[llvm-dev] BPF backend with vector operations - some strange error

[Alexei Starovoitov via llvm-dev]

On Sat, Jan 9, 2016 at 11:29 AM, RCU via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>   Hello.
>     I solved this issue (from the previous email).
>
>     Got inspired from
> http://comments.gmane.org/gmane.comp.compilers.llvm.devel/73619, (also
> https://groups.google.com/forum/#!topic/llvm-dev/LfltBGG9ru0),
> http://lists.llvm.org/pipermail/llvm-dev/2007-April/008843.html
>
>     What I did was to edit ConnexInstrInfo.td and replaced all occurrences:
>         PatLeaf<(imm)
>        %(which were ambiguous since the variable name ("in dag operator")
> does not have a type and this poses issues to the Type inference algorithm,
> since I added in ConnexRegisterInfo.td a second RegisterClass with type
> v2i64)
>     with
>         PatLeaf<(i64 imm)
>     namely:
>        - def i64immSExt32 : PatLeaf<(i64 imm),
>                 [{return isInt<32>(N->getSExtValue()); }]>;
>
>   Best regards,
>     Alex
>
>
> On 1/8/2016 1:31 AM, RCU wrote:
>>
>>    Hello.
>>      I've tried to add some simple arithmetic vector operations to the BPF
>> backend
>> available in the LLVM repo. Because I added in BPFRegisterInfo.td another
>> RegisterClass
>> (taken from the Mips backend):
>>    def MSA128W: RegisterClass<"BPF", [v2i64, v2f64], 128,
>>                             (sequence "W%u", 0, 31)>;
>> in order to support vector for example, ADD operations, I get the
>> following error when
>> building llc:
>>    JEQ_ri:         (BPFbrcc i64:i64:$dst,
>> (imm:i64)<<P:Predicate_i64immSExt32>>:$imm,
>> (imm:{i64:v4i32})<<P:Predicate_BPF_CC_EQ>>, (bb:Other):$BrDst)
>> Included from ~/LLVM/llvm38Nov2016/llvm/lib/Target/BPF/BPF.td:14:
>> ~/LLVM/llvm38Nov2016/llvm/lib/Target/BPF/BPFInstrInfo.td:131:1: error: In
>> JEQ_ri: Could
>> not infer all types in pattern!
>>    defm JEQ  : J<0x1, "jeq",  BPF_CC_EQ>;

Great that you found a solution.
Could you share what is the end goal for this vector instructions in BPF?
Are you actually trying to extend BPF ISA and add kernel support for it?
Or just using BPF backend as as a simplest/smallest playground?
Regardless please share the patches when they're ready. I'm curious
how you're adding vectorization. May be we can actually add them to kernel.