i965/vec4: track and use independently each flag channel

vec4_live_variables tracks now each flag channel independently, so
vec4_dead_code_eliminate can update the writemask of null registers,
based on which component are alive at the moment. This would allow
vec4_cmod_propagation to optimize out several movs involving null
registers.

v2: added support to track each flag channel independently at vec4
    live_variables, as v1 assumed that it was already doing it, as
    pointed by Francisco Jerez
v3: general cleaningn after Matt Turner's review

Reviewed-by: Matt Turner <mattst88@gmail.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp b/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp
index 6782379..aa9a657 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp
@@ -86,9 +86,10 @@ vec4_live_variables::setup_def_use()
                }
 	    }
 	 }
-         if (inst->reads_flag()) {
-            if (!BITSET_TEST(bd->flag_def, 0)) {
-               BITSET_SET(bd->flag_use, 0);
+         for (unsigned c = 0; c < 4; c++) {
+            if (inst->reads_flag(c) &&
+                !BITSET_TEST(bd->flag_def, c)) {
+               BITSET_SET(bd->flag_use, c);
             }
          }
 
@@ -110,8 +111,11 @@ vec4_live_variables::setup_def_use()
             }
          }
          if (inst->writes_flag()) {
-            if (!BITSET_TEST(bd->flag_use, 0)) {
-               BITSET_SET(bd->flag_def, 0);
+            for (unsigned c = 0; c < 4; c++) {
+               if ((inst->dst.writemask & (1 << c)) &&
+                   !BITSET_TEST(bd->flag_use, c)) {
+                  BITSET_SET(bd->flag_def, c);
+               }
             }
          }