Initialize ExtAddrMode::Scale

[vitalybuka]

Summary

Detected by msan with:
-Xclang -enable-noundef-analysis -mllvm -msan-eager-checks=1

[kda]

I wonder if this should be placed in the struct as a default initializer. (TargetInstrInfo.h)
Short term, I think you work is right and matches the spirit of existing code.
But it seems like a vulnerability if anyone else were to use the struct and not initialize all members.

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

if (!getMemOperandWithOffset(MemI, Base, Offset, OffsetIsScalable, TRI))
     return None;
 
   if (!Base->isReg())
     return None;
   ExtAddrMode AM;
   AM.BaseReg = Base->getReg();
   AM.Displacement = Offset;
   AM.ScaledReg = 0;
+  AM.Scale = 0;
   return AM;
 }
 
 bool AArch64InstrInfo::getMemOperandWithOffsetWidth(
     const MachineInstr &LdSt, const MachineOperand *&BaseOp, int64_t &Offset,
     bool &OffsetIsScalable, unsigned &Width,
     const TargetRegisterInfo *TRI) const {
   assert(LdSt.mayLoadOrStore() && "Expected a memory operation.");