Folding Not Supported in Certain Locations

[ritzdorf]

Version Information

• vyper Version (output of vyper --version OR linkable commit hash vyperlang/vyper@): b43ffac

Issue Description

Several Vyper constructs require or can be optimized if constant values
are provided. To achieve this, AST nodes can be folded to constants by
the compiler, however, the following locations do not support folding:

• length in slice(x, start, length) when x is msg.data or
  address.code:

  • isinstance(parent.args[2], vy_ast.Int) in
    _validate_msg_data_attribute()
  • isinstance(parent.args[2], vy_ast.Int) in
    _validate_address_code()

• length in slice(x, start, length):

  • if length_literal is not None condition in
    Slice.fetch_call_return()

• index in variable[index] when the variable is an array.

  • isinstance(node, vy_ast.Int) in
    _SequenceT.validate_index_type()

• index in variable[index] when the variable is a tuple.

  • not isinstance(node, vy_ast.Int) in
    TupleT.validate_index_type()

• x or y in x ** y:

  • left, right = _get_lr() in NumericT.validate_numeric_op()

• x in convert(x, T)

  • _convert._to_int(), _convert.to_decimal() and
    _convert._cast_bytestring() does not check if expr has a
    folded value.

• topic in raw_log(topic, data) .

  • not isinstance(node.args[0], vy_ast.List) in
    RawLog.infer_arg_types()

POC

The following example demonstrates the different issues.

@external
def foo():
    x: Bytes[32] = slice(msg.data, 0, 31 + 1) # StructureException

@external
def foo(tuple: (uint256,uint256)) -> uint256:
    return tuple[0+1] # InvalidType

k: constant(Bytes[3]) = b'aaa'
@external
def foo():

    a: Bytes[2] = convert (k, Bytes[2]) # compiles instead of failing
    b: Bytes[2] = convert (b'aaa', Bytes[2]) # TypeMismatch

a: constant(uint256) = 12
@external
def foo():
    # The following check is inserted by the compiler although it is not necessary
    # [assert, [iszero, [shr, 128, 12 <12>]]],
    b: uint128 = convert (a, uint128)

topic: constant(bytes32) = 0x1212121212121210212801291212121212121210121212121212121212121212
@external
def foo():
    raw_log([[topic]][0], b'') # InvalidType

[ritzdorf]

One more location to add: default values.

Example:

@external
def foo(x: int256 = 2**255-1):

does not compile with:

TypeMismatch('Expected int256 but literal can only be cast as uint256.', vyper.ast.nodes.Int:

[charles-cooper]

One more location to add: default values.

Example:

@external
def foo(x: int256 = 2**255-1):

does not compile with:

TypeMismatch('Expected int256 but literal can only be cast as uint256.', vyper.ast.nodes.Int:

this one is expected behavior i think, since 2**255 is out of bounds of the range of int256, and compile-time safemath should match runtime safemath.

[tserg]

The following have been fixed in 75fb059:

• index in variable[index] when the variable is an array.
• index in variable[index] when the variable is a tuple.

[tserg]

The x or y case in x ** y have been fixed in e1adb7b.