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coroutines: Fix compile error with symmetric transfers [PR94359]

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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.

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.

gcc/cp/ChangeLog:

2020-04-14  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94359
	* coroutines.cc (build_actor_fn): Check that the target can
	support the resume tailcall before mandating it.

gcc/testsuite/ChangeLog:

2020-04-14  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94359
	* g++.dg/coroutines/torture/symmetric-transfer-00-basic.C:
	Expect a run fail for targets without arbitrary indirect
	tail-calls.
This commit is contained in:
Iain Sandoe 2020-04-14 20:37:12 +01:00
parent fa9a57ed91
commit a126a1577f
4 changed files with 35 additions and 8 deletions
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6
gcc/cp/ChangeLog
View File

@ -1,3 +1,9 @@
2020-04-14 Iain Sandoe <iain@sandoe.co.uk>
PR c++/94359
* coroutines.cc (build_actor_fn): Check that the target can
support the resume tailcall before mandating it.
2020-04-14 Patrick Palka <ppalka@redhat.com>
PR c++/85278

22
gcc/cp/coroutines.cc
View File

@ -2376,14 +2376,22 @@ build_actor_fn (location_t loc, tree coro_frame_type, tree actor, tree fnbody,
tree resume = build_call_expr_loc
(loc, builtin_decl_explicit (BUILT_IN_CORO_RESUME), 1, addr);
/* In order to support an arbitrary number of coroutine continuations,
we must tail call them. However, some targets might not support this
for indirect calls, or calls between DSOs.
FIXME: see if there's an alternate strategy for such targets. */
/* Now we have the actual call, and we can mark it as a tail. */
CALL_EXPR_TAILCALL (resume) = true;
/* ... and for optimisation levels 0..1, mark it as requiring a tail-call
for correctness. It seems that doing this for optimisation levels that
normally perform tail-calling, confuses the ME (or it would be logical
to put this on unilaterally). */
if (optimize < 2)
CALL_EXPR_MUST_TAIL_CALL (resume) = true;
/* Temporarily, switch cfun so that we can use the target hook. */
push_struct_function (actor);
if (targetm.function_ok_for_sibcall (NULL_TREE, resume))
{
/* ... and for optimisation levels 0..1, which do not normally tail-
-call, mark it as requiring a tail-call for correctness. */
if (optimize < 2)
CALL_EXPR_MUST_TAIL_CALL (resume) = true;
}
pop_cfun ();
resume = coro_build_cvt_void_expr_stmt (resume, loc);
add_stmt (resume);
@ -3951,7 +3959,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
push_deferring_access_checks (dk_no_check);
/* Actor ... */
/* Build the actor... */
build_actor_fn (fn_start, coro_frame_type, actor, fnbody, orig, param_uses,
&local_var_uses, param_dtor_list, initial_await, final_await,
body_aw_points.await_number, frame_size);

7
gcc/testsuite/ChangeLog
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@ -1,3 +1,10 @@
2020-04-14 Iain Sandoe <iain@sandoe.co.uk>
PR c++/94359
* g++.dg/coroutines/torture/symmetric-transfer-00-basic.C:
Expect a run fail for targets without arbitrary indirect
tail-calls.
2020-04-14 Patrick Palka <ppalka@redhat.com>
PR c++/93207

8
gcc/testsuite/g++.dg/coroutines/torture/symmetric-transfer-00-basic.C
View File

@ -1,4 +1,10 @@
// { dg-do run }
// { dg-do run }
// See PR94359 - some targets are unable to make general indirect tailcalls
// for example, between different DSOs.
// { dg-xfail-run-if "" { hppa*-*-hpux11* } }
// { dg-xfail-run-if "" { ia64-*-linux-gnu } }
// { dg-xfail-run-if "" { { lp64 && { powerpc*-linux-gnu } } || { *-*-aix* } } }
// { dg-xfail-run-if "" { sparc*-*-* } }
#if __has_include(<coroutine>)