[C++ PATCH] Fix -std=c++11 -std=gnu++11 option handling (PR c++/77948)

Jakub Jelinek jakub@redhat.com
Sat Oct 29 17:09:00 GMT 2016

On Sat, Oct 29, 2016 at 12:41:43PM -0400, Jason Merrill wrote:
> On Sat, Oct 29, 2016 at 12:09 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> > Apparently the driver reorders the options, -std=* options come before
> > all -f* options, so both of the following patches work the same, except
> > when cc1plus is invoked by hand.  The first (inlined) patch solves it
> > more in line how e.g. -fgnu-keywords and similar options are handled, so I think
> > it is preferable (and I've successfully bootstrapped/regtested it on
> > x86_64-linux and i686-linux).  The second (attached) patch handles it
> > by not clearing -fext-numeric-literals during option processing
> > for -std=* options, just in post option handling clears it for the
> > strict c++11+ modes if the option is not specified explicitly.
> > If the driver wouldn't reorder the options, it would handle better
> > cases like -fext-numeric-literals -std=c++11 to mean the same thing
> > as -std=c++11 -fext-numeric-literals etc., but due to the reordering
> > it isn't needed and for consistency we'd also need to change -fgnu-keywords
> > etc.
> I lean toward the second patch because it keeps the logic in a single
> place, but it looks like it doesn't currently handle C++98
> differently.  I don't think we need to change the handling of other
> options to match.

The second patch has that
+      /* Unless -f{,no-}ext-numeric-literals has been used explicitly,
+        for -std=c++{11,14,1z} default to -fno-ext-numeric-literals.  */
+      if (flag_iso && !global_options_set.x_flag_ext_numeric_literals)
+       cpp_opts->ext_numeric_literals = 0;
in a block guarded with cxx_dialect >= cxx11.  So for -std=c++98 it will
just not disable them (the same as the other patch, and the same as
vanilla trunk/6/5 if just using -std=c++98 and not -std=c++11 -std=c++98;
or do you want to change behavior of -std=c++98 to reject those unless
using -std=gnu++98 or -std=c++98 -fext-numeric-literals?  Pedantically
they are GNU extensions, but if we want to be pedantic,
-pedantic/-pedantic-errors already rejects those anyway.


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