CUDA backend: matmul (#2241)

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Cheng 2025-06-07 04:24:04 +09:00 committed by GitHub
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7 changed files with 584 additions and 67 deletions

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@ -0,0 +1,78 @@
// Copyright © 2025 Apple Inc.
#pragma once
#include "mlx/backend/common/utils.h"
#include "mlx/utils.h"
#include <sstream>
namespace mlx::core {
inline std::tuple<Shape, Strides, Strides> collapse_batches(
const array& a,
const array& b) {
// Get and check the shape for the batched dims
Shape A_bshape{a.shape().begin(), a.shape().end() - 2};
Shape B_bshape{b.shape().begin(), b.shape().end() - 2};
if (A_bshape != B_bshape) {
std::ostringstream msg;
msg << "[matmul] Got matrices with incorrectly broadcasted shapes: " << "A "
<< a.shape() << ", B " << b.shape() << ".";
throw std::runtime_error(msg.str());
}
Strides A_bstride{a.strides().begin(), a.strides().end() - 2};
Strides B_bstride{b.strides().begin(), b.strides().end() - 2};
auto [batch_shape, batch_strides] =
collapse_contiguous_dims(A_bshape, std::vector{A_bstride, B_bstride});
auto a_batch_strides = batch_strides[0];
auto b_batch_strides = batch_strides[1];
if (batch_shape.empty()) {
batch_shape.push_back(1);
a_batch_strides.push_back(0);
b_batch_strides.push_back(0);
}
return std::make_tuple(batch_shape, a_batch_strides, b_batch_strides);
}
inline std::tuple<Shape, Strides, Strides, Strides>
collapse_batches(const array& a, const array& b, const array& c) {
// Get and check the shape for the batched dims
Shape A_bshape{a.shape().begin(), a.shape().end() - 2};
Shape B_bshape{b.shape().begin(), b.shape().end() - 2};
Shape C_bshape{c.shape().begin(), c.shape().end() - 2};
if (A_bshape != B_bshape || A_bshape != C_bshape) {
std::ostringstream msg;
msg << "[addmm] Got matrices with incorrectly broadcasted shapes: " << "A "
<< a.shape() << ", B " << b.shape() << ", B " << c.shape() << ".";
throw std::runtime_error(msg.str());
}
Strides A_bstride{a.strides().begin(), a.strides().end() - 2};
Strides B_bstride{b.strides().begin(), b.strides().end() - 2};
Strides C_bstride{c.strides().begin(), c.strides().end() - 2};
auto [batch_shape, batch_strides] = collapse_contiguous_dims(
A_bshape, std::vector{A_bstride, B_bstride, C_bstride});
auto A_batch_stride = batch_strides[0];
auto B_batch_stride = batch_strides[1];
auto C_batch_stride = batch_strides[2];
if (batch_shape.empty()) {
batch_shape.push_back(1);
A_batch_stride.push_back(0);
B_batch_stride.push_back(0);
C_batch_stride.push_back(0);
}
return std::make_tuple(
batch_shape, A_batch_stride, B_batch_stride, C_batch_stride);
}
} // namespace mlx::core

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@ -12,6 +12,7 @@ target_sources(
${CMAKE_CURRENT_SOURCE_DIR}/event.cu
${CMAKE_CURRENT_SOURCE_DIR}/fence.cpp
${CMAKE_CURRENT_SOURCE_DIR}/kernel_utils.cu
${CMAKE_CURRENT_SOURCE_DIR}/matmul.cpp
${CMAKE_CURRENT_SOURCE_DIR}/primitives.cu
${CMAKE_CURRENT_SOURCE_DIR}/slicing.cpp
${CMAKE_CURRENT_SOURCE_DIR}/utils.cpp
@ -53,6 +54,9 @@ target_link_libraries(mlx PUBLIC $<BUILD_INTERFACE:nvtx3-cpp>)
find_package(CUDAToolkit REQUIRED)
target_include_directories(mlx PRIVATE ${CUDAToolkit_INCLUDE_DIRS})
# Use cublasLt.
target_link_libraries(mlx PRIVATE CUDA::cublasLt)
# Suppress nvcc warnings on MLX headers.
target_compile_options(mlx PRIVATE $<$<COMPILE_LANGUAGE:CUDA>:-Xcudafe
--diag_suppress=997>)

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@ -34,14 +34,26 @@ CommandEncoder& DeviceStream::get_encoder() {
}
Device::Device(int device) : device_(device) {
CHECK_CUDA_ERROR(cudaDeviceGetAttribute(
&compute_capability_major_, cudaDevAttrComputeCapabilityMajor, device_));
CHECK_CUDA_ERROR(cudaDeviceGetAttribute(
&compute_capability_minor_, cudaDevAttrComputeCapabilityMinor, device_));
// Validate the requirements of device.
