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 69e39e8964df59452345043944d40c05c3e1ac20..405020b77e57f22d3e4756b90bef9bcddae2c00d 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 6b4b60224b74d3153073d73b89eb4689d5e25ca5..bd57e09fe0c19650bf9696a1d59091eff452628b 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 369941bb71e9f23a01dbbe866445a11adea0629a..2d0722aa1ebd08ee8fb0665a1de740f406ed96ce 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;
 }