Created attachment 40759 [details]
The demo in question is src/samples/stencil.c found in the demo repository. With swrastg_dri.so,
$ LIBGL_ALWAYS_SOFTWARE=1 GALLIUM_DRIVER=softpipe ./stencil
gives correct result, but
$ LIBGL_ALWAYS_SOFTWARE=1 GALLIUM_DRIVER=llvmpipe ./stencil
gives incorrect result on my x86 machine.
st/vega exhibits similar artifacts when used with llvmpipe.
Fixed with commit dbf996f30856c000e18e3700f741d4e92561b4ec.
Committed to 7.9 branch too.