ir_copy_propagation: New pass to rewrite dereferences to avoid copies.

This is pretty basic.  Right now it only handles pure assignments --
same type on each side, no swizzling, and only within basic blocks.

1 files changed, 313 insertions, 0 deletions

diff --git a/ir_copy_propagation.cpp b/ir_copy_propagation.cpp
new file mode 100644
index 0000000..8eb1ebd
--- /dev/null
+++ b/ir_copy_propagation.cpp
@@ -0,0 +1,313 @@
+/*
+ * 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_dead_code.cpp
+ *
+ * Eliminates dead assignments and variable declarations from the code.
+ */
+
+#include <stdio.h>
+#include "ir.h"
+#include "ir_visitor.h"
+#include "ir_basic_block.h"
+#include "ir_copy_propagation.h"
+#include "glsl_types.h"
+
+class acp_entry : public exec_node
+{
+public:
+   acp_entry(ir_variable *lhs, ir_variable *rhs)
+   {
+      assert(lhs);
+      assert(rhs);
+      this->lhs = lhs;
+      this->rhs = rhs;
+   }
+
+   ir_variable *lhs;
+   ir_variable *rhs;
+};
+
+class ir_copy_propagation_visitor : public ir_visitor {
+public:
+   ir_copy_propagation_visitor(exec_list *acp)
+   {
+      progress = false;
+      this->acp = acp;
+   }
+
+   /**
+    * \name Visit methods
+    *
+    * As typical for the visitor pattern, there must be one \c visit method for
+    * each concrete subclass of \c ir_instruction.  Virtual base classes within
+    * the hierarchy should not have \c visit methods.
+    */
+   /*@{*/
+   virtual void visit(ir_variable *);
+   virtual void visit(ir_loop *);
+   virtual void visit(ir_loop_jump *);
+   virtual void visit(ir_function_signature *);
+   virtual void visit(ir_function *);
+   virtual void visit(ir_expression *);
+   virtual void visit(ir_swizzle *);
+   virtual void visit(ir_dereference *);
+   virtual void visit(ir_assignment *);
+   virtual void visit(ir_constant *);
+   virtual void visit(ir_call *);
+   virtual void visit(ir_return *);
+   virtual void visit(ir_if *);
+   /*@}*/
+
+   /** List of acp_entry */
+   exec_list *acp;
+   bool progress;
+};
+
+
+void
+ir_copy_propagation_visitor::visit(ir_variable *ir)
+{
+   (void)ir;
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_loop *ir)
+{
+   (void)ir;
+}
+
+void
+ir_copy_propagation_visitor::visit(ir_loop_jump *ir)
+{
+   (void) ir;
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_function_signature *ir)
+{
+   (void)ir;
+}
+
+void
+ir_copy_propagation_visitor::visit(ir_function *ir)
+{
+   (void) ir;
+}
+
+void
+ir_copy_propagation_visitor::visit(ir_expression *ir)
+{
+   unsigned int operand;
+
+   for (operand = 0; operand < ir->get_num_operands(); operand++) {
+      ir->operands[operand]->accept(this);
+   }
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_swizzle *ir)
+{
+   ir->val->accept(this);
+}
+
+/**
+ * Replaces dereferences of ACP RHS variables with ACP LHS variables.
+ *
+ * This is where the actual copy propagation occurs.  Note that the
+ * rewriting of ir_dereference means that the ir_dereference instance
+ * must not be shared by multiple IR operations!
+ */
+void
+ir_copy_propagation_visitor::visit(ir_dereference *ir)
+{
+   ir_variable *var;
+
+   if (ir->mode == ir_dereference::ir_reference_array) {
+      ir->selector.array_index->accept(this);
+   }
+
+   var = ir->var->as_variable();
+   if (var) {
+      foreach_iter(exec_list_iterator, iter, *this->acp) {
+	 acp_entry *entry = (acp_entry *)iter.get();
+
