add check for tab character

Author: Tony Tao

llvm/lib/Target/SystemZ/MCTargetDesc/SystemZHLASMInstPrinter.cpp

@@ -36,6 +36,10 @@ void SystemZHLASMInstPrinter::printInst(const MCInst *MI, uint64_t Address,
   // Eat the first tab character and replace it with a space since it is
   // hardcoded in AsmWriterEmitter::EmitPrintInstruction
   // TODO: introduce a line prefix member to AsmWriter to avoid this problem
-  O << " " << Str.substr(1, Str.length());
+  if (!Str.empty() && Str.front() == '\t')
+    O << " " << Str.substr(1, Str.length());
+  else
+    O << Str;
+
   printAnnotation(O, Annot);
 }