/src/php-src/ext/opcache/jit/ir/ir_cfg.c

Source
/*
 * IR - Lightweight JIT Compilation Framework
 * (CFG - Control Flow Graph)
 * Copyright (C) 2022 Zend by Perforce.
 * Authors: Dmitry Stogov <dmitry@php.net>
 */

#include "ir.h"
#include "ir_private.h"

static int ir_remove_unreachable_blocks(ir_ctx *ctx);

IR_ALWAYS_INLINE void _ir_add_successors(const ir_ctx *ctx, ir_ref ref, ir_worklist *worklist)
{
  ir_use_list *use_list = &ctx->use_lists[ref];
  ir_ref *p, use, n = use_list->count;

  if (n < 2) {
    if (n == 1) {
      use = ctx->use_edges[use_list->refs];
      IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
      ir_worklist_push(worklist, use);
    }
  } else {
    p = &ctx->use_edges[use_list->refs];
    if (n == 2) {
      use = *p;
      IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
      ir_worklist_push(worklist, use);
      use = *(p + 1);
      IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
      ir_worklist_push(worklist, use);
    } else {
      for (; n > 0; p++, n--) {
        use = *p;
        IR_ASSERT(ir_op_flags[ctx->ir_base[use].op] & IR_OP_FLAG_CONTROL);
        ir_worklist_push(worklist, use);
      }
    }
  }
}

IR_ALWAYS_INLINE void _ir_add_predecessors(const ir_insn *insn, ir_worklist *worklist)
{
  ir_ref n, ref;
  const ir_ref *p;

  if (insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN) {
    n = insn->inputs_count;
    for (p = insn->ops + 1; n > 0; p++, n--) {
      ref = *p;
      IR_ASSERT(ref);
      ir_worklist_push(worklist, ref);
    }
  } else if (insn->op != IR_START) {
    if (EXPECTED(insn->op1)) {
      ir_worklist_push(worklist, insn->op1);
    }
  }
}

void ir_reset_cfg(ir_ctx *ctx)
{
  ctx->cfg_blocks_count = 0;
  ctx->cfg_edges_count = 0;
  if (ctx->cfg_blocks) {
    ir_mem_free(ctx->cfg_blocks);
    ctx->cfg_blocks = NULL;
    if (ctx->cfg_edges) {
      ir_mem_free(ctx->cfg_edges);
      ctx->cfg_edges = NULL;
    }
    if (ctx->cfg_map) {
      ir_mem_free(ctx->cfg_map);
      ctx->cfg_map = NULL;
    }
  }
}

static void ir_remove_phis_inputs(ir_ctx *ctx, ir_use_list *use_list, int new_inputs_count, ir_bitset life_inputs)
{
  ir_ref i, j, n, k, *p, *q, use;
  ir_insn *use_insn;

  if (new_inputs_count == 1) {
    for (k = use_list->count, p = q = &ctx->use_edges[use_list->refs]; k > 0; p++, k--) {
      use = *p;
      use_insn = &ctx->ir_base[use];
      if (use_insn->op == IR_PHI) {
        /* Convert PHI to COPY */
        n = use_insn->inputs_count;
        i = 2;
        for (j = 2; j <= n; j++) {
          ir_ref input = ir_insn_op(use_insn, j);

          if (ir_bitset_in(life_inputs, j - 1)) {
            use_insn->op1 = ir_insn_op(use_insn, j);
          } else if (input > 0) {
            ir_use_list_remove_one(ctx, input, use);
          }
        }
        use_insn->op = IR_COPY;
        use_insn->inputs_count = 1;
        for (j = 2; j <= n; j++) {
          ir_insn_set_op(use_insn, j, IR_UNUSED);
        }
        continue;
      }

      /*compact use list */
      if (p != q){
        *q = use;
      }
      q++;
    }

    if (p != q) {
      use_list->count -= (p - q);
      do {
        *q = IR_UNUSED; /* clenu-op the removed tail */
        q++;
      } while (p != q);
    }
  } else {
    for (k = use_list->count, p = &ctx->use_edges[use_list->refs]; k > 0; p++, k--) {
      use = *p;
      use_insn = &ctx->ir_base[use];
      if (use_insn->op == IR_PHI) {
        n = use_insn->inputs_count;
        i = 2;
        for (j = 2; j <= n; j++) {
          ir_ref input = ir_insn_op(use_insn, j);

          if (ir_bitset_in(life_inputs, j - 1)) {
            IR_ASSERT(input);
            if (i != j) {
              ir_insn_set_op(use_insn, i, input);
            }
            i++;
          } else if (input > 0) {
            ir_use_list_remove_one(ctx, input, use);
          }
        }
        use_insn->inputs_count = i - 1;
        for (j = i; j <= n; j++) {
          ir_insn_set_op(use_insn, j, IR_UNUSED);
        }
      }
    }
  }
}

static uint32_t IR_NEVER_INLINE ir_cfg_remove_dead_inputs(ir_ctx *ctx, uint32_t *_blocks, ir_block *blocks, uint32_t bb_count)
{
  uint32_t b, count = 0;
  ir_block *bb = blocks + 1;
  ir_insn *insn;
  ir_ref i, j, n, *ops, input;
  ir_bitset life_inputs = NULL;

  for (b = 1; b <= bb_count; b++, bb++) {
    bb->successors = count;
    count += ctx->use_lists[bb->end].count;
    bb->successors_count = 0;
    bb->predecessors = count;
    insn = &ctx->ir_base[bb->start];
    if (insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN) {
      n = insn->inputs_count;
      ops = insn->ops;
      for (i = 1, j = 1; i <= n; i++) {
        input = ops[i];
        if (_blocks[input]) {
          if (life_inputs) {
            ir_bitset_incl(life_inputs, i);
          }
          if (i != j) {
            ops[j] = ops[i];
          }
          j++;
        } else {
          if (ctx->use_lists[bb->start].count > 1) {
            /* Some inputs of this MERGE are deleted and we have to update the depended PHIs */
            if (!life_inputs) {
              int k;
              life_inputs = ir_bitset_malloc(n + 1);
              for (k = 1; k < i; k++) {
                ir_bitset_incl(life_inputs, k);
              }
            }
          }
          if (input > 0) {
            ir_use_list_remove_one(ctx, input, bb->start);
          }
        }
      }
      j--;
      if (j != n) {
        if (j == 1) {
          insn->op = IR_BEGIN;
        }
        insn->inputs_count = j;
        bb->predecessors_count = j;
        j++;
        for (;j <= n; j++) {
          ops[j] = IR_UNUSED;
        }
        if (life_inputs) {
          ir_remove_phis_inputs(ctx, &ctx->use_lists[bb->start], insn->inputs_count, life_inputs);
          ir_mem_free(life_inputs);
        }
      }
    }
    count += bb->predecessors_count;
  }
  return count;
}

int ir_build_cfg(ir_ctx *ctx)
{
  ir_ref n, *p, ref, start, end;
  uint32_t b;
  ir_insn *insn;
  ir_worklist worklist;
  uint32_t bb_init_falgs;
  uint32_t count, bb_count = 0;
  uint32_t edges_count = 0;
  ir_block *blocks, *bb;
  uint32_t *_blocks, *edges;
  ir_use_list *use_list;
  uint32_t len = ir_bitset_len(ctx->insns_count);
  ir_bitset bb_starts = ir_mem_calloc(len * 2, IR_BITSET_BITS / 8);
  ir_bitset bb_leaks = bb_starts + len;
  _blocks = ir_mem_calloc(ctx->insns_limit, sizeof(uint32_t));
  ir_worklist_init(&worklist, ctx->insns_count);

  /* First try to perform backward DFS search starting from "stop" nodes */

  /* Add all "stop" nodes */
  ref = ctx->ir_base[1].op1;
  while (ref) {
    ir_worklist_push(&worklist, ref);
    ref = ctx->ir_base[ref].op3;
  }

  while (ir_worklist_len(&worklist)) {
    ref = ir_worklist_pop(&worklist);
    insn = &ctx->ir_base[ref];

    if (insn->op == IR_NOP) {
      continue;
    }
    IR_ASSERT(IR_IS_BB_END(insn->op));
    /* Remember BB end */
    end = ref;
    /* Some successors of IF and SWITCH nodes may be inaccessible by backward DFS */
    use_list = &ctx->use_lists[end];
    n = use_list->count;
    if (n > 1 || (n == 1 && (ir_op_flags[insn->op] & IR_OP_FLAG_TERMINATOR) != 0)) {
      for (p = &ctx->use_edges[use_list->refs]; n > 0; p++, n--) {
        /* Remember possible inaccessible successors */
        ir_bitset_incl(bb_leaks, *p);
      }
    }
    /* Skip control nodes untill BB start */
    ref = insn->op1;
    while (1) {
      insn = &ctx->ir_base[ref];
      if (IR_IS_BB_START(insn->op)) {
        break;
      }
      ref = insn->op1; // follow connected control blocks untill BB start
    }
    /* Mark BB Start */
    bb_count++;
    _blocks[ref] = end;
    ir_bitset_incl(bb_starts, ref);
    /* Add predecessors */
    _ir_add_predecessors(insn, &worklist);
  }

