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From: Jason Merrill <jason@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r14-1592] c++: NRV and goto [PR92407] Date: Wed, 7 Jun 2023 01:33:35 +0000 (GMT) [thread overview] Message-ID: <20230607013335.7F2D3385735D@sourceware.org> (raw) https://gcc.gnu.org/g:b192e2007e1c98b548f4aa878523b485968d24a4 commit r14-1592-gb192e2007e1c98b548f4aa878523b485968d24a4 Author: Jason Merrill <jason@redhat.com> Date: Sun Jun 4 12:00:55 2023 -0400 c++: NRV and goto [PR92407] Here our named return value optimization was breaking the required destructor when the goto takes 'a' out of scope. The simplest fix is to disable the optimization in the presence of user labels. We could do better by disabling the optimization only if there is a backward goto across the variable declaration, but we don't currently track that. PR c++/92407 gcc/cp/ChangeLog: * typeck.cc (check_return_expr): Prevent NRV in the presence of named labels. gcc/testsuite/ChangeLog: * g++.dg/opt/nrv22.C: New test. Diff: --- gcc/cp/typeck.cc | 3 +++ gcc/testsuite/g++.dg/opt/nrv22.C | 30 ++++++++++++++++++++++++++++++ 2 files changed, 33 insertions(+) diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc index 11fcc7fcd3b..6618c6a2021 100644 --- a/gcc/cp/typeck.cc +++ b/gcc/cp/typeck.cc @@ -11155,6 +11155,9 @@ check_return_expr (tree retval, bool *no_warning) if (fn_returns_value_p && flag_elide_constructors) { if (named_return_value_okay_p + /* The current NRV implementation breaks if a backward goto needs to + destroy the object (PR92407). */ + && !cp_function_chain->x_named_labels && (current_function_return_value == NULL_TREE || current_function_return_value == bare_retval)) current_function_return_value = bare_retval; diff --git a/gcc/testsuite/g++.dg/opt/nrv22.C b/gcc/testsuite/g++.dg/opt/nrv22.C new file mode 100644 index 00000000000..eb889fa615b --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/nrv22.C @@ -0,0 +1,30 @@ +// PR c++/92407 +// { dg-do run } + +struct A +{ + A () { a++; } + A (const A &) { a++; } + ~A () { a--; } + static int a; +}; +int A::a = 0; + +A +foo () +{ + int cnt = 10; +lab: + A a; + if (cnt--) + goto lab; + return a; +} + +int +main () +{ + foo (); + if (A::a) + __builtin_abort (); +}
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