[LLVMdev] Question about ARM/vfp/NEON code generation

[Renato Golin]

On 27 May 2011 02:04, David Dunkle <ddunkle at arxan.com> wrote:
> In all cases, I get code that looks pretty very the same; its like what
> is below. However, I am expecting to see instruction level differences
> between the vfp3 and neon versions. When I do the same with gcc 4.2 I do
> see differences in the generated code.

Hi David,

You could see different instructions (as gcc does, you say), but it's
not necessary.

Your example has only floating point arithmetic, which both VFP3 and
NEON can do, so the final assembly will be similar. If you start using
integer arithmetic, than you can see vector instructions for NEON (if
it's vectorized) and not for VFP3.

All chips (to date) with NEON have VFP3, so it's safe to assume that a
-mfpu=neon will have VFP3, so all the decisions about code generated
for VFP3 can safely be assumed by targets with NEON.

Hope that answers your questions.

cheers,
--renato