rs6000.c (rs6000_expand_vector_init): For V4SF inits on power8 and above, use the VMRGEW instruction instead of a permute.

2016-09-20  Michael Meissner  <meissner@linux.vnet.ibm.com>

	* config/rs6000/rs6000.c (rs6000_expand_vector_init): For V4SF
	inits on power8 and above, use the VMRGEW instruction instead of a
	permute.

	* config/rs6000/altivec.md (UNSPEC_VMRGEW_DIRECT): New unspec.
	(p8_vmrgew_v4sf_direct): New VMRGEW insn for V4SF floating
	initialization.

From-SVN: r240272