with piglit 44456ba,
spec.ext_framebuffer_multisample.alpha-to-coverage-dual-src-blend
fails for the 2,4,6 and 8 variants.  The test regresses on bdw, bsw,
byt, hsw, ivb, skl, and snb.  Sample test output below:


/tmp/build_root/m64/lib/piglit/bin/ext_framebuffer_multisample-alpha-to-coverage-dual-src-blend 8 -auto -fbo
Probe color at (0,30)
  Expected: 0.015542 0.540720 0.003562 0.355078
  Observed: 0.015686 0.600000 0.003922 0.396078
Probe color at (0,60)
  Expected: 0.022253 0.469956 0.007782 0.328125
  Observed: 0.023529 0.564706 0.007843 0.388235
Probe color at (0,90)
  Expected: 0.006639 0.478194 0.123930 0.330859
  Observed: 0.007843 0.576471 0.121569 0.396078
Probe color at (0,120)
  Expected: 0.193928 0.624989 0.191135 0.375000
  Observed: 0.192157 0.698039 0.188235 0.423529
Probe color at (0,150)
  Expected: 0.340842 0.506519 0.016304 0.472266
  Observed: 0.341176 0.529412 0.015686 0.486275
Probe color at (0,180)
  Expected: 0.065178 0.331757 0.207457 0.634375
  Observed: 0.062745 0.274510 0.207843 0.596078
Probe color at (0,210)
  Expected: 0.183156 0.854469 0.762897 0.873047
  Observed: 0.180392 0.690196 0.760784 0.764706
Probe color at (0,240)
  Expected: 0.960013 1.000000 0.486724 1.000000
  Observed: 0.960784 0.913726 0.486275 1.000000