To reproduce I set the 'export NV50_PROG_OPTIMIZE=1'
because otherwise bugs in nouveau shader compiler cause severe misrenderings

Then you notice that random bits of the scenery appear and disappear randomly.
I bisected this issue to commit
'mesa,vbo: properly detect when vertex arrays need to be recalculated'

However, further commits appear to also break rendering in similar way.
To restore the functionality, I had to revert 6 commits:

fb4a34e60eb4c1bdc7b0fdcd98d1bf3038c354e8
'mesa: set _NEW_VARYING_VP_INPUTS flag only if fixed-func VP is enabled & valid'

6fc565a94bc0de7ad617c28db7b8b6dfa4102d49
'"vbo: do FLUSH_CURRENT before validating and updating state'

576c8c592a4be7047a00b0c8fe3851b09f10d8d4
'mesa: add _NEW_VARYING_VP_INPUTS for gl_context::varying_vp_inputs'

b0e048f0b955ef79e2de794172de053d27d7d8fa
'mesa: move gl_array_attrib::NewState to gl_array_object::NewArrays'

81afdd20f3f574ce29559d8ad77df5c77652009e
'vbo: don't check twice whether it's valid to render'

784dd51198433e5c299da4a7742c68d21d68d1c1
'mesa,vbo: properly detect when vertex arrays need to be recalculated'

Created attachment 65578 [details] [review]
additional revert

It turns out that clean revert of above isn't enough, and by doing diff between older revert patches and these, I get this patch, and when it applied only then the bug disappers.

Of course I didn't look at all at inner working of this, and I will soon.
So most likely these reverts weren't that useful

It turned out this this bug got fixed (accidently or not) recently, I just forgot to pull mesa.
So closing this till it breaks again :-)