[Python-Dev] Re: Re: Prospective Peephole Transformation

[Fredrik Lundh]

Phillip J. Eby wrote:

> Were these timings done with the code that turns (1,2,3) into a constant?

I used a stock 2.4 from python.org, which seems to do this (for tuples,
not for lists).

> Also, I presume that these timings still include extra LOAD_FAST operations that could be replaced 
> with DUP_TOP in the actual expansion, although I don't know how much difference that would make in 
> practice, since saving the argument fetch might be offset by the need to swap and pop at the end.

here's the disassembly:

>>> dis.dis(compile("if a in (1, 2, 3): pass", "", "exec"))
  1           0 LOAD_NAME                0 (a)
              3 LOAD_CONST               4 ((1, 2, 3))
              6 COMPARE_OP               6 (in)
              9 JUMP_IF_FALSE            4 (to 16)
             12 POP_TOP
             13 JUMP_FORWARD             1 (to 17)
        >>   16 POP_TOP
        >>   17 LOAD_CONST               3 (None)
             20 RETURN_VALUE

>>> dis.dis(compile("if a == 1 or a == 2 or a == 3: pass", "", "exec"))
  1           0 LOAD_NAME                0 (a)
              3 LOAD_CONST               0 (1)
              6 COMPARE_OP               2 (==)
              9 JUMP_IF_TRUE            26 (to 38)
             12 POP_TOP
             13 LOAD_NAME                0 (a)
             16 LOAD_CONST               1 (2)
             19 COMPARE_OP               2 (==)
             22 JUMP_IF_TRUE            13 (to 38)
             25 POP_TOP
             26 LOAD_NAME                0 (a)
             29 LOAD_CONST               2 (3)
             32 COMPARE_OP               2 (==)
             35 JUMP_IF_FALSE            4 (to 42)
        >>   38 POP_TOP
             39 JUMP_FORWARD             1 (to 43)
        >>   42 POP_TOP
        >>   43 LOAD_CONST               3 (None)
             46 RETURN_VALUE

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