[CodeGen] Add begin-end iterators to MachineInstr

[javed.absar]

Summary

Probably there are more use cases of this,
but I got triggered by the one included in this patch

[kparzysz]

There is already MachineInstr::operands. Why do we need this?

[rovka]

include/llvm/CodeGen/MachineInstr.h

308

This looks identical to operands_begin/operands_end. I don't see a good reason for having both.
I don't know what to say about being concise vs being explicit in this context. @echristo, WDYT?

lib/Target/ARM/ARMMCInstLower.cpp

156

Unless I'm missing something (Friday evening etc etc), you can use

for (const auto &MO : MI->operands())

to the same effect.

[echristo]

lib/Target/ARM/ARMMCInstLower.cpp

156

Agreed, and it's more clear what you mean here.

[javed.absar]

Ok, I see that now too. Will use MI->operands() as suggested, as that will suffice.

[rovka]

LGTM.

[javed.absar]

Thanks Diana.

include/llvm/CodeGen/MachineInstr.h

public:
   }
 
   /// Returns the number of non-implicit operands.
   unsigned getNumExplicitOperands() const;
 
   /// iterator/begin/end - Iterate over all operands of a machine instruction.
   using mop_iterator = MachineOperand *;
   using const_mop_iterator = const MachineOperand *;
+  using const_iterator  = const MachineOperand *;
 
   mop_iterator operands_begin() { return Operands; }
   mop_iterator operands_end() { return Operands + NumOperands; }
 
   const_mop_iterator operands_begin() const { return Operands; }
   const_mop_iterator operands_end() const { return Operands + NumOperands; }
 
+  const_iterator begin() const { return Operands; }
+  const_iterator end() const { return Operands + NumOperands; }
+
   iterator_range<mop_iterator> operands() {
     return make_range(operands_begin(), operands_end());
   }
   iterator_range<const_mop_iterator> operands() const {
     return make_range(operands_begin(), operands_end());
   }
   iterator_range<mop_iterator> explicit_operands() {
     return make_range(operands_begin(),

lib/Target/ARM/ARMMCInstLower.cpp

void llvm::LowerARMMachineInstrToMCInst(const MachineInstr *MI, MCInst &OutMI,
   case ARM::BICri:
   case ARM::RSBri:
   case ARM::RSBSri:
   case ARM::RSCri:
     EncodeImms = true;
     break;
   }
 
-  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
-    const MachineOperand &MO = MI->getOperand(i);
-
+  for (auto MO : *MI) {
     MCOperand MCOp;
     if (AP.lowerOperand(MO, MCOp)) {
       if (MCOp.isImm() && EncodeImms) {
         int32_t Enc = ARM_AM::getSOImmVal(MCOp.getImm());
         if (Enc != -1)
           MCOp.setImm(Enc);
       }
       OutMI.addOperand(MCOp);