[m-dev.] preliminary MLDS performance comparisons

[Fergus Henderson]

Now that I've implemented optimization of static ground terms,
it's time to redo some of those performance comparisons.

As well as implementing the `--static-ground-terms' optimization,
there was another change that may have had a significant effect:
for correctness reasons, I changed the MLDS back-end to never inline
`pragma c_code'.  That may have caused a significant decrease in
speed and perhaps also a small decrease in code size.
Sometime soon `pragma c_code' will be reimplemented in such a way that
it can safely be inlined, at which time we can expect an increase in
performance and perhaps a small increase in code size.

On 13-May-2000, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> Second, here's a comparison of code size.
> I compiled the compiler with the MLDS back-end, and compared this
> with its size when compiled with the LLDS back-end
> 
> 						------ size (kbytes) -------
> Compiled with			Improvement	file	text     data    bss
> -O2 --opt-space [*]                           5423    5331       79     44
> -O2 --opt-space -H		33%		4084	4035        7     47
> 
> [*] The standard library was compiled with --intermodule-optimization.

With the latest compiler, I get the following figures:

  -O2 --opt-space -H [*]	39%	        3897    3849        7     47

Note that the `text' size here includes 652 kb of read-only data.

> ----------
> 
> Finally, here's a comparison of the speed of the generated code.
> I compared two versions of the compiler, both compiled with -O2 --opt-space,
> one with the MLDS back-end (-H), the other with the LLDS back-end.
...
> Compiled with         Input file     Options	Slowdown	user time (s)
> -O2 --opt-space       inst_match.m   -C -O5			21.1
> -O2 --opt-space -H    inst_match.m   -C -O5	27%		26.8
> -O2 --opt-space       inst_match.m   -C -O0			 9.3
> -O2 --opt-space -H    inst_match.m   -C -O0	21%		11.4

BTW, I made a mistake when recording my results there: the input file
was table_gen.m, not inst_match.m.  (This caused me some confusion
when trying to reproduce my results ;-)

With the latest compiler, I get the following figures:

  -O2 --opt-space -H    table_gen.m    -C -O5	17%		24.6
  -O2 --opt-space -H    table_gen.m    -C -O0	10%		10.2

So it's still slower than the LLDS back-end at the same optimization
level, but the slowdown is smaller (ranging from 10%-17%, rather than
from 21%-27%).

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.
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