Re: Speedy compilers

"Jeff Jackson" <jeff-news@jeff-jackson.com> writes:


>I have a similar story to tell. I did a complete rewrite of the peephole
>optimizer of a compiler at what was then the Harris Computer Systems
>Division. The peephole optimizer deleted enough code that there
>was a net decrease in compile time. So, even at "Minimal" optimization,
>we ran peephole.


Yep, similar story here too. For the Mercury compiler, the
optimization level is specified as an integer (via e.g. `-O2' or
`-O6'). But level zero (`-O0') doesn't mean turn off all
optimizations, it just means try to compile as fast as possible. To
turn off all optimizations, you have to specify an optimization level
of -1 ;-).


I've also noticed the same kind of phenomenon with GNU C. Mercury
compiles via C, using gcc, and I've noticed that compilation speed for
Mercury-generated C code is often faster when using `gcc -O1' rather
than `gcc -O0'.


--
Fergus Henderson <fjh@cs.mu.oz.au>
WWW: <http://www.cs.mu.oz.au/~fjh>
PGP: finger fjh@128.250.37.3

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