* params.def (PARAM_MAX_POW_SQRT_DEPTH): New param.
* tree-ssa-math-opts.c: Include params.h
(pow_synth_sqrt_info): New struct.
(representable_as_half_series_p): New function.
(get_fn_chain): Likewise.
(print_nested_fn): Likewise.
(dump_fractional_sqrt_sequence): Likewise.
(dump_integer_part): Likewise.
(expand_pow_as_sqrts): Likewise.
(gimple_expand_builtin_pow): Use above to attempt to expand
pow as series of square roots. Removed now unused variables.
* gcc.target/aarch64/pow-sqrt-synth-1.c: New test.
* gcc.dg/pow-sqrt.x: New file.
* gcc.dg/pow-sqrt-1.c: New test.
* gcc.dg/pow-sqrt-2.c: Likewise.
* gcc.dg/pow-sqrt-3.c: Likewise.
From-SVN: r223167
