i965/fs: Add a saturation propagation optimization pass.

Transforms, for example,

mul     vgrf3, vgrf2, vgrf1
mov.sat vgrf4, vgrf3

into

mul.sat vgrf3, vgrf2, vgrf1
mov     vgrf4, vgrf3

which gives register_coalescing an opportunity to remove the MOV
instruction.

total instructions in shared programs: 1515039 -> 1504634 (-0.69%)
instructions in affected programs:     798586 -> 788181 (-1.30%)
GAINED:                                0
LOST:                                  4

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

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

@@ -63,6 +63,7 @@ i965_FILES = \
 	brw_fs_live_variables.cpp \
 	brw_fs_peephole_predicated_break.cpp \
 	brw_fs_reg_allocate.cpp \
+	brw_fs_saturate_propagation.cpp \
 	brw_fs_sel_peephole.cpp \
 	brw_fs_vector_splitting.cpp \
 	brw_fs_visitor.cpp \

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

@@ -3362,6 +3362,7 @@ fs_visitor::run()
 	 progress = dead_code_eliminate_local() || progress;
          progress = opt_peephole_sel() || progress;
          progress = dead_control_flow_eliminate(this) || progress;
+         progress = opt_saturate_propagation() || progress;
          progress = register_coalesce() || progress;
 	 progress = compute_to_mrf() || progress;
       } while (progress);

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

@@ -371,6 +371,7 @@ public:
    void try_replace_with_sel();
    bool opt_peephole_sel();
    bool opt_peephole_predicated_break();
+   bool opt_saturate_propagation();
    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_saturate_propagation.cpp

@@ -0,0 +1,104 @@
+/*
+ * 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_fs_live_variables.h"
+#include "brw_cfg.h"
+
+/** @file brw_fs_saturate_propagation.cpp
+ */
+
+static bool
+opt_saturate_propagation_local(fs_visitor *v, bblock_t *block)
+{
+   bool progress = false;
+   int ip = block->start_ip;
+
+   for (fs_inst *inst = (fs_inst *)block->start;
+        inst != block->end->next;
+        inst = (fs_inst *) inst->next) {
+      ip++;
+
+      if (inst->opcode != BRW_OPCODE_MOV ||
+          inst->dst.file != GRF ||
+          !inst->saturate)
+         continue;
+
+      int src_var = v->live_intervals->var_from_reg(&inst->src[0]);
+      int src_end_ip = v->live_intervals->end[src_var];
+      if (src_end_ip > ip && !inst->dst.equals(inst->src[0]))
+         continue;
+
+      int scan_ip = ip;
+      bool interfered = false;
+      for (fs_inst *scan_inst = (fs_inst *) inst->prev;
+           scan_inst != block->start->prev;
+           scan_inst = (fs_inst *) scan_inst->prev) {
+         scan_ip--;
+
+         if (scan_inst->dst.file == GRF &&
+             scan_inst->dst.reg == inst->src[0].reg &&
+             scan_inst->dst.reg_offset == inst->src[0].reg_offset) {
+            if (scan_inst->can_do_saturate()) {
+               scan_inst->saturate = true;
+               inst->saturate = false;
+               progress = true;
+            }
+            break;
+         }
+         for (int i = 0; i < 3; i++) {
+            if (scan_inst->src[i].file == GRF &&
+                scan_inst->src[i].reg == inst->src[0].reg &&
+                scan_inst->src[i].reg_offset == inst->src[0].reg_offset) {
+               interfered = true;
+               break;
+            }
+         }
+
+         if (interfered)
+            break;
+      }
+   }
+
+   return progress;
+}
+
+bool
+fs_visitor::opt_saturate_propagation()
+{
+   bool progress = false;
+
+   calculate_live_intervals();
+
+   cfg_t cfg(&instructions);
+
+   for (int b = 0; b < cfg.num_blocks; b++) {
+      progress = opt_saturate_propagation_local(this, cfg.blocks[b])
+                 || progress;
+   }
+
+   if (progress)
+      invalidate_live_intervals();
+
+   return progress;
+}