re PR rtl-optimization/576 (gcc performs invalid optimization with float operations...

re PR rtl-optimization/576 (gcc performs invalid optimization with float operations when different rounding mode.)

	PR rtl-optimization/576
	* real.c (real_arithmetic): Change return type from void to bool
	to return an indication that the result may be inexact.
	* real.h (real_arithmeric): Update prototype.
	* fold-const.c (const_binop):  Don't constant fold floating
	point expressions when the user specifies -frounding-math and
	the result may depend upon the run-time rounding mode.
	(fold_convert_const_real_from_real): Clean-up.
	(fold_initializer): Ignore flag_rounding_math for initializers.
	* simplify-rtx.c (simplify_binary_operation): Likewise, don't
	constant fold FP operations with flag_rounding_math if the
	result may depend upon the run-time rounding mode.

From-SVN: r94020