vTensor cleanup 3/N - Introduce conversion constructors for vec types (#5423)

Summary:
Pull Request resolved: #5423

## Context

Introduce implicit conversion functions to `vec` types. This allows the following pattern:

```cpp
utils::ivec3 v1{4, 5, 2};
utils::uvec3  v2 = v1;
```

Whereas before, we would have to do

```cpp
utils::ivec3 v1{4, 5, 2};
utils::uvec3 v2(
    safe_downcast<uint32_t>(v1[0],
    safe_downcast<uint32_t>(v1[1],
    safe_downcast<uint32_t>(v1[2]);
```

The connection with `vTensor` class cleanup is that this will allow for consolidation of `vTensor` class methods, specifically circumventing the need to provide two functions to retrieve the logical limits of the `Tensor`, one to retrieve it as a `ivec3` and another to retrieve it as a `uvec3`.
ghstack-source-id: 243309910
exported-using-ghexport

Reviewed By: jorgep31415

Differential Revision: D62878650

fbshipit-source-id: 8ed9e8ecfcc35aaf8ba6277fcf3e56c97e8fe8c7

Author: SS-JIA

backends/vulkan/runtime/utils/VecUtils.h

@@ -238,6 +238,28 @@ struct vec final {
   // NOLINTNEXTLINE
   Type data[N];
 
+  vec() = default;
+
+  // Standard constructor with initializer list
+  vec(std::initializer_list<Type> values) {
+    VK_CHECK_COND(values.size() == N);
+    std::copy(values.begin(), values.end(), data);
+  }
+
+  // Conversion constructor from an _integral_ vec type. Note that this is only
+  // defined if `OtherType` is an integral type to disallow implicit narrowing.
+  template <
+      typename OtherType,
+      typename std::enable_if<
+          !std::is_same<Type, OtherType>::value &&
+              std::is_integral<OtherType>::value,
+          int>::type = 0>
+  /* implicit */ vec(const vec<OtherType, N>& other) {
+    for (int i = 0; i < N; ++i) {
+      data[i] = safe_downcast<Type>(other[i]);
+    }
+  }
+
   const Type& operator[](const uint32_t& i) const {
     VK_CHECK_COND(i >= 0 && i < N, "Index out of bounds!");
     return data[i];

backends/vulkan/test/vulkan_compute_api_test.cpp

@@ -301,26 +301,70 @@ TEST_F(VulkanComputeAPITest, virtual_transpose_test) {
   }
 }
 
+utils::ivec3 make_temp_ivec3(int x, int y, int z) {
+  return utils::ivec3{x, y, z};
+}
+
 TEST_F(VulkanComputeAPITest, vec_test) {
-  utils::vec3 v3({1, 2, 3});
-  ASSERT_TRUE(v3[0] == 1);
-  ASSERT_TRUE(v3[1] == 2);
-  ASSERT_TRUE(v3[2] == 3);
-  v3 = {4, 5, 6};
-  ASSERT_TRUE(v3[0] == 4);
-  ASSERT_TRUE(v3[1] == 5);
-  ASSERT_TRUE(v3[2] == 6);
-
-  utils::uvec4 uv4({4, 3, 2, 1});
-  ASSERT_TRUE(uv4[0] == 4);
-  ASSERT_TRUE(uv4[1] == 3);
-  ASSERT_TRUE(uv4[2] == 2);
-  ASSERT_TRUE(uv4[3] == 1);
-  uv4 = {11, 13, 12, 88};
-  ASSERT_TRUE(uv4[0] == 11);
-  ASSERT_TRUE(uv4[1] == 13);
-  ASSERT_TRUE(uv4[2] == 12);
-  ASSERT_TRUE(uv4[3] == 88);
+  {
+    utils::vec3 v3({1, 2, 3});
+    ASSERT_TRUE(v3[0] == 1);
+    ASSERT_TRUE(v3[1] == 2);
+    ASSERT_TRUE(v3[2] == 3);
+    v3 = {4, 5, 6};
+    ASSERT_TRUE(v3[0] == 4);
+    ASSERT_TRUE(v3[1] == 5);
+    ASSERT_TRUE(v3[2] == 6);
+  }
+
+  {
+    utils::uvec4 uv4({4, 3, 2, 1});
+    ASSERT_TRUE(uv4[0] == 4);
+    ASSERT_TRUE(uv4[1] == 3);
+    ASSERT_TRUE(uv4[2] == 2);
+    ASSERT_TRUE(uv4[3] == 1);
+    uv4 = {11, 13, 12, 88};
+    ASSERT_TRUE(uv4[0] == 11);
+    ASSERT_TRUE(uv4[1] == 13);
+    ASSERT_TRUE(uv4[2] == 12);
+    ASSERT_TRUE(uv4[3] == 88);
+  }
+
+  // Test copy from same type
+  {
+    utils::ivec3 v{5, 6, 8};
+    utils::ivec3 v2 = v;
+
+    ASSERT_TRUE(v2[0] == 5);
+    ASSERT_TRUE(v2[1] == 6);
+    ASSERT_TRUE(v2[2] == 8);
+  }
+
+  // Test copy from different type
+  {
+    utils::uvec3 v{5, 6, 8};
+    utils::ivec3 v2 = v;
+
+    ASSERT_TRUE(v2[0] == 5);
+    ASSERT_TRUE(v2[1] == 6);
+    ASSERT_TRUE(v2[2] == 8);
+  }
+
+  // Test construction from temporary vec
+  {
+    utils::uvec3 v{make_temp_ivec3(4, 5, 10)};
+    ASSERT_TRUE(v[0] == 4);
+    ASSERT_TRUE(v[1] == 5);
+    ASSERT_TRUE(v[2] == 10);
+  }
+
+  // Test initalization from temporary vec
+  {
+    utils::uvec3 v = make_temp_ivec3(4, 5, 10);
+    ASSERT_TRUE(v[0] == 4);
+    ASSERT_TRUE(v[1] == 5);
+    ASSERT_TRUE(v[2] == 10);
+  }
 }
 
 TEST_F(VulkanComputeAPITest, retrieve_custom_shader_test) {