Subversion Repositories Kolibri OS

/*

 * 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.

 */

#include 

#include "main/compiler.h"

#include "glsl_types.h"

#include "loop_analysis.h"

#include "ir_hierarchical_visitor.h"

/**

 * Find an initializer of a variable outside a loop

 *

 * Works backwards from the loop to find the pre-loop value of the variable.

 * This is used, for example, to find the initial value of loop induction

 * variables.

 *

 * \param loop  Loop where \c var is an induction variable

 * \param var   Variable whose initializer is to be found

 *

 * \return

 * The \c ir_rvalue assigned to the variable outside the loop.  May return

 * \c NULL if no initializer can be found.

 */

ir_rvalue *

find_initial_value(ir_loop *loop, ir_variable *var)

{

   for (exec_node *node = loop->prev;

	!node->is_head_sentinel();

	node = node->prev) {

      ir_instruction *ir = (ir_instruction *) node;

      switch (ir->ir_type) {

      case ir_type_call:

      case ir_type_loop:

      case ir_type_loop_jump:

      case ir_type_return:

      case ir_type_if:

	 return NULL;

      case ir_type_function:

      case ir_type_function_signature:

	 assert(!"Should not get here.");

	 return NULL;

      case ir_type_assignment: {

	 ir_assignment *assign = ir->as_assignment();

	 ir_variable *assignee = assign->lhs->whole_variable_referenced();

	 if (assignee == var)

	    return (assign->condition != NULL) ? NULL : assign->rhs;

	 break;

      }

      default:

	 break;

      }

   }

   return NULL;

}

int

calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,

		     enum ir_expression_operation op)

{

   if (from == NULL || to == NULL || increment == NULL)

      return -1;

   void *mem_ctx = ralloc_context(NULL);

   ir_expression *const sub =

      new(mem_ctx) ir_expression(ir_binop_sub, from->type, to, from);

   ir_expression *const div =

      new(mem_ctx) ir_expression(ir_binop_div, sub->type, sub, increment);

   ir_constant *iter = div->constant_expression_value();

   if (iter == NULL)

      return -1;

   if (!iter->type->is_integer()) {

      ir_rvalue *cast =

	 new(mem_ctx) ir_expression(ir_unop_f2i, glsl_type::int_type, iter,

				    NULL);

      iter = cast->constant_expression_value();

   }

   int iter_value = iter->get_int_component(0);

   /* Make sure that the calculated number of iterations satisfies the exit

    * condition.  This is needed to catch off-by-one errors and some types of

    * ill-formed loops.  For example, we need to detect that the following

    * loop does not have a maximum iteration count.

    *

    *    for (float x = 0.0; x != 0.9; x += 0.2)

    *        ;

    */

   const int bias[] = { -1, 0, 1 };

   bool valid_loop = false;

   for (unsigned i = 0; i < Elements(bias); i++) {

      iter = (increment->type->is_integer())

	 ? new(mem_ctx) ir_constant(iter_value + bias[i])

	 : new(mem_ctx) ir_constant(float(iter_value + bias[i]));

      ir_expression *const mul =

	 new(mem_ctx) ir_expression(ir_binop_mul, increment->type, iter,

				    increment);

      ir_expression *const add =

	 new(mem_ctx) ir_expression(ir_binop_add, mul->type, mul, from);

      ir_expression *const cmp =

	 new(mem_ctx) ir_expression(op, glsl_type::bool_type, add, to);

      ir_constant *const cmp_result = cmp->constant_expression_value();

      assert(cmp_result != NULL);

      if (cmp_result->get_bool_component(0)) {

	 iter_value += bias[i];

	 valid_loop = true;

	 break;

      }

   }

   ralloc_free(mem_ctx);

   return (valid_loop) ? iter_value : -1;

}

class loop_control_visitor : public ir_hierarchical_visitor {

public:

   loop_control_visitor(loop_state *state)

   {

      this->state = state;

      this->progress = false;

   }

   virtual ir_visitor_status visit_leave(ir_loop *ir);

   loop_state *state;

   bool progress;

};

ir_visitor_status

loop_control_visitor::visit_leave(ir_loop *ir)

{

   loop_variable_state *const ls = this->state->get(ir);

   /* If we've entered a loop that hasn't been analyzed, something really,

    * really bad has happened.

