* builtins.c (expand_builtin): Use expand_builtin_pow to expand
calls for pow, powf, powl and their __builtin_ variants.
(expand_builtin_pow): If the second argument is a constant
integer and compiling with -ffast-math, use expand_powi to
generate RTL if powi_cost is less than POWI_MAX_MULTS.
(powi_cost): New function to return the number of multiplications
necessary to evaluate an Nth power, for integer constant N.
(expand_powi): New function to expand the RTL for evaluating
the Nth power of a floating point value, for integer constant N.
* doc/tm.texi (POWI_MAX_MULTS): Document new target macro.
* gcc.dg/builtins-24.c: New test case.
From-SVN: r68401
