* real.c (real_trunc, real_floor, real_ceil): New functions
	to implement trunc, floor and ceil respectively.
	* real.h (real_trunc, real_floor, real_ceil): Prototype here.
	* builtins.c (integer_valued_real_p): New function to test if
	a floating point expression has an integer valued result.
	(fold_trunc_transparent_mathfn): Optimize foo(foo(x)) as
	foo(x) where foo is an integer rounding function.  Similarly,
	optimize foo(bar(x)) as bar(x), and foo((double)(int)x) as
	(double)(int)x when both foo and bar are integer rounding
	functions and we don't need to honor errno.
	(fold_builtin_trunc, fold_builtin_floor, fold_builtin_ceil):
	New functions to fold trunc, floor and ceil.
	(fold_builtin): Use fold_builtin_trunc to fold BUILT_IN_TRUNC*,
	fold_builtin_floor to fold BUILT_IN_FLOOR* and fold_builtin_ceil
	to fold BUILT_IN_CEIL*.
	* fold-const.c (tree_expr_nonnegative_p): Handle FLOAT_EXPR and
	the remaining integer rounding functions.

	* gcc.dg/builtins-25.c: New testcase.
	* gcc.dg/builtins-26.c: New testcase.

From-SVN: r68903