1 files changed, 119 insertions, 0 deletions
diff --git a/src/intel/compiler/brw_dead_control_flow.cpp b/src/intel/compiler/brw_dead_control_flow.cpp
new file mode 100644
index 00000000000..114dc6cb212
--- /dev/null
+++ b/src/intel/compiler/brw_dead_control_flow.cpp
@@ -0,0 +1,119 @@
+/*
+ * Copyright © 2013 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/** @file brw_dead_control_flow.cpp
+ *
+ * This file implements the dead control flow elimination optimization pass.
+ */
+
+#include "brw_shader.h"
+#include "brw_cfg.h"
+
+/* Look for and eliminate dead control flow:
+ *
+ *   - if/endif
+ *   - else in else/endif
+ *   - then in if/else/endif
+ */
+bool
+dead_control_flow_eliminate(backend_shader *s)
+{
+   bool progress = false;
+
+   foreach_block_safe (block, s->cfg) {
+      bblock_t *prev_block = block->prev();
+
+      if (!prev_block)
+         continue;
+
+      backend_instruction *const inst = block->start();
+      backend_instruction *const prev_inst = prev_block->end();
+
+      /* ENDIF instructions, by definition, can only be found at the start of
+       * basic blocks.
+       */
+      if (inst->opcode == BRW_OPCODE_ENDIF &&
+          prev_inst->opcode == BRW_OPCODE_ELSE) {
+         bblock_t *const else_block = prev_block;
+         backend_instruction *const else_inst = prev_inst;
+
+         else_inst->remove(else_block);
+         progress = true;
+      } else if (inst->opcode == BRW_OPCODE_ENDIF &&
+                 prev_inst->opcode == BRW_OPCODE_IF) {
+         bblock_t *const endif_block = block;
+         bblock_t *const if_block = prev_block;
+         backend_instruction *const endif_inst = inst;
+         backend_instruction *const if_inst = prev_inst;
+
+         bblock_t *earlier_block = NULL, *later_block = NULL;
+
+         if (if_block->start_ip == if_block->end_ip) {
+            earlier_block = if_block->prev();
+         } else {
+            earlier_block = if_block;
+         }
+         if_inst->remove(if_block);
+
+         if (endif_block->start_ip == endif_block->end_ip) {
+            later_block = endif_block->next();
+         } else {
+            later_block = endif_block;
+         }
+         endif_inst->remove(endif_block);
+
+         assert((earlier_block == NULL) == (later_block == NULL));
+         if (earlier_block && earlier_block->can_combine_with(later_block)) {
+            earlier_block->combine_with(later_block);
+
+            /* If ENDIF was in its own block, then we've now deleted it and
+             * merged the two surrounding blocks, the latter of which the
+             * __next block pointer was pointing to.
+             */
+            if (endif_block != later_block) {
+               __next = earlier_block->next();
+            }
+         }
+
+         progress = true;
+      } else if (inst->opcode == BRW_OPCODE_ELSE &&
+                 prev_inst->opcode == BRW_OPCODE_IF) {
+         bblock_t *const else_block = block;
+         backend_instruction *const if_inst = prev_inst;
+         backend_instruction *const else_inst = inst;
+
+         /* Since the else-branch is becoming the new then-branch, the
+          * condition has to be inverted.
+          */
+         if_inst->predicate_inverse = !if_inst->predicate_inverse;
+         else_inst->remove(else_block);
+
+         progress = true;
+      }
+   }
+
+   if (progress)
+      s->invalidate_live_intervals();
+
+   return progress;
+}