i965/vec4: Don't dead code eliminate instructions writing the flag.

A future patch adds support for removing dead writes to the flag
register. This patch simplifies the logic until then.

total instructions in shared programs: 811813 -> 811869 (0.01%)
instructions in affected programs:     3378 -> 3434 (1.66%)

Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index cb87fecf8d8..d07e8c558c2 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -356,7 +356,11 @@ vec4_visitor::dead_code_eliminate()
             inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
             break;
          default:
-            inst->remove();
+            if (inst->writes_flag()) {
+               inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
+            } else {
+               inst->remove();
+            }
             break;
          }
          progress = true;