[Mesa-dev] [PATCH 13/16] i965/fs: Add a saturation propagation optimization pass.

[Matt Turner]

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: 1512588 -> 1501297 (-0.75%)
instructions in affected programs:     723097 -> 711806 (-1.56%)
GAINED:                                0
LOST:                                  4
---
 src/mesa/drivers/dri/i965/Makefile.sources         |   1 +
 src/mesa/drivers/dri/i965/brw_fs.cpp               |   1 +
 src/mesa/drivers/dri/i965/brw_fs.h                 |   1 +
 .../dri/i965/brw_fs_saturate_propagation.cpp       | 102 +++++++++++++++++++++
 4 files changed, 105 insertions(+)
 create mode 100644 src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp

diff --git a/src/mesa/drivers/dri/i965/Makefile.sources b/src/mesa/drivers/dri/i965/Makefile.sources
index 36d8261..3f901da 100644
--- a/src/mesa/drivers/dri/i965/Makefile.sources
+++ b/src/mesa/drivers/dri/i965/Makefile.sources
@@ -62,6 +62,7 @@ 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_value_numbering.cpp \
 	brw_fs_vector_splitting.cpp \
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 08837da..12b6d4a 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -3304,6 +3304,7 @@ fs_visitor::run()
          progress = opt_peephole_sel() || progress;
          progress = dead_control_flow_eliminate(this) || progress;
          vn_progress = opt_value_numbering();
+         progress = opt_saturate_propagation() || progress;
          progress = register_coalesce() || progress;
 	 progress = compute_to_mrf() || progress;
 
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 75de18e..07360ae 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -368,6 +368,7 @@ 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,
diff --git a/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp
new file mode 100644
index 0000000..91a1338
--- /dev/null
+++ b/src/mesa/drivers/dri/i965/brw_fs_saturate_propagation.cpp
@@ -0,0 +1,102 @@
+/*
+ * 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 &&
+             scan_inst->can_do_saturate()) {
+            scan_inst->saturate = true;
+            inst->saturate = false;
+            progress = true;
+         }
+	 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;
+}
-- 
1.8.3.2