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Fixed in Unity 2019.1
[UWP][IL2CPP] Empty animation state offsets components in a master build
Steps to reproduce:
1. Download 1095938_repro.zip
2. Change platform to UWP
3. Build "SampleScene" with IL2CPP backend
4. Open VS solution
5. Build VS solution (Master, x64, Local machine)
Expected results: Game objects do not change there position.
Actual results: Game objects which are animated are offset on Z axis when animation state with no clip is playing.
Reproduced with: 2019.1.0a7, 2018.3.0b8
Not reproducible with: 2018.2.14f1
Regression introduced in: 2018.3.0b1
I've root-caused the issue as a Microsoft compiler bug. It occurs when an Animation job is initialized with the GameObject's Transform were the 'y' position value is copied into both the 'y' and 'z' positions of the destination vector (the actual 'z' position is lost). Since Animation jobs typically modify the Transform data (according to the animation graph) this bug is only noticeable for "empty" animations.
The mangled copy operation comes from bad assembly code-gen, which appears to be a confluence of SSE Intrinsics and faulty compiler in-lining optimizations, hence it only repros in Master builds. I've implemented a fix that works around the compiler bug by circumventing the SSE code, which weren't needed in this operation to begin with. As a bonus, the new copy operation removes about 8 unnecessary assembly instructions.
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