ir_constant_variable: New pass to mark constant-assigned variables constant.

This removes a bunch of gratuitous moving around of constant values
from constructors.  Makes a shader ir I was looking at for structure
handling almost readable.

1 files changed, 165 insertions, 0 deletions

diff --git a/ir_constant_variable.cpp b/ir_constant_variable.cpp
new file mode 100644
index 0000000000..75590dfdbf
--- /dev/null
+++ b/ir_constant_variable.cpp
@@ -0,0 +1,165 @@
+/*
+ * Copyright © 2010 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.
+ */
+
+/**
+ * \file ir_constant_variable.cpp
+ *
+ * Marks variables assigned a single constant value over the course
+ * of the program as constant.
+ *
+ * The goal here is to trigger further constant folding and then dead
+ * code elimination.  This is common with vector/matrix constructors
+ * and calls to builtin functions.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "ir.h"
+#include "ir_print_visitor.h"
+#include "ir_visitor.h"
+#include "ir_optimization.h"
+#include "glsl_types.h"
+#include "linux_list.h"
+
+struct assignment_entry {
+   struct list link;
+   int assignment_count;
+   ir_variable *var;
+   ir_constant *constval;
+};
+
+class ir_constant_variable_visitor : public ir_hierarchical_visitor {
+public:
+   ir_constant_variable_visitor()
+   {
+      list_init(&list);
+   }
+
+   virtual ir_visitor_status visit_enter(ir_assignment *);
+
+   struct list list;
+};
+
+static struct assignment_entry *
+get_assignment_entry(ir_variable *var, struct list *list)
+{
+   struct assignment_entry *entry;
+
+   list_foreach_entry(entry, struct assignment_entry, list, link) {
+      if (entry->var == var)
+	 return entry;
+   }
+
+   entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
+   entry->var = var;
+   list_add(&entry->link, list);
+   return entry;
+}
+
+ir_visitor_status
+ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
+{
+   ir_constant *constval;
+   struct assignment_entry *entry;
+
+   entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
+   assert(entry);
+   entry->assignment_count++;
+
+   /* If it's already constant, don't do the work. */
+   if (entry->var->constant_value)
+      return visit_continue;
+
+   /* OK, now find if we actually have all the right conditions for
+    * this to be a constant value assigned to the var.
+    */
+   if (ir->condition) {
+      constval = ir->condition->constant_expression_value();
+      if (!constval || !constval->value.b[0])
+	 return visit_continue;
+   }
+
+   ir_variable *var = ir->lhs->whole_variable_referenced();
+   if (!var)
+      return visit_continue;
+
+   constval = ir->rhs->constant_expression_value();
+   if (!constval)
+      return visit_continue;
+
+   /* Mark this entry as having a constant assignment (if the
+    * assignment count doesn't go >1).  do_constant_variable will fix
+    * up the variable with the constant value later.
+    */
+   entry->constval = constval;
+
+   return visit_continue;
+}
+
+/**
+ * Does a copy propagation pass on the code present in the instruction stream.
+ */
+bool
+do_constant_variable(exec_list *instructions)
+{
+   bool progress = false;
+   ir_constant_variable_visitor v;
+
+   v.run(instructions);
+
+   while (!list_is_empty(&v.list)) {
+
+      struct assignment_entry *entry;
+      entry = list_entry(v.list.next, struct assignment_entry, link);
+
+      if (entry->assignment_count == 1 && entry->constval) {
+	 entry->var->constant_value = entry->constval;
+	 progress = true;
+      }
+      list_del(&entry->link);
+      free(entry);
+   }
+
+   return progress;
+}
+
+bool
+do_constant_variable_unlinked(exec_list *instructions)
+{
+   bool progress = false;
+
+   foreach_iter(exec_list_iterator, iter, *instructions) {
+      ir_instruction *ir = (ir_instruction *)iter.get();
+      ir_function *f = ir->as_function();
+      if (f) {
+	 foreach_iter(exec_list_iterator, sigiter, *f) {
+	    ir_function_signature *sig =
+	       (ir_function_signature *) sigiter.get();
+	    if (do_constant_variable(&sig->body))
+	       progress = true;
+	 }
+      }
+   }
+
+   return progress;
+}