int attr = 0;
cudaDeviceGetAttribute(&attr, cudaDevAttrConcurrentManagedAccess, device_);
CHECK_CUDA_ERROR(cudaDeviceGetAttribute(
&attr, cudaDevAttrConcurrentManagedAccess, device_));
if (attr != 1) {
throw std::runtime_error(fmt::format(
"Device {} does not support synchronization in managed memory.",
device_));
}
// The cublasLt handle is used by matmul.
make_current();
cublasLtCreate(&lt_);
}
Device::~Device() {
cublasLtDestroy(lt_);
}
void Device::make_current() {

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@ -6,6 +6,7 @@
#include "mlx/backend/cuda/worker.h"
#include "mlx/stream.h"
#include <cublasLt.h>
#include <thrust/execution_policy.h>
#include <unordered_map>
@ -46,6 +47,7 @@ class DeviceStream {
class Device {
public:
explicit Device(int device);
~Device();
Device(const Device&) = delete;
Device& operator=(const Device&) = delete;
@ -58,9 +60,21 @@ class Device {
int cuda_device() const {
return device_;
}
int compute_capability_major() const {
return compute_capability_major_;
}
int compute_capability_minor() const {
return compute_capability_minor_;
}
cublasLtHandle_t lt_handle() const {
return lt_;
}
private:
int device_;
int compute_capability_major_;
int compute_capability_minor_;
cublasLtHandle_t lt_;
std::unordered_map<int, DeviceStream> streams_;
};

474
mlx/backend/cuda/matmul.cpp Normal file
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@ -0,0 +1,474 @@
// Copyright © 2025 Apple Inc.
#include "mlx/backend/common/matmul.h"
#include "mlx/backend/cuda/device.h"
#include "mlx/backend/gpu/copy.h"
#include "mlx/dtype_utils.h"
#include "mlx/primitives.h"
#include <cublasLt.h>
#include <fmt/format.h>
#include <nvtx3/nvtx3.hpp>
#include <numeric>
namespace mlx::core {
namespace cu {
#define CHECK_CUBLAS_ERROR(cmd) check_cublas_error(#cmd, (cmd))
void check_cublas_error(const char* name, cublasStatus_t err) {
if (err != CUBLAS_STATUS_SUCCESS) {
// TODO: Use cublasGetStatusString when it is widely available.
throw std::runtime_error(
fmt::format("{} failed with code: {}.", name, static_cast<int>(err)));
}
}
class MatMul {
public:
MatMul(
Device& device,
Dtype dtype,
bool a_transposed,
uint64_t a_rows,
uint64_t a_cols,
int64_t lda,
bool b_transposed,
uint64_t b_rows,
uint64_t b_cols,
int64_t ldb,
int32_t batch_count,
int64_t a_batch_stride,
int64_t b_batch_stride) {
heuristic_.state = CUBLAS_STATUS_NOT_INITIALIZED;
auto type = dtype_to_cuda_type(dtype);
CHECK_CUBLAS_ERROR(cublasLtMatmulDescCreate(
&matmul_desc_, dtype_to_compute_type(dtype), type));
int32_t pointer_mode = CUBLASLT_POINTER_MODE_HOST;
CHECK_CUBLAS_ERROR(cublasLtMatmulDescSetAttribute(
matmul_desc_,
CUBLASLT_MATMUL_DESC_POINTER_MODE,
&pointer_mode,
sizeof(int32_t)));
cublasOperation_t op = CUBLAS_OP_N;
CHECK_CUBLAS_ERROR(cublasLtMatmulDescSetAttribute(
