Move some dims utils to common (#2223)

mlx/backend/common/utils.cpp

@@ -1,9 +1,16 @@
 // Copyright © 2023-2024 Apple Inc.
 
 #include "mlx/backend/common/utils.h"
+#include "mlx/primitives.h"
 
 namespace mlx::core {
 
+std::string get_primitive_string(Primitive* primitive) {
+  std::ostringstream op_t;
+  primitive->print(op_t);
+  return op_t.str();
+}
+
 std::tuple<Shape, std::vector<Strides>> collapse_contiguous_dims(
     const Shape& shape,
     const std::vector<Strides>& strides,
@@ -101,4 +108,105 @@ std::pair<Shape, Strides> collapse_contiguous_dims(
   return collapse_contiguous_dims(a.shape(), a.strides(), size_cap);
 }
 
+Dims get_block_dims_common(int dim0, int dim1, int dim2, int pow2 /* = 10 */) {
+  int pows[3] = {0, 0, 0};
+  int sum = 0;
+  while (true) {
+    int presum = sum;
+    // Check all the pows
+    if (dim0 >= (1 << (pows[0] + 1))) {
+      pows[0]++;
+      sum++;
+    }
+    if (sum == 10) {
+      break;
+    }
+    if (dim1 >= (1 << (pows[1] + 1))) {
+      pows[1]++;
+      sum++;
+    }
+    if (sum == 10) {
+      break;
+    }
+    if (dim2 >= (1 << (pows[2] + 1))) {
+      pows[2]++;
+      sum++;
+    }
+    if (sum == presum || sum == pow2) {
+      break;
+    }
+  }
+  return std::make_tuple(1ul << pows[0], 1ul << pows[1], 1ul << pows[2]);
+}
+
+Dims get_2d_grid_dims_common(const Shape& shape, const Strides& strides) {
+  // Dims with strides of 0 are ignored as they
+  // correspond to broadcasted dimensions
+  size_t grid_x = 1;
+  size_t grid_y = 1;
+  for (int i = 0; i < shape.size(); ++i) {
+    if (strides[i] == 0) {
+      continue;
+    }
+    if (grid_x * shape[i] < UINT32_MAX) {
+      grid_x *= shape[i];
+    } else {
+      grid_y *= shape[i];
+    }
+  }
+  if (grid_y > UINT32_MAX || grid_x > UINT32_MAX) {
+    throw std::runtime_error("Unable to safely factor shape.");
+  }
+  if (grid_y > grid_x) {
+    std::swap(grid_x, grid_y);
+  }
+  return std::make_tuple(
+      static_cast<uint32_t>(grid_x), static_cast<uint32_t>(grid_y), 1);
+}
+
+Dims get_2d_grid_dims_common(
+    const Shape& shape,
+    const Strides& strides,
+    size_t divisor) {
+  // Compute the 2d grid dimensions such that the total size of the grid is
+  // divided by divisor.
+  size_t grid_x = 1;
+  size_t grid_y = 1;
+  for (int i = 0; i < shape.size(); ++i) {
+    if (strides[i] == 0) {
+      continue;
+    }
+
+    // No need to add this shape we can just remove it from the divisor.
+    if (divisor % shape[i] == 0) {
+      divisor /= shape[i];
+      continue;
+    }
+
+    if (grid_x * shape[i] < UINT32_MAX) {
+      grid_x *= shape[i];
+    } else {
+      grid_y *= shape[i];
+    }
+
+    if (divisor > 1) {
+      if (grid_x % divisor == 0) {
+        grid_x /= divisor;
+        divisor = 1;
+      } else if (grid_y % divisor == 0) {
+        grid_y /= divisor;
+        divisor = 1;
+      }
+    }
+  }
+  if (grid_y > UINT32_MAX || grid_x > UINT32_MAX || divisor > 1) {
+    throw std::runtime_error("Unable to safely factor shape.");
+  }
+  if (grid_y > grid_x) {
+    std::swap(grid_x, grid_y);
+  }
+  return std::make_tuple(
+      static_cast<uint32_t>(grid_x), static_cast<uint32_t>(grid_y), 1);
+}
+
 } // namespace mlx::core

