[SystemZ] Use subregs for 64-bit truncating stores

Another patch to reduce the duplication of encoding information.
Rather than define separate patterns for truncating 64-bit stores,
use the 32-bit stores with a subreg.  No behavioral changed intended.

llvm-svn: 191365
diff --git a/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp b/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
index 6f6b2bf..d20487a 100644
--- a/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
@@ -819,7 +819,7 @@
                                            unsigned &StoreOpcode) const {
   if (RC == &SystemZ::GR32BitRegClass || RC == &SystemZ::ADDR32BitRegClass) {
     LoadOpcode = SystemZ::L;
-    StoreOpcode = SystemZ::ST32;
+    StoreOpcode = SystemZ::ST;
   } else if (RC == &SystemZ::GR64BitRegClass ||
              RC == &SystemZ::ADDR64BitRegClass) {
     LoadOpcode = SystemZ::LG;