From: Arsen Arsenović <arsen@aarsen.me>
Date: Fri, 23 Aug 2024 18:19:05 +0000 (+0200)
Subject: c++/coros: do not assume coros don't nest [PR113457]
X-Git-Tag: releases/gcc-14.3.0~70
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=805b9914846a1228b84a3c3dd8f9ba2f21f9ff59;p=thirdparty%2Fgcc.git

c++/coros: do not assume coros don't nest [PR113457]

In the testcase presented in the PR, during template expansion, an
tsubst of an operand causes a lambda coroutine to be processed, causing
it to get an initial suspend and final suspend.  The code for assigning
awaitable var names (get_awaitable_var) assumed that the sequence Is ->
Is -> Fs -> Fs is impossible (i.e. that one could only 'open' one
coroutine before closing it at a time), and reset the counter used for
unique numbering each time a final suspend occured.  This assumption is
false in a few cases, usually when lambdas are involved.

Instead of storing this counter in a static-storage variable, we can
store it in coroutine_info.  This struct is local to each function, so
we don't need to worry about "cross-contamination" nor resetting.

	PR c++/113457

gcc/cp/ChangeLog:

	* coroutines.cc (struct coroutine_info): Add integer field
	awaitable_number.  This is a counter used for assigning unique
	names to awaitable temporaries.
	(get_awaitable_var): Use awaitable_number from coroutine_info
	instead of the static int awn.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr113457-1.C: New test.
	* g++.dg/coroutines/pr113457.C: New test.

