https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94359
--- Comment #11 from Iain Sandoe <iains at gcc dot gnu.org> --- Created attachment 48251 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48251&action=edit Patch for testing coroutines: Fix compile error with symmetric transfers [PR94359] For symmetric transfers to work with C++20 coroutines, it is currently necessary to tail call the callee coroutine from resume method of the caller coroutine. The current codegen marks these resume calls as "MUST_TAIL_CALL" to indicate that the tail call is required for correctness, in the general case. Unfortunately, several targets have ABI constraints that prevent an indirect tail-call, which results in the PRs compile error. The change here tests the target sibcall hook for the resume expression and only marks it as requiring a tail call if that's supported. This doesn't fix the underlying problem; that really a solution is needed to allow the tail-calls (or equivalent) to take place - but that will be deferred until next stage 1. The test case is 'xfail-run-if'd for the targets mentioned in this PR since we still want to test that the compile proceeds without error. At compile-time we can't tell if missing the tail-call will cause a specific code to fail, so that most likely a warning for this case would produce a lot of false positives. gcc/cp/ChangeLog: 2020-04-09 Iain Sandoe <i...@sandoe.co.uk> PR c++/94359 * coroutines.cc (build_actor_fn): Check that the target can support the resume tail-call before mandating it. gcc/testsuite/ChangeLog: 2020-04-09 Iain Sandoe <i...@sandoe.co.uk> PR c++/94359 * g++.dg/coroutines/torture/symmetric-transfer-00-basic.C: Expect a run fail for targets without indirect tail-calls.
