On Feb 4, 2008 12:06 PM, Jan Hubicka <[EMAIL PROTECTED]> wrote: > > > On Feb 4, 2008 4:11 AM, H.J. Lu <[EMAIL PROTECTED]> wrote: > > > DImode is aligned at 8 byte in i386. Since 32bit doesn't have > > > 64bit register, can we align DImode at 4byte instead of 8 > > > for i386? It shouldn't have any negative impact on performance. > > > > I don't think DImode is aligned at 8 bytes on i386, at least not as > > far as struct layout is concerned. > > It is with -malign-double AFAIK. The reasons for doing so predate me. > I guess it was a speculation that since alignment on double appeared > that in future same alignment on long long might too.
-malign-double is (was?) indeed a performance improvement for numerical applications on 32bits. But DImode is still not 8 bytes aligned there (which makes a next-gen 32bit ABI for 64bit x86 difficult there, if you want to retain DImode/DFmode 8 byte alignment and re-use the kernel 32bit compatibility layer). Richard.
