compile times...

[Mike Bryan]

In article <6709 at hubcap.clemson.edu> hubcap at hubcap.clemson.edu (Mike Marshall) writes:
>He told me that his benchmark program ran on my DECstation 3100 as fast as
>it did on an IBM 3081 mainframe. But, he said, it took forever to compile.
>
>It compiles on our VAX-8810 running ULTRIX in about 20-30 seconds. On my
>workstation, it took about 8 minutes to compile.
>
>I am assuming that the reason that it takes so long on on my workstation 
>can be attributed to the fact that RISC compilers have so much more work
>to do than "regular" compilers.

I've seen similar things here.  I just recently compiled a set of
programs on a MicroVAX II and a DECSystem 5400.  Both systems have
16MB of memory; the MVII has an RA81, the 5400 has an RF71.  Overall,
the 5400 was faster by about a factor of 2.5.  However, on one
particularly large module (about 5000 lines), the compile time went up
from 40 seconds to 50 minutes.  Continuous "ps -axv" and "vmstat"
commands showed that (1) the program "uopt" wanted 18 MB of memory,
and was getting about 75% of system memory and 1% of the CPU time, and
(2), the system was paging *extremely* heavily.  Turning off
optimization (the "-O" flag) caused the compile time to go back down
to 30 seconds.

It appears that once you reach a certain complexity in a program, the
optimizer requires so much memory that your system starts thrashing
madly.  With all the new "wonderful" switches for "cc(1)", it would be
nice to have one saying "optimize until you reach 'too much memory'".
-- 
Mike Bryan, Applied Computing Devices, 100 N Campus Dr, Terre Haute IN 47802
Phone: 812/232-6051  FAX: 812/231-5280  Home: 812/232-0815
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"Did you make mankind after we made you?" --- XTC, "Dear God"