builtins.c (real_dconstp, [...]): New, split out from fold_builtin.

builtins.c (real_dconstp, [...]): New, split out from fold_builtin.

	* builtins.c (real_dconstp, fold_builtin_logarithm,
	fold_builtin_exponent): New, split out from fold_builtin.  Also
	generalize to add log2, log10, exp2 and exp10/pow10 equivalents.
	* emit-rtl.c (dconst3, dconst10, dconstthird): New.
	(init_emit_once): Initialize new dconsts, use ARRAY_SIZE in lieu
	of hardcoded array size.
	* fold-const.c (fold): Add cases for exp2, exp10 and pow10.
	(tree_expr_nonnegative_p): Likewise.
	* real.h (dconst3, dconst10, dconstthird): New.

testsuite:
	* gcc.dg/torture/builtin-explog-1.c: New testcase.

From-SVN: r71252