[mercury-users] foreign_decl vs. foreign_code

[Fergus Henderson]

On 13-Feb-2002, Michael Day <mikeday at bigpond.net.au> wrote:
> 
> I am using -O5 --intermodule-optimization
> --trans-intermod-opt --constraint-propagation, are there any other
> interesting optimizations I could try that are not enabled by default with
> -O5 or -O6?

You could try compiling without `--constraint-propagation'; the reason that
isn't enabled by default is that sometimes it slows things down.

If your program is small, you will probably get better performance by
adding `--inline-alloc' to MGNUCFLAGS.

If your program is large, you might get better performance by adding
`--opt-space' to MCFLAGS.

For the hlc.gc grade, you might get better performance by using a more
recent version of gcc, e.g. gcc 3.0.  (However the asm_fast.gc grade
doesn't work with gcc 3.0, so keep a copy of gcc 2.95.* around too.)

For the hlc.gc grade, you can also get slightly better performance by
defining MR_USE_REGPARM.  This enables some stuff which tells gcc to use
a more efficient calling convention that passes parameters in registers.
But this requires gcc >= 3.0, and you also you need to rebuild the Mercury
runtime and standard library with MR_USE_REGPARM defined.

For the hlc.gc grade, or if your program makes use of the C interface,
you could also try adding `-O3' to CFLAGS.  It hasn't helped in the
benchmarks that I've tried, but you never know ;-)

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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