According to IEEE 754 2008 4.3 'Rounding-direction attributes' the
rounding mode of the target format needs to be used. By not setting
the value so far we have always used the DFP rounding mode.

gcc/ChangeLog:

2018-09-12  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/s390.md (PFPO_RND_MODE_DFP, PFPO_RND_MODE_BFP): New
	constants.
	("trunc<BFP:mode><DFP_ALL:mode>2")
	("trunc<DFP_ALL:mode><BFP:mode>2")
	("extend<BFP:mode><DFP_ALL:mode>2")
	("extend<DFP_ALL:mode><BFP:mode>2"): Set proper rounding mode
	according to the target operand type.

gcc/testsuite/ChangeLog:

2018-09-12  Andreas Krebbel  <krebbel@linux.ibm.com>

	* gcc.target/s390/dfp_to_bfp_rounding.c: New test.

From-SVN: r264234