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From: ENGR@GSSI.MV.COM (Michael Furman)
Subject: Re: Style: multiple returns and relatives
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Date: Mon, 27 Nov 1995 16:38:13 GMT
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In article <1995Nov2421.20.06.18267@silverton.berkeley.edu>, 
djb@silverton.berkeley.edu says...
>
>> Extrinsic functional equivalence is undecidable, so in theory, we 
>> really couldn't expect an optimizing compiler to optimizer every
>> equivalent program to the same optimal code by simply considering
>> only the inputs and outputs. 
>
>Most of the theoretical comments in this thread have been wrong.

  You are correct - but only formally. I believe that pow(2, pow(2, 30)) - 
number of possible states for 1 gygabyte memory may be very well
approximated by infinity.


>
>Provided that there are only finitely many inputs, and finitely many
>possible optimized programs to consider (``I don't want more than a
>gigabyte of output code, thank you''), the optimization problem is
>solvable.
>
>Remember, we're starting from a working program W that always halts.
>Given another program P, and given an input, we want to know if P
>runs _more quickly_ than W and produces the same output. This is
>completely straightforward to test.
>
>---Dan

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