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Re: [patch] Speed up # of iterations analysis
- From: Paul Schlie <schlie at comcast dot net>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- Cc: <gcc-patches at gcc dot gnu dot org>
- Date: Sun, 03 Apr 2005 13:28:30 -0400
- Subject: Re: [patch] Speed up # of iterations analysis
(sorry, immediately previous response was improperly sent)
> Zdenek Dvorak wrote:
> 3) Removes simplify_using_outer_evolutions. This function does
> basically constant propagation in weird special cases, like
>
> for (i = 0; i < 50; i++)
> ...;
> for (; i < 100; i++)
> ...;
>
> to detect that the initial value of i in the second loop is 50.
> In practice, this just wastes time.
and typically inferior to eliminating the otherwise potentially expensive
arbitrary constant comparison (vs. a typically cheep/free zero comparison)
loop count testing in cases when the iteration count isn't used otherwise:
for (i = 50; i != 0; i--)
...;
for (i = 50; i != 0; i--)
...;