re PR target/81550 (gcc.target/powerpc/loop_align.c fails starting with r250482)

re PR target/81550 (gcc.target/powerpc/loop_align.c fails starting with r250482)

2018-01-29  Michael Meissner  <meissner@linux.vnet.ibm.com>

	PR target/81550
	* config/rs6000/rs6000.c (rs6000_setup_reg_addr_masks): If DFmode
	and SFmode can go in Altivec registers (-mcpu=power7 for DFmode,
	-mcpu=power8 for SFmode) don't set the PRE_INCDEC or PRE_MODIFY
	flags.  This restores the settings used before the 2017-07-24.
	Turning off pre increment/decrement/modify allows IVOPTS to
	optimize DF/SF loops where the index is an int.

From-SVN: r257166