Don't return identity for CONST or symbolic reference

Don't return identity for CONST or symbolic reference

gcc/

2012-08-09  H.J. Lu  <hongjiu.lu@intel.com>

	Backport from mainline
	2012-08-08  Richard Sandiford  <rdsandiford@googlemail.com>
		    H.J. Lu  <hongjiu.lu@intel.com>

	PR rtl-optimization/54157
	* combine.c (gen_lowpart_for_combine): Don't return identity
	for CONST or symbolic reference.

gcc/testsuite/

2012-08-09  H.J. Lu  <hongjiu.lu@intel.com>

	Backport from mainline
	2012-08-08  H.J. Lu  <hongjiu.lu@intel.com>

	PR rtl-optimization/54157
	* gcc.target/i386/pr54157.c: New file.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_7-branch@190256 138bc75d-0d04-0410-961f-82ee72b054a4