* simplify-rtx.c (SIGN_EXTEND): New macro.
	(simplify_unary_operation, simplify_binary_operation,
	simplify_relational_operation): Use SIGN_EXTEND.  Make low
	halves of (low, high) pairs unsigned if they weren't already.
	(simplify_ternary_operation): Cast INTVAL to unsigned before
	comparing to a MODE_BITSIZE.

From-SVN: r34109