path: root/src/mesa/drivers/dri/i965/brw_cfg.cpp

/*
 * Copyright © 2012 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.
 *
 * Authors:
 *    Eric Anholt <eric@anholt.net>
 *
 */

#include "brw_cfg.h"

/** @file brw_cfg.cpp
 *
 * Walks the shader instructions generated and creates a set of basic
 * blocks with successor/predecessor edges connecting them.
 */

static bblock_t *
pop_stack(exec_list *list)
{
   bblock_link *link = (bblock_link *)list->get_tail();
   bblock_t *block = link->block;
   link->link.remove();

   return block;
}

static exec_node *
link(void *mem_ctx, bblock_t *block)
{
   bblock_link *l = new(mem_ctx) bblock_link(block);
   return &l->link;
}

bblock_t::bblock_t(cfg_t *cfg) :
   cfg(cfg), start_ip(0), end_ip(0), num(0),
   if_block(NULL), else_block(NULL)
{
   start = NULL;
   end = NULL;

   parents.make_empty();
   children.make_empty();
}

void
bblock_t::add_successor(void *mem_ctx, bblock_t *successor)
{
   successor->parents.push_tail(::link(mem_ctx, this));
   children.push_tail(::link(mem_ctx, successor));
}

bool
bblock_t::is_predecessor_of(const bblock_t *block) const
{
   foreach_list_typed_safe (bblock_link, parent, link, &block->parents) {
      if (parent->block == this) {
         return true;
      }
   }

   return false;
}

bool
bblock_t::is_successor_of(const bblock_t *block) const
{
   foreach_list_typed_safe (bblock_link, child, link, &block->children) {
      if (child->block == this) {
         return true;
      }
   }

   return false;
}

static bool
ends_block(const backend_instruction *inst)
{
   enum opcode op = inst->opcode;

   return op == BRW_OPCODE_IF ||
          op == BRW_OPCODE_ELSE ||
          op == BRW_OPCODE_CONTINUE ||
          op == BRW_OPCODE_BREAK ||
          op == BRW_OPCODE_WHILE;
}

static bool
starts_block(const backend_instruction *inst)
{
   enum opcode op = inst->opcode;

   return op == BRW_OPCODE_DO ||
          op == BRW_OPCODE_ENDIF;
}

bool
bblock_t::can_combine_with(const bblock_t *that) const
{
   if ((const bblock_t *)this->link.next != that)
      return false;

   if (ends_block(this->end) ||
       starts_block(that->start))
      return false;

   return true;
}

void
bblock_t::combine_with(bblock_t *that)
{
   assert(this->can_combine_with(that));
   foreach_list_typed (bblock_link, link, link, &this->children) {
      assert(link->block == that);
   }
   foreach_list_typed (bblock_link, link, link, &that->parents) {
      assert(link->block == this);
   }

   this->end_ip = that->end_ip;
   this->end = that->end;
   this->else_block = that->else_block;

   this->cfg->remove_block(that);
}

void
bblock_t::dump(backend_visitor *v) const
{
   int ip = this->start_ip;
   for (backend_instruction *inst = (backend_instruction *)this->start;
	inst != this->end->next;
	inst = (backend_instruction *) inst->next) {
      fprintf(stderr, "%5d: ", ip);
      v->dump_instruction(inst);
      ip++;
   }
}

cfg_t::cfg_t(exec_list *instructions)
{
   mem_ctx = ralloc_context(NULL);
   block_list.make_empty();
   blocks = NULL;
   num_blocks = 0;

   bblock_t *cur = NULL;
   int ip = 0;

   bblock_t *entry = new_block();
   bblock_t *cur_if = NULL;    /**< BB ending with IF. */
   bblock_t *cur_else = NULL;  /**< BB ending with ELSE. */
   bblock_t *cur_endif = NULL; /**< BB starting with ENDIF. */
   bblock_t *cur_do = NULL;    /**< BB starting with DO. */
   bblock_t *cur_while = NULL; /**< BB immediately following WHILE. */
   exec_list if_stack, else_stack, do_stack, while_stack;
   bblock_t *next;

   set_next_block(&cur, entry, ip);

   entry->start = (backend_instruction *) instructions->get_head();

   foreach_in_list(backend_instruction, inst, instructions) {
      cur->end = inst;

      /* set_next_block wants the post-incremented ip */
      ip++;

      switch (inst->opcode) {
      case BRW_OPCODE_IF:
	 /* Push our information onto a stack so we can recover from
	  * nested ifs.
	  */
	 if_stack.push_tail(link(mem_ctx, cur_if));
	 else_stack.push_tail(link(mem_ctx, cur_else));

	 cur_if = cur;
	 cur_else = NULL;
         cur_endif = NULL;

	 /* Set up our immediately following block, full of "then"
	  * instructions.
	  */
	 next = new_block();
	 next->start = (backend_instruction *)inst->next;
	 cur_if->add_successor(mem_ctx, next);

	 set_next_block(&cur, next, ip);
	 break;

      case BRW_OPCODE_ELSE:
         cur_else = cur;

	 next = new_block();
	 next->start = (backend_instruction *)inst->next;
	 cur_if->add_successor(mem_ctx, next);

	 set_next_block(&cur, next, ip);
	 break;

      case BRW_OPCODE_ENDIF: {
         if (cur->start == inst) {
            /* New block was just created; use it. */
            cur_endif = cur;
         } else {
            cur_endif = new_block();
            cur_endif->start = inst;

            cur->end = (backend_instruction *)inst->prev;
            cur->add_successor(mem_ctx, cur_endif);

            set_next_block(&cur, cur_endif, ip - 1);
         }

         if (cur_else) {
            cur_else->add_successor(mem_ctx, cur_endif);
         } else {
            cur_if->add_successor(mem_ctx, cur_endif);
         }

         assert(cur_if->end->opcode == BRW_OPCODE_IF);
         assert(!cur_else || cur_else->end->opcode == BRW_OPCODE_ELSE);

         cur_if->if_block = cur_if;
         cur_if->else_block = cur_else;

	 if (cur_else) {
            cur_else->if_block = cur_if;
            cur_else->else_block = cur_else;
         }

         cur->if_block = cur_if;
         cur->else_block = cur_else;

