src/compiler/glsl/ir_variable_refcount.cpp

/*
 * 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_variable_refcount.cpp
 *
 * Provides a visitor which produces a list of variables referenced,
 * how many times they were referenced and assigned, and whether they
 * were defined in the scope.
 */

#include "ir.h"
#include "ir_visitor.h"
#include "ir_variable_refcount.h"
#include "compiler/glsl_types.h"
#include "util/hash_table.h"

ir_variable_refcount_visitor::ir_variable_refcount_visitor()
{
   this->mem_ctx = ralloc_context(NULL);
   this->ht = _mesa_pointer_hash_table_create(NULL);
}

static void
free_entry(struct hash_entry *entry)
{
   ir_variable_refcount_entry *ivre = (ir_variable_refcount_entry *) entry->data;

   /* Free assignment list */
   exec_node *n;
   while ((n = ivre->assign_list.pop_head()) != NULL) {
      struct assignment_entry *assignment_entry =
         exec_node_data(struct assignment_entry, n, link);
      free(assignment_entry);
   }

   delete ivre;
}

ir_variable_refcount_visitor::~ir_variable_refcount_visitor()
{
   ralloc_free(this->mem_ctx);
   _mesa_hash_table_destroy(this->ht, free_entry);
}

// constructor
ir_variable_refcount_entry::ir_variable_refcount_entry(ir_variable *var)
{
   this->var = var;
   assigned_count = 0;
   declaration = false;
   referenced_count = 0;
}


ir_variable_refcount_entry *
ir_variable_refcount_visitor::get_variable_entry(ir_variable *var)
{
   assert(var);

   struct hash_entry *e = _mesa_hash_table_search(this->ht, var);
   if (e)
      return (ir_variable_refcount_entry *)e->data;

   ir_variable_refcount_entry *entry = new ir_variable_refcount_entry(var);
   assert(entry->referenced_count == 0);
   _mesa_hash_table_insert(this->ht, var, entry);

   return entry;
}


ir_visitor_status
ir_variable_refcount_visitor::visit(ir_variable *ir)
{
   ir_variable_refcount_entry *entry = this->get_variable_entry(ir);
   if (entry)
      entry->declaration = true;

   return visit_continue;
}


ir_visitor_status
ir_variable_refcount_visitor::visit(ir_dereference_variable *ir)
{
   ir_variable *const var = ir->variable_referenced();
   ir_variable_refcount_entry *entry = this->get_variable_entry(var);

   if (entry)
      entry->referenced_count++;

   return visit_continue;
}


ir_visitor_status
ir_variable_refcount_visitor::visit_enter(ir_function_signature *ir)
{
   /* We don't want to descend into the function parameters and
    * dead-code eliminate them, so just accept the body here.
    */
   visit_list_elements(this, &ir->body);
   return visit_continue_with_parent;
}


ir_visitor_status
ir_variable_refcount_visitor::visit_leave(ir_assignment *ir)
{
   ir_variable_refcount_entry *entry;
   entry = this->get_variable_entry(ir->lhs->variable_referenced());
   if (entry) {
      entry->assigned_count++;

      /* Build a list for dead code optimisation. Don't add assignment if it
       * was declared out of scope (outside the instruction stream). Also don't
       * bother adding any more to the list if there are more references than
       * assignments as this means the variable is used and won't be optimised
       * out.
       */
      assert(entry->referenced_count >= entry->assigned_count);
      if (entry->referenced_count == entry->assigned_count) {
         struct assignment_entry *assignment_entry =
            (struct assignment_entry *)calloc(1, sizeof(*assignment_entry));
         assignment_entry->assign = ir;
         entry->assign_list.push_head(&assignment_entry->link);
      }
   }

   return visit_continue;
}