[ROCm] Implement float32 copy kernel (#2684)

cherry-pick of pytorch#163869

Author: jerrymannil

aten/src/ATen/native/cuda/Copy.cu

@@ -42,6 +42,19 @@ void bfloat16_copy_kernel_cuda(TensorIteratorBase &iter) {
     });
 }
 
+#ifdef USE_ROCM
+void bfloat16tofloat32_copy_kernel_cuda(TensorIteratorBase &iter) {
+    gpu_kernel_nocast(iter, [] GPU_LAMBDA(at::BFloat16 value) {
+        return static_cast<float>(value);
+    });
+}
+void float16tofloat32_copy_kernel_cuda(TensorIteratorBase &iter) {
+    gpu_kernel_nocast(iter, [] GPU_LAMBDA(at::Half value) {
+        return static_cast<float>(value);
+    });
+}
+#endif
+
 void float8_copy_kernel_cuda(TensorIteratorBase &iter) {
   ScalarType dtype = iter.dtype(0);
   ScalarType other_dtype = iter.dtype(1);
@@ -187,7 +200,17 @@ void direct_copy_kernel_cuda(TensorIteratorBase &iter) {
      } else {
        float16_copy_kernel_cuda(iter);
      }
-  } else if (isBitsType(dtype)) {
+  }
+#ifdef USE_ROCM
+  else if ((iter.dtype(1) == kBFloat16 || iter.dtype(1) == kHalf) && dtype == kFloat) {
+    if (iter.dtype(1) == kBFloat16) {
+      bfloat16tofloat32_copy_kernel_cuda(iter);
+    } else {
+      float16tofloat32_copy_kernel_cuda(iter);
+    }
+  }
+#endif
+  else if (isBitsType(dtype)) {
     TORCH_CHECK(dtype == iter.dtype(1), "copy_() does not support casting "
       "bits types to different bits types. Source dtype is ", iter.dtype(1), "target dtype is ", dtype);
     AT_DISPATCH_BIT_TYPES(dtype, "copy_", [&] {