Add direct copy fast path for portable copy op

Differential Revision: D73656456

Pull Request resolved: pytorch#10487

Author: GregoryComer

kernels/portable/cpu/op_copy.cpp

@@ -46,17 +46,24 @@ Tensor& copy_out(
   // @lint-ignore CLANGTIDY facebook-hte-CArray
   static constexpr const char op_name[] = "copy.out";
 
-  ET_SWITCH_REALHBBF16_TYPES(in.scalar_type(), ctx, "copy.out", CTYPE, [&]() {
-    utils::apply_bitensor_elementwise_fn<CTYPE, op_name>(
-        [](ET_UNUSED const CTYPE _, const CTYPE val_src) { return val_src; },
-        ctx,
-        in,
-        utils::SupportedTensorDtypes::REALHBBF16,
-        src,
-        utils::SupportedTensorDtypes::REALHBBF16,
-        out,
-        utils::SupportedTensorDtypes::REALHBBF16);
-  });
+  // Use direct copy fast path if broadcast is not needed and tensors are
+  // non-empty
+  if (internal::sizes_match_ignoring_leading_1s(out.sizes(), src.sizes()) &&
+      src.numel() > 0) {
+    std::memcpy(out.mutable_data_ptr(), src.const_data_ptr(), src.nbytes());
+  } else {
+    ET_SWITCH_REALHBBF16_TYPES(in.scalar_type(), ctx, "copy.out", CTYPE, [&]() {
+      utils::apply_bitensor_elementwise_fn<CTYPE, op_name>(
+          [](ET_UNUSED const CTYPE _, const CTYPE val_src) { return val_src; },
+          ctx,
+          in,
+          utils::SupportedTensorDtypes::REALHBBF16,
+          src,
+          utils::SupportedTensorDtypes::REALHBBF16,
+          out,
+          utils::SupportedTensorDtypes::REALHBBF16);
+    });
+  }
 
   return out;
 }
@@ -79,17 +86,24 @@ Tensor& copy_(
   // @lint-ignore CLANGTIDY facebook-hte-CArray
   static constexpr const char op_name[] = "copy_";
 
-  ET_SWITCH_REALHBBF16_TYPES(in.scalar_type(), ctx, "copy_", CTYPE, [&]() {
-    utils::apply_bitensor_elementwise_fn<CTYPE, op_name>(
-        [](ET_UNUSED const CTYPE _, const CTYPE val_src) { return val_src; },
-        ctx,
-        in,
-        utils::SupportedTensorDtypes::REALHBBF16,
-        src,
-        utils::SupportedTensorDtypes::REALHBBF16,
-        in,
-        utils::SupportedTensorDtypes::REALHBBF16);
-  });
+  // Use direct copy fast path if broadcast is not needed and tensors are
+  // non-empty
+  if (internal::sizes_match_ignoring_leading_1s(in.sizes(), src.sizes()) &&
+      src.numel() > 0) {
+    std::memcpy(in.mutable_data_ptr(), src.const_data_ptr(), in.nbytes());
+  } else {
+    ET_SWITCH_REALHBBF16_TYPES(in.scalar_type(), ctx, "copy_", CTYPE, [&]() {
+      utils::apply_bitensor_elementwise_fn<CTYPE, op_name>(
+          [](ET_UNUSED const CTYPE _, const CTYPE val_src) { return val_src; },
+          ctx,
+          in,
+          utils::SupportedTensorDtypes::REALHBBF16,
+          src,
+          utils::SupportedTensorDtypes::REALHBBF16,
+          in,
+          utils::SupportedTensorDtypes::REALHBBF16);
+    });
+  }
 
   return in;
 }