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;
}
/// Test whether OneUse, a use of Reg, dominates all of Reg's other uses.
static bool OneUseDominatesOtherUses(unsigned Reg, const MachineOperand &OneUse,
const MachineBasicBlock &MBB,
const MachineRegisterInfo &MRI,
const MachineDominatorTree &MDT,
LiveIntervals &LIS,
WebAssemblyFunctionInfo &MFI) {
const LiveInterval &LI = LIS.getInterval(Reg);
const MachineInstr *OneUseInst = OneUse.getParent();
VNInfo *OneUseVNI = LI.getVNInfoBefore(LIS.getInstructionIndex(*OneUseInst));
for (const MachineOperand &Use : MRI.use_nodbg_operands(Reg)) {
if (&Use == &OneUse)
continue;
const MachineInstr *UseInst = Use.getParent();
VNInfo *UseVNI = LI.getVNInfoBefore(LIS.getInstructionIndex(*UseInst));
if (UseVNI != OneUseVNI)
continue;
const MachineInstr *OneUseInst = OneUse.getParent();
if (UseInst == OneUseInst) {
// Another use in the same instruction. We need to ensure that the one
// selected use happens "before" it.
if (&OneUse > &Use)
return false;
} else {
// Test that the use is dominated by the one selected use.
while (!MDT.dominates(OneUseInst, UseInst)) {
// Actually, dominating is over-conservative. Test that the use would
// happen after the one selected use in the stack evaluation order.
//
// This is needed as a consequence of using implicit get_locals for
// uses and implicit set_locals for defs.
if (UseInst->getDesc().getNumDefs() == 0)
return false;
const MachineOperand &MO = UseInst->getOperand(0);
if (!MO.isReg())
return false;
unsigned DefReg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(DefReg) ||
!MFI.isVRegStackified(DefReg))
return false;
assert(MRI.hasOneUse(DefReg));
const MachineOperand &NewUse = *MRI.use_begin(DefReg);
const MachineInstr *NewUseInst = NewUse.getParent();
if (NewUseInst == OneUseInst) {
if (&OneUse > &NewUse)
return false;
break;
}
UseInst = NewUseInst;
}
}
}
return true;
}
/// Test whether MI is a child of some other node in an expression tree.
static bool IsChild(const MachineInstr *MI,
const WebAssemblyFunctionInfo &MFI) {
if (MI->getNumOperands() == 0)
return false;
const MachineOperand &MO = MI->getOperand(0);
if (!MO.isReg() || MO.isImplicit() || !MO.isDef())
return false;
unsigned Reg = MO.getReg();
return TargetRegisterInfo::isVirtualRegister(Reg) &&
MFI.isVRegStackified(Reg);
}