[llvm-dev] Vectorization in LLVM x86 backend

[Craig Topper via llvm-dev]

The X86 backend shouldn't be doing any additional vectorization. If there
are no vector types in IR, I don't think the X86 backend will create any.

~Craig

On Mon, Aug 21, 2017 at 8:49 AM, Charith Mendis via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> Hi all,
>
> Recently I compiled the attached .c file using Clang with "-mavx2 -mfma
> -m32 -O3" optimization flags.
>
> First I used -emit-llvm and inspected the LLVM IR and there are no vector
> instructions. Then I got the assembly output of the file in it I can
> clearly see vector instructions in it.
>
> Neither the SLPVectorizer or the LoopVectorizer is however doing any
> vectorization (also checked it using -debug-only flag) as witnessed by the
> LLVM IR dump.
>
> Therefore, the vectorization should happen in the backend(?).
>
> Can I know whether the x86 backend does additional vectorization of scalar
> code and if so in which passes?
>
> NB - I posed the same question with the source files in a previous email,
> but the limit of 100kB was reached.
>
> Thank You.
> --
> Kind regards,
> Charith Mendis
>
> Graduate Student,
> CSAIL,
> Massachusetts Institute of Technology
>
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>
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