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

[Renato Golin]

On 27 May 2011 19:47, Jim Grosbach <grosbach at apple.com> wrote:
> Not exactly. The distinction is clear, it's just not expressed as an
> either/or question. Specifically, the code generator considers NEON to be a
> proper superset of VFP3. So if it has only VFP3, that's all it will use. If
> it has NEON, it assumes it also has VFP3 and can use either.

Indeed.


> There's not,
> currently, a way to say "use only NEON instructions; don't generate any
> VFP3."

Which would be advantageous on some cases, where NEON instructions are
faster than VFP3.

But the way it's done today in LLVM is correct. The output doesn't
have to be different between NEON and VFP3 for VFP3 operations, but it
can be. GCC has some of that knowledge and it's just a matter of time
for LLVM to catch up. ;)

cheers,
--renato