// selfhost/shared/mir/loop_form_box.hako
// LoopFormBox — minimal loop structure builder (P2: continue/break snapshots + Exit PHI)

using "lang/src/shared/mir/mir_schema_box.hako" as MirSchemaBox

static box LoopFormBox {

  // while (i < limit) {
  //   if (i == break_value) break;
  //   if (i == skip_value) continue;
  //   sum = sum + i;
  //   i = i + 1;
  // }
  // Builds LoopForm structure with Header/Latch PHI + Exit PHI (continue/break aware)
  loop_counter(limit, skip_value, break_value) {
    if skip_value == null { skip_value = 2 }
    if break_value == null { break_value = limit }

    // Preheader (block 0): initialise loop-carried values and constants, then jump header
    local pre = new ArrayBox()
    pre.push(MirSchemaBox.inst_const(1, 0))          // r1 = 0 (initial i)
    pre.push(MirSchemaBox.inst_const(2, limit))      // r2 = limit
    pre.push(MirSchemaBox.inst_const(3, 1))          // r3 = step
    pre.push(MirSchemaBox.inst_const(4, 0))          // r4 = sum
    pre.push(MirSchemaBox.inst_const(5, skip_value)) // r5 = continue trigger
    pre.push(MirSchemaBox.inst_const(6, break_value))// r6 = break trigger
    pre.push(MirSchemaBox.inst_jump(1))              // goto header

    // Header (block 1): PHI(i), PHI(sum), compare, branch
    local header = new ArrayBox()
    local phi_i_inputs = new ArrayBox()
    phi_i_inputs.push(MirSchemaBox.phi_incoming(0, 1))   // from preheader
    phi_i_inputs.push(MirSchemaBox.phi_incoming(7, 18))  // from latch
    header.push(MirSchemaBox.inst_phi(10, phi_i_inputs)) // r10 = current i

    local phi_sum_inputs = new ArrayBox()
    phi_sum_inputs.push(MirSchemaBox.phi_incoming(0, 4))  // from preheader
    phi_sum_inputs.push(MirSchemaBox.phi_incoming(7, 19)) // from latch
    header.push(MirSchemaBox.inst_phi(11, phi_sum_inputs))// r11 = current sum

    header.push(MirSchemaBox.inst_compare("Lt", 10, 2, 12))  // r12 = (i < limit)
    header.push(MirSchemaBox.inst_branch(12, 2, 8))          // body or exit

    // Body entry (block 2): if (i == break) -> break else check continue
    local body_check_break = new ArrayBox()
    body_check_break.push(MirSchemaBox.inst_compare("Eq", 10, 6, 13)) // r13 = (i == break)
    body_check_break.push(MirSchemaBox.inst_branch(13, 3, 4))

    // Break path (block 3): jump directly to exit; exit PHI snapshots current sum
    local break_block = new ArrayBox()
    break_block.push(MirSchemaBox.inst_jump(8))

    // Continue check (block 4): if (i == skip) -> continue else body work
    local continue_check = new ArrayBox()
    continue_check.push(MirSchemaBox.inst_compare("Eq", 10, 5, 14)) // r14 = (i == skip)
    continue_check.push(MirSchemaBox.inst_branch(14, 5, 6))

    // Continue path (block 5): snapshot sum, increment i, jump latch
    local continue_block = new ArrayBox()
    continue_block.push(MirSchemaBox.inst_binop("Add", 10, 3, 15)) // r15 = i + step
    continue_block.push(MirSchemaBox.inst_jump(7))

    // Body work (block 6): sum += i; i += step; jump latch
    local body_block = new ArrayBox()
    body_block.push(MirSchemaBox.inst_binop("Add", 11, 10, 16)) // r16 = sum + i
    body_block.push(MirSchemaBox.inst_binop("Add", 10, 3, 17))  // r17 = i + step
    body_block.push(MirSchemaBox.inst_jump(7))

    // Latch (block 7): PHI merge for continue/normal, then jump header
    local latch_block = new ArrayBox()
    local latch_phi_i = new ArrayBox()
    latch_phi_i.push(MirSchemaBox.phi_incoming(5, 15)) // continue path
    latch_phi_i.push(MirSchemaBox.phi_incoming(6, 17)) // body path
    latch_block.push(MirSchemaBox.inst_phi(18, latch_phi_i)) // feeds header.i

    local latch_phi_sum = new ArrayBox()
    latch_phi_sum.push(MirSchemaBox.phi_incoming(5, 11)) // continue keeps sum
    latch_phi_sum.push(MirSchemaBox.phi_incoming(6, 16)) // body updated sum
    latch_block.push(MirSchemaBox.inst_phi(19, latch_phi_sum)) // feeds header.sum
    latch_block.push(MirSchemaBox.inst_jump(1))

    // Exit (block 8): Merge sums from header fallthrough and break edge, then return
    local exit_vals = new ArrayBox()
    exit_vals.push(MirSchemaBox.phi_incoming(1, 11)) // normal completion
    exit_vals.push(MirSchemaBox.phi_incoming(3, 11)) // break path
    local exit_block = new ArrayBox()
    exit_block.push(MirSchemaBox.inst_phi(20, exit_vals))
    exit_block.push(MirSchemaBox.inst_ret(20))

    // Assemble blocks
    local blocks = new ArrayBox()
    blocks.push(MirSchemaBox.block(0, pre))
    blocks.push(MirSchemaBox.block(1, header))
    blocks.push(MirSchemaBox.block(2, body_check_break))
    blocks.push(MirSchemaBox.block(3, break_block))
    blocks.push(MirSchemaBox.block(4, continue_check))
    blocks.push(MirSchemaBox.block(5, continue_block))
    blocks.push(MirSchemaBox.block(6, body_block))
    blocks.push(MirSchemaBox.block(7, latch_block))
    blocks.push(MirSchemaBox.block(8, exit_block))

    return MirSchemaBox.module(MirSchemaBox.fn_main(blocks))
  }
}