matmul_desc_,
CUBLASLT_MATMUL_DESC_TRANSA,
&op,
sizeof(cublasOperation_t)));
CHECK_CUBLAS_ERROR(cublasLtMatmulDescSetAttribute(
matmul_desc_,
CUBLASLT_MATMUL_DESC_TRANSB,
&op,
sizeof(cublasOperation_t)));
a_desc_ = create_matrix_layout(
type, a_rows, a_cols, a_transposed, lda, batch_count, a_batch_stride);
b_desc_ = create_matrix_layout(
type, b_rows, b_cols, b_transposed, ldb, batch_count, b_batch_stride);
out_desc_ = create_matrix_layout(
type, a_rows, b_cols, false, b_cols, batch_count, a_rows * b_cols);
// The recommended cublas workspace size is 4 MiB for pre-Hopper and 32 MiB
// for Hopper+:
// https://docs.nvidia.com/cuda/cublas/#cublassetworkspace
uint64_t MiB = 1024 * 1024;
uint64_t workspace_size =
device.compute_capability_major() >= 9 ? 32 * MiB : 4 * MiB;
CHECK_CUBLAS_ERROR(cublasLtMatmulPreferenceCreate(&pref_));
CHECK_CUBLAS_ERROR(cublasLtMatmulPreferenceSetAttribute(
pref_,
CUBLASLT_MATMUL_PREF_MAX_WORKSPACE_BYTES,
&workspace_size,
sizeof(uint64_t)));
}
MatMul(
Device& device,
Dtype dtype,
bool a_transposed,
uint64_t a_rows,
uint64_t a_cols,
int64_t lda,
bool b_transposed,
uint64_t b_rows,
uint64_t b_cols,
int64_t ldb,
bool c_transposed,
int64_t ldc,
int32_t batch_count,
int64_t a_batch_stride,
int64_t b_batch_stride,
int64_t c_batch_stride)
: MatMul(
device,
dtype,
a_transposed,
a_rows,
a_cols,
lda,
b_transposed,
b_rows,
b_cols,
ldb,
batch_count,
a_batch_stride,
b_batch_stride) {
auto type = dtype_to_cuda_type(dtype);
c_desc_ = create_matrix_layout(
type, a_rows, b_cols, c_transposed, ldc, batch_count, c_batch_stride);
}
~MatMul() {
cublasLtMatrixLayoutDestroy(a_desc_);
cublasLtMatrixLayoutDestroy(b_desc_);
cublasLtMatrixLayoutDestroy(c_desc_);
cublasLtMatrixLayoutDestroy(out_desc_);
cublasLtMatmulDescDestroy(matmul_desc_);
}
void run(
cu::CommandEncoder& encoder,
void* out,
void* a,
void* b,
void* c = nullptr,
float alpha = 1,
float beta = 0) {
if (heuristic_.state != CUBLAS_STATUS_SUCCESS) {
int ret = 0;
CHECK_CUBLAS_ERROR(cublasLtMatmulAlgoGetHeuristic(
encoder.device().lt_handle(),
matmul_desc_,
a_desc_,
b_desc_,
out_desc_,
out_desc_,
pref_,
1,
&heuristic_,
&ret));
if (ret == 0) {
throw std::runtime_error("Can not find algorithm for matmul.");
}
}
array workspace(
allocator::malloc(heuristic_.workspaceSize),
{static_cast<int>(heuristic_.workspaceSize)},
int8);
encoder.add_temporary(workspace);
encoder.launch_kernel([&](cudaStream_t stream) {
CHECK_CUBLAS_ERROR(cublasLtMatmul(
encoder.device().lt_handle(),
matmul_desc_,
&alpha,
a,
a_desc_,
b,
b_desc_,
&beta,
c ? c : out,
c ? c_desc_ : out_desc_,
out,
out_desc_,
&heuristic_.algo,
workspace.data<void>(),
workspace.nbytes(),
stream));
});
}
private:
cublasComputeType_t dtype_to_compute_type(Dtype dtype) {
switch (dtype) {
case uint8:
case uint16:
case int8:
case int16:
