re PR target/18701 (mmix-knuth-mmixware gcc.c-torture/execute failures: 20010224-1.c, 20020216-1.c, 20040218-1.c, 20040709-2.c)

	PR target/18701
	* combine.c (combine_simplify_rtx): Revert change of 2004-12-31.

From-SVN: r94005