Experimental codegen with no optimizations fails

[ritzdorf]

Version Information

• vyper Version (output of vyper --version): 0.4.0+commit.e9db8d9f
• OS: linux
• Python Version (output of python --version): Python 3.11.8

What's your issue about?

When trying to compile this contract:

@external
def foo() -> Bytes[32]:
    y: uint256 = 0
    if True:
        y += 1
    return abi_encode(y)

with the command:

vyper --experimental-codegen --optimize none a.vy

one gets the error:

AssertionError: Not implemented yet

Please note that compilation will be successful with --optimize gas and --optimize codesize.

This might be related to #4070