	 /* Pop the stack so we're in the previous if/else/endif */
	 cur_if = pop_stack(&if_stack);
	 cur_else = pop_stack(&else_stack);
	 break;
      }
      case BRW_OPCODE_DO:
	 /* Push our information onto a stack so we can recover from
	  * nested loops.
	  */
	 do_stack.push_tail(link(mem_ctx, cur_do));
	 while_stack.push_tail(link(mem_ctx, cur_while));

	 /* Set up the block just after the while.  Don't know when exactly
	  * it will start, yet.
	  */
	 cur_while = new_block();

         if (cur->start == inst) {
            /* New block was just created; use it. */
            cur_do = cur;
         } else {
            cur_do = new_block();
            cur_do->start = inst;

            cur->end = (backend_instruction *)inst->prev;
            cur->add_successor(mem_ctx, cur_do);

            set_next_block(&cur, cur_do, ip - 1);
         }
	 break;

      case BRW_OPCODE_CONTINUE:
	 cur->add_successor(mem_ctx, cur_do);

	 next = new_block();
	 next->start = (backend_instruction *)inst->next;
	 if (inst->predicate)
	    cur->add_successor(mem_ctx, next);

	 set_next_block(&cur, next, ip);
	 break;

      case BRW_OPCODE_BREAK:
	 cur->add_successor(mem_ctx, cur_while);

	 next = new_block();
	 next->start = (backend_instruction *)inst->next;
	 if (inst->predicate)
	    cur->add_successor(mem_ctx, next);

	 set_next_block(&cur, next, ip);
	 break;

      case BRW_OPCODE_WHILE:
	 cur_while->start = (backend_instruction *)inst->next;

	 cur->add_successor(mem_ctx, cur_do);
	 set_next_block(&cur, cur_while, ip);

	 /* Pop the stack so we're in the previous loop */
	 cur_do = pop_stack(&do_stack);
	 cur_while = pop_stack(&while_stack);
	 break;

      default:
	 break;
      }
   }

   assert(cur->end);

   cur->end_ip = ip;

   make_block_array();
}

cfg_t::~cfg_t()
{
   ralloc_free(mem_ctx);
}

void
cfg_t::remove_block(bblock_t *block)
{
   foreach_list_typed_safe (bblock_link, predecessor, link, &block->parents) {
      /* Remove block from all of its predecessors' successor lists. */
      foreach_list_typed_safe (bblock_link, successor, link,
                               &predecessor->block->children) {
         if (block == successor->block) {
            successor->link.remove();
            ralloc_free(successor);
         }
      }

      /* Add removed-block's successors to its predecessors' successor lists. */
      foreach_list_typed (bblock_link, successor, link, &block->children) {
         if (!successor->block->is_successor_of(predecessor->block)) {
            predecessor->block->children.push_tail(link(mem_ctx,
                                                        successor->block));
         }
      }
   }

   foreach_list_typed_safe (bblock_link, successor, link, &block->children) {
      /* Remove block from all of its childrens' parents lists. */
      foreach_list_typed_safe (bblock_link, predecessor, link,
                               &successor->block->parents) {
         if (block == predecessor->block) {
            predecessor->link.remove();
            ralloc_free(predecessor);
         }
      }

      /* Add removed-block's predecessors to its successors' predecessor lists. */
      foreach_list_typed (bblock_link, predecessor, link, &block->parents) {
         if (!predecessor->block->is_predecessor_of(successor->block)) {
            successor->block->parents.push_tail(link(mem_ctx,
                                                     predecessor->block));
         }
      }
   }

   block->link.remove();

   for (int b = block->num; b < this->num_blocks - 1; b++) {
      this->blocks[b] = this->blocks[b + 1];
      this->blocks[b]->num = b;
   }

   this->blocks[this->num_blocks - 1]->num = this->num_blocks - 2;
   this->num_blocks--;
}

bblock_t *
cfg_t::new_block()
{
   bblock_t *block = new(mem_ctx) bblock_t(this);

   return block;
}

void
cfg_t::set_next_block(bblock_t **cur, bblock_t *block, int ip)
{
   if (*cur) {
      assert((*cur)->end->next == block->start);
      (*cur)->end_ip = ip - 1;
   }

   block->start_ip = ip;
   block->num = num_blocks++;
   block_list.push_tail(&block->link);
   *cur = block;
}

void
cfg_t::make_block_array()
{
   blocks = ralloc_array(mem_ctx, bblock_t *, num_blocks);

   int i = 0;
   foreach_block (block, this) {
      blocks[i++] = block;
   }
   assert(i == num_blocks);
}

void
cfg_t::dump(backend_visitor *v) const
{
   foreach_block (block, this) {
      fprintf(stderr, "START B%d", block->num);
      foreach_list_typed(bblock_link, link, link, &block->parents) {
         fprintf(stderr, " <-B%d",
                 link->block->num);
      }
      fprintf(stderr, "\n");
      block->dump(v);
      fprintf(stderr, "END B%d", block->num);
      foreach_list_typed(bblock_link, link, link, &block->children) {
         fprintf(stderr, " ->B%d",
                 link->block->num);
      }
      fprintf(stderr, "\n");
   }
}