Implementing frame lowering

Frame lowering involves emitting function prologue and epilogue. The prologue happens at the beginning of a function. It sets up the stack frame of the called function. The epilogue happens last in a function, it restores the stack frame of the calling (parent) function.

The "stack" serves several purposes in the execution of a program, as follows:

• Keeping track of return address, when calling a function

• Storage of local variables in the context of a function call

• Passing arguments from the caller to the callee.

Thus there are 2 main functions that need to be defined when implementing frame lowering – emitPrologue() and emitEpilogue().

The emitPrologue() function can be defined as follows:

void TOYFrameLowering::emitPrologue(MachineFunction &MF) const {
  const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
  MachineBasicBlock &MBB = MF.front();
  MachineBasicBlock::iterator MBBI = MBB.begin();

  uint64_t StackSize = computeStackSize(MF);
  if...