static bool MaybeRewriteToFallthrough(MachineInstr &MI, MachineBasicBlock &MBB,
const MachineFunction &MF,
WebAssemblyFunctionInfo &MFI,
MachineRegisterInfo &MRI,
const WebAssemblyInstrInfo &TII,
unsigned FallthroughOpc,
unsigned CopyLocalOpc) {
if (DisableWebAssemblyFallthroughReturnOpt)
return false;
if (&MBB != &MF.back())
return false;
if (&MI != &MBB.back())
return false;
// If the operand isn't stackified, insert a COPY to read the operand and
// stackify it.
MachineOperand &MO = MI.getOperand(0);
unsigned Reg = MO.getReg();
if (!MFI.isVRegStackified(Reg)) {
unsigned NewReg = MRI.createVirtualRegister(MRI.getRegClass(Reg));
BuildMI(MBB, MI, MI.getDebugLoc(), TII.get(CopyLocalOpc), NewReg)
.addReg(Reg);
MO.setReg(NewReg);
MFI.stackifyVReg(NewReg);
}
// Rewrite the return.
MI.setDesc(TII.get(FallthroughOpc));
return true;
}
/// If desirable, rewrite NewReg to a drop register.
static bool MaybeRewriteToDrop(unsigned OldReg, unsigned NewReg,
MachineOperand &MO, WebAssemblyFunctionInfo &MFI,
MachineRegisterInfo &MRI) {
bool Changed = false;
if (OldReg == NewReg) {
Changed = true;
unsigned NewReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));
MO.setReg(NewReg);
MO.setIsDead();
MFI.stackifyVReg(NewReg);
}
return Changed;
}
