Mesa (master): i965/fs: Clear variable from live-set if it' s completely overwritten.

[Matt Turner]

Module: Mesa
Branch: master
Commit: 18d12336b964cad54bbc0780380c3dcf625abb3d
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=18d12336b964cad54bbc0780380c3dcf625abb3d

Author: Matt Turner <mattst88 at gmail.com>
Date:   Mon Apr 14 11:17:13 2014 -0700

i965/fs: Clear variable from live-set if it's completely overwritten.

One program affected:

instructions in affected programs:     246 -> 244 (-0.81%)

Reviewed-by: Eric Anholt <eric at anholt.net>

---

 src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp b/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
index 390ac9a..6672f84 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
@@ -85,6 +85,15 @@ fs_visitor::dead_code_eliminate()
             }
          }
 
+         if (inst->dst.file == GRF) {
+            if (!inst->is_partial_write()) {
+               int var = live_intervals->var_from_vgrf[inst->dst.reg];
+               for (int i = 0; i < inst->regs_written; i++) {
+                  BITSET_CLEAR(live, var + inst->dst.reg_offset + i);
+               }
+            }
+         }
+
          for (int i = 0; i < 3; i++) {
             if (inst->src[i].file == GRF) {
                int var = live_intervals->var_from_vgrf[inst->src[i].reg];