# emit_expr.ludic — lower an expression to IR, returning its register and type.

fn emit_load_at(addr: ptr, ty: ptr) -> Val {
  let r = emit_bind(sconcat("load ", sconcat(llty(ty), sconcat(", ptr ", addr))))
  return val(r, ty)
}

# short-circuit `and`/`or`: seed a slot with (left!=0), branch to decide whether
# to overwrite with (right!=0).
fn emit_logic(e: Node) -> Val {
  let slot = emit_alloca("i32")
  let la = emit_expr(e.a)
  let lc = emit_bind(sconcat("icmp ne i32 ", sconcat(la.code, ", 0")))
  let lz = emit_bind(sconcat("zext i1 ", sconcat(lc, " to i32")))
  emit("  store i32 ");  emit(lz);  emit(", ptr ");  emit(slot);  emit("\n")
  let ev = lbl("sc");  let done = lbl("scend")
  if streq(e.s, "and") { emit("  br i1 ");  emit(lc);  emit(", label %");  emit(ev);  emit(", label %");  emit(done);  emit("\n") }
  else { emit("  br i1 ");  emit(lc);  emit(", label %");  emit(done);  emit(", label %");  emit(ev);  emit("\n") }
  emit(ev);  emit(":\n")
  let rb = emit_expr(e.b)
  let rc = emit_bind(sconcat("icmp ne i32 ", sconcat(rb.code, ", 0")))
  let rz = emit_bind(sconcat("zext i1 ", sconcat(rc, " to i32")))
  emit("  store i32 ");  emit(rz);  emit(", ptr ");  emit(slot);  emit("\n")
  emit("  br label %");  emit(done);  emit("\n")
  emit(done);  emit(":\n")
  return val(emit_bind(sconcat("load i32, ptr ", slot)), "bool")
}

fn cmp_code(op: ptr) -> ptr {
  if streq(op, "<")  { return "slt" }
  if streq(op, "<=") { return "sle" }
  if streq(op, ">")  { return "sgt" }
  if streq(op, ">=") { return "sge" }
  if streq(op, "==") { return "eq" }
  return "ne"
}
fn is_cmp(op: ptr) -> bool {
  return streq(op,"<") or streq(op,"<=") or streq(op,">") or streq(op,">=") or streq(op,"==") or streq(op,"!=")
}
fn arith_code(op: ptr) -> ptr {
  if streq(op, "+") { return "add" }
  if streq(op, "-") { return "sub" }
  if streq(op, "*") { return "mul" }
  if streq(op, "/") { return "sdiv" }
  if streq(op, "&") { return "and" }
  if streq(op, "|") { return "or" }
  if streq(op, "^") { return "xor" }
  if streq(op, "<<") { return "shl" }
  if streq(op, ">>") { return "lshr" }             # logical shift (unsigned)
  return "srem"
}

# widen an int value to Q16.16 by shifting left 16 (a fixed value passes through)
fn to_fixed(v: Val) -> ptr {
  if streq(v.ty, "fixed") { return v.code }
  return emit_bind(sconcat("shl i32 ", sconcat(v.code, ", 16")))
}

fn emit_bin(e: Node) -> Val {
  if streq(e.s, "and") or streq(e.s, "or") { return emit_logic(e) }
  let a = emit_expr(e.a)
  let b = emit_expr(e.b)
  let fx = streq(a.ty, "fixed") or streq(b.ty, "fixed")
  if is_cmp(e.s) {
    var ac = a.code;  var bc = b.code
    if fx { ac = to_fixed(a);  bc = to_fixed(b) }
    let c = emit_bind(sconcat("icmp ", sconcat(cmp_code(e.s), sconcat(" i32 ", sconcat(ac, sconcat(", ", bc))))))
    return val(emit_bind(sconcat("zext i1 ", sconcat(c, " to i32"))), "bool")
  }
  if fx {
    let af = to_fixed(a);  let bf = to_fixed(b)
    if streq(e.s, "*") {
      let a64 = emit_bind(sconcat("sext i32 ", sconcat(af, " to i64")))
      let b64 = emit_bind(sconcat("sext i32 ", sconcat(bf, " to i64")))
      let m = emit_bind(sconcat("mul i64 ", sconcat(a64, sconcat(", ", b64))))
      let sh = emit_bind(sconcat("ashr i64 ", sconcat(m, ", 16")))
      return val(emit_bind(sconcat("trunc i64 ", sconcat(sh, " to i32"))), "fixed")
    }
    if streq(e.s, "/") {
      let a64 = emit_bind(sconcat("sext i32 ", sconcat(af, " to i64")))
      let ash = emit_bind(sconcat("shl i64 ", sconcat(a64, ", 16")))
      let b64 = emit_bind(sconcat("sext i32 ", sconcat(bf, " to i64")))
      let dv = emit_bind(sconcat("sdiv i64 ", sconcat(ash, sconcat(", ", b64))))
      return val(emit_bind(sconcat("trunc i64 ", sconcat(dv, " to i32"))), "fixed")
    }
    let r = emit_bind(sconcat(arith_code(e.s), sconcat(" i32 ", sconcat(af, sconcat(", ", bf)))))
    return val(r, "fixed")
  }
  let r = emit_bind(sconcat(arith_code(e.s), sconcat(" i32 ", sconcat(a.code, sconcat(", ", b.code)))))
  return val(r, "int")
}

