[PATCH RFC] bootstrap: Update requirement to C++11.

[Jason Merrill]

There seemed to be general agreement last November that we would move to
allowing C++11 features to be used in GCC 11; this patch implements that
direction.  Are changes needed anywhere else?

ChangeLog
2020-05-14  Jason Merrill  <jason@redhat.com>

	* configure.ac: Update bootstrap dialect to -std=gnu++11.

gcc/ChangeLog
2020-05-14  Jason Merrill  <jason@redhat.com>

	* doc/install.texi (Prerequisites): Update boostrap compiler
	requirement to C++11/GCC 4.8.
---
 gcc/doc/install.texi | 14 ++++++++------
 configure.ac         |  6 +++---
 ChangeLog            |  4 ++++
 configure            |  6 +++---
 4 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index 876b04f9c45..f47e3c76f73 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -238,15 +238,17 @@ described below.
 
 @heading Tools/packages necessary for building GCC
 @table @asis
-@item ISO C++98 compiler
-Necessary to bootstrap GCC, although versions of GCC prior
-to 4.8 also allow bootstrapping with a ISO C89 compiler and versions
-of GCC prior to 3.4 also allow bootstrapping with a traditional
-(K&R) C compiler.
+@item ISO C++11 compiler
+Necessary to bootstrap GCC.
+
+Versions of GCC prior to 11 also allow bootstrapping with an ISO C++98
+compiler, versions of GCC prior to 4.8 also allow bootstrapping with a
+ISO C89 compiler, and versions of GCC prior to 3.4 also allow
+bootstrapping with a traditional (K&R) C compiler.
 
 To build all languages in a cross-compiler or other configuration where
 3-stage bootstrap is not performed, you need to start with an existing
-GCC binary (version 3.4 or later) because source code for language
+GCC binary (version 4.8 or later) because source code for language
 frontends other than C might use GCC extensions.
 
 Note that to bootstrap GCC with versions of GCC earlier than 3.4, you
diff --git a/configure.ac b/configure.ac
index c78d9cbea62..63d92b73061 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1462,10 +1462,10 @@ case "$have_compiler:$host:$target:$enable_bootstrap" in
     ;;
 esac
 
-# When bootstrapping with GCC, build stage 1 in C++98 mode to ensure that a
-# C++98 compiler can still start the bootstrap.
+# When bootstrapping with GCC, build stage 1 in C++11 mode to ensure that a
+# C++11 compiler can still start the bootstrap.
 if test "$enable_bootstrap:$GXX" = "yes:yes"; then
-  CXX="$CXX -std=gnu++98"
+  CXX="$CXX -std=gnu++11"
 fi
 
 # Used for setting $lt_cv_objdir
diff --git a/ChangeLog b/ChangeLog
index a7fcf77b9b2..1d281855a3e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2020-05-14  Jason Merrill  <jason@redhat.com>
+
+	* configure.ac: Update bootstrap dialect to -std=gnu++11.
+
 2020-04-29  Thomas Schwinge  <thomas@codesourcery.com>
 
 	PR target/92713
diff --git a/configure b/configure
index 4cc938ebb7d..9b39035bbcc 100755
--- a/configure
+++ b/configure
@@ -5523,10 +5523,10 @@ $as_echo "$as_me: WARNING: trying to bootstrap a cross compiler" >&2;}
     ;;
 esac
 
-# When bootstrapping with GCC, build stage 1 in C++98 mode to ensure that a
-# C++98 compiler can still start the bootstrap.
+# When bootstrapping with GCC, build stage 1 in C++11 mode to ensure that a
+# C++11 compiler can still start the bootstrap.
 if test "$enable_bootstrap:$GXX" = "yes:yes"; then
-  CXX="$CXX -std=gnu++98"
+  CXX="$CXX -std=gnu++11"
 fi
 
 # Used for setting $lt_cv_objdir

base-commit: 4e1592f8e1d6366699e05c0824fc3dc39ca7314b
-- 
2.18.1