Work around g++ 4.2's behavior regarding strict aliasing.

	* configure.ac: Set STRICT_ALIASING_CXXFLAGS to
	`-fno-strict-aliasing' when the compiler is g++ 4.2.

ChangeLog

+2010-04-23  Roland Levillain  <roland@lrde.epita.fr>
+
+	Work around g++ 4.2's behavior regarding strict aliasing.
+
+	* configure.ac: Set STRICT_ALIASING_CXXFLAGS to
+	`-fno-strict-aliasing' when the compiler is g++ 4.2.
+
 2010-04-21  Roland Levillain  <roland@lrde.epita.fr>
 
 	Catch up with the new interface of Scribo's unit tests generator.

configure.ac

@@ -47,10 +47,25 @@ fi
 AC_LANG([C++])
 AC_PROG_CXX
 
-# Speed up compiling times.
+# GNU C++ compiler setup.
 if test "$GXX" = yes; then
+  # Speed up compiling times.
   CXXFLAGS="$CXXFLAGS -pipe"
+
+  # The code generated for mln::data::impl::memcpy__() by g++ 4.2 with
+  # a high optimization level (`-O3') and without
+  # `-fno-strict-aliasing' might be wrong, at least with Debian's g++
+  # 4.2 on IA-32 (see also milena/mln/memcpy_.hh).  We observed this
+  # behavior with e.g. milena/apps/graph-morpho/samples-image2d.cc.
+  # Note that Debian's g++ 4.0, 4.1, 4.3 and 4.4 are fine.
+  #
+  # So, when the C++ compiler is g++ 4.2, set STRICT_ALIASING_CXXFLAGS
+  # to `-fno-strict-aliasing'.
+  if $CXX --version | head -n 1 | grep '\b4\.2' >/dev/null 2>&1; then
+    STRICT_ALIASING_CXXFLAGS=-fno-strict-aliasing
+  fi
 fi
+AC_SUBST([STRICT_ALIASING_CXXFLAGS])
 
 
 # Adjusting warning options according to compilers.