On Mon, Feb 04, 2008 at 12:24:33PM +0100, Jan Hubicka wrote: > > > > -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). > > Perhaps it was intended for numerical applications, but it is > implemented by increasing maximal alignment that affect long long too. > > I think H. J. hit it with this auto alignment branch and I would say > that decreasing DImode alignment there to avoid long long triggering the > prologue is good thing to do. >
Yes, I run into it on the stack alignment branch. It is not a big deal. But it is a waste of space for no performance gain. However, it does break i386 psABI. We align DF scalar to 8 byte and DF field in struct to 4 byte for i386. Can we just align DI scalar to 4 byte and leave DI field in struct unchanged for i386? Thanks. H.J.