case int32:
return CUBLAS_COMPUTE_32I;
case float16:
case bfloat16:
return CUBLAS_COMPUTE_16F;
case float32:
return CUBLAS_COMPUTE_32F;
case float64:
case complex64:
return CUBLAS_COMPUTE_64F;
default:
throw std::runtime_error(fmt::format(
"Unsupported dtype in MatMul: {}.", dtype_to_string(dtype)));
}
}
cudaDataType_t dtype_to_cuda_type(Dtype dtype) {
switch (dtype) {
case uint8:
return CUDA_R_8U;
case uint16:
return CUDA_R_16U;
case int8:
return CUDA_R_8I;
case int16:
return CUDA_R_16I;
case int32:
return CUDA_R_32I;
case float16:
return CUDA_R_16F;
case bfloat16:
return CUDA_R_16BF;
case float32:
return CUDA_R_32F;
case float64:
return CUDA_R_64F;
case complex64:
return CUDA_C_32F;
default:
throw std::runtime_error(fmt::format(
"Unsupported dtype in MatMul: {}.", dtype_to_string(dtype)));
}
}
cublasLtMatrixLayout_t create_matrix_layout(
cudaDataType_t type,
uint64_t rows,
uint64_t cols,
bool transposed,
int64_t ld,
int32_t batch_count,
int64_t batch_stride) {
cublasLtMatrixLayout_t desc;
CHECK_CUBLAS_ERROR(cublasLtMatrixLayoutCreate(&desc, type, rows, cols, ld));
cublasLtOrder_t order =
transposed ? CUBLASLT_ORDER_COL : CUBLASLT_ORDER_ROW;
CHECK_CUBLAS_ERROR(cublasLtMatrixLayoutSetAttribute(
desc, CUBLASLT_MATRIX_LAYOUT_ORDER, &order, sizeof(cublasLtOrder_t)));
if (batch_count > 1) {
CHECK_CUBLAS_ERROR(cublasLtMatrixLayoutSetAttribute(
desc,
CUBLASLT_MATRIX_LAYOUT_BATCH_COUNT,
&batch_count,
sizeof(int32_t)));
CHECK_CUBLAS_ERROR(cublasLtMatrixLayoutSetAttribute(
desc,
CUBLASLT_MATRIX_LAYOUT_STRIDED_BATCH_OFFSET,
&batch_stride,
sizeof(int64_t)));
}
return desc;
}
cublasLtMatmulDesc_t matmul_desc_{nullptr};
cublasLtMatmulPreference_t pref_{nullptr};
cublasLtMatrixLayout_t a_desc_{nullptr};
cublasLtMatrixLayout_t b_desc_{nullptr};
cublasLtMatrixLayout_t c_desc_{nullptr};
cublasLtMatrixLayout_t out_desc_{nullptr};
cublasLtMatmulHeuristicResult_t heuristic_;
};
} // namespace cu
namespace {
std::tuple<bool, int64_t, array>
check_transpose(std::vector<array>& copies, const Stream& s, const array& arr) {
auto stx = arr.strides()[arr.ndim() - 2];
auto sty = arr.strides()[arr.ndim() - 1];
if (sty == 1 && stx == arr.shape(-1)) {
return std::make_tuple(false, stx, arr);
} else if (stx == 1 && sty == arr.shape(-2)) {
return std::make_tuple(true, sty, arr);
} else {
array arr_copy(arr.shape(), arr.dtype(), nullptr, {});
copy_gpu(arr, arr_copy, CopyType::General, s);
copies.push_back(arr_copy);
return std::make_tuple(false, arr.shape(-1), arr_copy);
}
}
} // namespace
void Matmul::eval_gpu(const std::vector<array>& inputs, array& out) {
nvtx3::scoped_range r("Matmul::eval_gpu");
auto& s = stream();
auto& encoder = cu::get_command_encoder(s);
assert(inputs.size() == 2);
auto& a_pre = inputs[0];
auto& b_pre = inputs[1];
// Return 0s if either input is empty.
