[m-dev.] 32-bit sources on 64-bit target

[Peter Wang]

On Fri, 8 Mar 2013 16:47:00 +1100, Julien Fischer <jfischer at opturion.com> wrote:
> On Fri, Mar 8, 2013 at 3:58 PM, Peter Wang <novalazy at gmail.com> wrote:
> > On Fri, 8 Mar 2013 15:03:19 +1100, Julien Fischer <jfischer at opturion.com> wrote:
> >> Hi Peter,
> >>
> >> On Fri, Mar 8, 2013 at 10:51 AM, Peter Wang <novalazy at gmail.com> wrote:
> >> > On Fri, 8 Mar 2013 00:38:58 +1100, Julien Fischer <jfischer at opturion.com> wrote:
> >> >> On Fri, Mar 8, 2013 at 12:17 AM, Paul Bone <paul at bone.id.au> wrote:
> >> >> > On Thu, Mar 07, 2013 at 06:00:24PM +1100, Julien Fischer wrote:
> >> >> >> On Thu, Mar 7, 2013 at 5:08 PM, Peter Wang <novalazy at gmail.com> wrote:
> >> >> >> > The compiler built from pre-generated sources WILL be installed.
> >> >> >> > For now, I can't think of why that would be a problem.
> >> >> >>
> >> >> >> It wouldn't be at the moment since the compiler (and other tools)
> >> >> >> are currently built with --mercury-linkage static.  It would be a problem,
> >> >> >> if that were not the case.
> >> >> >>
> >> >> >
> >> >> > How much of a performance gain does unboxed floats and 3 tag bits represent
> >> >> > specifically for the compiler?
> >> >
> >> > Suprisingly, significant: (default speedtest)
> >> >
> >> > mercury_compile.01 average of 6 with ignore=1     10.00
> >> > mercury_compile.02 average of 6 with ignore=1     12.08
> >>
> >> That's quite a difference.  Is mercury_compile.02 built directly from
> >> the source distribution
> >> C files.
> >
> > Yes.
> 
> And was mercury_compile.01 built with similar options, other than
> the number of tag bits and unboxed floats.

I simulated what a normal, but informed, user would do.  Unpack the
srcdist tarball, build it once, install (mercury_compile.02).
Unpack the tarball again, build it using the previously installed
compiler, install again to another location (mercury_compile.01).

> The options used for
> the source diet are:
> 
>     -O5 --opt-space --cross-compiling --no-smart-indexing
> 

I repeated the benchmark after installing the srcdist64 package[*].
Don't know why my computer was running slower last week, but the results
are consistent:

mercury_compile.01 average of 6 with ignore=1      9.19
mercury_compile.02 average of 6 with ignore=1     11.29
mercury_compile.03 average of 6 with ignore=1     11.32

The srcdist64 compiler is .03.  It shows that the number of tag bits and
unboxed floats make no difference to the compiler, so one of the other
options makes the difference.  (My guess is that --cross-compiling
disables compile-time evaluation which degrades tree_bitset, but only
because I'm a bit familiar with that module.)

We might consider disabling --cross-compiling for the srcdist64 package?

[*] For the srcdist64 package, I had to hack configure.ac to not force
mercury_cv_low_tag_bits=2 and mercury_cv_unboxed_floats=no when building
from generated sources.

Peter