[cfe-dev] [LLVMdev] __builtin___clear_cache

[Renato Golin]

On 14 March 2014 16:34, JF Bastien <jfb at google.com> wrote:
> How does this overlap with:
>
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140310/thread.html#208333

The builtin was created to call __clear_cache() on platforms that need
it (like ARM and MIPS), but to be ignored on others (like x86_64).

This builtin should call __clear_cache() from whatever library is
available at the moment, so there is no overlap, just supporting the
GCC builtin to avoid calling a noop function when not needed.


> The bug mentions doing the mov r7 and svc, when the above code already does
> it, I'm somewhat confused.

That's an idea that might not be a good one. I was thinking if, in
some occasions, we could emit directly the instructions, but that will
have to deal with lower level stuff that we don't want on the
intrinsic level. GCC just emits a call to __clear_cache() and, at the
very least, we should do the same for now.

That optimisation might come later, at a much lower level, but I have
my doubts if that's relevant. We shouldn't be clearing the cache on a
hot loop anyway. ;)

cheers,
--renato