if (a_pre.size() == 0 || b_pre.size() == 0) {
array zero(0, a_pre.dtype());
encoder.add_temporary(zero);
fill_gpu(zero, out, s);
return;
}
out.set_data(allocator::malloc(out.nbytes()));
/////////////////////////////////////////////////////////////////////////////
// Init checks and prep
int M = a_pre.shape(-2);
int N = b_pre.shape(-1);
int K = a_pre.shape(-1);
// Keep a vector with copies to be cleared in the completed buffer to release
// the arrays
std::vector<array> copies;
auto [a_transposed, lda, a] = check_transpose(copies, s, a_pre);
auto [b_transposed, ldb, b] = check_transpose(copies, s, b_pre);
for (auto& temp : copies) {
encoder.add_temporary(temp);
}
/////////////////////////////////////////////////////////////////////////////
// Check and collapse batch dimensions
auto [batch_shape, a_batch_strides, b_batch_strides] = collapse_batches(a, b);
auto batch_count = out.size() / (M * N);
// Collapse batches into M if needed
if (batch_count > 1 && !a_transposed && batch_shape.size() == 1 &&
a.strides()[a.ndim() - 2] == K && a_batch_strides.back() == M * K &&
b_batch_strides.back() == 0) {
M *= batch_shape.back();
batch_count = 1;
a_batch_strides = {0};
b_batch_strides = {0};
batch_shape = {1};
}
/////////////////////////////////////////////////////////////////////////////
// Invoke cublasLt
cu::MatMul matmul(
encoder.device(),
a.dtype(),
a_transposed,
M,
K,
lda,
b_transposed,
K,
N,
ldb,
batch_shape.back(),
a_batch_strides.back(),
b_batch_strides.back());
ContiguousIterator a_it(batch_shape, a_batch_strides, batch_shape.size() - 1);
ContiguousIterator b_it(batch_shape, b_batch_strides, batch_shape.size() - 1);
for (size_t i = 0; i < batch_count / batch_shape.back(); ++i) {
matmul.run(
encoder,
out.data<int8_t>() + out.itemsize() * i * batch_shape.back() * M * N,
a.data<int8_t>() + a.itemsize() * a_it.loc,
b.data<int8_t>() + b.itemsize() * b_it.loc);
a_it.step();
b_it.step();
}
}
void AddMM::eval_gpu(const std::vector<array>& inputs, array& out) {
nvtx3::scoped_range r("AddMM::eval_gpu");
auto& s = stream();
auto& encoder = cu::get_command_encoder(s);
assert(inputs.size() == 3);
auto& a_pre = inputs[0];
auto& b_pre = inputs[1];
auto& c_pre = inputs[2];
out.set_data(allocator::malloc(out.nbytes()));
/////////////////////////////////////////////////////////////////////////////
// Init checks and prep
int M = a_pre.shape(-2);
int N = b_pre.shape(-1);
int K = a_pre.shape(-1);
// Keep a vector with copies to be cleared in the completed buffer to release
// the arrays
std::vector<array> copies;
auto [a_transposed, lda, a] = check_transpose(copies, s, a_pre);
auto [b_transposed, ldb, b] = check_transpose(copies, s, b_pre);
auto [c_transposed, ldc, c] = check_transpose(copies, s, c_pre);
for (auto& temp : copies) {
encoder.add_temporary(temp);
}
/////////////////////////////////////////////////////////////////////////////
// Check and collapse batch dimensions
auto [batch_shape, a_batch_strides, b_batch_strides, c_batch_strides] =
collapse_batches(a, b, c);
auto batch_count = out.size() / (M * N);
// Collapse batches into M if needed
if (batch_count > 1 && !a_transposed && batch_shape.size() == 1 &&
a.strides()[a.ndim() - 2] == K && a_batch_strides.back() == M * K &&
c_batch_strides.back() == M * c.strides()[c.ndim() - 2] &&
b_batch_strides.back() == 0) {
M *= batch_shape.back();
batch_count = 1;
a_batch_strides = {0};
b_batch_strides = {0};
c_batch_strides = {0};
batch_shape = {1};
}
/////////////////////////////////////////////////////////////////////////////
// Invoke cublasLt
cu::MatMul matmul(
encoder.device(),
a.dtype(),
a_transposed,
M,
K,
lda,
b_transposed,
K,
N,
ldb,
c_transposed,
ldc,
