[Mesa-dev] [Bug 100303] Adding a single, meaningless if-else to a shader source leads to different image

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100303

--- Comment #4 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Roland Scheidegger from comment #2)
> 
> So, for some reason the compiler completely eliminated the conditional
> return in the loop inside the branch and figured it will just
> unconditionally return the value corresponding to not meeting that condition
> in the loop in the original code. (In fact all code in this function with
> the exception of the return statement is now effectively dead.)
> Not sure though which lowering stage did this damage...

I think there is a bug in do_lower_jumps(). I noticed a similar bug when
working on loop unrolling for NIR. I wrote the following tests that pass on NIR
unrolling/return lower but fail in GLSL IR.

piglit/tests/spec/glsl-1.10/execution/vs-nested-return-sibling-loop.shader_tes
piglit/tests/spec/glsl-1.10/execution/vs-nested-return-sibling-loop2.shader_test

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