On May 28, 2014, at 1:03 AM, Matthew Fortune <matthew.fort...@imgtec.com> wrote:
>> You shouldn't need to declare __builtin_* functions anyway. And if a >> function can be represented directly with GNU C vector extensions, it's >> preferred to implement it that way inline in the header rather than having >> built-in functions duplicating existing GNU C functionality. (Look at >> what AArch64 arm_neon.h does where possible, and what ARM arm_neon.h has >> been moved towards lately. I don't now what the msa.h functions do, so I >> don't know if this actually applies to any of them - but it's something to >> consider, so that built-in functions are only defined where actually >> needed.) > > In the aarch64 arm_neon.h header there are a decent number of inline asm > implementations too instead of builtins. It is not immediately obvious to me > as to what the deciding factor is between adding a builtin and using inline > asm when vector extensions do not support the operation. Do you happen to > know why inline asm is used in places? Most likely simplify implementation at the time. Inline-asm is useless when it comes to scheduling code. So the answer should be easy there. > > This looks like a reasonable idea to use GNU extensions where available. The > down-side to this approach is that it may be necessary to write quite > dis-similar headers for LLVM vs GCC which I think is part of the reason why > the header is written as it is. I don't know if that is a good reason to > require builtins or not though. Well clang supports Opencl and Opencl got many of its vector behaviors from gcc. So I doubt it would be too hard for so ifdefs in there. Thanks, Andrew > > Regards, > Matthew
