Move code from parse37base to reducechecks

uncompyle6/parsers/reducecheck/ifstmts_jump.py

@@ -0,0 +1,56 @@
+#  Copyright (c) 2020 Rocky Bernstein
+
+from uncompyle6.scanners.tok import Token
+
+
+def ifstmts_jump(
+    self, lhs, n, rule, ast, tokens, first, last
+) -> bool:
+    come_froms = ast[-1]
+    # 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.
+
+    # This is complicated, but note that the JUMP_IF instruction comes immediately
+    # *before* _ifstmts_jump so that's what we have to test
+    # the COME_FROM against. This can be complicated by intervening
+    # POP_TOP, and pseudo COME_FROM, ELSE instructions
+    #
+    pop_jump_index = first - 1
+    while pop_jump_index > 0 and tokens[pop_jump_index] in (
+        "ELSE",
+        "POP_TOP",
+        "JUMP_FORWARD",
+        "COME_FROM",
+    ):
+        pop_jump_index -= 1
+    come_froms = ast[-1]
+
+    # FIXME: something is fishy when and EXTENDED ARG is needed before the
+    # pop_jump_index instruction to get the argment. In this case, the
+    # _ifsmtst_jump can jump to a spot beyond the come_froms.
+    # That is going on in the non-EXTENDED_ARG case is that the POP_JUMP_IF
+    # jumps to a JUMP_(FORWARD) which is changed into an EXTENDED_ARG POP_JUMP_IF
+    # to the jumped forwareded address
+    if tokens[pop_jump_index].attr > 256:
+        return False
+
+    if isinstance(come_froms, Token):
+        if (
+            tokens[pop_jump_index].attr < tokens[pop_jump_index].offset
+            and ast[0] != "pass"
+        ):
+            # This is a jump backwards to a loop. All bets are off here when there the
+            # unless statement is "pass" which has no instructions associated with it.
+            return False
+        return (
+            come_froms.attr is not None
+            and tokens[pop_jump_index].offset > come_froms.attr
+        )
+
+    elif len(come_froms) == 0:
+        return False
+    else:
+        return tokens[pop_jump_index].offset > come_froms[-1].attr