On gen7 and earlier the scratch space size is limited to 12kB.
By enabling this optimization we may easily exceed this limit
without having any fallback.
arb_compute_shader/linker/bug-93840.shader_test crashes with
this lowering on IVB due to exceeding scratch size limit.
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2092
Fixes: 69244fc7
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>