[BUG] Burst compiler bug when converting uint constants to ulong?

We were trying to enable burst compiler for our job systems and found incorrect behavior when enabling burst compile for some jobs. After hours of debugging, I have finally narrowed it down to a single uint to ulong assignment that's not working correctly. Below is the code snippet that can reproduce the problem:

Code (CSharp):

1.  
2.     public struct Data : IComponentData
3.     {
4.         public ulong Value;
5.     }
6.     public class TestBurstComponentSystem : JobComponentSystem
7.     {
8.         [BurstCompile]
9.         private struct Job : IJobProcessComponentData<Data>
10.         {
11.             public void Execute(ref Data data)
12.             {
13.                 data.Value = uint.MaxValue;
14.             }
15.         }
16.  
17.         protected override JobHandle OnUpdate(JobHandle inputDeps)
18.         {
19.             return new Job().Schedule(this, inputDeps);
20.         }
21.     }
22.  

uint.MaxValue is 4294967295 and ulong has a larger range than uint so you would expect the value to be 4294967295 after the assignment in "data.Value = uint.MaxValue". However, when burst is enabled, the result ulong value will be 18446744073709551615.

I have created a demo project you can check to reproduce this:
https://github.com/xfxyjwf/burstbug

It has one scene in Scens/SampleScene with one text label showing the result of the assignment. When burst is enabled, the value shown in the center of the screen is 18446744073709551615 and as soon as you disable burst jobs in the "Jobs -> Use Burst Jobs" menu it will change back to the correct value 4294967295.

Some more info from the burst inspector:

The compiled IL instructions of the Job.Execute method:

Code (csharp):

1.  
2. IL_0001: ldarg.1
3. IL_0002: ldc.i4.m1
4. IL_0003: conv.u8 args(IL_0002)
5. IL_0004: stfld System.UInt64 TestBurstBug/Data::Value args(IL_0001, IL_0003)
6. IL_0009: ret
7.  

It pushes -1 as a 32-bit value onto the stack and then do an unsigned extension to convert it to a 64-bit value. That should produce 4294967295.

The converted LLVM IR (unoptimized), however, stores -1 directly into the field:

Code (csharp):

1.  
2. BL.0000:                                          ; preds = %BL.entry
3.   %0 = getelementptr %"TestBurstBug/Data.79", %"TestBurstBug/Data.79"* %data, i32 0, i32 0
4.   store i64 -1, i64* %0
5.   ret void
6. }
7.  

It seems to me the burst compiler is handling the conv.u8 instruction incorrectly.

This issue makes burst compiler unusable for us because every constant value in the range [2^31, 2^32) will be converted incorrectly (e.g., (longValue & 0x00000000FFFFFFFFL) doesn't work when burst is enabled).

Please help and let me know if it's a project configuration issue on our end.

 

Oh... new ecs release?

 

Thanks for the reply! I couldn't find 0.2.4-preview.38 though. Is it already released?

 

Confirmed that 0.2.4-preview.38 fixed the bug we were seeing. Thanks so much for the help!