  /* Backward DFS way miss some branches ending by infinite loops.  */
  /* Try forward DFS. (in most cases all nodes are already proceed). */

  /* START node may be inaccessible from "stop" nodes */
  ir_bitset_incl(bb_leaks, 1);

  /* Add not processed START and successor of IF and SWITCH */
  IR_BITSET_FOREACH_DIFFERENCE(bb_leaks, bb_starts, len, start) {
    ir_worklist_push(&worklist, start);
  } IR_BITSET_FOREACH_END();

  if (ir_worklist_len(&worklist)) {
    ir_bitset_union(worklist.visited, bb_starts, len);
    do {
      ref = ir_worklist_pop(&worklist);
      insn = &ctx->ir_base[ref];

      if (insn->op == IR_NOP) {
        continue;
      }
      IR_ASSERT(IR_IS_BB_START(insn->op));
      /* Remember BB start */
      start = ref;
      /* Skip control nodes untill BB end */
      while (1) {
        ref = ir_next_control(ctx, ref);
        insn = &ctx->ir_base[ref];
        if (IR_IS_BB_END(insn->op)) {
          break;
        }
      }
      /* Mark BB Start */
      bb_count++;
      _blocks[start] = ref;
      ir_bitset_incl(bb_starts, start);
      /* Add successors */
      _ir_add_successors(ctx, ref, &worklist);
    } while (ir_worklist_len(&worklist));
  }

  IR_ASSERT(bb_count > 0);

  /* Create array of basic blocks and count successor/predecessors edges for each BB */
  blocks = ir_mem_malloc((bb_count + 1) * sizeof(ir_block));
  b = 1;
  bb = blocks + 1;
  count = 0;
  /* SCCP already removed UNREACHABKE blocks, otherwise all blocks are marked as UNREACHABLE first */
  bb_init_falgs = (ctx->flags2 & IR_CFG_REACHABLE) ? 0 : IR_BB_UNREACHABLE;
  IR_BITSET_FOREACH(bb_starts, len, start) {
    insn = &ctx->ir_base[start];
    if (insn->op == IR_NOP) {
      _blocks[start] = 0;
      continue;
    }
    end = _blocks[start];
    _blocks[start] = b;
    _blocks[end] = b;
    IR_ASSERT(IR_IS_BB_START(insn->op));
    bb->start = start;
    bb->end = end;
    bb->successors = count;
    count += ctx->use_lists[end].count;
    bb->successors_count = 0;
    bb->predecessors = count;
    bb->dom_parent = 0;
    bb->dom_depth = 0;
    bb->dom_child = 0;
    bb->dom_next_child = 0;
    bb->loop_header = 0;
    bb->loop_depth = 0;
    if (insn->op == IR_START) {
      bb->flags = IR_BB_START;
      bb->predecessors_count = 0;
    } else {
      bb->flags = bb_init_falgs;
      if (insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN) {
        n = insn->inputs_count;
        bb->predecessors_count = n;
        edges_count += n;
        count += n;
      } else if (EXPECTED(insn->op1)) {
        if (insn->op == IR_ENTRY) {
          bb->flags |= IR_BB_ENTRY;
          ctx->entries_count++;
        }
        bb->predecessors_count = 1;
        edges_count++;
        count++;
      } else {
        IR_ASSERT(insn->op == IR_BEGIN); /* start of unreachable block */
        bb->predecessors_count = 0;
      }
    }
    b++;
    bb++;
  } IR_BITSET_FOREACH_END();
  bb_count = b - 1;
  if (UNEXPECTED(count != edges_count * 2)) {
    count = ir_cfg_remove_dead_inputs(ctx, _blocks, blocks, bb_count);
    IR_ASSERT(count != edges_count * 2);
  }
  ir_mem_free(bb_starts);

  /* Create an array of successor/predecessors control edges */
  edges = ir_mem_malloc(edges_count * 2 * sizeof(uint32_t));
  bb = blocks + 1;
  for (b = 1; b <= bb_count; b++, bb++) {
    insn = &ctx->ir_base[bb->start];
    if (bb->predecessors_count > 1) {
      uint32_t *q = edges + bb->predecessors;
      n = insn->inputs_count;
      for (p = insn->ops + 1; n > 0; p++, q++, n--) {
        ref = *p;
        IR_ASSERT(ref);
        ir_ref pred_b = _blocks[ref];
        ir_block *pred_bb = &blocks[pred_b];
        IR_ASSERT(pred_b > 0);
        *q = pred_b;
        edges[pred_bb->successors + pred_bb->successors_count++] = b;
      }
    } else if (bb->predecessors_count == 1) {
      ref = insn->op1;
      IR_ASSERT(ref);
      IR_ASSERT(IR_OPND_KIND(ir_op_flags[insn->op], 1) == IR_OPND_CONTROL);
      ir_ref pred_b = _blocks[ref];
      ir_block *pred_bb = &blocks[pred_b];
      edges[bb->predecessors] = pred_b;
      edges[pred_bb->successors + pred_bb->successors_count++] = b;
    }
  }

  ctx->cfg_blocks_count = bb_count;
  ctx->cfg_edges_count = edges_count * 2;
  ctx->cfg_blocks = blocks;
  ctx->cfg_edges = edges;
  ctx->cfg_map = _blocks;

  if (!(ctx->flags2 & IR_CFG_REACHABLE)) {
    uint32_t reachable_count = 0;

    /* Mark reachable blocks */
    ir_worklist_clear(&worklist);
    ir_worklist_push(&worklist, 1);
    while (ir_worklist_len(&worklist) != 0) {
      uint32_t *p;

      reachable_count++;
      b = ir_worklist_pop(&worklist);
      bb = &blocks[b];
      bb->flags &= ~IR_BB_UNREACHABLE;
      n = bb->successors_count;
      if (n > 1) {
        for (p = edges + bb->successors; n > 0; p++, n--) {
          ir_worklist_push(&worklist, *p);
        }
      } else if (n == 1) {
        ir_worklist_push(&worklist, edges[bb->successors]);
      }
    }
    if (reachable_count != ctx->cfg_blocks_count) {
      ir_remove_unreachable_blocks(ctx);
    }
  }

  ir_worklist_free(&worklist);

  return 1;
}

static void ir_remove_predecessor(ir_ctx *ctx, ir_block *bb, uint32_t from)
{
  uint32_t i, *p, *q, n = 0;

  p = q = &ctx->cfg_edges[bb->predecessors];
  for (i = 0; i < bb->predecessors_count; i++, p++) {
    if (*p != from) {
      if (p != q) {
        *q = *p;
      }
      q++;
      n++;
    }
  }
  IR_ASSERT(n != bb->predecessors_count);
  bb->predecessors_count = n;
}

static void ir_remove_merge_input(ir_ctx *ctx, ir_ref merge, ir_ref from)
{
  ir_ref i, j, n;
  ir_use_list *use_list;
  ir_bitset life_inputs;
  ir_insn *insn = &ctx->ir_base[merge];

  IR_ASSERT(insn->op == IR_MERGE || insn->op == IR_LOOP_BEGIN);
  n = insn->inputs_count;
  i = 1;
  life_inputs = ir_bitset_malloc(n + 1);
  for (j = 1; j <= n; j++) {
    ir_ref input = ir_insn_op(insn, j);

    if (input != from) {
      if (i != j) {
        ir_insn_set_op(insn, i, input);
      }
      ir_bitset_incl(life_inputs, j);
      i++;
    }
  }
  i--;
  for (j = i + 1; j <= n; j++) {
    ir_insn_set_op(insn, j, IR_UNUSED);
  }
  if (i == 1) {
    insn->op = IR_BEGIN;
  }
  insn->inputs_count = i;

  use_list = &ctx->use_lists[merge];
  if (use_list->count > 1) {
    ir_remove_phis_inputs(ctx, use_list, i, life_inputs);
  }

  ir_mem_free(life_inputs);
  ir_use_list_remove_all(ctx, from, merge);
}

/* CFG constructed after SCCP pass doesn't have unreachable BBs, otherwise they should be removed */
static int ir_remove_unreachable_blocks(ir_ctx *ctx)
{
  uint32_t b, *p, i;
  uint32_t unreachable_count = 0;
  uint32_t bb_count = ctx->cfg_blocks_count;
  ir_block *bb = ctx->cfg_blocks + 1;

  for (b = 1; b <= bb_count; b++, bb++) {
    if (bb->flags & IR_BB_UNREACHABLE) {
#if 0
      do {if (!unreachable_count) ir_dump_cfg(ctx, stderr);} while(0);
#endif
      if (bb->successors_count) {
        for (i = 0, p = &ctx->cfg_edges[bb->successors]; i < bb->successors_count; i++, p++) {
          ir_block *succ_bb = &ctx->cfg_blocks[*p];

          if (!(succ_bb->flags & IR_BB_UNREACHABLE)) {
            ir_remove_predecessor(ctx, succ_bb, b);
            ir_remove_merge_input(ctx, succ_bb->start, bb->end);
          }
        }
      } else {
        ir_ref prev, ref = bb->end;
        ir_insn *insn = &ctx->ir_base[ref];

