llvm dev - Jan 2013 - [LLVMdev] Does loop vectorizer inquire about target's SIMD capabilities?

On 3 January 2013 21:53, Nadav Rotem <nrotem at apple.com> wrote:
> > I am asking this because I would like to have loop vectorization
> disabled for targets that don't support SIMD instructions (for example,
> standard mips32).
> > Loop vectorization bloats the code size and prolongs compilation time
> without any improvement to performance for such targets.
> >
>
> Yes. Also, notice that the loop vectorizer tries to be more conservative
> when the 'optforsize' attribute is used.
>
Isn't the vectorizer disabled by default? Or are you requesting that if the
user chooses -vectorize the compiler prints a warning (unused param since
no SIMD)?

cheers,
--renato
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On Jan 3, 2013, at 2:05 PM, Renato Golin <renato.golin at linaro.org>
wrote:
> Isn't the vectorizer disabled by default? 
The loop vectorizer is now enabled by default. 
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On 3 January 2013 22:09, Nadav Rotem <nrotem at apple.com> wrote:
> The loop vectorizer is now enabled by default.
>
I thought that was just a temporary arrangement to get the feel for it, not
to actually have it on all the time (next release). Is it just for -O3 or
lower too?

This can cause problems, for instance on ARMv7, the default is that NEON is
present, but Tegra2 doesn't have NEON, only VFP. It means an optimizing
compilation that used to work on it will fail, unless you specify no NEON
or no vectorization explicitly, no?

I'd prefer if -vectorization had to be passed explicitly to get it done on
production releases of LLVM or something else (-O4 or -OV, for example).

cheers,
--renato
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