im2col based conv2d (#802)

* im2col implementation for conv2d.

* Fix for the im2col implementation to match the current conv2d.

* Small optimization.

* Add a cuda kernel.

* Handle arbitrary layouts.

* Im2Col cuda code.

candle-kernels/src/conv.cu

@@ -51,6 +51,71 @@ __device__ void conv1d(
   dst[dst_i] = static_cast<T>(d);
 }
 
+template <typename T>
+__device__ void im2col(
+    const size_t dst_numel,
+    const size_t h_out,
+    const size_t w_out,
+    const size_t h_k,
+    const size_t w_k,
+    const size_t stride,
+    const size_t padding,
+    const size_t dilation,
+    const size_t *info,
+    const T *src,
+    T *dst
+) {
+  const size_t dst_i = blockIdx.x * blockDim.x + threadIdx.x;
+  // dst: (b_size, h_out, w_out, c_in, h_k, w_k)
+  // src: (b_size, c_in, h_in, w_in)
+  if (dst_i >= dst_numel) {
+    return;
+  }
+  const size_t *src_dims = info;
+  const size_t *src_s = info + 4;
+  const size_t b_in = src_dims[0];
+  const size_t c_in = src_dims[1];
+  const size_t h_in = src_dims[2];
+  const size_t w_in = src_dims[3];
+
+  const size_t dst_s4 = w_k; 
+  const size_t dst_s3 = h_k * dst_s4;
+  const size_t dst_s2 = c_in * dst_s3;
+  const size_t dst_s1 = w_out * dst_s2;
+  const size_t dst_s0 = h_out * dst_s1;
+
+  size_t tmp_dst_i = dst_i;
+  const size_t b_idx = tmp_dst_i / dst_s0;
+  tmp_dst_i -= b_idx * dst_s0;
+  const size_t h_idx = tmp_dst_i / dst_s1;
+  tmp_dst_i -= h_idx * dst_s1;
+  const size_t w_idx = tmp_dst_i / dst_s2;
+  tmp_dst_i -= w_idx * dst_s2;
+  const size_t c_idx = tmp_dst_i / dst_s3;
+  tmp_dst_i -= c_idx * dst_s3;
+  const size_t h_k_idx = tmp_dst_i / dst_s4;
+  tmp_dst_i -= h_k_idx * dst_s4;
+  const size_t w_k_idx = tmp_dst_i;
+  size_t src_h_idx = h_idx * stride + h_k_idx * dilation;
+  size_t src_w_idx = w_idx * stride + w_k_idx * dilation;
+  if (src_h_idx < padding || src_h_idx >= h_in + padding) {
+    dst[dst_i] = static_cast<T>(0);
+  }
+  else if (src_w_idx < padding || src_w_idx >= w_in + padding) {
+    dst[dst_i] = static_cast<T>(0);
+  }
+  else {
+    src_h_idx -= padding;
+    src_w_idx -= padding;
+    const size_t src_i =
+      b_idx * src_s[0]
+      + c_idx * src_s[1]
+      + src_h_idx * src_s[2]
+      + src_w_idx * src_s[3];
+    dst[dst_i] = src[src_i];
+  }
+}
+
 // Naive implementation of conv2d.
 template <typename T, typename A>
 __device__ void conv2d(
@@ -363,6 +428,23 @@ extern "C" __global__ void FN_NAME(  \
   conv2d<TYPENAME, TYPEACC>(src_numel, w_out, h_out, stride, padding, dilation, info, src, kernel, dst); \
 } \
 
+#define IM2COL_OP(TYPENAME, FN_NAME) \
+extern "C" __global__ void FN_NAME(  \
+    const size_t dst_numel, \
+    const size_t h_out, \
+    const size_t w_out, \
+    const size_t h_k, \
+    const size_t w_k, \
+    const size_t stride, \
+    const size_t padding, \
+    const size_t dilation, \
+    const size_t *info, \
+    const TYPENAME *src, \
+    TYPENAME *dst \
+) {  \
+  im2col<TYPENAME>(dst_numel, h_out, w_out, h_k, w_k, stride, padding, dilation, info, src, dst); \
+} \
+
 #define CONVT2D_OP(TYPENAME, TYPEACC, FN_NAME) \
 extern "C" __global__ void FN_NAME(  \
     const size_t src_numel, \
@@ -428,6 +510,7 @@ CONVT2D_OP(__nv_bfloat16, float, conv_transpose2d_bf16)
 AVG_POOL2D_OP(__nv_bfloat16, float, avg_pool2d_bf16)
 MAX_POOL2D_OP(__nv_bfloat16, max_pool2d_bf16)
 UPSAMPLE_NEAREST2D_OP(__nv_bfloat16, upsample_nearest2d_bf16)
+IM2COL_OP(__nv_bfloat16, im2col_bf16)
 #endif
 
 #if __CUDA_ARCH__ >= 530
@@ -437,6 +520,7 @@ CONVT2D_OP(__half, float, conv_transpose2d_f16)
 AVG_POOL2D_OP(__half, float, avg_pool2d_f16)
 MAX_POOL2D_OP(__half, max_pool2d_f16)
 UPSAMPLE_NEAREST2D_OP(__half, upsample_nearest2d_f16)
+IM2COL_OP(__half, im2col_f16)
 #endif
 
 CONV1D_OP(float, float, conv1d_f32)
@@ -468,3 +552,8 @@ UPSAMPLE_NEAREST2D_OP(float, upsample_nearest2d_f32)
 UPSAMPLE_NEAREST2D_OP(double, upsample_nearest2d_f64)
 UPSAMPLE_NEAREST2D_OP(uint8_t, upsample_nearest2d_u8)
 UPSAMPLE_NEAREST2D_OP(uint32_t, upsample_nearest2d_u32)
+
+IM2COL_OP(float, im2col_f32)
+IM2COL_OP(double, im2col_f64)
+IM2COL_OP(uint8_t, im2col_u8)
+IM2COL_OP(uint32_t, im2col_u32)