* builtins.c (fold_builtin_logb, fold_builtin_significand): New.
	(fold_builtin_1): Use them.
	* fold-const.c (tree_expr_nonnegative_warnv_p): Handle
	BUILT_IN_SIGNIFICAND.

testsuite:
	* gcc.dg/torture/builtin-logb-1.c: New test.
	* gcc.dg/torture/builtin-math-2.c: Test logb/ilogb.
	* gcc.dg/torture/builtin-nonneg-1.c: Test significand.
	* gcc.dg/torture/builtin-frexp-1.c: Use -fno-finite-math-only on
	sh* targets.

From-SVN: r122257