ix86_data_alignment: bad defaults?

Jan Hubicka hubicka@ucw.cz
Fri Feb 23 21:47:00 GMT 2007


> > 
> > > > I like the "min (256, MAX_OFILE_ALIGNMENT)" fix...
> > > 
> > > So do I.
> > 
> > Ok to apply then?  Tested via djgpp cross-compile and cross-host.
> 
> Yes, this is OK. (to be very pedantic, we can assert that
> MAX_OFILE_ALIGNMENT>=256 on x86-64 targets, but well). I fully agree with
> Richard's interpretation concerning BIGGEST_ALIGNMENT meaning - ie in
> special cases for perofrmance it definitly makes sense to use higher
> alignments than BIGGEST_ALIGNMENT (such as cache line or page
> alignments), BIGGEST_ALIGNMENT is what CPU require and runtime must
> provide when asked for.

One extra bit - we do use alignments of base > 32 bytes for code
alignment.  What would be the behaviour on targets with
MAX_OFILE_ALIGNMENT set to 16 bytes?

I.e. if we end up with gas producing many nops that would then on random
basis end up 16 or 32 byte aligned, it might be good idea to forcingly
reduce alignments to base 16 on those targets.

Honza



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