i965: Don't implicitly set predicate default state in brw_CMP.

i965: Don't implicitly set predicate default state in brw_CMP.

Previously, brw_CMP with a null destination implicitly set the default
state to make future instructions predicated.  This is messy and
confusing - emitting a CMP that populates the flag register and later
using it to predicate instructions are logically separate.  With the
main compiler, we may even schedule instructions between the CMP and the
user of the flag value.

This patch simplifies brw_CMP to just emit a CMP instruction, and not
mess with predication.  It also updates all necessary callers.  These
mostly fell into two patterns:

1. brw_CMP followed by brw_IF.

   We don't need to do anything special here; brw_IF already sets up
   predication appropriately.

2. brw_CMP followed by a single predicated instruction.

   The old model was to call brw_CMP, emit the next (predicated)
   instruction, then disable predication for any instructions beyond
   that.  Instead, just explicitly set predicate_control on the single
   instruction we want to predicate.  It's no more code, and requires
   less cross-module knowledge.

This drops setting flag_value to 0xff as well, which is a field only
used by the SF compile.  There is only one brw_CMP call in the SF code,
which is in do_twoside_caller, and called at the start of
brw_emit_tri_setup, where flag_value is already 0xff.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>