Help me understanding why Burst is generating this code

Code (CSharp):

1. [BurstCompile]
2. struct JobWithGenericJob<T> : IJob where T : unmanaged, ITest
3. {
4.     [NativeDisableUnsafePtrRestriction]
5.     readonly unsafe T* _test;
6.     public JobWithGenericJob(IntPtr test)
7.     {
8.         unsafe
9.         {
10.              _test = (T*) test;
11.         }
12.     }
13.     public void Execute()
14.     {
15.     }
16. }

if Execute is:

Code (CSharp):

1.  public void Execute()
2.     {
3.         unsafe
4.         {
5.             var test = _test;
6.  
7.             for (int i = 0; i < 10_000_000; ++i)
8.                 test[i].SetValue(i * i);
9.         }
10.     }

the result is:



however if execute is this:

Code (CSharp):

1.  public void Execute()
2.     {
3.         unsafe
4.         {
5.             for (int i = 0; i < 10_000_000; ++i)
6.                 _test[i].SetValue(i * i);
7.         }
8.     }

the result is this:



can someone please explain the reason of the difference?

 

if I write this:

Code (CSharp):

1. struct Test : ITest
2. {
3.     public int _value;
4.  
5.     public void SetValue(int value)
6.     {
7.         _value = value;
8.     }
9. }
10.      
11. [BurstCompile]
12. struct JobWithGeneric : IJob
13. {
14.      NativeArray<Test> _test;
15.        
16.      public JobWithGeneric(NativeArray<Test> test)
17.      {
18.          _test = test;
19.      }
20.        
21.      public void Execute()
22.      {
23.          for (int i = 0; i < 10_000_000; ++i) _test[i].SetValue((int) (i * i));
24.      }
25. }

Burst seems to be empty?

 

What happens if you change to this:

Code (CSharp):

1.  
2. public void Execute() {
3.     for (int i = 0; i < 10_000_000; ++i) {
4.         var test = _test[i];
5.         test.SetValue((int)( i * i));
6.         _test[i] = test;
7.     }
8. }
9.  

Your code is the same as the above without the last line. So unless the struct does something unconventional (like settings an static variable or working with some pointer, etc) your could will go nowhere and the optimization will discard everything.

[]'s

 

right, I forgot that NativeArray returns a copy, I wonder if Burst should warn me about it. What about the first post?