mlx/backend/common/utils.h

@@ -2,12 +2,15 @@
 
 #pragma once
 
+#include <tuple>
 #include <vector>
 
 #include "mlx/array.h"
 
 namespace mlx::core {
 
+std::string get_primitive_string(Primitive* primitive);
+
 inline int64_t
 elem_to_loc(int elem, const Shape& shape, const Strides& strides) {
   int64_t loc = 0;
@@ -70,6 +73,28 @@ std::pair<Shape, Strides> collapse_contiguous_dims(
     const array& a,
     int64_t size_cap = std::numeric_limits<int32_t>::max());
 
+// Compute the thread block dimensions which fit the given
+// input dimensions.
+// - The thread block dimensions will be powers of two
+// - The thread block size will be less than 2^pow2
+using Dims = std::tuple<uint32_t, uint32_t, uint32_t>;
+Dims get_block_dims_common(int dim0, int dim1, int dim2, int pow2 = 10);
+
+// Computes a 2D grid where each element is < UINT_MAX
+// Assumes:
+// - overall size (product of non-broadcasted dimensions) is < UINT_MAX^2
+// - shape and strides correspond to a contiguous (no holes) but
+//   possibly broadcasted array
+Dims get_2d_grid_dims_common(const Shape& shape, const Strides& strides);
+
+// Same as above but we do an implicit division with divisor.
+// Basically, equivalent to factorizing
+//    Prod(s \forall s in shape if strides[s] > 0) / divisor.
+Dims get_2d_grid_dims_common(
+    const Shape& shape,
+    const Strides& strides,
+    size_t divisor);
+
 struct ContiguousIterator {
   inline void step() {
     int dims = shape_.size();

mlx/backend/cuda/CMakeLists.txt

@@ -11,6 +11,7 @@ target_sources(
           ${CMAKE_CURRENT_SOURCE_DIR}/eval.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/event.cu
           ${CMAKE_CURRENT_SOURCE_DIR}/fence.cu
+          ${CMAKE_CURRENT_SOURCE_DIR}/kernel_utils.cu
           ${CMAKE_CURRENT_SOURCE_DIR}/primitives.cu
           ${CMAKE_CURRENT_SOURCE_DIR}/slicing.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/utils.cpp

mlx/backend/cuda/kernel_utils.cu

@@ -0,0 +1,26 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/backend/common/utils.h"
+#include "mlx/backend/cuda/kernel_utils.cuh"
+
+namespace mlx::core {
+
+dim3 get_block_dims(int dim0, int dim1, int dim2, int pow2) {
+  Dims dims = get_block_dims_common(dim0, dim1, dim2, pow2);
+  return dim3(std::get<0>(dims), std::get<1>(dims), std::get<2>(dims));
+}
+
+dim3 get_2d_grid_dims(const Shape& shape, const Strides& strides) {
+  Dims dims = get_2d_grid_dims_common(shape, strides);
+  return dim3(std::get<0>(dims), std::get<1>(dims), std::get<2>(dims));
+}
+
+dim3 get_2d_grid_dims(
+    const Shape& shape,
+    const Strides& strides,
+    size_t divisor) {
+  Dims dims = get_2d_grid_dims_common(shape, strides, divisor);
+  return dim3(std::get<0>(dims), std::get<1>(dims), std::get<2>(dims));
+}
+
+} // namespace mlx::core

mlx/backend/cuda/kernel_utils.cuh

@@ -1,7 +1,13 @@
 // Copyright © 2025 Apple Inc.
 