        IR_ASSERT(ir_op_flags[insn->op] & IR_OP_FLAG_TERMINATOR);
        /* remove from terminators list */
        prev = ctx->ir_base[1].op1;
        if (prev == ref) {
          ctx->ir_base[1].op1 = insn->op3;
        } else {
          while (prev) {
            if (ctx->ir_base[prev].op3 == ref) {
              ctx->ir_base[prev].op3 = insn->op3;
              break;
            }
            prev = ctx->ir_base[prev].op3;
          }
        }
      }
      ctx->cfg_map[bb->start] = 0;
      ctx->cfg_map[bb->end] = 0;
      unreachable_count++;
    }
  }

  if (unreachable_count) {
    ir_block *dst_bb;
    uint32_t n = 1;
    uint32_t *edges;

    dst_bb = bb = ctx->cfg_blocks + 1;
    for (b = 1; b <= bb_count; b++, bb++) {
      if (!(bb->flags & IR_BB_UNREACHABLE)) {
        if (dst_bb != bb) {
          memcpy(dst_bb, bb, sizeof(ir_block));
          ctx->cfg_map[dst_bb->start] = n;
          ctx->cfg_map[dst_bb->end] = n;
        }
        dst_bb->successors_count = 0;
        dst_bb++;
        n++;
      }
    }
    ctx->cfg_blocks_count = bb_count = n - 1;

    /* Rebuild successor/predecessors control edges */
    edges = ctx->cfg_edges;
    bb = ctx->cfg_blocks + 1;
    for (b = 1; b <= bb_count; b++, bb++) {
      ir_insn *insn = &ctx->ir_base[bb->start];
      ir_ref *p, ref;

      n = bb->predecessors_count;
      if (n > 1) {
        uint32_t *q = edges + bb->predecessors;

        IR_ASSERT(n == insn->inputs_count);
        for (p = insn->ops + 1; n > 0; p++, q++, n--) {
          ref = *p;
          IR_ASSERT(ref);
          ir_ref pred_b = ctx->cfg_map[ref];
          ir_block *pred_bb = &ctx->cfg_blocks[pred_b];
          *q = pred_b;
          edges[pred_bb->successors + pred_bb->successors_count++] = b;
        }
      } else if (n == 1) {
        ref = insn->op1;
        IR_ASSERT(ref);
        IR_ASSERT(IR_OPND_KIND(ir_op_flags[insn->op], 1) == IR_OPND_CONTROL);
        ir_ref pred_b = ctx->cfg_map[ref];
        ir_block *pred_bb = &ctx->cfg_blocks[pred_b];
        edges[bb->predecessors] = pred_b;
        edges[pred_bb->successors + pred_bb->successors_count++] = b;
      }
    }
  }

  return 1;
}

static void compute_postnum(const ir_ctx *ctx, uint32_t *cur, uint32_t b)
{
  uint32_t i, *p;
  ir_block *bb = &ctx->cfg_blocks[b];

  if (bb->postnum != 0) {
    return;
  }

  if (bb->successors_count) {
    bb->postnum = -1; /* Marker for "currently visiting" */
    p = ctx->cfg_edges + bb->successors;
    i = bb->successors_count;
    do {
      compute_postnum(ctx, cur, *p);
      p++;
    } while (--i);
  }
  bb->postnum = (*cur)++;
}

/* Computes dominator tree using algorithm from "A Simple, Fast Dominance Algorithm" by
 * Cooper, Harvey and Kennedy. */
static IR_NEVER_INLINE int ir_build_dominators_tree_slow(ir_ctx *ctx)
{
  uint32_t blocks_count, b, postnum;
  ir_block *blocks, *bb;
  uint32_t *edges;
  bool changed;

  blocks = ctx->cfg_blocks;
  edges  = ctx->cfg_edges;
  blocks_count = ctx->cfg_blocks_count;

  /* Clear the dominators tree */
  for (b = 0, bb = &blocks[0]; b <= blocks_count; b++, bb++) {
    bb->idom = 0;
    bb->dom_depth = 0;
    bb->dom_child = 0;
    bb->dom_next_child = 0;
  }

  ctx->flags2 &= ~IR_NO_LOOPS;

  postnum = 1;
  compute_postnum(ctx, &postnum, 1);

  /* Find immediate dominators by iterative fixed-point algorithm */
  blocks[1].idom = 1;
  do {
    changed = 0;
    /* Iterating in Reverse Post Order */
    for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
      IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
      IR_ASSERT(bb->predecessors_count > 0);
      if (bb->predecessors_count == 1) {
        uint32_t pred_b = edges[bb->predecessors];

        if (blocks[pred_b].idom > 0 && bb->idom != pred_b) {
          bb->idom = pred_b;
          changed = 1;
        }
      } else if (bb->predecessors_count) {
        uint32_t idom = 0;
        uint32_t k = bb->predecessors_count;
        uint32_t *p = edges + bb->predecessors;

        do {
          uint32_t pred_b = *p;
          ir_block *pred_bb = &blocks[pred_b];
          ir_block *idom_bb;

          if (pred_bb->idom > 0) {
            idom = pred_b;
            idom_bb = &blocks[idom];

            while (--k > 0) {
              pred_b = *(++p);
              pred_bb = &blocks[pred_b];
              if (pred_bb->idom > 0) {
                while (idom != pred_b) {
                  while (pred_bb->postnum < idom_bb->postnum) {
                    pred_b = pred_bb->idom;
                    pred_bb = &blocks[pred_b];
                  }
                  while (idom_bb->postnum < pred_bb->postnum) {
                    idom = idom_bb->idom;
                    idom_bb = &blocks[idom];
                  }
                }
              }
            }

            if (bb->idom != idom) {
              bb->idom = idom;
              changed = 1;
            }
            break;
          }
          p++;
        } while (--k > 0);
      }
    }
  } while (changed);

  /* Build dominators tree */
  blocks[1].idom = 0;
  blocks[1].dom_depth = 0;

  /* Construct children lists sorted by block number */
  for (b = blocks_count, bb = &blocks[b]; b >= 2; b--, bb--) {
    ir_block *idom_bb = &blocks[bb->idom];
    bb->dom_depth = 0;
    bb->dom_next_child = idom_bb->dom_child;
    idom_bb->dom_child = b;
  }

  /* Recalculate dom_depth for all blocks */
  for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
    uint32_t idom = bb->idom;
    uint32_t dom_depth = 0;
    while (idom) {
      dom_depth++;
      if (blocks[idom].dom_depth > 0) {
        dom_depth += blocks[idom].dom_depth;
        break;
      } else {
        idom = blocks[idom].idom;
      }
    }
    bb->dom_depth = dom_depth;
  }

  return 1;
}

/* A single pass modification of "A Simple, Fast Dominance Algorithm" by
 * Cooper, Harvey and Kennedy, that relays on IR block ordering.
 * It may fallback to the general slow fixed-point algorithm.  */
static int ir_build_dominators_tree_iterative(ir_ctx *ctx);
int ir_build_dominators_tree(ir_ctx *ctx)
{
  uint32_t blocks_count, b;
  ir_block *blocks, *bb;
  uint32_t *edges;
  ir_list worklist;

  ir_list_init(&worklist, ctx->cfg_blocks_count / 2);

  ctx->flags2 |= IR_NO_LOOPS;

  /* Find immediate dominators */
  blocks = ctx->cfg_blocks;
  edges  = ctx->cfg_edges;
  blocks_count = ctx->cfg_blocks_count;
  blocks[1].idom = 1;
  blocks[1].dom_depth = 0;

  /* Iterating in Reverse Post Order */
  for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
    IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
    IR_ASSERT(bb->predecessors_count > 0);
    uint32_t k = bb->predecessors_count;
    uint32_t *p = edges + bb->predecessors;
    uint32_t idom = *p;
    ir_block *idom_bb;

    if (UNEXPECTED(idom >= b)) {
      /* In rare cases, LOOP_BEGIN.op1 may be a back-edge. Skip back-edges. */
      ctx->flags2 &= ~IR_NO_LOOPS;
//      IR_ASSERT(k > 1 && "Wrong blocks order: BB is before its single predecessor");
      if (UNEXPECTED(k <= 1)) {
slow_case:
        ir_list_free(&worklist);
        return ir_build_dominators_tree_slow(ctx);
      }
      ir_list_push(&worklist, idom);
      while (1) {
        k--;
        p++;
        idom = *p;
        if (idom < b) {
          break;
        }
        if (UNEXPECTED(k == 0)) {
          goto slow_case;
        }
        ir_list_push(&worklist, idom);
      }
    }
    IR_ASSERT(blocks[idom].idom > 0);
    IR_ASSERT(k != 0);

    while (--k > 0) {
      uint32_t pred_b = *(++p);

      if (pred_b < b) {
        IR_ASSERT(blocks[pred_b].idom > 0);
        while (idom != pred_b) {
          while (pred_b > idom) {
            pred_b = blocks[pred_b].idom;
          }
          while (idom > pred_b) {
            idom = blocks[idom].idom;
          }
        }
      } else {
        ctx->flags2 &= ~IR_NO_LOOPS;
        IR_ASSERT(bb->predecessors_count > 1);
        ir_list_push(&worklist, pred_b);
      }
    }
    bb->idom = idom;
    idom_bb = &blocks[idom];
    bb->dom_depth = idom_bb->dom_depth + 1;
  }

