Re[2]: Using -Wall and -Woverloaded-virtual together changes the behaviour of the code

[Vadim Zeitlin <vz-gcc at zeitlins dot org>]

On Tue, 27 Mar 2018 15:08:31 +0200 Mason <slash.tmp@free.fr> wrote:

M> On 23/03/2018 18:47, Vadim Zeitlin wrote:
M> 
M> > I'm running into a rather crazy problem that I can't minimize enough to
M> > create a bug report for, so I'd like to ask here if anybody might have any
M> > ideas about it by chance. The problem is that the behaviour of some piece
M> > of C++ code changes, when compiling using MinGW g++ 7.2 (20180123 version
M> > from Debian Buster) and "-O2", depending on whether both of -Wall and
M> > -Woverloaded-virtual command line options are specified or not.
M> 
M> That is an interesting problem ^_^

 That's a polite way of putting it :-)

M> I wanted to try reproducing, but it seems that Ubuntu only packages old
M> versions of mingw-w64 (6.3 in 17.10; 5.3 in 16.04 LTS)
M> 
M> Do you know if your issue occurs with older versions of mingw-w64?

 No, I don't think so. We did use 6.3 for this project before and didn't
have any such problems with it and my test case works just fine with it
too.

M> In my opinion, if the problem does not occur on "vanilla" gcc, then
M> the issue might lie with the mingw-w64 specific bits.

 It seems it's even worse than that as mingw-w64 from Fedora doesn't seem
to have any problems with the test case neither. So it might be a Debian
problem, and not a gcc one, after all. But looking at Debian-specific
changes at

https://anonscm.debian.org/cgit/collab-maint/gcc-mingw-w64.git/tree/debian/patches/

I really don't see anything even remotely related, so I still have no idea
what's going on here.

 Regards,
VZ

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