configure.ac: Set aliasing_flags to -fno-strict-aliasing if...

gcc/ChangeLog:

	* configure.ac: Set aliasing_flags to -fno-strict-aliasing if
	the host compiler is affected by placement new aliasing bug.
	* configure: Regenerate.
	* Makefile.in (ALIASING_FLAGS): New variable.
	(ALL_CXXFLAGS): Add $(ALIASING_FLAGS).

From-SVN: r226499

gcc/ChangeLog

+2015-08-03  Ulrich Weigand  <Ulrich.Weigand@de.ibm.com>
+
+	* configure.ac: Set aliasing_flags to -fno-strict-aliasing if
+	the host compiler is affected by placement new aliasing bug.
+	* configure: Regenerate.
+	* Makefile.in (ALIASING_FLAGS): New variable.
+	(ALL_CXXFLAGS): Add $(ALIASING_FLAGS).
+
 2015-08-03  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	PR target/66731

gcc/Makefile.in

@@ -180,6 +180,8 @@ NOCOMMON_FLAG = @nocommon_flag@
 
 NOEXCEPTION_FLAGS = @noexception_flags@
 
+ALIASING_FLAGS = @aliasing_flags@
+
 # This is set by --disable-maintainer-mode (default) to "#"
 # FIXME: 'MAINT' will always be set to an empty string, no matter if
 # --disable-maintainer-mode is used or not.  This is because the
@@ -986,7 +988,8 @@ ALL_CFLAGS = $(T_CFLAGS) $(CFLAGS-$@) \
 
 # The C++ version.
 ALL_CXXFLAGS = $(T_CFLAGS) $(CFLAGS-$@) $(CXXFLAGS) $(INTERNAL_CFLAGS) \
-  $(COVERAGE_FLAGS) $(NOEXCEPTION_FLAGS) $(WARN_CXXFLAGS) @DEFS@
+  $(COVERAGE_FLAGS) $(ALIASING_FLAGS) $(NOEXCEPTION_FLAGS) \
+  $(WARN_CXXFLAGS) @DEFS@
 
 # Likewise.  Put INCLUDES at the beginning: this way, if some autoconf macro
 # puts -I options in CPPFLAGS, our include files in the srcdir will always

gcc/configure

@@ -789,6 +789,7 @@ c_strict_warn
 strict_warn
 c_loose_warn
 loose_warn
+aliasing_flags
 CPP
 EGREP
 GREP
@@ -6526,6 +6527,42 @@ fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 fi
 
+# Check whether compiler is affected by placement new aliasing bug (PR 29286).
+# If the host compiler is affected by the bug, and we build with optimization
+# enabled (which happens e.g. when cross-compiling), the pool allocator may
+# get miscompiled.  Use -fno-strict-aliasing to work around this problem.
+# Since there is no reliable feature check for the presence of this bug,
+# we simply use a GCC version number check.  (This should never trigger for
+# stages 2 or 3 of a native bootstrap.)
+aliasing_flags=
+if test "$GCC" = yes; then
+  saved_CXXFLAGS="$CXXFLAGS"
+
+  # The following test compilation will succeed if and only if $CXX accepts
+  # -fno-strict-aliasing *and* is older than GCC 4.3.
+  CXXFLAGS="$CXXFLAGS -fno-strict-aliasing"
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CXX is affected by placement new aliasing bug" >&5
+$as_echo_n "checking whether $CXX is affected by placement new aliasing bug... " >&6; }
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+#if (__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+#error compiler not affected by placement new aliasing bug
+#endif
+
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }; aliasing_flags='-fno-strict-aliasing'
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+  CXXFLAGS="$saved_CXXFLAGS"
+fi
+
 
 
 
@@ -18301,7 +18338,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 18304 "configure"
+#line 18341 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -18407,7 +18444,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 18410 "configure"
+#line 18447 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H

gcc/configure.ac

@@ -416,6 +416,32 @@ struct X<long long> { typedef long long t; };
 ]], [[X<int64_t>::t x;]])],[],[AC_MSG_ERROR([error verifying int64_t uses long long])])
 fi
 
+# Check whether compiler is affected by placement new aliasing bug (PR 29286).
+# If the host compiler is affected by the bug, and we build with optimization
+# enabled (which happens e.g. when cross-compiling), the pool allocator may
+# get miscompiled.  Use -fno-strict-aliasing to work around this problem.
+# Since there is no reliable feature check for the presence of this bug,
+# we simply use a GCC version number check.  (This should never trigger for
+# stages 2 or 3 of a native bootstrap.)
+aliasing_flags=
+if test "$GCC" = yes; then
+  saved_CXXFLAGS="$CXXFLAGS"
+
+  # The following test compilation will succeed if and only if $CXX accepts
+  # -fno-strict-aliasing *and* is older than GCC 4.3.
+  CXXFLAGS="$CXXFLAGS -fno-strict-aliasing"
+  AC_MSG_CHECKING([whether $CXX is affected by placement new aliasing bug])
+  AC_COMPILE_IFELSE([
+#if (__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+#error compiler not affected by placement new aliasing bug
+#endif
+],
+    [AC_MSG_RESULT([yes]); aliasing_flags='-fno-strict-aliasing'],
+    [AC_MSG_RESULT([no])])
+
+  CXXFLAGS="$saved_CXXFLAGS"
+fi
+AC_SUBST(aliasing_flags)