fn emit_call(e: Node) -> Val {
  let name = e.a.s
  if streq(name, "self") { if nself == 0 { return val("0", "entity") };  return val(emit_bind(sconcat("load i32, ptr ", self_stk[nself - 1])), "entity") }
  if streq(name, "key") { return val(emit_bind("load i32, ptr @L_key"), "int") }
  if streq(name, "save") { emit("  call void @L_save()\n");  return val("0", "void") }
  if streq(name, "ui_build") { emit("  call void @ui_build()\n");  return val("0", "void") }
  if streq(name, "load") { return val(emit_bind("call i32 @L_load()"), "bool") }
  if streq(name, "quit") { emit("  store i32 0, ptr @L_running\n");  return val("0", "void") }
  if streq(name, "len") { return emit_len(e) }
  if streq(name, "push") { return emit_push(e) }
  if streq(name, "fx") { let a = emit_expr(e.kids[0]);  return val(emit_bind(sconcat("shl i32 ", sconcat(a.code, ", 16"))), "fixed") }
  if streq(name, "flr") { let a = emit_expr(e.kids[0]);  return val(emit_bind(sconcat("ashr i32 ", sconcat(a.code, ", 16"))), "int") }
  if is_intrinsic(name) { return emit_intrinsic(name, e) }
  if is_intrinsic2(name) { return emit_intrinsic2(name, e) }
  if is_math_builtin(name) { return emit_math_builtin(name, e) }
  var fn2 = find_fn(name)
  var cname = name
  if ptr_is_null(fn2) {
    # a builtin like clear()/reg() is satisfied by its rt_ function
    let rtname = sconcat("rt_", name)
    fn2 = find_fn(rtname)
    if ptr_is_null(fn2) { perr(sconcat("unknown function ", name)) }
    cname = rtname
  }
  # evaluate args first (their IR is emitted before the call instruction)
  let args = new []ptr
  let atys = new []ptr
  var i = 0
  while i < len(e.kids) { let v = emit_expr(e.kids[i]);  push(args, v.code);  push(atys, v.ty);  i = i + 1 }
  let rl = llty(fn2.ty)
  emit("  ")
  var rreg = "0"
  if not streq(rl, "void") { rreg = nreg();  emit(rreg);  emit(" = ") }
  emit("call ");  emit(rl);  emit(" @fn_");  emit(cname);  emit("(")
  i = 0
  while i < len(args) {
    if i > 0 { emit(", ") }
    emit(llty(atys[i]));  emit(" ");  emit(args[i])
    i = i + 1
  }
  emit(")\n")
  return val(rreg, fn2.ty)
}

fn emit_expr(e: Node) -> Val {
  if ptr_is_null(e) { return val("0", "int") }
  if e.kind == E_INT  { return val(itoa(e.ival), "int") }
  if e.kind == E_FLOAT { return val(itoa(e.ival), "fixed") }
  if e.kind == E_BOOL { return val(itoa(e.ival), "bool") }
  if e.kind == E_STR  { return val(emit_str_const(e.s), "str") }
  if e.kind == E_NEW  {
    if is_slice_ty(e.s) { return emit_new_slice(e.s) }
    return emit_new_struct(e.s)
  }
  if e.kind == E_ID {
    let li = loc_find(e.s)
    if li >= 0 { return emit_load_at(loc_reg[li], loc_ty[li]) }
    let g = find_global(e.s)
    if not ptr_is_null(g) {
      if g.kind == N_CONST { return val(itoa(g.a.ival), "int") }
      let r = emit_bind(sconcat("load ", sconcat(llty(g.ty), sconcat(", ptr @g_", e.s))))
      return val(r, g.ty)
    }
    # a UI_<name> that is not a const/var resolves to its widget index
    if is_ui_ident(e.s) { return val(itoa(ui_index_of(e.s)), "int") }
    perr(sconcat("unknown identifier ", e.s))
  }
  if e.kind == E_MEMBER {
    if e.a.kind == E_ID {                        # `Enum.Variant` -> its ordinal, a compile-time int
      let ord = enum_ordinal(e.a.s, e.s)
      if ord >= 0 { return val(itoa(ord), "int") }
    }
    let bt = static_type(e.a)                    # `x.field` where field is @Computed -> inline it
    if not ptr_is_null(bt) {
      let cx = computed_expr(bt, e.s)
      if not ptr_is_null(cx) { return emit_expr(qualify_fields(cx, e.a)) }
    }
    let a = emit_member_addr(e);  return emit_load_at(a, g_addr_ty)
  }
  if e.kind == E_INDEX  { let a = emit_index_addr(e);   return emit_load_at(a, g_addr_ty) }
  if e.kind == E_CALL   { return emit_call(e) }
  if e.kind == E_BIN    { return emit_bin(e) }
  if e.kind == E_UN {
    let a = emit_expr(e.a)
    if streq(e.s, "-") { return val(emit_bind(sconcat("sub i32 0, ", a.code)), "int") }
    if streq(e.s, "~") { return val(emit_bind(sconcat("xor i32 ", sconcat(a.code, ", -1"))), "int") }
    let c = emit_bind(sconcat("icmp eq i32 ", sconcat(a.code, ", 0")))
    return val(emit_bind(sconcat("zext i1 ", sconcat(c, " to i32"))), "bool")
  }
  perr("cannot emit expression")
  return val("0", "int")
}