[m-dev.] preliminary MLDS performance comparisons

[Fergus Henderson]

Some more benchmark results, this time with `-O4 --opt-space' for mmc,
(but still `-O2' for gcc):

Compiled with         Input file     Options	Slowdown	user time (s)
-O4 --opt-space       table_gen.m    -C -O5	   		24.1
-O4 --opt-space -H    table_gen.m    -C -O5	13%   		21.4
-O4 --opt-space       table_gen.m    -C -O0	   		9.0
-O4 --opt-space -H    table_gen.m    -C -O0	11%   		9.9

I also tried compiling the `-O4 --opt-space -H' version with
`gcc -Os', which is supposed to optimize for code size.  But compared
to `gcc -O2', `-Os' slowed the Mercury compiler down by about 4%, and
decreased code size by only 0.5%.  `gcc -O3' didn't help either;
compared to `gcc -O2', the version compiled with `gcc -O3' was about
2% slower and 16% bigger.

P.S. from the gcc documentation:
 | `-Os'
 |      Optimize for size.  `-Os' enables all `-O2' optimizations that do
 |      not typically increase code size.  It also performs further
 |      optimizations designed to reduce code size.

-- 
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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