[cfe-dev] [llvm-dev] generate vectorized code

[Mehdi Amini via cfe-dev]

> On Mar 16, 2016, at 5:38 PM, Rail Shafigulin <rail at esenciatech.com> wrote:
> 
> On Wed, Mar 16, 2016 at 11:48 AM, Mehdi Amini <mehdi.amini at apple.com <mailto:mehdi.amini at apple.com>> wrote:
> Hi Rail,
> 
> Two hints to begin with:
> 
> 1) Makes sure you example is vectorized on X86 for example
> 2) Is your target correctly overriding the TTI (declaring the vector register size for example) so that the vectorizer can kicks-in (see X86TTIImpl::getRegisterBitWidth for instance). Alternatively you can test the SLP vectorizer by passing to clang: -mllvm -slp-max-reg-size -mllvm 512  (I don't see an equivalent option for the loop vectorizer though).
> 
> Well, it sort of worked. I added a getRegisterBitWidth(...) but then I got this error:
> 
> fatal error: error in backend: Cannot select: 0x5e949a8: v4i32 = BUILD_VECTOR 0x5e91ae8, 0x5e91ae8, 0x5e91ae8, 0x5e91ae8 [ORD=16] [ID=16]
>   0x5e91ae8: i32 = Constant<0> [ID=5]
>   0x5e91ae8: i32 = Constant<0> [ID=5]
>   0x5e91ae8: i32 = Constant<0> [ID=5]
>   0x5e91ae8: i32 = Constant<0> [ID=5]
> 
> What am I missing?

I means that you have a vectorized IR that reached your backend, but your backend is not ready to deal with all the vector constructs in SelectionDAG. 
You need to express how to legalize/select the BUILD_VECTOR in SelectionDAG to instructions that your target supports. You can look at what other targets are doing.

-- 
Mehdi

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