[llvm-bugs] [Bug 41772] New: MachineMemOperand::print - null pointer dereferences

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41772

            Bug ID: 41772
           Summary: MachineMemOperand::print - null pointer dereferences
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: francisvm at yahoo.com, llvm-bugs at lists.llvm.org,
                    luke.cheeseman2 at arm.com, spatel+llvm at rotateright.com

The main implementation dereferences the TargetInstrInfo pointer:

void MachineMemOperand::print(raw_ostream &OS, ModuleSlotTracker &MST,
                              SmallVectorImpl<StringRef> &SSNs,
                              const LLVMContext &Context,
                              const MachineFrameInfo *MFI,
                              const TargetInstrInfo *TII) {
....
  if (getFlags() & MachineMemOperand::MOTargetFlag1)
    OS << '"' << getTargetMMOFlagName(*TII, MachineMemOperand::MOTargetFlag1)
       << "\" ";
  if (getFlags() & MachineMemOperand::MOTargetFlag2)
    OS << '"' << getTargetMMOFlagName(*TII, MachineMemOperand::MOTargetFlag2)
       << "\" ";
  if (getFlags() & MachineMemOperand::MOTargetFlag3)
    OS << '"' << getTargetMMOFlagName(*TII, MachineMemOperand::MOTargetFlag3)
       << "\" ";
....
}

But we have helper variants:

void MachineMemOperand::print(raw_ostream &OS) const {
  ModuleSlotTracker DummyMST(nullptr);
  print(OS, DummyMST);
}

void MachineMemOperand::print(raw_ostream &OS, ModuleSlotTracker &MST) const {
  SmallVector<StringRef, 0> SSNs;
  LLVMContext Ctx;
  print(OS, MST, SSNs, Ctx, nullptr, nullptr);
}

That both result in the TTI arg being passed a nullptr.

We either need to update these helpers to always take a TTI arg (reference
instead of a pointer?) or to make the print function check that TTI isn't null
before calling getTargetMMOFlagName).

Found in scan-build CI:
https://llvm.org/reports/scan-build/report-MachineOperand.cpp-print-14-1.html#EndPath

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