  /* Construct children lists sorted by block number */
  for (b = blocks_count, bb = &blocks[b]; b >= 2; b--, bb--) {
    ir_block *idom_bb = &blocks[bb->idom];
    bb->dom_next_child = idom_bb->dom_child;
    idom_bb->dom_child = b;
  }

  blocks[1].idom = 0;

  if (ir_list_len(&worklist) != 0) {
    uint32_t dom_depth;
    uint32_t succ_b;
    bool complete = 1;

    /* Check if all the back-edges lead to the loop headers */
    do {
      b = ir_list_pop(&worklist);
      bb = &blocks[b];
      succ_b = ctx->cfg_edges[bb->successors];
      if (bb->successors_count != 1) {
        /* LOOP_END/END may be linked with the following ENTRY by a fake edge */
        if (bb->successors_count != 2) {
          complete = 0;
          break;
        } else if (blocks[succ_b].flags & IR_BB_ENTRY) {
          succ_b = ctx->cfg_edges[bb->successors + 1];
        } else if (!(blocks[ctx->cfg_edges[bb->successors + 1]].flags & IR_BB_ENTRY)) {
          complete = 0;
          break;
        }
      }
      dom_depth = blocks[succ_b].dom_depth;;
      while (bb->dom_depth > dom_depth) {
        b = bb->dom_parent;
        bb = &blocks[b];
      }
      if (UNEXPECTED(b != succ_b)) {
        complete = 0;
        break;
      }
    } while (ir_list_len(&worklist) != 0);

    if (UNEXPECTED(!complete)) {
      ir_list_free(&worklist);
      return ir_build_dominators_tree_iterative(ctx);
    }
  }

  ir_list_free(&worklist);

  return 1;
}

static int ir_build_dominators_tree_iterative(ir_ctx *ctx)
{
  bool changed;
  uint32_t blocks_count, b;
  ir_block *blocks, *bb;
  uint32_t *edges;

  /* Find immediate dominators */
  blocks = ctx->cfg_blocks;
  edges  = ctx->cfg_edges;
  blocks_count = ctx->cfg_blocks_count;

  /* Clear the dominators tree, but keep already found dominators */
  for (b = 0, bb = &blocks[0]; b <= blocks_count; b++, bb++) {
    bb->dom_depth = 0;
    bb->dom_child = 0;
    bb->dom_next_child = 0;
  }

  /* Find immediate dominators by iterative fixed-point algorithm */
  blocks[1].idom = 1;
  do {
    changed = 0;

    for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
      IR_ASSERT(!(bb->flags & IR_BB_UNREACHABLE));
      IR_ASSERT(bb->predecessors_count > 0);
      uint32_t k = bb->predecessors_count;
      uint32_t *p = edges + bb->predecessors;
      uint32_t idom = *p;

      if (blocks[idom].idom == 0) {
        while (1) {
          k--;
          p++;
          idom = *p;
          if (blocks[idom].idom > 0) {
            break;
          }
          IR_ASSERT(k > 0);
        }
      }
      IR_ASSERT(k != 0);
      while (--k > 0) {
        uint32_t pred_b = *(++p);

        if (blocks[pred_b].idom > 0) {
          IR_ASSERT(blocks[pred_b].idom > 0);
          while (idom != pred_b) {
            while (pred_b > idom) {
              pred_b = blocks[pred_b].idom;
            }
            while (idom > pred_b) {
              idom = blocks[idom].idom;
            }
          }
        }
      }
      if (bb->idom != idom) {
        bb->idom = idom;
        changed = 1;
      }
    }
  } while (changed);

  /* Build dominators tree */
  blocks[1].idom = 0;
  blocks[1].dom_depth = 0;
  for (b = 2, bb = &blocks[2]; b <= blocks_count; b++, bb++) {
    uint32_t idom = bb->idom;
    ir_block *idom_bb = &blocks[idom];

    bb->dom_depth = idom_bb->dom_depth + 1;
  }

  /* Construct children lists sorted by block number */
  for (b = blocks_count, bb = &blocks[b]; b >= 2; b--, bb--) {
    ir_block *idom_bb = &blocks[bb->idom];
    bb->dom_next_child = idom_bb->dom_child;
    idom_bb->dom_child = b;
  }

  return 1;
}

static bool ir_dominates(const ir_block *blocks, uint32_t b1, uint32_t b2)
{
  uint32_t b1_depth = blocks[b1].dom_depth;
  const ir_block *bb2 = &blocks[b2];

  while (bb2->dom_depth > b1_depth) {
    b2 = bb2->dom_parent;
    bb2 = &blocks[b2];
  }
  return b1 == b2;
}

int ir_find_loops(ir_ctx *ctx)
{
  uint32_t b, j, n, count;
  uint32_t *entry_times, *exit_times, *sorted_blocks, time = 1;
  ir_block *blocks = ctx->cfg_blocks;
  uint32_t *edges = ctx->cfg_edges;
  ir_worklist work;

  if (ctx->flags2 & IR_NO_LOOPS) {
    return 1;
  }

  /* We don't materialize the DJ spanning tree explicitly, as we are only interested in ancestor
   * queries. These are implemented by checking entry/exit times of the DFS search. */
  ir_worklist_init(&work, ctx->cfg_blocks_count + 1);
  entry_times = ir_mem_malloc((ctx->cfg_blocks_count + 1) * 3 * sizeof(uint32_t));
  exit_times = entry_times + ctx->cfg_blocks_count + 1;
  sorted_blocks = exit_times + ctx->cfg_blocks_count + 1;

  memset(entry_times, 0, (ctx->cfg_blocks_count + 1) * sizeof(uint32_t));

  ir_worklist_push(&work, 1);
  while (ir_worklist_len(&work)) {
    ir_block *bb;
    int child;

next:
    b = ir_worklist_peek(&work);
    if (!entry_times[b]) {
      entry_times[b] = time++;
    }

    /* Visit blocks immediately dominated by "b". */
    bb = &blocks[b];
    for (child = bb->dom_child; child > 0; child = blocks[child].dom_next_child) {
      if (ir_worklist_push(&work, child)) {
        goto next;
      }
    }

    /* Visit join edges. */
    if (bb->successors_count) {
      uint32_t *p = edges + bb->successors;
      for (j = 0; j < bb->successors_count; j++, p++) {
        uint32_t succ = *p;

        if (blocks[succ].idom == b) {
          continue;
        } else if (ir_worklist_push(&work, succ)) {
          goto next;
        }
      }
    }
    exit_times[b] = time++;
    ir_worklist_pop(&work);
  }

  /* Sort blocks by level, which is the opposite order in which we want to process them */
  sorted_blocks[1] = 1;
  j = 1;
  n = 2;
  while (j != n) {
    uint32_t i = j;
    j = n;
    for (; i < j; i++) {
      int child;
      for (child = blocks[sorted_blocks[i]].dom_child; child > 0; child = blocks[child].dom_next_child) {
        sorted_blocks[n++] = child;
      }
    }
  }
  count = n;

  /* Identify loops. See Sreedhar et al, "Identifying Loops Using DJ Graphs". */
  uint32_t prev_dom_depth = blocks[sorted_blocks[n - 1]].dom_depth;
  uint32_t prev_irreducible = 0;
  while (n > 1) {
    b = sorted_blocks[--n];
    ir_block *bb = &blocks[b];

    IR_ASSERT(bb->dom_depth <= prev_dom_depth);
    if (UNEXPECTED(prev_irreducible) && bb->dom_depth != prev_dom_depth) {
      /* process delyed irreducible loops */
      do {
        b = sorted_blocks[prev_irreducible];
        bb = &blocks[b];
        if ((bb->flags & IR_BB_IRREDUCIBLE_LOOP) && !bb->loop_depth) {
          /* process irreducible loop */
          uint32_t hdr = b;

          bb->loop_depth = 1;
          if (ctx->ir_base[bb->start].op == IR_MERGE) {
            ctx->ir_base[bb->start].op = IR_LOOP_BEGIN;
          }

          /* find the closing edge(s) of the irreucible loop */
          IR_ASSERT(bb->predecessors_count > 1);
          uint32_t *p = &edges[bb->predecessors];
          j = bb->predecessors_count;
          do {
            uint32_t pred = *p;

            if (entry_times[pred] > entry_times[b] && exit_times[pred] < exit_times[b]) {
              if (!ir_worklist_len(&work)) {
                ir_bitset_clear(work.visited, ir_bitset_len(ir_worklist_capasity(&work)));
              }
              blocks[pred].loop_header = 0; /* support for merged loops */
              ir_worklist_push(&work, pred);
            }
            p++;
          } while (--j);
          if (ir_worklist_len(&work) == 0) continue;

