Fix accessing nullptr in some ops

Summary:
When dim is 0, some data pointers in a tensor, like Tensor.strides() and Tensor.sizes() is nullptr. We should not access it, even though it's a no-op in a memcpy.

This is enforced in fbcode but not xplat.

Reviewed By: manuelcandales

Differential Revision: D48477031

fbshipit-source-id: 582da830dc47869cad2a8675cf928e3c8f1d8e43

Author: kirklandsign

kernels/portable/cpu/op_constant_pad_nd.cpp

@@ -101,10 +101,11 @@ void apply_padding_to_dim(
     size_t copy_len = in_step_len * self_sizes[dim];
     size_t copy_nbytes = copy_len * sizeof(CTYPE);
 
-    memcpy(out_data, self_data, copy_nbytes);
-
-    out_data += copy_len;
-    self_data += copy_len;
+    if (copy_nbytes > 0) {
+      memcpy(out_data, self_data, copy_nbytes);
+      out_data += copy_len;
+      self_data += copy_len;
+    }
   }
   // Otherwise, call this function recursively
   else {

kernels/portable/cpu/op_slice_copy.cpp

@@ -144,6 +144,10 @@ Tensor& slice_copy_Tensor_out(
   size_t leading_dims = getLeadingDims(input, dim);
   size_t trailing_dims = getTrailingDims(input, dim);
 
+  if (trailing_dims == 0) {
+    return out;
+  }
+
   size_t length_per_step = trailing_dims * input.element_size();
 
   const char* input_data = input.const_data_ptr<char>();

kernels/portable/cpu/op_slice_scatter.cpp

@@ -145,6 +145,10 @@ Tensor& slice_scatter_out(
   auto error = resize_like_input(input, out);
   ET_CHECK_MSG(error == Error::Ok, "Failed to resize output tensor.");
 
+  if (input.numel() == 0) {
+    return out;
+  }
+
   // If user do not set value to end_val, set end to input.size(dim) (largest
   // value available)
   int64_t end = end_val.has_value() ? end_val.value() : input.size(dim);

kernels/portable/cpu/util/transpose_util.h

@@ -86,20 +86,23 @@ void transpose_tensors(
   auto dim = a.dim();
   auto data_a = a.const_data_ptr<T>();
   auto data_out = out.mutable_data_ptr<T>();
-  auto a_sizes = a.sizes();
-  auto a_strides = a.strides();
 
   size_t out_index[kTensorDimensionLimit];
   memset(out_index, 0, sizeof(out_index));
 
   StridesType new_strides[kTensorDimensionLimit];
-  memcpy(new_strides, a_strides.data(), dim * sizeof(StridesType));
-
   SizesType new_sizes[kTensorDimensionLimit];
-  memcpy(new_sizes, a_sizes.data(), dim * sizeof(SizesType));
 
-  std::swap(new_sizes[dim0], new_sizes[dim1]);
-  std::swap(new_strides[dim1], new_strides[dim0]);
+  if (dim != 0) {
+    auto a_strides = a.strides();
+    memcpy(new_strides, a_strides.data(), dim * sizeof(StridesType));
+
+    auto a_sizes = a.sizes();
+    memcpy(new_sizes, a_sizes.data(), dim * sizeof(SizesType));
+
+    std::swap(new_sizes[dim0], new_sizes[dim1]);
+    std::swap(new_strides[dim1], new_strides[dim0]);
+  }
 
   // non_1_dim_indices stores the indices of the dimensions that have a value
   // greater than 1. Dimensions can only have a value of 1 or larger.