batch_shape.back(),
a_batch_strides.back(),
b_batch_strides.back(),
c_batch_strides.back());
ContiguousIterator a_it(batch_shape, a_batch_strides, batch_shape.size() - 1);
ContiguousIterator b_it(batch_shape, b_batch_strides, batch_shape.size() - 1);
ContiguousIterator c_it(batch_shape, c_batch_strides, batch_shape.size() - 1);
for (size_t i = 0; i < batch_count / batch_shape.back(); ++i) {
matmul.run(
encoder,
out.data<int8_t>() + out.itemsize() * i * batch_shape.back() * M * N,
a.data<int8_t>() + a.itemsize() * a_it.loc,
b.data<int8_t>() + b.itemsize() * b_it.loc,
c.data<int8_t>() + c.itemsize() * c_it.loc,
alpha_,
beta_);
a_it.step();
b_it.step();
c_it.step();
}
}
} // namespace mlx::core

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@ -73,7 +73,6 @@ bool fast::ScaledDotProductAttention::use_fallback(
NO_GPU(Abs)
NO_GPU(Add)
NO_GPU(AddMM)
NO_GPU(ArcCos)
NO_GPU(ArcCosh)
NO_GPU(ArcSin)
@ -124,7 +123,6 @@ NO_GPU(LogicalOr)
NO_GPU(LogAddExp)
NO_GPU(LogSumExp)
NO_GPU_MULTI(LUF)
NO_GPU(Matmul)
NO_GPU(Maximum)
NO_GPU(Minimum)
NO_GPU(Multiply)

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@ -6,7 +6,7 @@
#include <sstream>
#include "mlx/backend/common/broadcasting.h"
#include "mlx/backend/common/utils.h"
#include "mlx/backend/common/matmul.h"
#include "mlx/backend/gpu/copy.h"
#include "mlx/backend/metal/device.h"
#include "mlx/backend/metal/kernels.h"
@ -21,69 +21,6 @@ namespace mlx::core {
namespace {
inline auto collapse_batches(const array& a, const array& b) {
// Get and check the shape for the batched dims
Shape A_bshape{a.shape().begin(), a.shape().end() - 2};
Shape B_bshape{b.shape().begin(), b.shape().end() - 2};
if (A_bshape != B_bshape) {
std::ostringstream msg;
msg << "[matmul] Got matrices with incorrectly broadcasted shapes: " << "A "
<< a.shape() << ", B " << b.shape() << ".";
throw std::runtime_error(msg.str());
}
Strides A_bstride{a.strides().begin(), a.strides().end() - 2};
Strides B_bstride{b.strides().begin(), b.strides().end() - 2};
auto [batch_shape, batch_strides] =
collapse_contiguous_dims(A_bshape, std::vector{A_bstride, B_bstride});
auto A_batch_stride = batch_strides[0];
auto B_batch_stride = batch_strides[1];
if (batch_shape.empty()) {
batch_shape.push_back(1);
A_batch_stride.push_back(0);
B_batch_stride.push_back(0);
}
return std::make_tuple(batch_shape, A_batch_stride, B_batch_stride);
}
inline auto collapse_batches(const array& a, const array& b, const array& c) {
// Get and check the shape for the batched dims
Shape A_bshape{a.shape().begin(), a.shape().end() - 2};
Shape B_bshape{b.shape().begin(), b.shape().end() - 2};
Shape C_bshape{c.shape().begin(), c.shape().end() - 2};
if (A_bshape != B_bshape || A_bshape != C_bshape) {
std::ostringstream msg;
msg << "[addmm] Got matrices with incorrectly broadcasted shapes: " << "A "
<< a.shape() << ", B " << b.shape() << ", B " << c.shape() << ".";
throw std::runtime_error(msg.str());
}
Strides A_bstride{a.strides().begin(), a.strides().end() - 2};
Strides B_bstride{b.strides().begin(), b.strides().end() - 2};
Strides C_bstride{c.strides().begin(), c.strides().end() - 2};
auto [batch_shape, batch_strides] = collapse_contiguous_dims(
A_bshape, std::vector{A_bstride, B_bstride, C_bstride});
auto A_batch_stride = batch_strides[0];
auto B_batch_stride = batch_strides[1];
auto C_batch_stride = batch_strides[2];
if (batch_shape.empty()) {
batch_shape.push_back(1);
A_batch_stride.push_back(0);
B_batch_stride.push_back(0);
C_batch_stride.push_back(0);
}
return std::make_tuple(
batch_shape, A_batch_stride, B_batch_stride, C_batch_stride);
}
std::tuple<bool, int64_t, array> check_transpose(
std::vector<array>& copies,
const Stream& s,