+	 if (var == entry->lhs) {
+	    ir->var = entry->rhs;
+	    this->progress = true;
+	    break;
+	 }
+      }
+   } else {
+      ir->var->accept(this);
+   }
+}
+
+void
+ir_copy_propagation_visitor::visit(ir_assignment *ir)
+{
+   if (ir->condition)
+      ir->condition->accept(this);
+
+   /* Ignores the LHS.  Don't want to rewrite the LHS to point at some
+    * other storage!
+    */
+
+   ir->rhs->accept(this);
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_constant *ir)
+{
+   (void) ir;
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_call *ir)
+{
+   (void)ir;
+
+   /* Note, if we were to do copy propagation to parameters of calls, we'd
+    * have to be careful about out params.
+    */
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_return *ir)
+{
+   ir_rvalue *val = ir->get_value();
+
+   if (val)
+      val->accept(this);
+}
+
+
+void
+ir_copy_propagation_visitor::visit(ir_if *ir)
+{
+   ir->condition->accept(this);
+}
+
+static void
+propagate_copies(ir_instruction *ir, exec_list *acp)
+{
+   ir_copy_propagation_visitor v(acp);
+
+   ir->accept(&v);
+}
+
+static void
+kill_invalidated_copies(ir_assignment *ir, exec_list *acp)
+{
+   ir_dereference *lhs_deref = ir->lhs->as_dereference();
+
+   /* Only handle simple dereferences for now. */
+   if (lhs_deref &&
+       lhs_deref->mode == ir_dereference::ir_reference_variable) {
+      ir_variable *var = lhs_deref->var->as_variable();
+
+      foreach_iter(exec_list_iterator, iter, *acp) {
+	 acp_entry *entry = (acp_entry *)iter.get();
+
+	 if (entry->lhs == var || entry->rhs == var) {
+	    entry->remove();
+	 }
+      }
+   } else {
+      /* FINISHME: Only clear out the entries we overwrote here. */
+      acp->make_empty();
+   }
+}
+
+/**
+ * Adds an entry to the available copy list if it's a plain assignment
+ * of a variable to a variable.
+ */
+static void
+add_copy(ir_assignment *ir, exec_list *acp)
+{
+   acp_entry *entry;
+
+   if (ir->condition) {
+      ir_constant *condition = ir->condition->as_constant();
+      if (!condition || !condition->value.b[0])
+	 return;
+   }
+
+   ir_dereference *lhs_deref = ir->lhs->as_dereference();
+   if (!lhs_deref || lhs_deref->mode != ir_dereference::ir_reference_variable)
+      return;
+   ir_variable *lhs_var = lhs_deref->var->as_variable();
+
+   ir_dereference *rhs_deref = ir->rhs->as_dereference();
+   if (!rhs_deref || rhs_deref->mode != ir_dereference::ir_reference_variable)
+      return;
+   ir_variable *rhs_var = rhs_deref->var->as_variable();
+
+   entry = new acp_entry(lhs_var, rhs_var);
+   acp->push_tail(entry);
+}
+
+static void
+copy_propagation_basic_block(ir_instruction *first,
+			     ir_instruction *last)
+{
+   ir_instruction *ir;
+   /* List of avaialble_copy */
+   exec_list acp;
+
+   for (ir = first;; ir = (ir_instruction *)ir->next) {
+      ir_assignment *ir_assign = ir->as_assignment();
+
+      propagate_copies(ir, &acp);
+
+      if (ir_assign) {
+	 kill_invalidated_copies(ir_assign, &acp);
+
+	 add_copy(ir_assign, &acp);
+      }
+      if (ir == last)
+	 break;
+   }
+}
+
+/**
+ * Does a copy propagation pass on the code present in the instruction stream.
+ */
+bool
+do_copy_propagation(exec_list *instructions)
+{
+   bool progress = false;
+
+   call_for_basic_blocks(instructions, copy_propagation_basic_block);
+
+   /* FINISHME: Return a legit progress value. */
+   return progress;
+}