	6326	+	return ConstInt { magnitude: truncated, bits, signed, negative: false };
	6327	+	}
	6328	+
6305	6329		/// Try to fold a binary operation on two integer constants.
6306	6330		/// Returns the resulting constant value if successful.
6307	6331		fn foldIntBinOp(op: ast::BinaryOp, left: ConstInt, right: ConstInt) -> ?ConstValue {
6308	6332		// Use the wider bit width and propagate signedness.
6309	6333		let mut bits = left.bits;

6313	6337		let signed = left.signed or right.signed;
6314	6338		let l = constIntToSigned(left);
6315	6339		let r = constIntToSigned(right);
6316	6340
6317	6341		match op {
6318		-	// Shifts operate on unsigned magnitudes directly.
	6342	+	// Shift counts are masked to the left operand's width, matching
	6343	+	// the runtime word instructions.
6319	6344		case ast::BinaryOp::Shl => {
6320		-	return ConstValue::Int(ConstInt {
6321		-	magnitude: left.magnitude << right.magnitude, bits, signed, negative: left.negative,
6322		-	});
	6345	+	let raw = (0 - left.magnitude) if left.negative else left.magnitude;
	6346	+	let shamt = right.magnitude % left.bits as u64;
	6347	+	return ConstValue::Int(constIntFromBits(raw << shamt, left.bits, left.signed));
6323	6348		},
6324	6349		case ast::BinaryOp::Shr => {
6325	6350		return ConstValue::Int(ConstInt {
6326	6351		magnitude: left.magnitude >> right.magnitude, bits, signed, negative: left.negative,
6327	6352		});