Index: llvm/lib/Target/SystemZ/MCTargetDesc/SystemZInstPrinter.cpp
===================================================================
--- llvm/lib/Target/SystemZ/MCTargetDesc/SystemZInstPrinter.cpp
+++ llvm/lib/Target/SystemZ/MCTargetDesc/SystemZInstPrinter.cpp
@@ -41,8 +41,12 @@
 
 void SystemZInstPrinter::printOperand(const MCOperand &MO, const MCAsmInfo *MAI,
                                       raw_ostream &O) {
-  if (MO.isReg())
-    O << '%' << getRegisterName(MO.getReg());
+  if (MO.isReg()) {
+    if (!MO.getReg())
+      O << '0';
+    else
+      O << '%' << getRegisterName(MO.getReg());
+  }
   else if (MO.isImm())
     O << MO.getImm();
   else if (MO.isExpr())
Index: llvm/lib/Target/SystemZ/SystemZInstrInfo.td
===================================================================
--- llvm/lib/Target/SystemZ/SystemZInstrInfo.td
+++ llvm/lib/Target/SystemZ/SystemZInstrInfo.td
@@ -2069,7 +2069,7 @@
     def PPA : SideEffectTernaryRRFc<"ppa", 0xB2E8, GR64, GR64, imm32zx4>;
   def : Pat<(int_s390_ppa_txassist GR32:$src),
             (PPA (INSERT_SUBREG (i64 (IMPLICIT_DEF)), GR32:$src, subreg_l32),
-                 0, 1)>;
+                 zero_reg, 1)>;
 }
 
 //===----------------------------------------------------------------------===//