rs6000.c (swap_web_entry): Update preceding commentary to simplify permute mask adjustment equation.

[gcc]

2015-09-10  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* config/rs6000/rs6000.c (swap_web_entry): Update preceding
	commentary to simplify permute mask adjustment equation.
	(special_handling_values): Add SH_VPERM.
	(const_load_sequence_p): New function.
	(insn_is_swappable_p): Add logic to recognize an UNSPEC_VPERM with
	the mask loaded from the constant pool.
	(adjust_vperm): New function.
	(handle_special_swappables): Call adjust_vperm.
	(dump_swap_insn_table): Handle SH_VPERM.

[gcc/testsuite]

2015-09-10  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* gcc.target/powerpc/swaps-p8-20.c: New test.
	* gcc.target/powerpc/swaps-p8-21.c: New test.

From-SVN: r227664