PR rtl-optimization/54457
        * simplify-rtx.c (simplify_subreg):
	Simplify (subreg:M (op:N ((x:N) (y:N)), 0)
     	to (op:M (subreg:M (x:N) 0) (subreg:M (x:N) 0)), where
	the outer subreg is effectively a truncation to the original mode M.

testsuite/ChangeLog:

        PR rtl-optimization/54457
        * gcc.target/i386/pr54457.c: New test.

From-SVN: r191928