i965/fs: New peephole optimization to flatten IF/BREAK/ENDIF.

total instructions in shared programs: 1550713 -> 1550449 (-0.02%)
instructions in affected programs:     7931 -> 7667 (-3.33%)

Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/mesa/drivers/dri/i965/Makefile.sources

@@ -60,6 +60,7 @@ i965_FILES = \
 	brw_fs_fp.cpp \
 	brw_fs_generator.cpp \
 	brw_fs_live_variables.cpp \
+	brw_fs_peephole_predicated_break.cpp \
 	brw_fs_reg_allocate.cpp \
 	brw_fs_sel_peephole.cpp \
 	brw_fs_vector_splitting.cpp \

src/mesa/drivers/dri/i965/brw_fs.cpp

@@ -3172,6 +3172,7 @@ fs_visitor::run()
 	 progress = opt_cse() || progress;
 	 progress = opt_copy_propagate() || progress;
          progress = opt_peephole_sel() || progress;
+         progress = opt_peephole_predicated_break() || progress;
 	 progress = dead_code_eliminate() || progress;
 	 progress = dead_code_eliminate_local() || progress;
          progress = dead_control_flow_eliminate(this) || progress;

src/mesa/drivers/dri/i965/brw_fs.h

@@ -364,6 +364,7 @@ public:
    bool try_emit_mad(ir_expression *ir, int mul_arg);
    void try_replace_with_sel();
    bool opt_peephole_sel();
+   bool opt_peephole_predicated_break();
    void emit_bool_to_cond_code(ir_rvalue *condition);
    void emit_if_gen6(ir_if *ir);
    void emit_unspill(fs_inst *inst, fs_reg reg, uint32_t spill_offset,

src/mesa/drivers/dri/i965/brw_fs_peephole_predicated_break.cpp

@@ -0,0 +1,96 @@
+/*
+ * 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.
+ */
+
+#include "brw_fs.h"
+#include "brw_cfg.h"
+
+/** @file brw_fs_peephole_predicated_break.cpp
+ *
+ * Loops are often structured as
+ *
+ * loop:
+ *    CMP.f0
+ *    (+f0) IF
+ *    BREAK
+ *    ENDIF
+ *    ...
+ *    WHILE loop
+ *
+ * This peephole pass removes the IF and ENDIF instructions and predicates the
+ * BREAK, dropping two instructions from the loop body.
+ */
+
+bool
+fs_visitor::opt_peephole_predicated_break()
+{
+   bool progress = false;
+
+   cfg_t cfg(&instructions);
+
+   for (int b = 0; b < cfg.num_blocks; b++) {
+      bblock_t *block = cfg.blocks[b];
+
+      /* BREAK and CONTINUE instructions, by definition, can only be found at
+       * the ends of basic blocks.
+       */
+      fs_inst *inst = (fs_inst *) block->end;
+      if (inst->opcode != BRW_OPCODE_BREAK && inst->opcode != BRW_OPCODE_CONTINUE)
+         continue;
+
+      fs_inst *if_inst = (fs_inst *) inst->prev;
+      if (if_inst->opcode != BRW_OPCODE_IF)
+         continue;
+
+      fs_inst *endif_inst = (fs_inst *) inst->next;
+      if (endif_inst->opcode != BRW_OPCODE_ENDIF)
+         continue;
+
+      /* For Sandybridge with IF with embedded comparison we need to emit an
+       * instruction to set the flag register.
+       */
+      if (brw->gen == 6 && if_inst->conditional_mod) {
+         fs_inst *cmp_inst = CMP(reg_null_d, if_inst->src[0], if_inst->src[1],
+                                 if_inst->conditional_mod);
+         if_inst->insert_before(cmp_inst);
+         inst->predicate = BRW_PREDICATE_NORMAL;
+      } else {
+         inst->predicate = if_inst->predicate;
+         inst->predicate_inverse = if_inst->predicate_inverse;
+      }
+
+      if_inst->remove();
+      endif_inst->remove();
+
+      /* By removing the ENDIF instruction we removed a basic block. Skip over
+       * it for the next iteration.
+       */
+      b++;
+
+      progress = true;
+   }
+
+   if (progress)
+      invalidate_live_intervals();
+
+   return progress;
+}