i965/vec4: Don't register coalesce into source of VS_OPCODE_UNPACK_FLAGS_SIMD4X2

This prevents regressions in a bunch of clipping and interpolation tests
caused by the next patch (i965/vec4: Optimize OR with 0 into a MOV).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>

src/intel/compiler/brw_vec4.cpp

@@ -1285,6 +1285,15 @@ vec4_visitor::opt_register_coalesce()
                }
             }
 
+            /* VS_OPCODE_UNPACK_FLAGS_SIMD4X2 generates a bunch of mov(1)
+             * instructions, and this optimization pass is not capable of
+             * handling that.  Bail on these instructions and hope that some
+             * later optimization pass can do the right thing after they are
+             * expanded.
+             */
+            if (scan_inst->opcode == VS_OPCODE_UNPACK_FLAGS_SIMD4X2)
+               break;
+
             /* This doesn't handle saturation on the instruction we
              * want to coalesce away if the register types do not match.
              * But if scan_inst is a non type-converting 'mov', we can fix