Re: Extremely long compile times

[John Carter <john dot carter at tait dot co dot nz>]

On Fri, 18 Oct 2002, Charles wrote:

> I've tried this with both gcc 3.1.1 and gcc 3.2.  This particular program
> takes over 2 hours to compile.  

Generally it helps to use the -pipe option. This stop it from using 
temporary disk files and just pipes it from preprocessor to compiler to 
assembler.

Optimization these days seems to be very cunning and take a _lot_ of time. 
During development add the -O0 flag. Compiles a lot faster and easier to 
debug.

Experiment with the -f optimization flags. Perhaps there is just one 
optimization that is really chewing up the time.

> According to -time, 100% of the time is
> spent in "cfg cleanup".  The program is generated by a language converter
> we are working on and contains only a "main" function with a very large
> number of local variables and initializing of arrays one element at a time.

It could be that gcc is doing a linear search somewhere under the 
expectation that there aren't a huge number of local variables. Can you 
try break it up into smaller compilation units?

> Does anyone know what could be causing this and/or what we could look for
> to correct it?

Try pull the sources for gcc out and compile them with profiling on (-pg) 
and then see if there are any hot spots.

-- 


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

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