    */

   if (ls == NULL) {

      assert(ls != NULL);

      return visit_continue;

   }

   /* Search the loop terminating conditions for one of the form 'i < c' where

    * i is a loop induction variable, c is a constant, and < is any relative

    * operator.

    */

   int max_iterations = ls->max_iterations;

   if(ir->from && ir->to && ir->increment)

      max_iterations = calculate_iterations(ir->from, ir->to, ir->increment, (ir_expression_operation)ir->cmp);

   if(max_iterations < 0)

      max_iterations = INT_MAX;

   foreach_list(node, &ls->terminators) {

      loop_terminator *t = (loop_terminator *) node;

      ir_if *if_stmt = t->ir;

      /* If-statements can be either 'if (expr)' or 'if (deref)'.  We only care

       * about the former here.

       */

      ir_expression *cond = if_stmt->condition->as_expression();

      if (cond == NULL)

	 continue;

      switch (cond->operation) {

      case ir_binop_less:

      case ir_binop_greater:

      case ir_binop_lequal:

      case ir_binop_gequal: {

	 /* The expressions that we care about will either be of the form

	  * 'counter < limit' or 'limit < counter'.  Figure out which is

	  * which.

	  */

	 ir_rvalue *counter = cond->operands[0]->as_dereference_variable();

	 ir_constant *limit = cond->operands[1]->as_constant();

	 enum ir_expression_operation cmp = cond->operation;

	 if (limit == NULL) {

	    counter = cond->operands[1]->as_dereference_variable();

	    limit = cond->operands[0]->as_constant();

	    switch (cmp) {

	    case ir_binop_less:    cmp = ir_binop_greater; break;

	    case ir_binop_greater: cmp = ir_binop_less;    break;

	    case ir_binop_lequal:  cmp = ir_binop_gequal;  break;

	    case ir_binop_gequal:  cmp = ir_binop_lequal;  break;

	    default: assert(!"Should not get here.");

	    }

	 }

	 if ((counter == NULL) || (limit == NULL))

	    break;

	 ir_variable *var = counter->variable_referenced();

	 ir_rvalue *init = find_initial_value(ir, var);

	 foreach_list(iv_node, &ls->induction_variables) {

	    loop_variable *lv = (loop_variable *) iv_node;

	    if (lv->var == var) {

	       const int iterations = calculate_iterations(init, limit,

							   lv->increment,

							   cmp);

	       if (iterations >= 0) {

		  /* If the new iteration count is lower than the previously

		   * believed iteration count, update the loop control values.

		   */

		  if (iterations < max_iterations) {

		     ir->from = init->clone(ir, NULL);

		     ir->to = limit->clone(ir, NULL);

		     ir->increment = lv->increment->clone(ir, NULL);

		     ir->counter = lv->var;

		     ir->cmp = cmp;

		     max_iterations = iterations;

		  }

		  /* Remove the conditional break statement.  The loop

		   * controls are now set such that the exit condition will be

		   * satisfied.

		   */

		  if_stmt->remove();

		  assert(ls->num_loop_jumps > 0);

		  ls->num_loop_jumps--;

		  this->progress = true;

	       }

	       break;

	    }

	 }

	 break;

      }

      default:

	 break;

      }

   }

   /* If we have proven the one of the loop exit conditions is satisifed before

    * running the loop once, remove the loop.

    */

   if (max_iterations == 0)

      ir->remove();

   else

      ls->max_iterations = max_iterations;

   return visit_continue;

}

bool

set_loop_controls(exec_list *instructions, loop_state *ls)

{

   loop_control_visitor v(ls);

   v.run(instructions);

   return v.progress;

}