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Compilation getting slower


This data, from Dan Pascu, suggests that GCC is steadily getting
gradually slower as regards compile time.  A 10% slowdown since a few
versions ago is not a disaster, but it is significant.

So I think people should know about this, and perhaps investigate
what causes the slowdown.  Maybe it is avoidable.


From: Dan Pascu <dan@services.iiruc.ro>
Sender: Dan Pascu <dan@dawn.iiruc.ro>
Subject: Re: WindowMaker and GNOME  (fwd)
To: rms@gnu.org

It's the time required to compile Window Maker using various compilers
The configuration of window Maker was the same in all cases (a simple
./configure).
and the time was measured with "time make" a number of times in each
case and the average value was computed.

On 10 Aug, Richard Stallman wrote:
> ...  To test for a slowdown in GCC, you
> should compare two setups that are identical except for the version of
> GCC that is in use.  To test for a slowdown in Glibc you should
> compare two setups that are identical except for the version of Glibc
> that is in use.
> 
> Would you like to test that?

The tests were done like that. Except the one (only) that was with
libc5, all were done with glibc2.1 and various gcc versions on the same
Debian 2.2 system (i.e. only the compiler was changed).
The didtribution I noted in the table for each case was from where the
compiler (binary) was took. But all of the compilers were installed on
the same Debian 2.2 system.
I don't think that the fact I took a binary from RedHat and installed
it on Debian makes much difference. I also compiled a egcs1.1.2 and get
the same results as the egcs1.1.2 I used from various distributions.
There were only very small differences between the same version of the
compiler (took from various sources, or compiled by myself) as columns
2 and 3 show, but always there was a big increase in the compile time
when the version of the compiler changed.

In fact the conclusion I came about was not because I made the test,
but because I saw that the compile time raised about 1.5 times after
installing new compiler versions on the same system. That made me make
this test, just to check what was the increase in compile time.

Here is the table again, I hope that now is much clearer.

compiler | egcs1.1.2 | egcs1.1.2  | egcs1.1.2  | pgcc1.1.3  | gcc-2.95
 flags   | & libc5   | & glibc2.1 | & glibc2.1 | & glibc2.1 | & glibc2.1
         | Slack4.0  | Debian2.2  | RedHat6.0  | Enoch      | Debian2.2
-------------------------------------------------------------------------
none     |   1m44s   |   2m07s    |   2m03s    |   2m09s    |   2m11s
-------------------------------------------------------------------------
-g       |   2m05s   |   2m28s    |   2m26s    |   2m33s    |   2m34s
-------------------------------------------------------------------------
-O       |   2m02s   |   2m41s    |   2m36s    |   2m46s    |   3m01s
-------------------------------------------------------------------------
-g -O    |   2m21s   |   3m01s    |   2m56s    |   3m06s    |   3m22s
-------------------------------------------------------------------------
-O2      |   2m26s   |   3m07s    |   3m01s    |   3m16s    |   3m43s
-------------------------------------------------------------------------
-g -O2   |   2m46s   |   3m28s    |   3m21s    |   3m36s    |   4m04s
-------------------------------------------------------------------------
-O6      |   2m35s   |   3m15s    |   3m08s    |   3m36s    |   3m52s
-------------------------------------------------------------------------
-g -O6   |   2m55s   |   3m35s    |   3m28s    |   3m56s    |   4m12s
-------------------------------------------------------------------------


-- 
Dan



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