[AVR] Don't assert on an undefined operand

Not all operands are correctly disassembled at the moment. This means
that some machine instructions won't have all the necessary operands
set.
To avoid asserting, print an error instead until the necessary support
has been implemented.

Differential Revision: https://reviews.llvm.org/D73958

Author: aykevl

llvm/lib/Target/AVR/MCTargetDesc/AVRInstPrinter.cpp

@@ -100,6 +100,16 @@ const char *AVRInstPrinter::getPrettyRegisterName(unsigned RegNum,
 
 void AVRInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
                                   raw_ostream &O) {
+  if (OpNo >= MI->size()) {
+    // Not all operands are correctly disassembled at the moment. This means
+    // that some machine instructions won't have all the necessary operands
+    // set.
+    // To avoid asserting, print <unknown> instead until the necessary support
+    // has been implemented.
+    O << "<unknown>";
+    return;
+  }
+
   const MCOperand &Op = MI->getOperand(OpNo);
   const MCOperandInfo &MOI = this->MII.get(MI->getOpcode()).OpInfo[OpNo];
 
@@ -125,6 +135,16 @@ void AVRInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
 /// being encoded as a pc-relative value.
 void AVRInstPrinter::printPCRelImm(const MCInst *MI, unsigned OpNo,
                                    raw_ostream &O) {
+  if (OpNo >= MI->size()) {
+    // Not all operands are correctly disassembled at the moment. This means
+    // that some machine instructions won't have all the necessary operands
+    // set.
+    // To avoid asserting, print <unknown> instead until the necessary support
+    // has been implemented.
+    O << "<unknown>";
+    return;
+  }
+
   const MCOperand &Op = MI->getOperand(OpNo);
 
   if (Op.isImm()) {