re PR target/79170 (memcmp builtin expansion sequence can overflow)

re PR target/79170 (memcmp builtin expansion sequence can overflow)

2017-01-27  Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	PR target/79170
	* gcc.dg/memcmp-1.c: Improved to catch failures seen in PR 79170.

2017-01-27  Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	PR target/79170
	* config/rs6000/altivec.md (*setb_internal): Rename to setb_signed.
	(setb_unsigned) New pattern for setb with CCUNS.
	* config/rs6000/rs6000.c (expand_block_compare): Use a different
	subfc./subfe sequence to avoid overflow problems.  Generate a
	shorter sequence with cmpld/setb for power9.
	* config/rs6000/rs6000.md (subf<mode>3_carry_dot2): Add a new pattern
	for generating subfc. instruction.
	(cmpstrsi): Add TARGET_POPCNTD predicate as the generate sequence
	now uses this instruction.

From-SVN: r245041