[Bug c++/104494] New: -Wsuggest-attribute=noreturn catch 22

[Bug c++/104494] New: -Wsuggest-attribute=noreturn catch 22

[f.heckenbach@fh-soft.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104494

            Bug ID: 104494
           Summary: -Wsuggest-attribute=noreturn catch 22
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.heckenbach@fh-soft.de
  Target Milestone: ---

% cat test3.cpp 
void f ()
{
  [] { throw 42; } ();
}
% g++ -Wsuggest-attribute=noreturn -O3 test3.cpp -c
test3.cpp: In function 'void f()':
test3.cpp:1:6: warning: function might be candidate for attribute 'noreturn'
[-Wsuggest-attribute=noreturn]

% cat test3.cpp 
[[noreturn]] void f ()
{
  [] { throw 42; } ();
}
% g++ -Wsuggest-attribute=noreturn -O3 test3.cpp -c
test3.cpp: In function 'void f()':
test3.cpp:4:1: warning: 'noreturn' function does return

clang also gives the latter warning (it doesn't seem to have the
-Wsuggest-attribute=noreturn flag), so maybe something in the standard does
make f unsuitable for [[noreturn]]. But then -Wsuggest-attribute=noreturn
should not suggest so.

[Bug c++/104494] -Wsuggest-attribute=noreturn catch 22

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104494

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org
           Keywords|                            |diagnostic

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think the attribute suggestion happens with some IPA analysis which
figures the lambda is after inlining the lambda but the diagnostic about
a noreturn function returning happens before.

That would mean the attribute suggestion should be based on local analysis
only, not using IPA discovered noreturn.

Not sure how that's easily possible.  We don't suggest noreturn for the
lambda because the C++ FE says it's OK to miss it there.