vc4: Add dead code elimination.

This cleans up a bunch of noise in the compiled coordinate shaders (since
we don't need the varying outputs), and also from writemasked instructions
with negated src operands.

4 files changed, 94 insertions, 3 deletions

diff --git a/src/gallium/drivers/vc4/Makefile.sources b/src/gallium/drivers/vc4/Makefile.sources
index 1a1b4d00d71..6977a067bd7 100644
--- a/src/gallium/drivers/vc4/Makefile.sources
+++ b/src/gallium/drivers/vc4/Makefile.sources
@@ -5,6 +5,7 @@ C_SOURCES := \
 	vc4_draw.c \
 	vc4_emit.c \
 	vc4_opt_algebraic.c \
+	vc4_opt_dead_code.c \
 	vc4_program.c \
 	vc4_qir.c \
 	vc4_qpu_emit.c \
diff --git a/src/gallium/drivers/vc4/vc4_opt_dead_code.c b/src/gallium/drivers/vc4/vc4_opt_dead_code.c
new file mode 100644
index 00000000000..26e4ddfd233
--- /dev/null
+++ b/src/gallium/drivers/vc4/vc4_opt_dead_code.c
@@ -0,0 +1,74 @@
+/*
+ * Copyright © 2014 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_dead_code.c
+ *
+ * This is a simmple dead code eliminator for QIR with no control flow.
+ *
+ * It walks from the bottom of the instruction list, removing instructions
+ * with a destination that is never used, and marking the sources of non-dead
+ * instructions as used.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "vc4_qir.h"
+
+bool
+qir_opt_dead_code(struct qcompile *c)
+{
+        bool progress = false;
+        bool debug = false;
+        bool *used = calloc(c->num_temps, sizeof(bool));
+
+        struct simple_node *node, *t;
+        for (node = c->instructions.prev, t = node->prev;
+             &c->instructions != node;
+             node = t, t = t->prev) {
+                struct qinst *inst = (struct qinst *)node;
+
+                if (inst->dst.file == QFILE_TEMP &&
+                    !used[inst->dst.index] &&
+                    !qir_has_side_effects(inst)) {
+                        if (debug) {
+                                fprintf(stderr, "Removing: ");
+                                qir_dump_inst(inst);
+                                fprintf(stderr, "\n");
+                        }
+                        remove_from_list(&inst->link);
+                        free(inst);
+                        progress = true;
+                        continue;
+                }
+
+                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;
+                }
+        }
+
+        free(used);
+
+        return progress;
+}
diff --git a/src/gallium/drivers/vc4/vc4_qir.c b/src/gallium/drivers/vc4/vc4_qir.c
index 308154ff34a..13714115214 100644
--- a/src/gallium/drivers/vc4/vc4_qir.c
+++ b/src/gallium/drivers/vc4/vc4_qir.c
@@ -32,6 +32,7 @@
 struct qir_op_info {
         const char *name;
         uint8_t ndst, nsrc;
+        bool has_side_effects;
 };
 
 static const struct qir_op_info qir_op_info[] = {
@@ -57,9 +58,9 @@ static const struct qir_op_info qir_op_info[] = {
         [QOP_LOG2] = { "log2", 1, 2 },
         [QOP_PACK_COLORS] = { "pack_colors", 1, 4 },
         [QOP_PACK_SCALED] = { "pack_scaled", 1, 2 },
-        [QOP_VPM_WRITE] = { "vpm_write", 0, 1 },
-        [QOP_VPM_READ] = { "vpm_read", 0, 1 },
-        [QOP_TLB_COLOR_WRITE] = { "tlb_color", 0, 1 },
+        [QOP_VPM_WRITE] = { "vpm_write", 0, 1, true },
+        [QOP_VPM_READ] = { "vpm_read", 0, 1, true },
+        [QOP_TLB_COLOR_WRITE] = { "tlb_color", 0, 1, true },
         [QOP_VARY_ADD_C] = { "vary_add_c", 1, 1 },
 };
 
@@ -81,6 +82,18 @@ qir_get_op_nsrc(enum qop qop)
                 abort();
 }
 
+bool
+qir_has_side_effects(struct qinst *inst)
+{
+        for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
+                if (inst->src[i].file == QFILE_VARY ||
+                    inst->src[i].file == QFILE_UNIF)
+                        return true;
+        }
+
+        return qir_op_info[inst->op].has_side_effects;
+}
+
 static void
 qir_print_reg(struct qreg reg)
 {
@@ -228,6 +241,7 @@ qir_optimize(struct qcompile *c)
                 bool progress = false;
 
                 OPTPASS(qir_opt_algebraic);
+                OPTPASS(qir_opt_dead_code);
 
                 if (!progress)
                         break;
diff --git a/src/gallium/drivers/vc4/vc4_qir.h b/src/gallium/drivers/vc4/vc4_qir.h
index c0e0f85dede..c6c2a6476c4 100644
--- a/src/gallium/drivers/vc4/vc4_qir.h
+++ b/src/gallium/drivers/vc4/vc4_qir.h
@@ -147,6 +147,7 @@ void qir_emit(struct qcompile *c, struct qinst *inst);
 struct qreg qir_get_temp(struct qcompile *c);
 int qir_get_op_nsrc(enum qop qop);
 bool qir_reg_equals(struct qreg a, struct qreg b);
+bool qir_has_side_effects(struct qinst *inst);
 
 void qir_dump(struct qcompile *c);
 void qir_dump_inst(struct qinst *inst);
@@ -154,6 +155,7 @@ const char *qir_get_stage_name(enum qstage stage);
 
 void qir_optimize(struct qcompile *c);
 bool qir_opt_algebraic(struct qcompile *c);
+bool qir_opt_dead_code(struct qcompile *c);
 
 #define QIR_ALU1(name)                                                   \
 static inline struct qreg                                                \