python-uncompyle6/uncompyle6/parsers/reducecheck/ifelsestmt2.py

#  Copyright (c) 2020-2022 Rocky Bernstein

IFELSE_STMT_RULES = frozenset(
    [
        (
            "ifelsestmt",
            (
                "testexpr_then",
                "pass",
                "filler",
                "else_suitel",
                "COME_FROM",
                "POP_TOP",
            ),
        ),
        (
            "ifelsestmt",
            (
                "testexpr_then",
                "c_stmts_opt",
                "\\e_filler",
                "else_suitel",
                "come_froms",
                "POP_TOP",
            ),
        ),
        (
            "ifelsestmt",
            (
                "testexpr_then",
                "\\e_c_stmts_opt",
                "\\e_filler",
                "else_suitel",
                "come_froms",
                "POP_TOP",
            ),
        ),
        # We may do something like add these in the future:
    ]
)


def ifelsestmt2(self, lhs, n, rule, tree, tokens, first, last):

    if (last + 1) < n and tokens[last + 1] == "COME_FROM_LOOP" and lhs != "ifelsestmtc":
        # ifelsestmt jumped outside of loop. No good.
        return True

    # print("XXX", first, last)
    # for t in range(first, last):
    #     print(tokens[t])
    # print("=" * 30)

    if rule not in IFELSE_STMT_RULES:
        # print("XXX", rule)
        return False

    # Avoid if/else where the "then" is a "raise_stmt1" for an
    # assert statement. Parse this as an "assert" instead.
    stmts = tree[1]
    if stmts in ("c_stmts",) and len(stmts) == 1:
        raise_stmt1 = stmts[0]
        if raise_stmt1 == "raise_stmt1" and raise_stmt1[0] in ("LOAD_ASSERT",):
            return True

    # Make sure all of the "come froms" offset at the
    # end of the "if" come from somewhere inside the "if".
    # Since the come_froms are ordered so that lowest
    # offset COME_FROM is last, it is sufficient to test
    # just the last one.
    if len(tree) == 6 and tree[-1] == "POP_TOP":
        # FIXME: There is weirdness in the grammar we need to work around.
        # we need to clean up the grammar.
        last_token = tree[-2]
        if last_token == "COME_FROM" and tokens[first].offset > last_token.attr:
            if (
                self.insts[self.offset2inst_index[last_token.attr]].opname
                != "SETUP_LOOP"
            ):
                return True

    testexpr = tree[0]

    # Check that the condition portion of the "if"
    # jumps to the "else" part.
    if testexpr[0] in ("testtrue", "testfalse", "testfalse_then"):
        if_condition = testexpr[0]

        else_suite = tree[3]
        assert else_suite.kind.startswith("else_suite")

        if len(if_condition) > 1 and if_condition[1].kind.startswith("jmp_"):
            if last == n:
                last -= 1
            jmp = if_condition[1]
            jmp_target = int(jmp[0].pattr)

            # Below we check that jmp_target is jumping to a feasible
            # location. It should be to the transition after the "then"
            # block and to the beginning of the "else" block.
            # However the "if/else" is inside a loop the false test can be
            # back to the loop.

            # FIXME: the below logic for jf_cfs could probably be
            # simplified.
            if tree[2] == "filler":
                jump_else_end = tree[3]
            else:
                jump_else_end = tree[2]

            if jump_else_end == "jf_cfs":
                jump_else_end = jump_else_end[0]

            if jump_else_end == "JUMP_FORWARD":
                endif_target = int(jump_else_end.pattr)
                last_offset = tokens[last].off2int()
                if endif_target != last_offset:
                    return True
            last_offset = tokens[last].off2int(prefer_last=False)
            if jmp_target <= last_offset:
                # jmp_target should be jumping to the end of the if/then/else
                # but is it jumping to the beginning of the "else" or before
                return True
            if (
                jump_else_end in ("jf_cfs", "jump_forward_else")
                and jump_else_end[0] == "JUMP_FORWARD"
            ):
                # If the "else" jump jumps before the end of the the "if .. else end", then this
                # is not this kind of "ifelsestmt".
                jump_else_forward = jump_else_end[0]
                jump_else_forward_target = jump_else_forward.attr
                if jump_else_forward_target < last_offset:
                    return True
                pass
            if (
                jump_else_end in ("jb_elsec", "jb_elsel", "jf_cfs", "jb_cfs")
                and jump_else_end[-1] == "COME_FROM"
            ):
                if jump_else_end[-1].off2int() != jmp_target:
                    return True

            if tokens[first].off2int() > jmp_target:
                return True

            return (jmp_target > last_offset) and tokens[last] != "JUMP_FORWARD"

    return False