(cherry picked from commit 5cca7517c5868b7b9aa13992145eb6082ac5d5b9)
---

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index ee0fbc454e6..953297c3c49 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -95,6 +95,10 @@ struct GTY((for_user)) coroutine_info
   tree return_void;   /* The expression for p.return_void() if it exists.  */
   location_t first_coro_keyword; /* The location of the keyword that made this
 				    function into a coroutine.  */
+
+  /* Temporary variable number assigned by get_awaitable_var.  */
+  int awaitable_number = 0;
+
   /* Flags to avoid repeated errors for per-function issues.  */
   bool coro_ret_type_error_emitted;
   bool coro_promise_error_emitted;
@@ -981,15 +985,18 @@ enum suspend_point_kind {
 static tree
 get_awaitable_var (suspend_point_kind suspend_kind, tree v_type)
 {
-  static int awn = 0;
+  auto cinfo = get_coroutine_info (current_function_decl);
+  gcc_checking_assert (cinfo);
   char *buf;
   switch (suspend_kind)
     {
-      default: buf = xasprintf ("Aw%d", awn++); break;
-      case CO_YIELD_SUSPEND_POINT: buf =  xasprintf ("Yd%d", awn++); break;
-      case INITIAL_SUSPEND_POINT: buf =  xasprintf ("Is"); break;
-      case FINAL_SUSPEND_POINT: buf =  xasprintf ("Fs"); awn = 0; break;
-  }
+    default: buf = xasprintf ("Aw%d", cinfo->awaitable_number++); break;
+    case CO_YIELD_SUSPEND_POINT:
+      buf = xasprintf ("Yd%d", cinfo->awaitable_number++);
+      break;
+    case INITIAL_SUSPEND_POINT: buf = xasprintf ("Is"); break;
+    case FINAL_SUSPEND_POINT: buf = xasprintf ("Fs"); break;
+    }
   tree ret = get_identifier (buf);
   free (buf);
   ret = build_lang_decl (VAR_DECL, ret, v_type);
diff --git a/gcc/testsuite/g++.dg/coroutines/pr113457-1.C b/gcc/testsuite/g++.dg/coroutines/pr113457-1.C
new file mode 100644
index 00000000000..fcf67e15271
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr113457-1.C
@@ -0,0 +1,25 @@
+// https://gcc.gnu.org/PR113457
+#include <coroutine>
+
+struct coro
+{
+  struct promise_type
+  {
+    std::suspend_never initial_suspend ();
+    std::suspend_never final_suspend () noexcept;
+    void return_void ();
+    void unhandled_exception ();
+    coro get_return_object ();
+  };
+};
+
+struct not_quite_suspend_never : std::suspend_never
+{};
+
+coro
+foo ()
+{
+  co_await std::suspend_never{},
+    [] () -> coro { co_return; },
+    co_await not_quite_suspend_never{};
+}
diff --git a/gcc/testsuite/g++.dg/coroutines/pr113457.C b/gcc/testsuite/g++.dg/coroutines/pr113457.C
new file mode 100644
index 00000000000..add45a2f892
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr113457.C
@@ -0,0 +1,178 @@
+// https://gcc.gnu.org/PR113457
+namespace std {
+template <typename _Tp, typename _Up = _Tp &&> _Up __declval(int);
+template <typename _Tp> auto declval() noexcept -> decltype(__declval<_Tp>(0));
+template <typename _Tp> struct remove_cv {
+  using type = __remove_cv(_Tp);
+};
+template <typename _Tp> using remove_cv_t = typename remove_cv<_Tp>::type;
+template <typename _Tp> struct remove_reference {
+  using type = __remove_reference(_Tp);
+};
+template <typename _Tp>
+using remove_reference_t = typename remove_reference<_Tp>::type;
+template <typename _Tp> inline constexpr bool is_array_v = __is_array(_Tp);
+template <typename _Tp> struct remove_cvref {};
+namespace ranges {
+} // namespace ranges
+template <typename _Tp>
+[[__nodiscard__]] constexpr typename std::remove_reference<_Tp>::type &&
+move(_Tp &&__t) noexcept {
+  return static_cast<typename std::remove_reference<_Tp>::type &&>(__t);
+}
+template <typename _Iterator> struct iterator_traits;
+namespace __detail {
+template <typename _Iter, typename _Tp> struct __iter_traits_impl {
+  using type = iterator_traits<_Iter>;
+};
+template <typename _Iter, typename _Tp = _Iter>
+using __iter_traits = typename __iter_traits_impl<_Iter, _Tp>::type;
+} // namespace __detail
+template <typename> struct indirectly_readable_traits {};
+namespace __detail {
+template <typename _Tp>
+using __iter_value_t =
+    typename __iter_traits<_Tp, indirectly_readable_traits<_Tp>>::value_type;
+}
+template <typename _Tp>
+using iter_value_t = __detail::__iter_value_t<_Tp>;
+namespace ranges::__access {
+template <typename _Tp> auto __begin(_Tp &__t) {
+    return __t + 0;
+}
+} // namespace ranges::__access
+namespace __detail {
+template <typename _Tp>
+using __range_iter_t =
+    decltype(ranges::__access::__begin(std::declval<_Tp &>()));
+}
+template <typename _Tp> struct iterator_traits<_Tp *> {
+  using value_type = remove_cv_t<_Tp>;
+};
+  namespace ranges {
+  namespace __access {
+  struct _Begin {
+    template <typename _Tp>
+    constexpr auto operator() [[nodiscard]] (_Tp &&__t) const
+	{
+      if constexpr (is_array_v<remove_reference_t<_Tp>>)
+      {
+        return __t + 0;
+      }
+    }
+  };
+  } // namespace __access
+  inline namespace _Cpo {
+  inline constexpr ranges::__access::_Begin begin{};
+  } // namespace _Cpo
+  template <typename _Tp>
+  concept range = requires(_Tp &__t) { ranges::begin(__t); };
+  template <typename _Tp> using iterator_t = std::__detail::__range_iter_t<_Tp>;
+  template <range _Range>
+  using range_value_t = iter_value_t<iterator_t<_Range>>;
+  template <range _Range>
+  struct elements_of {
+    _Range range;
+  };
+  template <typename _Range>
+  elements_of(_Range &&) -> elements_of<_Range &&>;
+  } // namespace ranges
+  inline namespace __n4861 {
+  template <typename _Result, typename = void>
+  struct __coroutine_traits_impl {};
+  template <typename _Result> struct __coroutine_traits_impl<_Result, void> {
+    using promise_type = typename _Result::promise_type;
+  };
+  template <typename _Result, typename... _ArgTypes>
+  struct coroutine_traits : __coroutine_traits_impl<_Result> {};
+  template <typename _Promise = void> struct coroutine_handle;
+  template <typename _Promise> struct coroutine_handle {
+    constexpr void *address() const noexcept { return _M_fr_ptr; }
+    constexpr static coroutine_handle from_address(void *__a) noexcept {
+      coroutine_handle __self;
+      return __self;
+    }
+    constexpr operator coroutine_handle<>() const noexcept {
+      return coroutine_handle<>::from_address(address());
+    }
+    void *_M_fr_ptr = nullptr;
+  };
+  struct suspend_always {
+    constexpr bool await_ready() const noexcept { return false; }
+    constexpr void await_suspend(coroutine_handle<>) const noexcept {}
+    constexpr void await_resume() const noexcept {}
+  };
+  } // namespace __n4861
+  template <typename _Ref, typename _V = void>
+  class generator;
+  namespace __gen {
+  template <typename _Yielded> class _Promise_erased {
+    template <typename _Gen> struct _Recursive_awaiter;
+    struct _Final_awaiter;
+  public:
+    suspend_always initial_suspend() const noexcept;
+    suspend_always yield_value(_Yielded __val) noexcept;
+    template <typename _R2, typename _V2>
+    auto yield_value(
+        ranges::elements_of<generator<_R2, _V2> &&> __r) noexcept {
+      return _Recursive_awaiter{std::move(__r.range)};
+    }
+    template <typename _R>
+    auto yield_value(ranges::elements_of<_R> __r) noexcept {
+      auto __n = []( ranges::iterator_t<_R> __i)
+          -> generator<_Yielded, ranges::range_value_t<_R>>
+	  {
+        co_yield static_cast<_Yielded>(*__i);
+      };
+      return
+      yield_value
+      (
+      ranges::elements_of
+      (
+      __n
+      (  ranges::begin(__r.range))));
+    }
+    _Final_awaiter final_suspend() noexcept;
+    void unhandled_exception() {}
+  };
+  template <typename _Yielded>
+  struct _Promise_erased<_Yielded>::_Final_awaiter {
+    bool await_ready() noexcept;
+    template <typename _Promise>
+    void await_suspend(std::coroutine_handle<_Promise> __c) noexcept {}
+    void await_resume() noexcept {}
+  };
+  template <typename _Yielded>
+  template <typename _Gen>
+  struct _Promise_erased<_Yielded>::_Recursive_awaiter {
+    _Gen _M_gen;
+    constexpr bool await_ready() const noexcept { return false; }
+    template <typename _Promise>
+    void
+    await_suspend(std::coroutine_handle<_Promise> __p) noexcept {}
+    void await_resume() {}
+  };
+  } // namespace __gen
+  template <typename _Ref, typename _V>
+  struct generator
+  {
+    struct promise_type
+    :   __gen::_Promise_erased<const int &>
+    {
+      generator get_return_object() noexcept;
+    };
+  };
+} // namespace std
+using namespace std;
+template <typename... Ranges>
+auto concat(Ranges &&...ranges) -> generator<double, double> {
+  (
+  co_yield
+  ranges::elements_of(ranges), ...);
+}
+auto main() -> int {
+  int const numbers1[] = {4, 8, 15, 16, 23, 42};
+  double const numbers2[] = {4, 8, 15, 16, 23, 42};
+  concat(numbers1, numbers2)
+  ;
+}