https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101130
Bug ID: 101130
Summary: Broken backward compatibility after
__attribute__-noexcept order change
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: alex at webprise dot net
Target Milestone: ---
Testcase:
void f() {
[]() __attribute__((__noinline__)) noexcept {
void g() noexcept; g(), g();
}();
}
This started to produce (3!) syntax error messages in g++9.1 whereas g++8.5 and
below accept them and do the expected thing.
The new accepted syntax is:
void f() {
[]() noexcept __attribute__((__noinline__)) {
void g() noexcept; g(), g();
}();
}
I do not know whether the change was on purpose, and apparently it has to do
with https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90333 and
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60503. As to the backward
compatibility, I do not know whether many users actually depend on it, but at
least my codebase does depend on this nice trick (to force object code
deduplication for slow paths). The problem is that all versions of clang++
still accept the old syntax and so this affects compiler independence (icpc
accepts both since much time ago), so maybe I should open the bug on them;-)
Using the standard C++ attributes [[__gnu__::__noinline__]] is also not an
option since as a warning message states for both g++ and clang++ and the
assembly output evidences, this applies to the application operator type, not
to the operator itself and so does nothing (a solution is proposed for C++2b).
