[CodeGen] Fixed unreachable with -print-machineinstrs and custom pseudo source value

[tpr]

Summary

Rev 327580 "[CodeGen] Use MIR syntax for MachineMemOperand printing"
broke -print-machineinstrs for us on AMDGPU, because we have custom
pseudo source values, and MIR serialization does not implement that.

This commit at least restores the functionality of -print-machineinstrs,
even if it does not properly implement the missing MIR serialization
functionality.

Change-Id: I44961c0b90bf6d48c01484ed7a4e466fd300db66

[thegameg]

Thanks! I remember wanting to do this, I must have missed it, sorry.

It LGTM but it's missing a test case for -print-machineinstrs (no need for the whole thing, -print-before or -print-after should do it), so that we don't break this again in the future.

(adding some more reviewers which might be interested in this)

lib/CodeGen/MachineOperand.cpp

case PseudoSourceValue::GlobalValueCallEntry:
           OS, /*PrintType=*/false, MST);
       break;
     case PseudoSourceValue::ExternalSymbolCallEntry:
       OS << "call-entry &";
       printLLVMNameWithoutPrefix(
           OS, cast<ExternalSymbolPseudoSourceValue>(PVal)->getSymbol());
       break;
     case PseudoSourceValue::TargetCustom:
-      llvm_unreachable("TargetCustom pseudo source values are not supported");
+      // FIXME: This is not necessarily the correct MIR serialization format for
+      // a custom pseudo source value, but at least it allows
+      // -print-machineinstrs to work on a target with custom pseudo source
+      // values.
+      OS << "custom ";
+      PVal->printCustom(OS);
       break;
     }
   }
   MachineOperand::printOperandOffset(OS, getOffset());
   if (getBaseAlignment() != getSize())
     OS << ", align " << getBaseAlignment();
   auto AAInfo = getAAInfo();
   if (AAInfo.TBAA) {