[llvm-commits] [PATCH] RDRAND intrinsics

[Benjamin Kramer]

On 06.07.2012, at 22:52, Eli Friedman wrote:

> On Fri, Jul 6, 2012 at 1:00 PM, Benjamin Kramer <benny.kra at gmail.com> wrote:
>> The attached patch adds support for intel's rdrand intrinsics to LLVM.
>> 
>> The tricky part is that the intrinsics have to return two values (the random value and the carry flag). This is solved with a pointer argument and a cmov to materialize CF, which matches GCC's output. This approach requires some custom lowering code, but I don't see a way to do it with tablegenerated patterns only.
> 
> It would be much more friendly to the optimizer to use multiple return
> values... but it might not be worth the hassle, considering that
> rdrand is relatively slow.

I tried this first as it also looks cleaner, but I couldn't find a way to smuggle it past legalization into the target specific lowering.

- Ben