Hello, Jason, On Apr 6, 2022, Jason Merrill <ja...@redhat.com> wrote:
> On 4/6/22 15:36, Alexandre Oliva wrote: > Please adjust your patch subject lines for the new guidelines adopted > as part of the git transition: > https://gcc.gnu.org/contribute.html#patches Oh, wow, I had missed those guidelines entirely! *blush* Thanks for the pointer. I'm taking note of it for future submissions. >> On targets that return this from cdtors, cxx_eval_call_expression may >> flag flowing off the end of a dtor. That's preempted for ctors, and >> avoided entirely when dtors return void, but when they return this, >> the return value should be conceptually disregarded, without making >> room for such internal ABI details to make a program ill-formed, as in >> g++.dg/cpp2a/constexpr-dtor12.C on arm-eabi. > Is there a PR for this issue? I'm afraid not, it's just one of many testsuite fails that I've been working on cleaning up. > The patch looks fine, but why doesn't the implicit return 'this' on > arm-eabi already make the result non-null? That's a good question that I didn't have an answer for. It's the explicit 'return' statement in T::~T(), turned into a goto, that interrupts the iteration over the stmt list containing the return stmt: <<< Unknown tree: must_not_throw_expr { <<< Unknown tree: cleanup_stmt <<< Unknown tree: cleanup_stmt <<cleanup_point <<< Unknown tree: expr_stmt (void) (((struct T *) this)->D.4458.s = (TARGET_EXPR <D.4487, operato\ r new (4)>;, TARGET_EXPR <D.4488, 1>;, *(int *) D.4487 = NON_LVALUE_EXPR <42>;,\ D.4488 = 0;;, (int *) D.4487;)) >>>>>; // predicted unlikely by goto predictor.; goto <D.4489>; (void) S::~S (&((struct T *) this)->D.4458) >>>; *(struct T *) this = {CLOBBER} >>>; } (*) <D.4489>:; return this; >>> (*) eval'ing this block sets jump_target to <D.4489>, which satisfies the returns(tree*) predicate, so cxx_eval_statement_list bails. Now, ISTM that the goto target selected for the return stmt bypasses the subobject dtor call and the full-object clobber. That sounds like another bug, no? -- Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ Free Software Activist GNU Toolchain Engineer Disinformation flourishes because many people care deeply about injustice but very few check the facts. Ask me about <https://stallmansupport.org>
