https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65862
--- Comment #4 from Wilco <wdijkstr at arm dot com> --- (In reply to Vladimir Makarov from comment #3) But I can not just revert the patch making ALL_REGS available > to make coloring heuristic more fotunate for your particular case, as it > reopens the old PR for which the patch was created and i have no other > solutions for the old PR. I tried reverting the ALL_REGS patch and I don't see any regressions - in fact allocations are slightly better (fewer registers with ALL_REGS preference which is what we need - a strong decision to allocate to either FP or int regs). So what was the motivation for it? Note that it would be trivial to prefer ALL_REGS for some operands if necessary. The only case I can imagine is load and store which on some targets are quite orthogonal. I tried doing m=r#w and m=w#r on AArch64 and that works fine (this tells the preferencing code that ALL_REGS is best but it still keeps a clear INT/FP separation in the patterns which you may need for disassembly etc). IMHO that is a better solution than to automatically change the patterns r=r+r; w=w+w into rw=rw+rw and assume that ALL_REGS preference on all operands has zero cost eventhough the cost calculation explicitly states otherwise.