          /* collect members of the irreducible loop */
          while (ir_worklist_len(&work)) {
            b = ir_worklist_pop(&work);
            if (b != hdr) {
              ir_block *bb = &blocks[b];
              bb->loop_header = hdr;
              if (bb->predecessors_count) {
                uint32_t *p = &edges[bb->predecessors];
                uint32_t n = bb->predecessors_count;
                do {
                  uint32_t pred = *p;
                  while (blocks[pred].loop_header > 0) {
                    pred = blocks[pred].loop_header;
                  }
                  if (pred != hdr) {
                    if (entry_times[pred] > entry_times[hdr] && exit_times[pred] < exit_times[hdr]) {
                      /* "pred" is a descendant of "hdr" */
                      ir_worklist_push(&work, pred);
                    } else {
                      /* another entry to the irreducible loop */
                      bb->flags |= IR_BB_IRREDUCIBLE_LOOP;
                      if (ctx->ir_base[bb->start].op == IR_MERGE) {
                        ctx->ir_base[bb->start].op = IR_LOOP_BEGIN;
                      }
                    }
                  }
                  p++;
                } while (--n);
              }
            }
          }
        }
      } while (--prev_irreducible != n);
      prev_irreducible = 0;
      b = sorted_blocks[n];
      bb = &blocks[b];
    }

    if (bb->predecessors_count > 1) {
      bool irreducible = 0;
      uint32_t *p = &edges[bb->predecessors];

      j = bb->predecessors_count;
      do {
        uint32_t pred = *p;

        /* A join edge is one for which the predecessor does not
           immediately dominate the successor.  */
        if (bb->idom != pred) {
          /* In a loop back-edge (back-join edge), the successor dominates
             the predecessor.  */
          if (ir_dominates(blocks, b, pred)) {
            if (!ir_worklist_len(&work)) {
              ir_bitset_clear(work.visited, ir_bitset_len(ir_worklist_capasity(&work)));
            }
            blocks[pred].loop_header = 0; /* support for merged loops */
            ir_worklist_push(&work, pred);
          } else {
            /* Otherwise it's a cross-join edge.  See if it's a branch
               to an ancestor on the DJ spanning tree.  */
            if (entry_times[pred] > entry_times[b] && exit_times[pred] < exit_times[b]) {
              irreducible = 1;
              break;
            }
          }
        }
        p++;
      } while (--j);

      if (UNEXPECTED(irreducible)) {
        bb->flags |= IR_BB_LOOP_HEADER | IR_BB_IRREDUCIBLE_LOOP;
        ctx->flags2 |= IR_CFG_HAS_LOOPS | IR_IRREDUCIBLE_CFG;
        /* Remember the position of the first irreducible loop to process all the irreducible loops
         * after the reducible loops with the same dominator tree depth
         */
        if (!prev_irreducible) {
          prev_irreducible = n;
          prev_dom_depth = bb->dom_depth;
        }
        ir_list_clear(&work.l);
      } else if (ir_worklist_len(&work)) {
        /* collect members of the reducible loop */
        uint32_t hdr = b;

        bb->flags |= IR_BB_LOOP_HEADER;
        ctx->flags2 |= IR_CFG_HAS_LOOPS;
        bb->loop_depth = 1;
        if (ctx->ir_base[bb->start].op == IR_MERGE) {
          ctx->ir_base[bb->start].op = IR_LOOP_BEGIN;
        }
        while (ir_worklist_len(&work)) {
          b = ir_worklist_pop(&work);
          if (b != hdr) {
            ir_block *bb = &blocks[b];
            bb->loop_header = hdr;
            if (bb->predecessors_count) {
              uint32_t *p = &edges[bb->predecessors];
              uint32_t n = bb->predecessors_count;
              do {
                uint32_t pred = *p;
                while (blocks[pred].loop_header > 0) {
                  pred = blocks[pred].loop_header;
                }
                if (pred != hdr) {
                  ir_worklist_push(&work, pred);
                }
                p++;
              } while (--n);
            }
          }
        }
      }
    }
  }
  IR_ASSERT(!prev_irreducible);

  if (ctx->flags2 & IR_CFG_HAS_LOOPS) {
    for (n = 1; n < count; n++) {
      b = sorted_blocks[n];
      ir_block *bb = &blocks[b];
      if (bb->loop_header > 0) {
        ir_block *loop = &blocks[bb->loop_header];
        uint32_t loop_depth = loop->loop_depth;

        if (bb->flags & IR_BB_LOOP_HEADER) {
          loop_depth++;
        }
        bb->loop_depth = loop_depth;
        if (bb->flags & (IR_BB_ENTRY|IR_BB_LOOP_WITH_ENTRY)) {
          loop->flags |= IR_BB_LOOP_WITH_ENTRY;
          if (loop_depth > 1) {
            /* Set IR_BB_LOOP_WITH_ENTRY flag for all the enclosing loops */
            bb = &blocks[loop->loop_header];
            while (1) {
              if (bb->flags & IR_BB_LOOP_WITH_ENTRY) {
                break;
              }
              bb->flags |= IR_BB_LOOP_WITH_ENTRY;
              if (bb->loop_depth == 1) {
                break;
              }
              bb = &blocks[loop->loop_header];
            }
          }
        }
      }
    }
  }

  ir_mem_free(entry_times);
  ir_worklist_free(&work);

  return 1;
}

static uint32_t _ir_skip_empty_blocks(const ir_ctx *ctx, uint32_t b)
{
  while (1) {
    ir_block *bb = &ctx->cfg_blocks[b];

    if ((bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) == IR_BB_EMPTY) {
      IR_ASSERT(bb->successors_count == 1);
      b = ctx->cfg_edges[bb->successors];
    } else {
      return b;
    }
  }
}

/* A variation of "Bottom-up Positioning" algorithm described by
 * Karl Pettis and Robert C. Hansen "Profile Guided Code Positioning"
 */
typedef struct _ir_edge_info {
  uint32_t from;
  uint32_t to;
  float    freq;
} ir_edge_info;

typedef struct _ir_chain {
  uint32_t head;
  uint32_t next;
  union {
    uint32_t prev;
    uint32_t tail;
  };
} ir_chain;

static int ir_edge_info_cmp(const void *b1, const void *b2)
{
  ir_edge_info *e1 = (ir_edge_info*)b1;
  ir_edge_info *e2 = (ir_edge_info*)b2;

  if (e1->freq != e2->freq) {
    return e1->freq < e2->freq ? 1 : -1;
  }
  /* In case of equal frequencies, try to avoid penalization of one of the "equal" paths by
   * preferring the first RPO successor (in conditional branches) and the last RPO predecessor
   * (in merge points).
   *
   * See "Static Basic Block Reordering Heuristics for Implicit Control Flow in Baseline JITs"
   * Polito Guillermo, Ducasse Stephane, and Tesone Pablo (2021)
   */
  if (e1->from != e2->from) {
    return e2->from - e1->from;
  } else {
    return e1->to - e2->to;
  }
}

static IR_NEVER_INLINE uint32_t ir_chain_head_path_compress(ir_chain *chains, uint32_t src, uint32_t head)
{
  IR_ASSERT(head != 0);
  do {
    head = chains[head].head;
  } while (chains[head].head != head);
  do {
    uint32_t next = chains[src].head;
    chains[src].head = head;
    src = next;
  } while (chains[src].head != head);
  return head;
}

IR_ALWAYS_INLINE uint32_t ir_chain_head(ir_chain *chains, uint32_t src)
{
  uint32_t head = chains[src].head;
  if (chains[head].head == head) {
    return head;
  } else {
    return ir_chain_head_path_compress(chains, src, head);
  }
}

static void ir_join_chains(ir_chain *chains, uint32_t src, uint32_t dst)
{
  uint32_t dst_tail = chains[dst].tail;
  uint32_t src_tail = chains[src].tail;

  chains[dst_tail].next = src;
  chains[dst].prev = src_tail;
  chains[src_tail].next = dst;
  chains[src].tail = dst_tail;
  chains[dst].head = src;
}

static void ir_insert_chain_before(ir_chain *chains, uint32_t c, uint32_t before)
{
  ir_chain *this = &chains[c];
  ir_chain *next = &chains[before];

  IR_ASSERT(chains[c].head == c);
  if (chains[before].head != before) {
    this->head = next->head;
  } else {
    next->head = c;
  }
  this->next = before;
  this->prev = next->prev;
  next->prev = c;
  chains[this->prev].next = c;
}

#ifndef IR_DEBUG_BB_SCHEDULE_GRAPH
# ifdef IR_DEBUG
#  define IR_DEBUG_BB_SCHEDULE_GRAPH 1
# else
#  define IR_DEBUG_BB_SCHEDULE_GRAPH 0
# endif
#endif

