coros: mark .CO_YIELD as LEAF [PR106973]

We rely on .CO_YIELD calls being followed by an assignment (optionally)
and then a switch/if in the same basic block.  This implies that a
.CO_YIELD can never end a block.  However, since a call to .CO_YIELD is
still a call, if the function containing it calls setjmp, GCC thinks
that the .CO_YIELD can introduce abnormal control flow, and generates an
edge for the call.

We know this is not the case; .CO_YIELD calls get removed quite early on
and have no effect, and result in no other calls, so .CO_YIELD can be
considered a leaf function, preventing generating an edge when calling
it.

PR c++/106973 - coroutine generator and setjmp

	PR c++/106973

gcc/ChangeLog:

	* internal-fn.def (CO_YIELD): Mark as ECF_LEAF.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/pr106973.C: New test.

2 files changed, 23 insertions, 1 deletions

diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index 75b527b..23b4ab0 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -569,7 +569,7 @@ DEF_INTERNAL_FN (DIVMOD, ECF_CONST | ECF_LEAF, NULL)
 
 /* For coroutines.  */
 DEF_INTERNAL_FN (CO_ACTOR, ECF_NOTHROW | ECF_LEAF, NULL)
-DEF_INTERNAL_FN (CO_YIELD, ECF_NOTHROW, NULL)
+DEF_INTERNAL_FN (CO_YIELD, ECF_NOTHROW | ECF_LEAF, NULL)
 DEF_INTERNAL_FN (CO_SUSPN, ECF_NOTHROW, NULL)
 DEF_INTERNAL_FN (CO_FRAME, ECF_PURE | ECF_NOTHROW | ECF_LEAF, NULL)
 
diff --git a/gcc/testsuite/g++.dg/coroutines/pr106973.C b/gcc/testsuite/g++.dg/coroutines/pr106973.C
new file mode 100644
index 0000000..6db6cbc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr106973.C
@@ -0,0 +1,22 @@
+// https://gcc.gnu.org/PR106973
+// { dg-require-effective-target indirect_jumps }
+#include <coroutine>
+#include <setjmp.h>
+
+struct generator;
+struct generator_promise {
+  generator get_return_object();
+  std::suspend_always initial_suspend();
+  std::suspend_always final_suspend() noexcept;
+  std::suspend_always yield_value(int);
+  void unhandled_exception();
+};
+
+struct generator {
+  using promise_type = generator_promise;
+};
+jmp_buf foo_env;
+generator foo() {
+  setjmp(foo_env);
+  co_yield 1;
+}