On 5/23/23 12:24 AM, Kewen.Lin wrote: > on 2023/5/23 01:31, Carl Love wrote: >> The builtins were requested for use in GLibC. As of version 2.31 they >> were added as inline asm. They requested a builtin so the asm could be >> removed. > > So IMHO we also want the similar support for mffscrn, that is to make > use of mffscrn and mffscrni on Power9 and later, but falls back to > __builtin_set_fpscr_rn + mffs similar on older platforms.
So __builtin_set_fpscr_rn everything we want (sets the RN bits) and uses mffscrn/mffscrni on P9 and later and uses older insns on pre-P9. The only problem is we don't return the current FPSCR bits, as the bif is defined to return void. Crazy idea, but could we extend the built-in with an overload that returns the FPSCR bits? To be honest, I like the __builtin_set_fpscr_rn name better than __builtin_mffscrn[i]. The built-in machinery can see that the usage is expecting a return value or not and for the pre-P9 code, can skip generating the ending mffs if we don't want the return value. Peter
