[SystemZ] Optimize floating-point comparisons with zero

This follows the same lines as the integer code.  In the end it seemed
easier to have a second 4-bit mask in TSFlags to specify the compare-like
CC values.  That eats one more TSFlags bit than adding a CCHasUnordered
would have done, but it feels more concise.

llvm-svn: 187883
diff --git a/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp b/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
index c2a6a7f..9ee60aa 100644
--- a/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
@@ -770,6 +770,9 @@
   case SystemZ::LR:   return SystemZ::LTR;
   case SystemZ::LGFR: return SystemZ::LTGFR;
   case SystemZ::LGR:  return SystemZ::LTGR;
+  case SystemZ::LER:  return SystemZ::LTEBR;
+  case SystemZ::LDR:  return SystemZ::LTDBR;
+  case SystemZ::LXR:  return SystemZ::LTXBR;
   default:            return 0;
   }
 }