Mail Archives: djgpp-workers/1998/02/10/13:31:40
> >> Why do the switches used to compile the library still include
> >> -fno-strength-reduce? Doesn't this belong to pre-2.7.2.1 gcc and is
> >> solved in later versions?
Hmm - I thought that 2.7.2.1 jsut disabled it by default but that the
bug still existed. It was supposed to be rather rare to come across
it though.
> and see section 4.22. Basically, the theory is that strength reduction tends
> to replace multiplication with shifts and adds, costing more registers which
> the x86 can ill afford.
This depends on the cost table used. If you use gcc 2.7.2.x which
only knows about 386/486 then it will probably not make the best
decisions here. Gcc 2.8, and of course pgcc are much better at strengh
reduction determination.
> They do give the caveat, however, that one should try different flags and
> see. Has anyone done this with the libc, or do they plan to?
The only place it makes a huge difference is floating point code. It
would be worthwhile to try unrolling loops w/ strength reduction there.
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