[Mesa-dev] [PATCH 11/11] i965/vec4: Fix handling of multiple register reads and writes in dead_code_eliminate().

[Francisco Jerez]

---
This change obsoletes "[PATCH 26/32] i965/vec4: Don't assume a value
is dead when its VGRF is only partially overwritten." [1].  With
per-subregister liveness information we can now fix it properly.

[1] http://lists.freedesktop.org/archives/mesa-dev/2015-February/076109.html

 .../dri/i965/brw_vec4_dead_code_eliminate.cpp      | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp b/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
index e4ce496..980e266 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
@@ -80,8 +80,10 @@ vec4_visitor::dead_code_eliminate()
          if (inst->dst.file == GRF && !inst->has_side_effects()) {
             bool result_live[4] = { false };
 
-            for (int c = 0; c < 4; c++) {
-               result_live[c] = BITSET_TEST(live, var_from_reg(alloc, inst->dst, c));
+            for (unsigned i = 0; i < inst->regs_written; i++) {
+               for (int c = 0; c < 4; c++)
+                  result_live[c] |= BITSET_TEST(
+                     live, var_from_reg(alloc, offset(inst->dst, i), c));
             }
 
             /* If the instruction can't do writemasking, then it's all or
@@ -122,9 +124,12 @@ vec4_visitor::dead_code_eliminate()
          }
 
          if (inst->dst.file == GRF && !inst->predicate) {
-            for (int c = 0; c < 4; c++) {
-               if (inst->dst.writemask & (1 << c)) {
-                  BITSET_CLEAR(live, var_from_reg(alloc, inst->dst, c));
+            for (unsigned i = 0; i < inst->regs_written; i++) {
+               for (int c = 0; c < 4; c++) {
+                  if (inst->dst.writemask & (1 << c)) {
+                     BITSET_CLEAR(live, var_from_reg(alloc,
+                                                     offset(inst->dst, i), c));
+                  }
                }
             }
          }
@@ -135,8 +140,11 @@ vec4_visitor::dead_code_eliminate()
 
          for (int i = 0; i < 3; i++) {
             if (inst->src[i].file == GRF) {
-               for (int c = 0; c < 4; c++) {
-                  BITSET_SET(live, var_from_reg(alloc, inst->src[i], c));
+               for (unsigned j = 0; j < inst->regs_read(i); j++) {
+                  for (int c = 0; c < 4; c++) {
+                     BITSET_SET(live, var_from_reg(alloc,
+                                                   offset(inst->src[i], j), c));
+                  }
                }
             }
          }
-- 
2.1.3