S/390: Don't emit prefetch instructions for clrmem

S/390: Don't emit prefetch instructions for clrmem

gcc/ChangeLog:

2018-07-31  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/s390.c (s390_expand_setmem): Make the unrolling to
	depend on whether prefetch instructions will be emitted or not.
	Use TARGET_SETMEM_PFD for checking whether prefetch instructions
	will be emitted or not.
	* config/s390/s390.h (TARGET_SETMEM_PREFETCH_DISTANCE)
	(TARGET_SETMEM_PFD): New macros.

gcc/testsuite/ChangeLog:

2018-07-31  Andreas Krebbel  <krebbel@linux.ibm.com>

	* gcc.target/s390/memset-1.c: Improve testcase.

From-SVN: r263165