+// This file includes host-only utilies for writing CUDA kernels, the difference
+// from backend/cuda/kernels/utils.cuh is that the latter file only include
+// device-only code.
+
 #pragma once
 
+#include "mlx/array.h"
+
 #include <cuComplex.h>
 #include <cuda_bf16.h>
 #include <cuda_fp16.h>
@@ -32,4 +38,12 @@ struct CTypeToCudaType<complex64_t> {
 template <typename T>
 using cuda_type_t = typename CTypeToCudaType<T>::type;
 
+// Compute the grid and block dimensions, check backend/common/utils.h for docs.
+dim3 get_block_dims(int dim0, int dim1, int dim2, int pow2 = 10);
+dim3 get_2d_grid_dims(const Shape& shape, const Strides& strides);
+dim3 get_2d_grid_dims(
+    const Shape& shape,
+    const Strides& strides,
+    size_t divisor);
+
 } // namespace mlx::core

mlx/backend/cuda/primitives.cu

@@ -1,7 +1,7 @@
 // Copyright © 2025 Apple Inc.
 
 #include "mlx/backend/cuda/device.h"
-#include "mlx/backend/cuda/dtype_utils.cuh"
+#include "mlx/backend/cuda/kernel_utils.cuh"
 #include "mlx/backend/cuda/kernels/arange.cuh"
 #include "mlx/backend/cuda/kernels/fp16_math.cuh"
 #include "mlx/distributed/primitives.h"

mlx/backend/cuda/utils.h

@@ -1,5 +1,7 @@
 // Copyright © 2025 Apple Inc.
 
+// This file include utilies that are used by C++ code (i.e. .cpp files).
+
 #pragma once
 
 #include <cuda_runtime.h>

mlx/backend/metal/utils.cpp

@@ -1,8 +1,7 @@
 // Copyright © 2023-2024 Apple Inc.
 
 #include "mlx/backend/metal/utils.h"
-
-using namespace mlx;
+#include "mlx/backend/common/utils.h"
 
 namespace mlx::core {
 
@@ -59,109 +58,20 @@ std::string type_to_name(const array& a) {
   return type_to_name(a.dtype());
 }
 
-MTL::Size get_block_dims(int dim0, int dim1, int dim2, int pow2 /* = 10 */) {
-  int pows[3] = {0, 0, 0};
-  int sum = 0;
-  while (true) {
-    int presum = sum;
-    // Check all the pows
-    if (dim0 >= (1 << (pows[0] + 1))) {
-      pows[0]++;
-      sum++;
-    }
-    if (sum == 10) {
-      break;
-    }
-    if (dim1 >= (1 << (pows[1] + 1))) {
-      pows[1]++;
-      sum++;
-    }
-    if (sum == 10) {
-      break;
-    }
-    if (dim2 >= (1 << (pows[2] + 1))) {
-      pows[2]++;
-      sum++;
-    }
-    if (sum == presum || sum == pow2) {
-      break;
-    }
-  }
-  return MTL::Size{1ul << pows[0], 1ul << pows[1], 1ul << pows[2]};
+MTL::Size get_block_dims(int dim0, int dim1, int dim2, int pow2) {
+  Dims dims = get_block_dims_common(dim0, dim1, dim2, pow2);
+  return MTL::Size(std::get<0>(dims), std::get<1>(dims), std::get<2>(dims));
 }
 
 MTL::Size get_2d_grid_dims(const Shape& shape, const Strides& strides) {
-  // Dims with strides of 0 are ignored as they
-  // correspond to broadcasted dimensions
-  size_t grid_x = 1;
-  size_t grid_y = 1;
-  for (int i = 0; i < shape.size(); ++i) {
-    if (strides[i] == 0) {
-      continue;
-    }
-    if (grid_x * shape[i] < UINT32_MAX) {
-      grid_x *= shape[i];
-    } else {
-      grid_y *= shape[i];
-    }
-  }
-  if (grid_y > UINT32_MAX || grid_x > UINT32_MAX) {
-    throw std::runtime_error("Unable to safely factor shape.");
-  }
-  if (grid_y > grid_x) {
-    std::swap(grid_x, grid_y);
-  }
-  return MTL::Size(
-      static_cast<uint32_t>(grid_x), static_cast<uint32_t>(grid_y), 1);
+  Dims dims = get_2d_grid_dims_common(shape, strides);
+  return MTL::Size(std::get<0>(dims), std::get<1>(dims), std::get<2>(dims));
 }
 