#if IR_DEBUG_BB_SCHEDULE_GRAPH
static void ir_dump_cfg_freq_graph(ir_ctx *ctx, float *bb_freq, uint32_t edges_count, ir_edge_info *edges, ir_chain *chains)
{
  uint32_t b, i;
  ir_block *bb;
  uint8_t c, *colors;
  bool is_head, is_empty;
  uint32_t max_colors = 12;

  colors = alloca(sizeof(uint8_t) * (ctx->cfg_blocks_count + 1));
  memset(colors, 0, sizeof(uint8_t) * (ctx->cfg_blocks_count + 1));
  i = 0;
  for (b = 1; b < ctx->cfg_blocks_count + 1; b++) {
    if (chains[b].head == b) {
      colors[b] = (i % max_colors) + 1;
      i++;
    }
  }

  fprintf(stderr, "digraph {\n");
  fprintf(stderr, "\trankdir=TB;\n");
  for (b = 1; b <= ctx->cfg_blocks_count; b++) {
    bb = &ctx->cfg_blocks[b];
    c = (chains[b].head) ? colors[ir_chain_head(chains, b)] : 0;
    is_head = chains[b].head == b;
    is_empty = (bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) == IR_BB_EMPTY;
    if (c) {
      fprintf(stderr, "\tBB%d [label=\"BB%d: (%d),%0.3f\\n%s\\n%s\",colorscheme=set312,fillcolor=%d%s%s]\n", b, b,
        bb->loop_depth, bb_freq[b],
        ir_op_name[ctx->ir_base[bb->start].op], ir_op_name[ctx->ir_base[bb->end].op],
        c,
        is_head ? ",penwidth=3" : "",
        is_empty ? ",style=\"dotted,filled\"" : ",style=\"filled\"");
    } else {
      fprintf(stderr, "\tBB%d [label=\"BB%d: (%d),%0.3f\\n%s\\n%s\"%s%s]\n", b, b,
        bb->loop_depth, bb_freq[b],
        ir_op_name[ctx->ir_base[bb->start].op], ir_op_name[ctx->ir_base[bb->end].op],
        is_head ? ",penwidth=3" : "",
        is_empty ? ",style=\"dotted\"" : "");
    }
  }
  fprintf(stderr, "\n");

  for (i = 0; i < edges_count; i++) {
    fprintf(stderr, "\tBB%d -> BB%d [label=\"%0.3f\"]\n", edges[i].from, edges[i].to, edges[i].freq);
  }
  fprintf(stderr, "}\n");
}
#endif

#ifdef IR_DEBUG
static void ir_dump_edges(ir_ctx *ctx, uint32_t edges_count, ir_edge_info *edges)
{
  uint32_t i;

  fprintf(stderr, "Edges:\n");
  for (i = 0; i < edges_count; i++) {
    fprintf(stderr, "\tBB%d -> BB%d %0.3f\n", edges[i].from, edges[i].to, edges[i].freq);
  }
}

static void ir_dump_chains(ir_ctx *ctx, ir_chain *chains)
{
  uint32_t b, tail, i;

  fprintf(stderr, "Chains:\n");
  for (b = 1; b < ctx->cfg_blocks_count + 1; b++) {
    if (chains[b].head == b) {
      tail = chains[b].tail;
      i = b;
      fprintf(stderr, "(BB%d", i);
      while (i != tail) {
        i = chains[i].next;
        fprintf(stderr, ", BB%d", i);
      }
      fprintf(stderr, ")\n");
    }
  }
}
#endif

static int ir_schedule_blocks_bottom_up(ir_ctx *ctx)
{
  uint32_t max_edges_count = ctx->cfg_edges_count / 2;
  uint32_t edges_count = 0;
  uint32_t b, i, loop_depth;
  float *bb_freq, freq;
  ir_block *bb;
  ir_edge_info *edges, *e;
  ir_chain *chains;
  ir_bitqueue worklist;
  ir_bitset visited;
  uint32_t *schedule_end, count;

  ctx->cfg_schedule = ir_mem_malloc(sizeof(uint32_t) * (ctx->cfg_blocks_count + 2));
  schedule_end = ctx->cfg_schedule + ctx->cfg_blocks_count;

  /* 1. Create initial chains for each BB */
  chains = ir_mem_malloc(sizeof(ir_chain) * (ctx->cfg_blocks_count + 1));
  chains[0].head = 0;
  chains[0].next = 0;
  chains[0].prev = 0;
  for (b = 1; b <= ctx->cfg_blocks_count; b++) {
    chains[b].head = b;
    chains[b].next = b;
    chains[b].prev = b;
  }

  /* 2. Collect information about BBs and EDGEs frequencies */
  edges = ir_mem_malloc(sizeof(ir_edge_info) * max_edges_count);
  bb_freq = ir_mem_calloc(ctx->cfg_blocks_count + 1, sizeof(float));
  bb_freq[1] = 1.0f;
  visited = ir_bitset_malloc(ctx->cfg_blocks_count + 1);
  ir_bitqueue_init(&worklist, ctx->cfg_blocks_count + 1);
  ir_bitqueue_add(&worklist, 1);
  while ((b = ir_bitqueue_pop(&worklist)) != (uint32_t)-1) {
restart:
    bb = &ctx->cfg_blocks[b];
    if (bb->predecessors_count) {
      uint32_t n = bb->predecessors_count;
      uint32_t *p = ctx->cfg_edges + bb->predecessors;
      for (; n > 0; p++, n--) {
        uint32_t predecessor = *p;
        /* Basic Blocks are ordered in a way that usual predecessors ids are less than successors.
         * So we may compare blocks ids (predecessor < b) instead of a more expensive check for back edge
         * (b != predecessor && ctx->cfg_blocks[predecessor].loop_header != b)
         */
        if (predecessor < b) {
          if (!ir_bitset_in(visited, predecessor)) {
            b = predecessor;
            ir_bitqueue_del(&worklist, b);
            goto restart;
          }
        } else if (b != predecessor && ctx->cfg_blocks[predecessor].loop_header != b) {
          /* not a loop back-edge */
          IR_ASSERT(b == predecessor || ctx->cfg_blocks[predecessor].loop_header == b);
        }
      }
    }

    ir_bitset_incl(visited, b);

    if ((bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) == IR_BB_EMPTY) {
      uint32_t successor = ctx->cfg_edges[bb->successors];

      /* move empty blocks to the end */
      IR_ASSERT(chains[b].head == b);
      chains[b].head = 0;
      *schedule_end = b;
      schedule_end--;

      if (successor > b) {
        bb_freq[successor] += bb_freq[b];
        b = successor;
        ir_bitqueue_del(&worklist, b);
        goto restart;
      } else {
        continue;
      }
    }

    loop_depth = bb->loop_depth;
    if (bb->flags & IR_BB_LOOP_HEADER) {
      // TODO: Estimate the loop iterations count
      bb_freq[b] *= 10;
    }

    if (bb->successors_count) {
      uint32_t n = bb->successors_count;
      uint32_t *p = ctx->cfg_edges + bb->successors;

      if (n == 1) {
        uint32_t successor = *p;

        IR_ASSERT(edges_count < max_edges_count);
        freq = bb_freq[b];
        if (successor > b) {
          IR_ASSERT(!ir_bitset_in(visited, successor));
          bb_freq[successor] += freq;
          ir_bitqueue_add(&worklist, successor);
        }
        successor = _ir_skip_empty_blocks(ctx, successor);
        edges[edges_count].from = b;
        edges[edges_count].to = successor;
        edges[edges_count].freq = freq;
        edges_count++;
      } else if (n == 2 && ctx->ir_base[bb->end].op == IR_IF) {
        uint32_t successor1 = *p;
        ir_block *successor1_bb = &ctx->cfg_blocks[successor1];
        ir_insn *insn1 = &ctx->ir_base[successor1_bb->start];
        uint32_t successor2 = *(p + 1);
        ir_block *successor2_bb = &ctx->cfg_blocks[successor2];
        ir_insn *insn2 = &ctx->ir_base[successor2_bb->start];
        int prob1, prob2, probN = 100;

        if (insn1->op2) {
          prob1 = insn1->op2;
          if (insn2->op2) {
            prob2 = insn2->op2;
            probN = prob1 + prob2;
          } else {
            if (prob1 > 100) {
              prob1 = 100;
            }
            prob2 = 100 - prob1;
          }

