Andrew Pinski <pins...@gmail.com> writes: > On Fri, May 25, 2018 at 3:35 PM, Steve Ellcey <sell...@cavium.com> wrote: >> I was curious if there was any reason that REG_ALLOC_ORDER is not >> defined for Aarch64. Has anyone tried this to see if it could help >> performance? It is defined for many other platforms. > > https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01815.html > https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01822.html
It looks like the immediate reason for reverting was the effect of listing the argument registers in reverse order. I wonder how much that actually helps with IRA and LRA? They track per-register costs, and would be able to increase the cost of a pseudo that conflicts with a hard-register call argument. It just felt like it might have been a "best practice" idea passed down from the old local.c and global.c days. Thanks, Richard