 MTL::Size
 get_2d_grid_dims(const Shape& shape, const Strides& strides, size_t divisor) {
-  // Compute the 2d grid dimensions such that the total size of the grid is
-  // divided by divisor.
-  size_t grid_x = 1;
-  size_t grid_y = 1;
-  for (int i = 0; i < shape.size(); ++i) {
-    if (strides[i] == 0) {
-      continue;
-    }
-
-    // No need to add this shape we can just remove it from the divisor.
-    if (divisor % shape[i] == 0) {
-      divisor /= shape[i];
-      continue;
-    }
-
-    if (grid_x * shape[i] < UINT32_MAX) {
-      grid_x *= shape[i];
-    } else {
-      grid_y *= shape[i];
-    }
-
-    if (divisor > 1) {
-      if (grid_x % divisor == 0) {
-        grid_x /= divisor;
-        divisor = 1;
-      } else if (grid_y % divisor == 0) {
-        grid_y /= divisor;
-        divisor = 1;
-      }
-    }
-  }
-  if (grid_y > UINT32_MAX || grid_x > UINT32_MAX || divisor > 1) {
-    throw std::runtime_error("Unable to safely factor shape.");
-  }
-  if (grid_y > grid_x) {
-    std::swap(grid_x, grid_y);
-  }
-  return MTL::Size(
-      static_cast<uint32_t>(grid_x), static_cast<uint32_t>(grid_y), 1);
-}
-
-std::string get_primitive_string(Primitive* primitive) {
-  std::ostringstream op_t;
-  primitive->print(op_t);
-  return op_t.str();
+  Dims dims = get_2d_grid_dims_common(shape, strides, divisor);
+  return MTL::Size(std::get<0>(dims), std::get<1>(dims), std::get<2>(dims));
 }
 
 } // namespace mlx::core

mlx/backend/metal/utils.h

@@ -13,22 +13,9 @@ namespace mlx::core {
 std::string type_to_name(const Dtype& t);
 std::string type_to_name(const array& a);
 
-// Compute the thread block dimensions which fit the given
-// input dimensions.
-// - The thread block dimensions will be powers of two
-// - The thread block size will be less than 2^pow2
+// Compute the grid and block dimensions, check backend/common/utils.h for docs.
 MTL::Size get_block_dims(int dim0, int dim1, int dim2, int pow2 = 10);
-
-// Computes a 2D grid where each element is < UINT_MAX
-// Assumes:
-// - overall size (product of non-broadcasted dimensions) is < UINT_MAX^2
-// - shape and strides correspond to a contiguous (no holes) but
-//   possibly broadcasted array
 MTL::Size get_2d_grid_dims(const Shape& shape, const Strides& strides);
-
-// Same as above but we do an implicit division with divisor.
-// Basically, equivalent to factorizing
-//    Prod(s \forall s in shape if strides[s] > 0) / divisor.
 MTL::Size
 get_2d_grid_dims(const Shape& shape, const Strides& strides, size_t divisor);
 
@@ -58,8 +45,6 @@ inline void debug_set_primitive_buffer_label(
 #endif
 }
 
-std::string get_primitive_string(Primitive* primitive);
-
 template <typename T>
 constexpr bool is_numeric_except_char = std::is_arithmetic_v<T> &&
     !std::is_same_v<T, char> && !std::is_same_v<T, signed char> &&