        } else if (insn2->op2) {
          prob2 = insn2->op2;
          if (prob2 > 100) {
            prob2 = 100;
          }
          prob1 = 100 - prob2;
        } else if (successor1_bb->loop_depth >= loop_depth
            && successor2_bb->loop_depth < loop_depth) {
          prob1 = 90;
          prob2 = 10;
        } else if (successor1_bb->loop_depth < loop_depth
            && successor2_bb->loop_depth >= loop_depth) {
          prob1 = 10;
          prob2 = 90;
        } else if (successor2_bb->flags & IR_BB_EMPTY) {
          prob1 = 51;
          prob2 = 49;
        } else if (successor1_bb->flags & IR_BB_EMPTY) {
          prob1 = 49;
          prob2 = 51;
        } else {
          prob1 = prob2 = 50;
        }
        do {
          freq = bb_freq[b] * (float)prob1 / (float)probN;
          if (successor1 > b) {
            IR_ASSERT(!ir_bitset_in(visited, successor1));
            bb_freq[successor1] += freq;
            if (successor1_bb->successors_count == 0 && insn1->op2 == 1) {
              /* move cold block without successors to the end */
              IR_ASSERT(chains[successor1].head == successor1);
              chains[successor1].head = 0;
              *schedule_end = successor1;
              schedule_end--;
              break;
            } else {
              ir_bitqueue_add(&worklist, successor1);
            }
          }
          /* try to join edges early to reduce number of edges and the cost of their sorting */
          if (prob1 > prob2
           && (successor1_bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) != IR_BB_EMPTY) {
            uint32_t src = chains[b].next;
            IR_ASSERT(chains[src].head == src);
            IR_ASSERT(src == ir_chain_head(chains, b));
            IR_ASSERT(chains[successor1].head == successor1);
            ir_join_chains(chains, src, successor1);
            if (!IR_DEBUG_BB_SCHEDULE_GRAPH) break;
          }
          successor1 = _ir_skip_empty_blocks(ctx, successor1);
          IR_ASSERT(edges_count < max_edges_count);
          edges[edges_count].from = b;
          edges[edges_count].to = successor1;
          edges[edges_count].freq = freq;
          edges_count++;
        } while (0);
        do {
          freq = bb_freq[b] * (float)prob2 / (float)probN;
          if (successor2 > b) {
            IR_ASSERT(!ir_bitset_in(visited, successor2));
            bb_freq[successor2] += freq;
            if (successor2_bb->successors_count == 0 && insn2->op2 == 1) {
              /* move cold block without successors to the end */
              IR_ASSERT(chains[successor2].head == successor2);
              chains[successor2].head = 0;
              *schedule_end = successor2;
              schedule_end--;
              break;
            } else {
              ir_bitqueue_add(&worklist, successor2);
            }
          }
          if (prob2 > prob1
           && (successor2_bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) != IR_BB_EMPTY) {
            uint32_t src = chains[b].next;
            IR_ASSERT(chains[src].head == src);
            IR_ASSERT(src == ir_chain_head(chains, b));
            IR_ASSERT(chains[successor2].head == successor2);
            ir_join_chains(chains, src, successor2);
            if (!IR_DEBUG_BB_SCHEDULE_GRAPH) break;
          }
          successor2 = _ir_skip_empty_blocks(ctx, successor2);
          IR_ASSERT(edges_count < max_edges_count);
          edges[edges_count].from = b;
          edges[edges_count].to = successor2;
          edges[edges_count].freq = freq;
          edges_count++;
        } while (0);
      } else {
        int prob;

        for (; n > 0; p++, n--) {
          uint32_t successor = *p;
          ir_block *successor_bb = &ctx->cfg_blocks[successor];
          ir_insn *insn = &ctx->ir_base[successor_bb->start];

          if (insn->op == IR_CASE_DEFAULT) {
            prob = insn->op2;
            if (!prob) {
              prob = 100 / bb->successors_count;
            }
          } else if (insn->op == IR_CASE_VAL) {
            prob = insn->op3;
            if (!prob) {
              prob = 100 / bb->successors_count;
            }
          } else if (insn->op == IR_ENTRY) {
            if ((ctx->flags & IR_MERGE_EMPTY_ENTRIES) && (successor_bb->flags & IR_BB_EMPTY)) {
              prob = 99; /* prefer empty ENTRY block to go first */
            } else {
              prob = 1;
            }
          } else {
            prob = 100 / bb->successors_count;
          }
          freq = bb_freq[b] * (float)prob / 100.0f;
          if (successor > b) {
            IR_ASSERT(!ir_bitset_in(visited, successor));
            bb_freq[successor] += freq;
            ir_bitqueue_add(&worklist, successor);
          }
          successor = _ir_skip_empty_blocks(ctx, successor);
          IR_ASSERT(edges_count < max_edges_count);
          edges[edges_count].from = b;
          edges[edges_count].to = successor;
          edges[edges_count].freq = freq;
          edges_count++;
        }
      }
    }
  }
  ir_bitqueue_free(&worklist);
  ir_mem_free(visited);

  /* 2. Sort EDGEs according to their frequencies */
  qsort(edges, edges_count, sizeof(ir_edge_info), ir_edge_info_cmp);

#ifdef IR_DEBUG
  if (ctx->flags & IR_DEBUG_BB_SCHEDULE) {
    ir_dump_edges(ctx, edges_count, edges);
  }
#endif

  /* 3. Process EDGEs in the decreasing frequency order and join the connected chains */
  for (e = edges, i = edges_count; i > 0; e++, i--) {
    uint32_t dst = chains[e->to].head;
    if (dst == e->to) {
      uint32_t src = chains[e->from].next;
      if (chains[src].head == src) {
        IR_ASSERT(src == ir_chain_head(chains, e->from) && chains[src].tail == e->from);
        if (src != dst) {
          ir_join_chains(chains, src, dst);
        } else if (ctx->cfg_blocks[e->from].successors_count < 2) {
          /* Try to rotate loop chian to finish it with a conditional branch */
          uint32_t tail = e->from;
          uint32_t prev = src;
          uint32_t next = chains[prev].next;
          uint32_t best = 0;

          while (prev != tail) {
            if (ctx->ir_base[ctx->cfg_blocks[prev].end].op == IR_IF) {
              if (ctx->ir_base[ctx->cfg_blocks[prev].start].op == IR_LOOP_BEGIN
               && ctx->cfg_blocks[prev].loop_depth > 1) {
                best = next;
                break;
              } else if (!best || bb_freq[next] < bb_freq[best]) {
                /* Find the successor of IF with the least frequency */
                best = next;
              }
            }
            prev = next;
            next = chains[next].next;
          }
          if (best) {
            /* change the head of the chain */
            chains[src].head = best;
            chains[best].head = best;
          }
        }
#if !IR_DEBUG_BB_SCHEDULE_GRAPH
        e->from = 0; /* reset "from" to avoid check on step #5 */
#endif
      }
    }
  }

#if IR_DEBUG_BB_SCHEDULE_GRAPH
  if (ctx->flags & IR_DEBUG_BB_SCHEDULE) {
    ir_dump_cfg_freq_graph(ctx, bb_freq, edges_count, edges, chains);
  }
#endif

  ir_mem_free(bb_freq);

#ifdef IR_DEBUG
  if (ctx->flags & IR_DEBUG_BB_SCHEDULE) {
    ir_dump_chains(ctx, chains);
  }
#endif

  /* 4. Merge empty entry blocks */
  if ((ctx->flags & IR_MERGE_EMPTY_ENTRIES) && ctx->entries_count) {
    for (i = 0; i < ctx->entries_count; i++) {
      b = ctx->entries[i];
      IR_ASSERT(ctx->cfg_blocks[b].flags & IR_BB_ENTRY);
      if (b && chains[b].head == b && chains[b].tail == b) {
        bb = &ctx->cfg_blocks[b];
        if (bb->flags & IR_BB_EMPTY) {
          uint32_t successor;

          do {
            IR_ASSERT(bb->successors_count == 1);
            successor = ctx->cfg_edges[bb->successors];
            bb = &ctx->cfg_blocks[successor];
          } while ((bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) == IR_BB_EMPTY);
          IR_ASSERT(chains[successor].head);
          ir_insert_chain_before(chains, b, successor);
        }
      }
    }

#ifdef IR_DEBUG
    if (ctx->flags & IR_DEBUG_BB_SCHEDULE) {
      ir_dump_chains(ctx, chains);
    }
#endif
  }

  /* 5. Align loop headers */
  for (b = 1; b <= ctx->cfg_blocks_count; b++) {
    if (chains[b].head == b) {
      bb = &ctx->cfg_blocks[b];
      if (bb->loop_depth) {
        if ((bb->flags & IR_BB_LOOP_HEADER) || ir_chain_head(chains, bb->loop_header) == b) {
          bb->flags |= IR_BB_ALIGN_LOOP;
        }
      }
    }
  }

  /* 6. Group chains according to the most frequent edge between them */
  // TODO: Try to find a better heuristic
  for (e = edges, i = edges_count; i > 0; e++, i--) {
#if !IR_DEBUG_BB_SCHEDULE_GRAPH
    if (!e->from) continue;
#endif
    uint32_t src = ir_chain_head(chains, e->from);
    uint32_t dst = ir_chain_head(chains, e->to);
    if (src != dst) {
      if (dst == 1) {
        ir_join_chains(chains, dst, src);
      } else {
        ir_join_chains(chains, src, dst);
      }
    }
  }

#ifdef IR_DEBUG
  if (ctx->flags & IR_DEBUG_BB_SCHEDULE) {
    ir_dump_chains(ctx, chains);
  }
#endif

  /* 7. Form a final BB order */
  count = 0;
  for (b = 1; b <= ctx->cfg_blocks_count; b++) {
    if (chains[b].head == b) {
      uint32_t tail = chains[b].tail;
      uint32_t i = b;
      while (1) {
        count++;
        ctx->cfg_schedule[count] = i;
        if (i == tail) break;
        i = chains[i].next;
      }
    }
  }

