rms_norm.h

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#ifndef TVM_TOPI_NN_RMS_NORM_H_
#define TVM_TOPI_NN_RMS_NORM_H_
 
#include <tvm/te/operation.h>
#include <tvm/topi/reduction.h>
#include <tvm/topi/tags.h>
 
#include <string>
 
namespace tvm {
namespace topi {
namespace nn {
 
using namespace tvm::te;
 
inline Tensor rms_norm(const Tensor& data, const Tensor& weight, const ffi::Array<int64_t>& axis,
                       double epsilon, std::string name = "T_rms_norm",
                       std::string tag = kInjective) {
  using namespace tvm::prim;
  const auto& data_type = data->dtype;
  const auto& weight_type = weight.defined() ? weight->dtype : data_type;
  TVM_FFI_ICHECK(data_type == weight_type) << "rms_norm: data and weight must have the same type";
 
  const auto& data_fp32 = cast(data, PrimType::Float(32));
  const auto& weight_fp32 = cast(weight, PrimType::Float(32));
 
  auto square = multiply(data_fp32, data_fp32);
  auto square_sum = sum(square, axis, /*keepdims=*/false, /*atleast1d=*/true);
 
  auto ndim = data_fp32->shape.size();
  TVM_FFI_ICHECK_NE(ndim, 0) << "Cannot reduce a 0 dim Tensor";
  auto real_axis = GetRealAxis(static_cast<int>(ndim), axis);
  auto reduce_extent = MakeConst(PrimType(data_fp32->dtype), 1);
  for (int i : real_axis) {
    reduce_extent *= data_fp32->shape[i];
  }
  auto rsqrt_func = [&](const ffi::Array<PrimVar>& indices) {
    ffi::Array<PrimVar> non_reduce_indices;
    for (int i = 0, n = static_cast<int>(indices.size()); i < n; ++i) {
      if (std::find(real_axis.begin(), real_axis.end(), i) == real_axis.end()) {
        non_reduce_indices.push_back(indices[i]);
      }
    }
    auto output = tvm::prim::rsqrt(square_sum(non_reduce_indices) / reduce_extent +
                                   MakeConst(PrimType(data_type), epsilon));
    return output;
  };
  auto rsqrt_shape = ffi::Array<PrimExpr>();
  for (int i = 0, n = static_cast<int>(data_fp32->shape.size()); i < n; ++i) {
    if (std::find(real_axis.begin(), real_axis.end(), i) == real_axis.end()) {
      rsqrt_shape.push_back(data_fp32->shape[i]);
    }
  }
  auto rsqrt = tvm::te::compute(rsqrt_shape, rsqrt_func, "rsqrt", tag);
 
  auto rms_norm_func = [&](const ffi::Array<PrimVar>& indices) {
    ffi::Array<PrimVar> reduce_indices, non_reduce_indices;
    for (int i = 0, n = static_cast<int>(indices.size()); i < n; ++i) {
      if (std::find(real_axis.begin(), real_axis.end(), i) != real_axis.end()) {
        reduce_indices.push_back(indices[i]);
      } else {
        non_reduce_indices.push_back(indices[i]);
      }
    }
    auto output = rsqrt(non_reduce_indices) * data_fp32(indices) * weight_fp32(reduce_indices);
    return output;
  };
  auto rms_norm = tvm::te::compute(data_fp32->shape, rms_norm_func, name, tag);
 
  return cast(rms_norm, data_type);
}
 
}  // namespace nn
}  // namespace topi
}  // namespace tvm
 
#endif  // TVM_TOPI_NN_RMS_NORM_H_