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vector-loads-and-stores.md

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Proposal ID CP007
Name Buffer Tags
Previous Names Buffer tied to a Context
Date of Creation 30 March 2017
Target SYCL 1.2.1
Current Status Accepted with changes
Reply-to Ruyman Reyes ruyman@codeplay.com
Original author Ruyman Reyes ruyman@codeplay.com
Contributors Ruyman Reyes ruyman@codeplay.com, Gordon Brown gordon@codeplay.com

Vector Load and Store Operations

Motivation

In the current SYCL 1.2 specification the vector load and store operations are not supported. These are operations which exist in OpenCL for loading and storing elements of a vector from and to an array of elements of the same type as the cahnnels of the vector.

For example:

float floatData[1024];

buffer<float, 1> floatBuffer(floatData, range<1>(1024));

queue.submit([&](handler &cgh){

  auto acc = buf.get_access<access::mode::read>(cgh);

  cgh.parallel_for(range<1>(1024), [=](item<1> idx){

    size_t offset = (idx.get_global(0) / 4);

    float4 f4;

    f4.load(offset, acc.get_pointer());

    result = someComputation(f4);

    result.store(offset, acc.get_pointer());
  });

});

The proposal is to add the load and store member function templates to the vec class.

Load and Store Member Functions

template <access::address_space addressSpace>
void load(size_t offset, multi_ptr<dataT, addressSpace> ptr);

template <access::address_space addressSpace>
void store(size_t offset, multi_ptr<dataT, addressSpace> ptr);

In the declarations above dataT and numElements are template parameters of the vec class template and reflect the channel type and dimensionality of a vec class template specialisation.

The load() member function template will read values of type dataT from the memory at the address of the multi_ptr, offset in elements of dataT by numElements * offset and writes those values to the channels of this vec.

The store() member function template will read channels of this vec and writes those values to the memory at the address of the multi_ptr, offset in elements of dataT by numElements * offset.

The reason for having a multi_ptr parameter rather than an accessor is so that localy created pointers can also be used as well as pointers passed from the host.

The data type of the multi_ptr is dataT the data type of the components of the vec class template specialisation. This requires thhat the pointer passed to eiither load() or store() must match the type of the vec instance itself.