S/390: Fix rounding for _Decimal128 to _Decimal32 conversion

We do not have a direct conversion instruction from 128 bit DFP to 32
bit DFP so this needs to be done in two steps.  The first needs to be
done with the "prepare for shorter precision rounding mode" in order
to produce a correct result.

gcc/ChangeLog:

2016-03-11  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* config/s390/s390.md ("trunctddd2"): Turn former define_insn into
	define_expand.
	("*trunctddd2"): New pattern definition.
	("trunctdsd2"): Set prep_for_short_prec rounding mode for the
	TD->DD truncation.

gcc/testsuite/ChangeLog:

2016-03-11  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* gcc.target/s390/dfp-1.c: New test.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@234134 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 49 insertions, 3 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0cfc1e2eadd..6e85072e916 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,13 @@
 2016-03-11  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
 
+	* config/s390/s390.md ("trunctddd2"): Turn former define_insn into
+	define_expand.
+	("*trunctddd2"): New pattern definition.
+	("trunctdsd2"): Set prep_for_short_prec rounding mode for the
+	TD->DD truncation.
+
+2016-03-11  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
+
 	* config/s390/s390.md (BFP_RND_*, DFP_RND_*): Add new constant
 	definitions for BFP and DFP rounding modes.
 	("fixuns_truncdddi2", "fixuns_trunctddi2")
diff --git a/gcc/config/s390/s390.md b/gcc/config/s390/s390.md
index 185a3f8511b..5a9f1c8a606 100644
--- a/gcc/config/s390/s390.md
+++ b/gcc/config/s390/s390.md
@@ -4847,12 +4847,22 @@
 ; trunctddd2 and truncddsd2 instruction pattern(s).
 ;
 
-(define_insn "trunctddd2"
+
+(define_expand "trunctddd2"
+  [(parallel
+    [(set (match_operand:DD 0 "register_operand" "")
+	  (float_truncate:DD (match_operand:TD 1 "register_operand" "")))
+     (unspec:DI [(const_int DFP_RND_CURRENT)] UNSPEC_ROUND)
+     (clobber (scratch:TD))])]
+  "TARGET_HARD_DFP")
+
+(define_insn "*trunctddd2"
   [(set (match_operand:DD 0 "register_operand" "=f")
 	(float_truncate:DD (match_operand:TD 1 "register_operand" "f")))
-   (clobber (match_scratch:TD 2 "=f"))]
+   (unspec:DI [(match_operand:DI 2 "const_mask_operand" "I")] UNSPEC_ROUND)
+   (clobber (match_scratch:TD 3 "=f"))]
   "TARGET_HARD_DFP"
-  "ldxtr\t%2,0,%1,0\;ldr\t%0,%2"
+  "ldxtr\t%3,%2,%1,0\;ldr\t%0,%3"
   [(set_attr "length"  "6")
    (set_attr "type"    "ftruncdd")])
 
@@ -4868,6 +4878,7 @@
   [(parallel
     [(set (match_dup 3)
 	  (float_truncate:DD (match_operand:TD 1 "register_operand" "")))
+     (unspec:DI [(const_int DFP_RND_PREP_FOR_SHORT_PREC)] UNSPEC_ROUND)
      (clobber (match_scratch:TD 2 ""))])
    (set (match_operand:SD 0 "register_operand" "")
 	(float_truncate:SD (match_dup 3)))]
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index be04568f5dd..254b6bccff3 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2016-03-11  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
+
+	* gcc.target/s390/dfp-1.c: New test.
+
 2016-03-10  Nick Clifton  <nickc@redhat.com>
 
 	PR target/70044
diff --git a/gcc/testsuite/gcc.target/s390/dfp-1.c b/gcc/testsuite/gcc.target/s390/dfp-1.c
new file mode 100644
index 00000000000..109d9fb63f8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/dfp-1.c
@@ -0,0 +1,23 @@
+/* We do not have a direct conversion instruction from 128 bit DFP to
+   32 bit DFP so this needs to be done in two steps.  The first needs
+   to be done with the "prepare for shorter precision rounding mode"
+   in order to produce a correct result.  Otherwise the 8th digit of
+   the number will change from 4 to 5 in the first rounding step which
+   then will turn the last digit of the 32 bit DFP number (the 3) into
+   a 4.  Although with direct rounding it would stay a 3.  */
+
+/* { dg-do run } */
+/* { dg-options "-O3 -march=z10 -mzarch" } */
+
+_Decimal32 __attribute__((noinline))
+foo (_Decimal128 a)
+{
+  return (_Decimal32)a;
+}
+
+int
+main ()
+{
+    if (foo (1.23456349999999999DL) != 1.234563DF)
+    __builtin_abort ();
+}