From 1f6c1c82eb5001a844b5ac535f6aba4a3257031f Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Fri, 13 Mar 2020 14:30:39 -0400 Subject: [PATCH] c++: Avoid a suspicious -Wnoexcept warning [PR93805] In this PR we're emitting -Wnoexcept warnings about potentially-throwing NSDMIs when computing the noexcept specification of a class's defaulted default constructor. Although these warnings are in some sense valid, this patch takes the route of suppressing them, because: 1. the warning message is confusing in its current form; 2. warning for 'struct C { B b = B(); };' but not for 'struct C { B b; };' is inconsistent; and 3. emitting a warning here arguably doesn't fall under the umbrella of -Wnoexcept, whose documentation says it warns only when a noexcept-expression evaluates to false, but there are no noexcept-expressions here. gcc/cp/ChangeLog: PR c++/93805 * except.c (maybe_noexcept_warning): Add TODO comment. * method.c (walk_field_subobs): Pass tf_none to expr_noexcept_p. gcc/testsuite/ChangeLog: PR c++/93805 * g++.dg/warn/Wnoexcept2.C: New test. --- gcc/cp/ChangeLog | 6 ++++++ gcc/cp/except.c | 5 ++++- gcc/cp/method.c | 2 +- gcc/testsuite/ChangeLog | 5 +++++ gcc/testsuite/g++.dg/warn/Wnoexcept2.C | 15 +++++++++++++++ 5 files changed, 31 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/g++.dg/warn/Wnoexcept2.C diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index 3340f47d506..59db03c0b07 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,3 +1,9 @@ +2020-03-23 Patrick Palka + + PR c++/93805 + * except.c (maybe_noexcept_warning): Add TODO. + * method.c (walk_field_subobs): Pass tf_none to expr_noexcept_p. + 2020-03-23 nathans PR c++/94044 diff --git a/gcc/cp/except.c b/gcc/cp/except.c index 262ba5d309c..7e93c51f9ea 100644 --- a/gcc/cp/except.c +++ b/gcc/cp/except.c @@ -1160,7 +1160,10 @@ struct GTY(()) pending_noexcept { static GTY(()) vec *pending_noexcept_checks; /* FN is a FUNCTION_DECL that caused a noexcept-expr to be false. Warn if - it can't throw. */ + it can't throw. + + TODO: Consider extending -Wnoexcept to do something like walk_subtrees in the + case of a defaulted function that obtained a noexcept(false) spec. */ static void maybe_noexcept_warning (tree fn) diff --git a/gcc/cp/method.c b/gcc/cp/method.c index c131fd41536..41b9ff86bdd 100644 --- a/gcc/cp/method.c +++ b/gcc/cp/method.c @@ -1988,7 +1988,7 @@ walk_field_subobs (tree fields, special_function_kind sfk, tree fnname, if (nsdmi == error_mark_node) *spec_p = error_mark_node; else if (*spec_p != error_mark_node - && !expr_noexcept_p (nsdmi, complain)) + && !expr_noexcept_p (nsdmi, tf_none)) *spec_p = noexcept_false_spec; } /* Don't do the normal processing. */ diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 1d053e07721..5f079f1fca9 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2020-03-23 Patrick Palka + + PR c++/93805 + * g++.dg/warn/Wnoexcept2.C: New test. + 2020-03-23 Jakub Jelinek PR c++/91993 diff --git a/gcc/testsuite/g++.dg/warn/Wnoexcept2.C b/gcc/testsuite/g++.dg/warn/Wnoexcept2.C new file mode 100644 index 00000000000..60541be3575 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Wnoexcept2.C @@ -0,0 +1,15 @@ +// PR c++/93805 +// { dg-do compile { target c++11 } } +// { dg-additional-options "-Wnoexcept" } + +struct B +{ + B() {} +}; + +struct C +{ + B b = B(); +}; + +C c; // { dg-bogus "noexcept-expression" } -- 2.30.2