i965/fs: Fully recompute liveout at each step.

Since we start with an overestimation of livein (0xffffffff), successive
steps can actually take away values.  This means we can't simply OR in
new liveout values; we need to recompute it from scratch at each
iteration of the fixed-point algorithm.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp

@@ -211,7 +211,7 @@ fs_copy_prop_dataflow::run()
          for (int i = 0; i < bitset_words; i++) {
             const BITSET_WORD old_liveout = bd[b].liveout[i];
 
-            bd[b].liveout[i] |=
+            bd[b].liveout[i] =
                bd[b].copy[i] | (bd[b].livein[i] & ~bd[b].kill[i]);
 
             if (old_liveout != bd[b].liveout[i])