[llvm-dev] RFC: Generic IR reductions

Amara Emerson via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 1 06:36:32 PST 2017

I think you mean take a single vector operand, not two vector
operands. If the intrinsic took two vectors then we would naturally
expect the result to be a vector, where each element is the result of
a scalar operation between each respective element in the vector
operands. Just like  a normal binary operator.

On 1 February 2017 at 10:59, Renato Golin <renato.golin at linaro.org> wrote:
> On 1 February 2017 at 08:27, Renato Golin <renato.golin at linaro.org> wrote:
>> Sorry, I meant min/max + reduce, just like above.
>>   %sum = add <N x float>, <N x float> %a, <N x float> %b
>>   %min = @llvm.minnum(<N x float> %sum)
>>    %red = @llvm.reduce(%min, float %acc)
> No, this is wrong. I actually meant overriding the max/min intrinsics
> to take vectors instead of two scalar options.
> The semantics of those intrinsics is to get a number of parameters and
> return the max/min on their own type. A vector is just a different
> packing of parameters, all of which have the same type, so there's no
> semantic difference other than the number of arguments.
> However, when they're lowered, they'll end up a a short sequence of
> instruction (if supported) in the same way.
> You'd only emit a max/min in vectorisation if the target supports it
> and the cost is low. For instance, in AArch64 it would only emit it if
> SVE support is enabled.
> Makes sense?
> cheers,
> --renato

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