PR tree-optimization/57741
	* tree-vect-loop.c (vect_is_simple_iv_evolution): Disallow
	non-INTEGRAL_TYPE_P non-SCALAR_FLOAT_TYPE_P SSA_NAME step_exprs,
	or SCALAR_FLOAT_TYPE_P SSA_NAMEs if !flag_associative_math.
	Allow REAL_CST step_exprs if flag_associative_math.
	(get_initial_def_for_induction): Handle SCALAR_FLOAT_TYPE_P step_expr.

	* gcc.dg/vect/pr57741-1.c: New test.
	* gcc.dg/vect/pr57741-2.c: New test.
	* gcc.dg/vect/pr57741-3.c: New test.

From-SVN: r200600