vc4: Move SF removal to a separate peephole pass.

The DCE pass is going to change significantly to handle control flow,
while we don't really need to change it for the SF handling.  We also need
to add some more SF peephole optimization for SF updates generated by
control flow support.

No change on shader-db.

src/gallium/drivers/vc4/Makefile.sources

@@ -26,6 +26,7 @@ C_SOURCES := \
 	vc4_opt_constant_folding.c \
 	vc4_opt_copy_propagation.c \
 	vc4_opt_dead_code.c \
+	vc4_opt_peephole_sf.c \
 	vc4_opt_small_immediates.c \
 	vc4_opt_vpm.c \
 	vc4_program.c \

src/gallium/drivers/vc4/vc4_opt_dead_code.c

@@ -82,7 +82,6 @@ qir_opt_dead_code(struct vc4_compile *c)
 {
         bool progress = false;
         bool *used = calloc(c->num_temps, sizeof(bool));
-        bool sf_used = false;
 
         list_for_each_entry_safe_rev(struct qinst, inst, &c->instructions,
                                      link) {
@@ -109,22 +108,6 @@ qir_opt_dead_code(struct vc4_compile *c)
                         continue;
                 }
 
-                if (qir_depends_on_flags(inst))
-                        sf_used = true;
-                if (inst->sf) {
-                        if (!sf_used) {
-                                if (debug) {
-                                        fprintf(stderr, "Removing SF on: ");
-                                        qir_dump_inst(c, inst);
-                                        fprintf(stderr, "\n");
-                                }
-
-                                inst->sf = false;
-                                progress = true;
-                        }
-                        sf_used = false;
-                }
-
                 for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
                         if (inst->src[i].file == QFILE_TEMP)
                                 used[inst->src[i].index] = true;

src/gallium/drivers/vc4/vc4_opt_peephole_sf.c

@@ -0,0 +1,82 @@
+/*
+ * Copyright © 2016 Broadcom
+ *
+ * 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 vc4_opt_peephole_sf.c
+ *
+ * Quick optimization to eliminate unused SF updates.
+ */
+
+#include "vc4_qir.h"
+#include "util/u_math.h"
+
+static bool debug;
+
+static void
+dump_from(struct vc4_compile *c, struct qinst *inst)
+{
+        if (!debug)
+                return;
+
+        fprintf(stderr, "optimizing: ");
+        qir_dump_inst(c, inst);
+        fprintf(stderr, "\n");
+}
+
+static void
+dump_to(struct vc4_compile *c, struct qinst *inst)
+{
+        if (!debug)
+                return;
+
+        fprintf(stderr, "to: ");
+        qir_dump_inst(c, inst);
+        fprintf(stderr, "\n");
+}
+
+bool
+qir_opt_peephole_sf(struct vc4_compile *c)
+{
+        bool progress = false;
+        bool sf_live = false;
+
+        /* Walk the block from bottom to top, tracking if the SF is used, and
+         * removing unused ones.
+         */
+        list_for_each_entry_rev(struct qinst, inst, &c->instructions, link) {
+                if (inst->sf) {
+                        if (!sf_live) {
+                                dump_from(c, inst);
+                                inst->sf = false;
+                                dump_to(c, inst);
+                                progress = true;
+                        }
+                        sf_live = false;
+                }
+
+                if (qir_depends_on_flags(inst))
+                        sf_live = true;
+        }
+
+        return progress;
+}

src/gallium/drivers/vc4/vc4_qir.c

@@ -540,6 +540,7 @@ qir_optimize(struct vc4_compile *c)
                 OPTPASS(qir_opt_algebraic);
                 OPTPASS(qir_opt_constant_folding);
                 OPTPASS(qir_opt_copy_propagation);
+                OPTPASS(qir_opt_peephole_sf);
                 OPTPASS(qir_opt_dead_code);
                 OPTPASS(qir_opt_small_immediates);
                 OPTPASS(qir_opt_vpm);

src/gallium/drivers/vc4/vc4_qir.h

@@ -496,6 +496,7 @@ bool qir_opt_algebraic(struct vc4_compile *c);
 bool qir_opt_constant_folding(struct vc4_compile *c);
 bool qir_opt_copy_propagation(struct vc4_compile *c);
 bool qir_opt_dead_code(struct vc4_compile *c);
+bool qir_opt_peephole_sf(struct vc4_compile *c);
 bool qir_opt_small_immediates(struct vc4_compile *c);
 bool qir_opt_vpm(struct vc4_compile *c);
 void vc4_nir_lower_blend(nir_shader *s, struct vc4_compile *c);