  IR_ASSERT(ctx->cfg_schedule + count == schedule_end);
  ctx->cfg_schedule[ctx->cfg_blocks_count + 1] = 0;

  ir_mem_free(edges);
  ir_mem_free(chains);

  return 1;
}

/* A variation of "Top-down Positioning" algorithm described by
 * Karl Pettis and Robert C. Hansen "Profile Guided Code Positioning"
 */
static int ir_schedule_blocks_top_down(ir_ctx *ctx)
{
  ir_bitqueue blocks;
  uint32_t b, best_successor, last_non_empty;
  ir_block *bb, *best_successor_bb;
  ir_insn *insn;
  uint32_t *list, *schedule_end;
  uint32_t count = 0;

  ir_bitqueue_init(&blocks, ctx->cfg_blocks_count + 1);
  blocks.pos = 0;
  list = ir_mem_malloc(sizeof(uint32_t) * (ctx->cfg_blocks_count + 2));
  list[ctx->cfg_blocks_count + 1] = 0;
  schedule_end = list + ctx->cfg_blocks_count;
  for (b = 1; b <= ctx->cfg_blocks_count; b++) {
    ir_bitset_incl(blocks.set, b);
  }

  while ((b = ir_bitqueue_pop(&blocks)) != (uint32_t)-1) {
    bb = &ctx->cfg_blocks[b];
    /* Start trace */
    last_non_empty = 0;
    do {
      if (UNEXPECTED(bb->flags & IR_BB_PREV_EMPTY_ENTRY) && ir_bitqueue_in(&blocks, b - 1)) {
        /* Schedule the previous empty ENTRY block before this one */
        uint32_t predecessor = b - 1;

        ir_bitqueue_del(&blocks, predecessor);
        count++;
        list[count] = predecessor;
      }
      if ((bb->flags & (IR_BB_START|IR_BB_ENTRY|IR_BB_EMPTY)) == IR_BB_EMPTY) {
        /* move empty blocks to the end */
        *schedule_end = b;
        schedule_end--;
      } else {
        count++;
        list[count] = b;
        last_non_empty = b;
      }
      best_successor_bb = NULL;
      if (bb->successors_count == 1) {
        best_successor = ctx->cfg_edges[bb->successors];
        if (ir_bitqueue_in(&blocks, best_successor)) {
          best_successor_bb = &ctx->cfg_blocks[best_successor];
        }
      } else if (bb->successors_count > 1) {
        uint32_t prob, best_successor_prob;
        uint32_t *p, successor;
        ir_block *successor_bb;

        for (b = 0, p = &ctx->cfg_edges[bb->successors]; b < bb->successors_count; b++, p++) {
          successor = *p;
          if (ir_bitqueue_in(&blocks, successor)) {
            successor_bb = &ctx->cfg_blocks[successor];
            insn = &ctx->ir_base[successor_bb->start];
            if (insn->op == IR_IF_TRUE || insn->op == IR_IF_FALSE) {
              prob = insn->op2;
              if (!prob) {
                prob = 100 / bb->successors_count;
                if (!(successor_bb->flags & IR_BB_EMPTY)) {
                  prob++;
                }
              }
            } else if (insn->op == IR_CASE_DEFAULT) {
              prob = insn->op2;
              if (!prob) {
                prob = 100 / bb->successors_count;
              }
            } else if (insn->op == IR_CASE_VAL) {
              prob = insn->op3;
              if (!prob) {
                prob = 100 / bb->successors_count;
              }
            } else if (insn->op == IR_ENTRY) {
              if ((ctx->flags & IR_MERGE_EMPTY_ENTRIES) && (successor_bb->flags & IR_BB_EMPTY)) {
                prob = 99; /* prefer empty ENTRY block to go first */
              } else {
                prob = 1;
              }
            } else {
              prob = 100 / bb->successors_count;
            }
            if (!best_successor_bb
             || successor_bb->loop_depth > best_successor_bb->loop_depth
             || prob > best_successor_prob) {
              best_successor = successor;
              best_successor_bb = successor_bb;
              best_successor_prob = prob;
            }
          }
        }
      }
      if (!best_successor_bb) {
        /* Try to continue trace using the other successor of the last IF */
        if ((bb->flags & IR_BB_EMPTY) && last_non_empty) {
          bb = &ctx->cfg_blocks[last_non_empty];
          if (bb->successors_count == 2 && ctx->ir_base[bb->end].op == IR_IF) {
            b = ctx->cfg_edges[bb->successors];

            if (!ir_bitqueue_in(&blocks, b)) {
              b = ctx->cfg_edges[bb->successors + 1];
            }
            if (ir_bitqueue_in(&blocks, b)) {
              bb = &ctx->cfg_blocks[b];
              ir_bitqueue_del(&blocks, b);
              continue;
            }
          }
        }
        /* End trace */
        break;
      }
      b = best_successor;
      bb = best_successor_bb;
      ir_bitqueue_del(&blocks, b);
    } while (1);
  }

  IR_ASSERT(list + count == schedule_end);
  ctx->cfg_schedule = list;
  ir_bitqueue_free(&blocks);

  return 1;
}

int ir_schedule_blocks(ir_ctx *ctx)
{
  ir_ref ref;

  if (ctx->cfg_blocks_count <= 2) {
    return 1;
  }

  /* Mark "stop" blocks termintated with UNREACHABLE as "unexpected" */
  ref = ctx->ir_base[1].op1;
  while (ref) {
    ir_insn *insn = &ctx->ir_base[ref];

    if (insn->op == IR_UNREACHABLE && ctx->ir_base[insn->op1].op != IR_TAILCALL) {
      ir_block *bb = &ctx->cfg_blocks[ctx->cfg_map[ref]];
      uint32_t n = bb->predecessors_count;

      if (n == 1) {
        ir_insn *start_insn = &ctx->ir_base[bb->start];
        if (start_insn->op == IR_IF_TRUE
         || start_insn->op == IR_IF_FALSE
         || start_insn->op == IR_CASE_DEFAULT) {
          if (!start_insn->op2) start_insn->op2 = 1;
        } else if (start_insn->op == IR_CASE_VAL) {
          if (!start_insn->op3) start_insn->op3 = 1;
        }
      } else if (n > 1) {
        uint32_t *p = &ctx->cfg_edges[bb->predecessors];

        for (; n > 0; p++, n--) {
          bb = &ctx->cfg_blocks[*p];
          if (bb->predecessors_count == 1) {
            ir_insn *start_insn = &ctx->ir_base[bb->start];
            if (start_insn->op == IR_IF_TRUE
             || start_insn->op == IR_IF_FALSE
             || start_insn->op == IR_CASE_DEFAULT) {
              if (!start_insn->op2) start_insn->op2 = 1;
            } else if (start_insn->op == IR_CASE_VAL) {
              if (!start_insn->op3) start_insn->op3 = 1;
            }
          }
        }
      }
    }
    ref = insn->op3;
  }

  /* The bottom-up Pettis-Hansen algorithm is expensive - O(n^3),
   * use it only for relatively small functions.
   *
   * TODO: make the choice between top-down and bottom-up algorithm configurable
   */
  if (UNEXPECTED(ctx->flags2 & IR_IRREDUCIBLE_CFG) || ctx->cfg_blocks_count > 256) {
    return ir_schedule_blocks_top_down(ctx);
  } else {
    return ir_schedule_blocks_bottom_up(ctx);
  }
}

/* JMP target optimisation */
uint32_t ir_skip_empty_target_blocks(const ir_ctx *ctx, uint32_t b)
{
  return _ir_skip_empty_blocks(ctx, b);
}

uint32_t ir_next_block(const ir_ctx *ctx, uint32_t b)
{
  ir_block *bb;

  if (ctx->cfg_schedule) {
    uint32_t ret = ctx->cfg_schedule[++b];

    /* Check for empty ENTRY block */
    while (ret && ((ctx->cfg_blocks[ret].flags & (IR_BB_START|IR_BB_EMPTY)) == IR_BB_EMPTY)) {
      ret = ctx->cfg_schedule[++b];
    }
    return ret;
  }

  b++;
  while (1) {
    if (b > ctx->cfg_blocks_count) {
      return 0;
    }

    bb = &ctx->cfg_blocks[b];

    if ((bb->flags & (IR_BB_START|IR_BB_EMPTY)) == IR_BB_EMPTY) {
      b++;
    } else {
      break;
    }
  }
  return b;
}

void ir_get_true_false_blocks(const ir_ctx *ctx, uint32_t b, uint32_t *true_block, uint32_t *false_block)
{
  ir_block *bb;
  uint32_t *p, use_block;

  *true_block = 0;
  *false_block = 0;
  bb = &ctx->cfg_blocks[b];
  IR_ASSERT(ctx->ir_base[bb->end].op == IR_IF);
  IR_ASSERT(bb->successors_count == 2);
  p = &ctx->cfg_edges[bb->successors];
  use_block = *p;
  if (ctx->ir_base[ctx->cfg_blocks[use_block].start].op == IR_IF_TRUE) {
    *true_block = ir_skip_empty_target_blocks(ctx, use_block);
    use_block = *(p+1);
    IR_ASSERT(ctx->ir_base[ctx->cfg_blocks[use_block].start].op == IR_IF_FALSE);
    *false_block = ir_skip_empty_target_blocks(ctx, use_block);
  } else {
    IR_ASSERT(ctx->ir_base[ctx->cfg_blocks[use_block].start].op == IR_IF_FALSE);
    *false_block = ir_skip_empty_target_blocks(ctx, use_block);
    use_block = *(p+1);
    IR_ASSERT(ctx->ir_base[ctx->cfg_blocks[use_block].start].op == IR_IF_TRUE);
    *true_block = ir_skip_empty_target_blocks(ctx, use_block);
  }
  IR_ASSERT(*true_block && *false_block);
}

Coverage Report

Created: 2026-02-14 06:52