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/*

 * 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 opt_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 "ir.h"

#include "ir_visitor.h"

#include "ir_optimization.h"

#include "glsl_types.h"

namespace {

struct assignment_entry {

   exec_node link;

   int assignment_count;

   ir_variable *var;

   ir_constant *constval;

   bool our_scope;

};

class ir_constant_variable_visitor : public ir_hierarchical_visitor {

public:

   virtual ir_visitor_status visit_enter(ir_dereference_variable *);

   virtual ir_visitor_status visit(ir_variable *);

   virtual ir_visitor_status visit_enter(ir_assignment *);

   virtual ir_visitor_status visit_enter(ir_call *);

   exec_list list;

};

} /* unnamed namespace */

static struct assignment_entry *

get_assignment_entry(ir_variable *var, exec_list *list)

{

   struct assignment_entry *entry;

   foreach_list_typed(struct assignment_entry, entry, link, list) {

      if (entry->var == var)

	 return entry;

   }

   entry = (struct assignment_entry *)calloc(1, sizeof(*entry));

   entry->var = var;

   list->push_head(&entry->link);

   return entry;

}

ir_visitor_status

ir_constant_variable_visitor::visit(ir_variable *ir)

{

   struct assignment_entry *entry = get_assignment_entry(ir, &this->list);

   entry->our_scope = true;

   return visit_continue;

}

/* Skip derefs of variables so that we can detect declarations. */

ir_visitor_status

ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)

{

   (void)ir;

   return visit_continue_with_parent;

}

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)

      return visit_continue;

   ir_variable *var = ir->whole_variable_written();

   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;

}

ir_visitor_status

ir_constant_variable_visitor::visit_enter(ir_call *ir)

{

   /* Mark any out parameters as assigned to */

   exec_list_iterator sig_iter = ir->callee->parameters.iterator();

   foreach_iter(exec_list_iterator, iter, *ir) {

      ir_rvalue *param_rval = (ir_rvalue *)iter.get();

      ir_variable *param = (ir_variable *)sig_iter.get();

      if (param->mode == ir_var_function_out ||

	  param->mode == ir_var_function_inout) {

	 ir_variable *var = param_rval->variable_referenced();

	 struct assignment_entry *entry;

	 assert(var);

	 entry = get_assignment_entry(var, &this->list);

	 entry->assignment_count++;

      }

      sig_iter.next();

   }

   /* Mark the return storage as having been assigned to */

   if (ir->return_deref != NULL) {

      ir_variable *var = ir->return_deref->variable_referenced();

      struct assignment_entry *entry;

      assert(var);

      entry = get_assignment_entry(var, &this->list);

      entry->assignment_count++;

   }

   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 (!v.list.is_empty()) {

      struct assignment_entry *entry;

      entry = exec_node_data(struct assignment_entry, v.list.head, link);

      if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {

	 entry->var->constant_value = entry->constval;

	 progress = true;

      }

      entry->link.remove();

      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;

}