i965: Do dead-code elimination in a single pass.

The first pass marked dead instructions as opcode = NOP, and a second
pass deleted those instructions so that the live ranges used in the
first pass wouldn't change.

But since we're walking the instructions in reverse order, we can just
do everything in one pass. The only thing we have to do is walk the
blocks in reverse as well.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>

diff --git a/src/mesa/drivers/dri/i965/brw_cfg.h b/src/mesa/drivers/dri/i965/brw_cfg.h
index 69e39e8..405020b 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_cfg.h
+++ b/src/mesa/drivers/dri/i965/brw_cfg.h
@@ -314,6 +314,9 @@ struct cfg_t {
 #define foreach_block_safe(__block, __cfg)                     \
    foreach_list_typed_safe (bblock_t, __block, link, &(__cfg)->block_list)
 
+#define foreach_block_reverse_safe(__block, __cfg)             \
+   foreach_list_typed_reverse_safe (bblock_t, __block, link, &(__cfg)->block_list)
+
 #define foreach_inst_in_block(__type, __inst, __block)         \
    foreach_in_list(__type, __inst, &(__block)->instructions)
 

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 6b4b602..bd57e09 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
@@ -45,13 +45,13 @@ fs_visitor::dead_code_eliminate()
    BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
    BITSET_WORD *flag_live = ralloc_array(NULL, BITSET_WORD, 1);
 
-   foreach_block (block, cfg) {
+   foreach_block_reverse_safe(block, cfg) {
       memcpy(live, live_intervals->block_data[block->num].liveout,
              sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
       memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
              sizeof(BITSET_WORD));
 
-      foreach_inst_in_block_reverse(fs_inst, inst, block) {
+      foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
          if (inst->dst.file == VGRF && !inst->has_side_effects()) {
             bool result_live = false;
 
@@ -72,7 +72,6 @@ fs_visitor::dead_code_eliminate()
                   inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
                } else {
                   inst->opcode = BRW_OPCODE_NOP;
-                  continue;
                }
             }
          }
@@ -81,7 +80,6 @@ fs_visitor::dead_code_eliminate()
             if (!BITSET_TEST(flag_live, inst->flag_subreg)) {
                inst->opcode = BRW_OPCODE_NOP;
                progress = true;
-               continue;
             }
          }
 
@@ -93,7 +91,6 @@ fs_visitor::dead_code_eliminate()
              !inst->writes_accumulator) {
             inst->opcode = BRW_OPCODE_NOP;
             progress = true;
-            continue;
          }
 
          if (inst->dst.file == VGRF) {
@@ -109,9 +106,10 @@ fs_visitor::dead_code_eliminate()
             BITSET_CLEAR(flag_live, inst->flag_subreg);
          }
 
-         /* Don't mark dead instructions' sources as live */
-         if (inst->opcode == BRW_OPCODE_NOP)
+         if (inst->opcode == BRW_OPCODE_NOP) {
+            inst->remove(block);
             continue;
+         }
 
          for (int i = 0; i < inst->sources; i++) {
             if (inst->src[i].file == VGRF) {
@@ -132,15 +130,8 @@ fs_visitor::dead_code_eliminate()
    ralloc_free(live);
    ralloc_free(flag_live);
 
-   if (progress) {
-      foreach_block_and_inst_safe (block, backend_instruction, inst, cfg) {
-         if (inst->opcode == BRW_OPCODE_NOP) {
-            inst->remove(block);
-         }
-      }
-
+   if (progress)
       invalidate_live_intervals();
-   }
 
    return progress;
 }

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 369941b..2d0722a 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
@@ -71,13 +71,13 @@ vec4_visitor::dead_code_eliminate()
    BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
    BITSET_WORD *flag_live = ralloc_array(NULL, BITSET_WORD, 1);
 
-   foreach_block(block, cfg) {
+   foreach_block_reverse_safe(block, cfg) {
       memcpy(live, live_intervals->block_data[block->num].liveout,
              sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
       memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
              sizeof(BITSET_WORD));
 
-      foreach_inst_in_block_reverse(vec4_instruction, inst, block) {
+      foreach_inst_in_block_reverse_safe(vec4_instruction, inst, block) {
          if ((inst->dst.file == VGRF && !inst->has_side_effects()) ||
              (inst->dst.is_null() && inst->writes_flag())){
             bool result_live[4] = { false };
@@ -115,7 +115,7 @@ vec4_visitor::dead_code_eliminate()
                         inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
                      } else {
                         inst->opcode = BRW_OPCODE_NOP;
-                        continue;
+                        break;
                      }
                   }
                }
@@ -130,7 +130,6 @@ vec4_visitor::dead_code_eliminate()
             if (!combined_live) {
                inst->opcode = BRW_OPCODE_NOP;
                progress = true;
-               continue;
             }
          }
 
@@ -150,9 +149,10 @@ vec4_visitor::dead_code_eliminate()
                BITSET_CLEAR(flag_live, c);
          }
 
-         /* Don't mark dead instructions' sources as live */
-         if (inst->opcode == BRW_OPCODE_NOP)
+         if (inst->opcode == BRW_OPCODE_NOP) {
+            inst->remove(block);
             continue;
+         }
 
          for (int i = 0; i < 3; i++) {
             if (inst->src[i].file == VGRF) {
@@ -176,15 +176,8 @@ vec4_visitor::dead_code_eliminate()
    ralloc_free(live);
    ralloc_free(flag_live);
 
-   if (progress) {
-      foreach_block_and_inst_safe(block, backend_instruction, inst, cfg) {
-         if (inst->opcode == BRW_OPCODE_NOP) {
-            inst->remove(block);
-         }
-      }
-
+   if (progress)
       invalidate_live_intervals();
-   }
 
    return progress;
 }