[Mesa-dev] [Bug 111141] [REGRESSION] [BISECTED] [DXVK] 1-bit booleans and Elite Dangerous shader mis-optimization

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111141

--- Comment #9 from Jason Ekstrand <jason at jlekstrand.net> ---
It's not nonsense at all.  I could see a few possible explanations of the
failure on AMD but not Intel:

 1. The shader depends on undefined behavior and the optimization change caused
that undefined behavior to be different and Intel just happens to work by luck.

 1. The optimization change caused NIR to turn a valid shader into something
which depends on undefined behavior and Intel just happens to work by luck.

 2. The optimization change caused NIR to generate a slightly different shader
which exposed a bug in the AMD LLVM back-end or the NIR -> LLVM translator.

I'd give the three even odds at this point.  I just finished looking quite a
bit at that shader in the context of
https://bugs.freedesktop.org/show_bug.cgi?id=111152 and it has 23 undefined
values at the top of the shader.  Let me look at it a bit and see where some of
them are used.  They may be harmless.

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