Fwd: [PATCH 2/4] libstdc++: Adjust build of PCH files accounting configured host support.

[Iain Sandoe <iains.gcc@gmail.com>]

Well, I did try to CC it to this list .. 

> Begin forwarded message:
> 
> From: Iain Sandoe via Gcc-patches <gcc-patches@gcc.gnu.org>
> Subject: [PATCH 2/4] libstdc++: Adjust build of PCH files accounting configured host support.
> Date: 4 November 2021 at 20:02:16 GMT
> To: gcc-patches@gcc.gnu.org
> Cc: Iain Sandoe <iains.gcc@gmail.com>
> Reply-To: iain@sandoe.co.uk
> 
> This takes account of the overall configuration for host PCH support
> when deciding if we should build the libstdc++ PCH files.
> 
> We now require both the support is configured and that we are hosted.
> A non-fatal configure warning is given if the user attempts to
> --disable-host-pch-support --enable-libstdcxx-pch since the latter
> conflicts with the former (but does not prevent a useable libstdc++
> library build).
> 
> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
> 
> libstdc++-v3/ChangeLog:
> 
> 	* acinclude.m4: Account for configured host PCH support.
> 	* configure: Regenerate.
> 	* configure.ac: Act on --enable-host-pch-support.
> ---
> libstdc++-v3/acinclude.m4 | 49 ++++++++++++++++-----------
> libstdc++-v3/configure    | 71 ++++++++++++++++++++++++++-------------
> libstdc++-v3/configure.ac | 11 ++++--
> 3 files changed, 86 insertions(+), 45 deletions(-)
> 
> diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
> index 90ecc4a87a2..87652306691 100644
> --- a/libstdc++-v3/acinclude.m4
> +++ b/libstdc++-v3/acinclude.m4
> @@ -3225,7 +3225,7 @@ AC_DEFUN([GLIBCXX_ENABLE_WCHAR_T], [
> ])
> 
> 
> -dnl
> +≈
> dnl Check to see if building and using a C++ precompiled header can be done.
> dnl
> dnl --enable-libstdcxx-pch=yes
> @@ -3240,29 +3240,40 @@ dnl Substs:
> dnl  glibcxx_PCHFLAGS
> dnl
> AC_DEFUN([GLIBCXX_ENABLE_PCH], [
> -  GLIBCXX_ENABLE(libstdcxx-pch,$1,,[build pre-compiled libstdc++ headers])
> +  dnl This is only allowed if host support is enabled, and we are hosted.
> +  if test "$1" = "yes" && test "$2" = "yes"; then
> +    can_pch=yes
> +  else
> +    can_pch=no
> +  fi
> +  GLIBCXX_ENABLE(libstdcxx-pch,$can_pch,,[build pre-compiled libstdc++ headers])
>   if test $enable_libstdcxx_pch = yes; then
> -    AC_CACHE_CHECK([for compiler with PCH support],
> -      [glibcxx_cv_prog_CXX_pch],
> -      [ac_save_CXXFLAGS="$CXXFLAGS"
> -       CXXFLAGS="$CXXFLAGS -Werror -Winvalid-pch -Wno-deprecated"
> -       AC_LANG_SAVE
> -       AC_LANG_CPLUSPLUS
> -       echo '#include <math.h>' > conftest.h
> -       if $CXX $CXXFLAGS $CPPFLAGS -x c++-header conftest.h \
> +    if test "$2" != "yes"; then
> +      glibcxx_cv_prog_CXX_pch=no
> +      AC_MSG_WARN([PCH headers cannot be built since host PCH is disabled])
> +    else
> +      AC_CACHE_CHECK([for compiler with PCH support],
> +        [glibcxx_cv_prog_CXX_pch],
> +        [ac_save_CXXFLAGS="$CXXFLAGS"
> +         CXXFLAGS="$CXXFLAGS -Werror -Winvalid-pch -Wno-deprecated"
> +         AC_LANG_SAVE
> +         AC_LANG_CPLUSPLUS
> +         echo '#include <math.h>' > conftest.h
> +         if $CXX $CXXFLAGS $CPPFLAGS -x c++-header conftest.h \
> 			  -o conftest.h.gch 1>&5 2>&1 &&
> 		echo '#error "pch failed"' > conftest.h &&
> 	  echo '#include "conftest.h"' > conftest.cc &&
> 	       $CXX -c $CXXFLAGS $CPPFLAGS conftest.cc 1>&5 2>&1 ;
> -       then
> -	 glibcxx_cv_prog_CXX_pch=yes
> -       else
> -	 glibcxx_cv_prog_CXX_pch=no
> -       fi
> -       rm -f conftest*
> -       CXXFLAGS=$ac_save_CXXFLAGS
> -       AC_LANG_RESTORE
> -      ])
> +         then
> +	   glibcxx_cv_prog_CXX_pch=yes
> +         else
> +	   glibcxx_cv_prog_CXX_pch=no
> +         fi
> +         rm -f conftest*
> +         CXXFLAGS=$ac_save_CXXFLAGS
> +         AC_LANG_RESTORE
> +        ])
> +    fi
>     enable_libstdcxx_pch=$glibcxx_cv_prog_CXX_pch
>   fi
> 
> 
> diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
> index 2d68b3672b9..ce82f16c859 100644
> --- a/libstdc++-v3/configure.ac
> +++ b/libstdc++-v3/configure.ac
> @@ -103,7 +103,6 @@ if test "$enable_vtable_verify" = yes; then
>   postdep_objects_CXX="${postdep_objects_CXX} ${glibcxx_builddir}/../libgcc/vtv_end.o"
> fi
> 
> -
> # libtool variables for C++ shared and position-independent compiles.
> #
> # Use glibcxx_lt_pic_flag to designate the automake variable
> @@ -147,8 +146,16 @@ GLIBCXX_ENABLE_HOSTED
> # Enable descriptive messages to standard output on termination.
> GLIBCXX_ENABLE_VERBOSE
> 
> +# The current default is that PCH is supported by the host unless otherwise
> +# stated.
> +AC_ARG_ENABLE(host_pch_support,
> +AS_HELP_STRING([--disable-host-pch-support],
> +	       [Disable host support for precompiled headers]),
> +host_pch_support=$enableval,
> +host_pch_support=yes)
> +
> # Enable compiler support that doesn't require linking.
> -GLIBCXX_ENABLE_PCH($is_hosted)
> +GLIBCXX_ENABLE_PCH($is_hosted, $host_pch_support)
> GLIBCXX_ENABLE_THREADS
> GLIBCXX_ENABLE_ATOMIC_BUILTINS
> GLIBCXX_ENABLE_LOCK_POLICY
> -- 
> 2.24.3 (Apple Git-128)
>