https://gcc.gnu.org/g:f3131a07e5095ddb07adbd75ddba546a5e9bcbde
commit f3131a07e5095ddb07adbd75ddba546a5e9bcbde
Author: Arsen Arsenović <ar...@aarsen.me>
Date: Mon Jul 22 15:49:20 2024 +0200
cp+coroutines: teach convert_to_void to diagnose discarded co_awaits
co_await expressions are nearly calls to Awaitable::await_resume, and,
as such, should inherit its nodiscard. A discarded co_await expression
should, hence, act as if its call to await_resume was discarded.
This patch teaches convert_to_void how to discard 'through' a
CO_AWAIT_EXPR. When we discard a CO_AWAIT_EXPR, we can also just discard
the await_resume() call conveniently embedded within it. This results
in a [[nodiscard]] diagnostic that the PR noted was missing.
gcc/cp/ChangeLog:
PR c++/110171
* coroutines.cc (co_await_get_resume_call): New function.
Returns the await_resume expression of a given co_await.
* cp-tree.h (co_await_get_resume_call): New function.
* cvt.cc (convert_to_void): Handle CO_AWAIT_EXPRs and call
maybe_warn_nodiscard on their resume exprs.
gcc/testsuite/ChangeLog:
PR c++/110171
* g++.dg/coroutines/pr110171-1.C: New test.
* g++.dg/coroutines/pr110171.C: New test.
Diff:
---
gcc/cp/coroutines.cc | 15 +++++++++++-
gcc/cp/cp-tree.h | 3 +++
gcc/cp/cvt.cc | 8 +++++++
gcc/testsuite/g++.dg/coroutines/pr110171-1.C | 34 ++++++++++++++++++++++++++++
gcc/testsuite/g++.dg/coroutines/pr110171.C | 32 ++++++++++++++++++++++++++
5 files changed, 91 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 4ddd98673c8d..2b16b4814d10 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -596,6 +596,19 @@ coro_get_destroy_function (tree decl)
return NULL_TREE;
}
+/* Given a CO_AWAIT_EXPR AWAIT_EXPR, return its resume call. */
+
+tree*
+co_await_get_resume_call (tree await_expr)
+{
+ gcc_checking_assert (TREE_CODE (await_expr) == CO_AWAIT_EXPR);
+ tree vec = TREE_OPERAND (await_expr, 3);
+ if (!vec)
+ return nullptr;
+ return &TREE_VEC_ELT (vec, 2);
+}
+
+
/* These functions assumes that the caller has verified that the state for
the decl has been initialized, we try to minimize work here. */
@@ -4566,7 +4579,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree
*destroyer)
param_info *parm_i = param_uses->get (arg);
if (parm_i->trivial_dtor)
continue;
- add_decl_expr (parm_i->guard_var);;
+ add_decl_expr (parm_i->guard_var);
}
add_decl_expr (coro_promise_live);
add_decl_expr (coro_gro_live);
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 0382467431fc..7d50aac4b6b8 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8768,6 +8768,9 @@ extern tree coro_get_actor_function (tree);
extern tree coro_get_destroy_function (tree);
extern tree coro_get_ramp_function (tree);
+extern tree* co_await_get_resume_call (tree await_expr);
+
+
/* contracts.cc */
extern tree make_postcondition_variable (cp_expr);
extern tree make_postcondition_variable (cp_expr, tree);
diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index d95e01c118c4..7b4bd8a9dc44 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -1502,6 +1502,14 @@ convert_to_void (tree expr, impl_conv_void implicit,
tsubst_flags_t complain)
maybe_warn_nodiscard (expr, implicit);
break;
+ case CO_AWAIT_EXPR:
+ {
+ auto awr = co_await_get_resume_call (expr);
+ if (awr && *awr)
+ *awr = convert_to_void (*awr, implicit, complain);
+ break;
+ }
+
default:;
}
expr = resolve_nondeduced_context (expr, complain);
diff --git a/gcc/testsuite/g++.dg/coroutines/pr110171-1.C
b/gcc/testsuite/g++.dg/coroutines/pr110171-1.C
new file mode 100644
index 000000000000..d8aff5824870
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr110171-1.C
@@ -0,0 +1,34 @@
+// { dg-do compile }
+#include <coroutine>
+
+struct must_check_result
+{
+ bool await_ready() { return false; }
+ void await_suspend(std::coroutine_handle<>) {}
+ [[nodiscard]] bool await_resume() { return {}; }
+};
+
+struct task {};
+
+namespace std
+{
+ template<typename... Args>
+ struct coroutine_traits<task, Args...>
+ {
+ struct promise_type
+ {
+ task get_return_object() { return {}; }
+ suspend_always initial_suspend() noexcept { return {}; }
+ suspend_always final_suspend() noexcept { return {}; }
+ void return_void() {}
+ void unhandled_exception() {}
+ };
+ };
+}
+
+task example(auto)
+{
+ co_await must_check_result(); // { dg-warning "-Wunused-result" }
+}
+
+void f() { example(1); }
diff --git a/gcc/testsuite/g++.dg/coroutines/pr110171.C
b/gcc/testsuite/g++.dg/coroutines/pr110171.C
new file mode 100644
index 000000000000..4b82e23656cd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr110171.C
@@ -0,0 +1,32 @@
+// { dg-do compile }
+#include <coroutine>
+
+struct must_check_result
+{
+ bool await_ready() { return false; }
+ void await_suspend(std::coroutine_handle<>) {}
+ [[nodiscard]] bool await_resume() { return {}; }
+};
+
+struct task {};
+
+namespace std
+{
+ template<typename... Args>
+ struct coroutine_traits<task, Args...>
+ {
+ struct promise_type
+ {
+ task get_return_object() { return {}; }
+ suspend_always initial_suspend() noexcept { return {}; }
+ suspend_always final_suspend() noexcept { return {}; }
+ void return_void() {}
+ void unhandled_exception() {}
+ };
+ };
+}
+
+task example()
+{
+ co_await must_check_result(); // { dg-warning "-Wunused-result" }
+}
