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why does dead code costs time?

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Hi,

I'm interested in compilers optimizations, so I study python compilation process

I ran that script:

    import timeit

    def f(x):
        return None

    def g(x):
        return None
        print(x)

    number = 10000

    print(timeit.timeit('f(1)',setup="from __main__ import f", number=number))
    print(timeit.timeit('g(1)',setup="from __main__ import g", number=number))   

    print(dis.dis(f))
    print(dis.dis(g))

It gives this output:

    0.003460251959040761
    0.004164454061537981
     17           0 LOAD_CONST               0 (None) 
                  3 RETURN_VALUE         
    None
     20           0 LOAD_GLOBAL              0 (None) 
                  3 RETURN_VALUE         

     21           4 LOAD_GLOBAL              1 (print) 
                  7 LOAD_FAST                0 (x) 
                 10 CALL_FUNCTION            1 (1 positional, 0 keyword pair) 
                 13 POP_TOP              
    None

I do not understand why the dead code `print(x)` takes time (~20% in
that case). As we see in the opcode, a call to g(1) returns immediately, so
there should be no delay at all. Where am i wrong?

mmhh... it comes to me now that the gap must be in function loading time...
I'll check ceval.c

However, isn't there a room for a slight optim here? (in this case, the
dead code is obvious, but it may be hidden by complex loops and
conditions)

Cheers


-- 
Bruno Dupuis

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why does dead code costs time? Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> - 2012-12-05 16:46 +0100
  Re: why does dead code costs time? Neil Cerutti <neilc@norwich.edu> - 2012-12-05 16:15 +0000
    Re: why does dead code costs time? Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> - 2012-12-05 17:40 +0100
      Re: why does dead code costs time? Ramchandra Apte <maniandram01@gmail.com> - 2012-12-09 06:11 -0800
        Re: why does dead code costs time? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-12-09 16:47 +0000
          Re: why does dead code costs time? Ramchandra Apte <maniandram01@gmail.com> - 2012-12-12 21:23 -0800
            Re: why does dead code costs time? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-12-13 06:01 +0000
              Re: why does dead code costs time? rusi <rustompmody@gmail.com> - 2012-12-12 22:27 -0800
                Re: why does dead code costs time? Cameron Simpson <cs@zip.com.au> - 2012-12-13 17:51 +1100
                Re: why does dead code costs time? rusi <rustompmody@gmail.com> - 2012-12-12 22:59 -0800
                Re: why does dead code costs time? Chris Angelico <rosuav@gmail.com> - 2012-12-13 18:03 +1100
          Re: why does dead code costs time? Ramchandra Apte <maniandram01@gmail.com> - 2012-12-12 21:23 -0800
    Re: why does dead code costs time? Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> - 2012-12-05 18:19 +0100
      Re: why does dead code costs time? Tim Roberts <timr@probo.com> - 2012-12-05 21:20 -0800
  Re: why does dead code costs time? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-12-05 17:34 +0000
    Re: why does dead code costs time? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-12-05 17:39 +0000
    Re: why does dead code costs time? Ian Kelly <ian.g.kelly@gmail.com> - 2012-12-05 10:59 -0700
    Re: why does dead code costs time? Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> - 2012-12-05 19:24 +0100
    Re: why does dead code costs time? Terry Reedy <tjreedy@udel.edu> - 2012-12-05 15:41 -0500
    Re: why does dead code costs time? Chris Kaynor <ckaynor@zindagigames.com> - 2012-12-05 12:49 -0800
    Re: why does dead code costs time? Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> - 2012-12-05 21:50 +0100
    Re: why does dead code costs time? Bruno Dupuis <python.ml.bruno.dupuis@lisael.org> - 2012-12-05 22:58 +0100

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