# emit_stmt.ludic — lower statements. Terminators set g_term so the rest of a
# block is skipped until a new basic block opens.

fn emit_block(b: Node) -> void {
  var i = 0
  while i < len(b.kids) {
    if g_term { return }
    emit_stmt(b.kids[i])
    i = i + 1
  }
}

# store `val` (llvm type `lt`) into address `addr`
fn store_at(lt: ptr, v: ptr, addr: ptr) -> void {
  emit("  store ");  emit(lt);  emit(" ");  emit(v);  emit(", ptr ");  emit(addr);  emit("\n")
}

fn emit_assign(st: Node) -> void {
  # resolve the target's address and type
  let t = st.a
  var addr = "0"
  var ty = "int"
  if t.kind == E_ID {
    let li = loc_find(t.s)
    if li >= 0 {
      # a `let` binding is immutable: rebinding it is an error (mutating THROUGH
      # it — `x.field = …`, `x[i] = …` — is fine, and lands in the branches below).
      if loc_mut[li] == 0 { perr(sconcat("cannot assign to immutable '", sconcat(t.s, sconcat("' (declared with let; use var) — line ", itoa(st.line))))) }
      addr = loc_reg[li];  ty = loc_ty[li]
    }
    else {
      let g = find_global(t.s)
      if ptr_is_null(g) { perr(sconcat("assign to unknown ", t.s)) }
      addr = sconcat("@g_", t.s);  ty = g.ty
    }
  } else {
    if t.kind == E_MEMBER { addr = emit_member_addr(t);  ty = g_addr_ty }
    else { if t.kind == E_INDEX { addr = emit_index_addr(t);  ty = g_addr_ty }
      else { perr("bad assignment target") } }
  }
  let lt = llty(ty)
  let rv = emit_expr(st.b)
  var v = rv.code
  if not streq(st.s, "=") {
    let cur = emit_bind(sconcat("load ", sconcat(lt, sconcat(", ptr ", addr))))
    var opc = "add"
    if streq(st.s, "-=") { opc = "sub" }
    if streq(st.s, "*=") { opc = "mul" }
    if streq(st.s, "/=") { opc = "sdiv" }
    v = emit_bind(sconcat(opc, sconcat(" i32 ", sconcat(cur, sconcat(", ", v)))))
  }
  store_at(lt, v, addr)
}

fn emit_if(st: Node) -> void {
  let c = emit_expr(st.a)
  let cc = emit_bind(sconcat("icmp ne i32 ", sconcat(c.code, ", 0")))
  let has_else = not ptr_is_null(st.c)
  let tl = lbl("then");  let el = lbl("else");  let en = lbl("ifend")
  if has_else { emit("  br i1 ");  emit(cc);  emit(", label %");  emit(tl);  emit(", label %");  emit(el);  emit("\n") }
  else { emit("  br i1 ");  emit(cc);  emit(", label %");  emit(tl);  emit(", label %");  emit(en);  emit("\n") }
  emit(tl);  emit(":\n");  g_term = false
  emit_block(st.b)
  if not g_term { emit("  br label %");  emit(en);  emit("\n") }
  if has_else {
    emit(el);  emit(":\n");  g_term = false
    # else is either a block or a nested if-statement
    if st.c.kind == S_IF { emit_stmt(st.c) } else { emit_block(st.c) }
    if not g_term { emit("  br label %");  emit(en);  emit("\n") }
  }
  emit(en);  emit(":\n");  g_term = false
}

fn emit_while(st: Node) -> void {
  let cl = lbl("wcond");  let bl = lbl("wbody");  let en = lbl("wend")
  emit("  br label %");  emit(cl);  emit("\n")
  emit(cl);  emit(":\n")
  let c = emit_expr(st.a)
  let cc = emit_bind(sconcat("icmp ne i32 ", sconcat(c.code, ", 0")))
  emit("  br i1 ");  emit(cc);  emit(", label %");  emit(bl);  emit(", label %");  emit(en);  emit("\n")
  emit(bl);  emit(":\n");  g_term = false
  loop_push(cl, en)
  emit_block(st.b)
  loop_pop()
  if not g_term { emit("  br label %");  emit(cl);  emit("\n") }
  emit(en);  emit(":\n");  g_term = false
}

fn emit_for(st: Node) -> void {
  let slot = emit_alloca("i32")
  let lo = emit_expr(st.a)
  store_at("i32", lo.code, slot)
  loc_push(st.s, slot, "int")
  let cl = lbl("fcond");  let bl = lbl("fbody");  let ct = lbl("fcont");  let en = lbl("fend")
  emit("  br label %");  emit(cl);  emit("\n")
  emit(cl);  emit(":\n")
  let iv = emit_bind(sconcat("load i32, ptr ", slot))
  let hi = emit_expr(st.b)
  let cc = emit_bind(sconcat("icmp slt i32 ", sconcat(iv, sconcat(", ", hi.code))))
  emit("  br i1 ");  emit(cc);  emit(", label %");  emit(bl);  emit(", label %");  emit(en);  emit("\n")
  emit(bl);  emit(":\n");  g_term = false
  loop_push(ct, en)
  emit_block(st.c)
  loop_pop()
  if not g_term { emit("  br label %");  emit(ct);  emit("\n") }
  emit(ct);  emit(":\n")
  let i2 = emit_bind(sconcat("load i32, ptr ", slot))
  let i3 = emit_bind(sconcat("add i32 ", sconcat(i2, ", 1")))
  store_at("i32", i3, slot)
  emit("  br label %");  emit(cl);  emit("\n")
  emit(en);  emit(":\n");  g_term = false
}

