system.h: Include <initializer_list> in system.h unconditionally

On Sun, May 01, 2022 at 07:06:53PM +0100, Jonathan Wakely wrote:
> > >> the reason is that "gcc/analyzer/region-model.cc” uses initializer_lists, and it seems that <initializer_list>
> > >> is not transitively included by any used headers for _LIBCPP_VERSION < 4000.  I fixed that locally by
> > >> adding initializer_list into system.h (and adding INCLUDE_INITIALIZER_LIST to the top of gcc/analyzer/region-model.cc)
> > >> - with that change those versions do bootstrap and test OK***
> > >
> > > From what I can see, with libstdc++ it works because <utility> which is
> > > included by system.h includes <initializer_list>.
> > > If I rename initializer_list in analyzer/region-model.ii to initializer_listx, I
> > > also get:
> > > ../../gcc/analyzer/region-model.cc: In function ‘void ana::selftest::test_binop_svalue_folding()’:
> > > ../../gcc/analyzer/region-model.cc:4966:48: error: deducing from brace-enclosed initializer list requires ‘#include <initializer_list>’
> > > 4508 |
> > >  +++ |+#include <initializer_list>
> > > 4509 | static void
> > > ......
> > > 4966 |     for (auto op : {BIT_IOR_EXPR, TRUTH_OR_EXPR})
> > >      |                                                ^
> > > ../../gcc/analyzer/region-model.cc:4978:49: error: deducing from brace-enclosed initializer list requires ‘#include <initializer_list>’
> > > 4978 |     for (auto op : {BIT_AND_EXPR, TRUTH_AND_EXPR})
> > >      |                                                 ^
> > >
> > > I think we have 2 options, one is do what you wrote above,
> > > INCLUDE_INITIALIZER_LIST defined before system.h to get #include <initializer_list>.
> > > The other option is just to include that unconditionally, it is a very small
> > > header.  For libstdc++ it will make no difference as it is included anyway
> > > and the header is really small there, libc++ includes <cstddef> which isn't
> > > normally included and system.h includes <stddef.h> instead.
> >
> > I’d say unconditionally would be OK. I suppose the chance that any host
> > C++ is good enough to build GCC as-is but fails to provide
> > <initializer_list> is zero?
> >
>
> Yes, definitely.
>
> > I’d be OK to do this change without a new RC even.

2022-05-02  Jakub Jelinek  <jakub@redhat.com>

	* system.h: Include initializer_list.

(cherry picked from commit 4a0e89b10f)

gcc/system.h

@@ -239,6 +239,7 @@ extern int errno;
 # include <functional>
 #endif
 # include <cstring>
+# include <initializer_list>
 # include <new>
 # include <utility>
 # include <type_traits>