String.memcpy and String.memset in profiler

Hey guys

I'm currently doing some intensive optimization of my project, and I keep seeing String.memcpy() and String.memset() in the hierarchy:



These are only 2 of the instances in my sample, but you can clearly see they're being called hundreds of times per frame.

I understand that simply doing something like this will generate these calls:

Code (CSharp):

1. Debug.Log("I'm a new string instance!");

But the algorithm in the above image deals entirely with bounding boxes. Nowhere am I using strings.

Does anyone know what is going on here?

Thanks,
Ves

 

This affected me lately and may affect others, so I thought I'd provide an answer 7+ years down the line.

This bug(?) results from using set operations on dereferenced pointers, e.g.

*((ByteArray256*)bytes) = default;

I first noticed it when I started porting to

unsafe

code.

Full example to test for yourself, should show up

String.memset()

in your profiler:

Code (CSharp):

1. using System.Runtime.InteropServices;
2. using UnityEngine;
3.  
4. public class UnsafeTest : MonoBehaviour
5. {
6.     byte[] array = new byte[1024];
7.  
8.     void Update()
9.     {
10.         unsafe { fixed (byte* bytes = array) {
11.             for (int i = 0; i < 100000; i++)
12.             *((ByteArray256*) bytes) = default;
13.    
14.         }}
15.     }
16.  
17.     [StructLayout(LayoutKind.Explicit)]
18.     public unsafe struct ByteArray256
19.     {
20.         [FieldOffset(0)] public fixed byte bytes[256];
21.     }
22. }

Not sure how important the specifics are, but a large blit / zeroing operation like this tends to trigger it to at least display in the profiler.