fn emit_return(st: Node) -> void {
  if not ptr_is_null(st.a) {
    let v = emit_expr(st.a)
    store_at(llty(ret_ty), v.code, "%retval")
  }
  emit("  br label %ret\n")
  g_term = true
}

fn arm_is_default(arm: Node) -> bool {
  var p = 0
  while p < len(arm.kids) { if arm.kids[p].kind == E_ID and streq(arm.kids[p].s, "_") { return true }; p = p + 1 }
  return false
}

fn emit_match(st: Node) -> void {
  let sv = emit_expr(st.a)
  let endl = lbl("mend")
  var deflt: Node = ptr_null()
  var i = 0
  while i < len(st.kids) {
    let arm = st.kids[i]
    if arm_is_default(arm) { deflt = arm }
    else {
      var acc = "0"
      var first = true
      var p = 0
      while p < len(arm.kids) {
        let pv = emit_expr(arm.kids[p])
        let c = emit_bind(sconcat("icmp eq i32 ", sconcat(sv.code, sconcat(", ", pv.code))))
        if first { acc = c;  first = false }
        else { acc = emit_bind(sconcat("or i1 ", sconcat(acc, sconcat(", ", c)))) }
        p = p + 1
      }
      let bodyl = lbl("mbody");  let nextl = lbl("marm")
      emit("  br i1 ");  emit(acc);  emit(", label %");  emit(bodyl);  emit(", label %");  emit(nextl);  emit("\n")
      emit(bodyl);  emit(":\n");  g_term = false
      emit_block(arm.a)
      if not g_term { emit("  br label %");  emit(endl);  emit("\n") }
      emit(nextl);  emit(":\n");  g_term = false
    }
    i = i + 1
  }
  if not ptr_is_null(deflt) { emit_block(deflt.a) }
  if not g_term { emit("  br label %");  emit(endl);  emit("\n") }
  emit(endl);  emit(":\n");  g_term = false
}

fn emit_stmt(st: Node) -> void {
  if st.kind == S_LET {
    var ty = st.ty
    if ptr_is_null(ty) { let v0 = emit_expr(st.a);  ty = v0.ty
      let slot = emit_alloca(llty(ty));  store_at(llty(ty), v0.code, slot);  loc_push(st.s, slot, ty);  loc_set_mut(st.ival);  return }
    let slot = emit_alloca(llty(ty))
    if ptr_is_null(st.a) {
      var z = "0"
      if streq(llty(ty), "ptr") { z = "null" }
      store_at(llty(ty), z, slot)
    } else { let v = emit_expr(st.a);  store_at(llty(ty), v.code, slot) }
    loc_push(st.s, slot, ty)
    loc_set_mut(st.ival)
    return
  }
  if st.kind == S_ASSIGN { emit_assign(st); return }
  if st.kind == S_IF { emit_if(st); return }
  if st.kind == S_WHILE { emit_while(st); return }
  if st.kind == S_FOR { emit_for(st); return }
  if st.kind == S_RETURN { emit_return(st); return }
  if st.kind == S_BREAK { emit("  br label %");  emit(brk_lbl[nloop - 1]);  emit("\n");  g_term = true;  return }
  if st.kind == S_CONTINUE { emit("  br label %");  emit(cnt_lbl[nloop - 1]);  emit("\n");  g_term = true;  return }
  if st.kind == S_MATCH { emit_match(st);  return }
  if st.kind == S_QUERY { emit_query(st);  return }
  if st.kind == S_SPAWN { emit_spawn(st);  return }
  if st.kind == S_DESPAWN { emit_despawn(st);  return }
  if st.kind == S_TOGGLE { emit_toggle(st);  return }
  if st.kind == S_MACHINE { emit_machine(st);  return }
  if st.kind == S_BECOME { emit_become(st);  return }
  if st.kind == S_EXPR { let v = emit_expr(st.a);  return }
  perr("cannot emit statement")
}

fn loop_push(cont: ptr, brk: ptr) -> void {
  if nloop < len(cnt_lbl) { cnt_lbl[nloop] = cont;  brk_lbl[nloop] = brk }
  else { push(cnt_lbl, cont);  push(brk_lbl, brk) }
  nloop = nloop + 1
}
fn loop_pop() -> void { nloop = nloop - 1 }