+/// TailDuplicateAndUpdate - Tail duplicate the block and cleanup.
+bool
+TailDuplicatePass::TailDuplicateAndUpdate(MachineBasicBlock *MBB,
+ bool IsSimple,
+ MachineFunction &MF) {
+ // Save the successors list.
+ SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
+ MBB->succ_end());
+
+ SmallVector<MachineBasicBlock*, 8> TDBBs;
+ SmallVector<MachineInstr*, 16> Copies;
+ if (!TailDuplicate(MBB, IsSimple, MF, TDBBs, Copies))
+ return false;
+
+ ++NumTails;
+
+ SmallVector<MachineInstr*, 8> NewPHIs;
+ MachineSSAUpdater SSAUpdate(MF, &NewPHIs);
+
+ // TailBB's immediate successors are now successors of those predecessors
+ // which duplicated TailBB. Add the predecessors as sources to the PHI
+ // instructions.
+ bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken();
+ if (PreRegAlloc)
+ UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs);
+
+ // If it is dead, remove it.
+ if (isDead) {
+ NumInstrDups -= MBB->size();
+ RemoveDeadBlock(MBB);
+ ++NumDeadBlocks;
+ }
+
+ // Update SSA form.
+ if (!SSAUpdateVRs.empty()) {
+ for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) {
+ unsigned VReg = SSAUpdateVRs[i];
+ SSAUpdate.Initialize(VReg);
+
+ // If the original definition is still around, add it as an available
+ // value.
+ MachineInstr *DefMI = MRI->getVRegDef(VReg);
+ MachineBasicBlock *DefBB = nullptr;
+ if (DefMI) {
+ DefBB = DefMI->getParent();
+ SSAUpdate.AddAvailableValue(DefBB, VReg);
+ }
+
+ // Add the new vregs as available values.
+ DenseMap<unsigned, AvailableValsTy>::iterator LI =
+ SSAUpdateVals.find(VReg);
+ for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) {
+ MachineBasicBlock *SrcBB = LI->second[j].first;
+ unsigned SrcReg = LI->second[j].second;
+ SSAUpdate.AddAvailableValue(SrcBB, SrcReg);
+ }
+
+ // Rewrite uses that are outside of the original def's block.
+ MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg);
+ while (UI != MRI->use_end()) {
+ MachineOperand &UseMO = *UI;
+ MachineInstr *UseMI = UseMO.getParent();
+ ++UI;
+ if (UseMI->isDebugValue()) {
+ // SSAUpdate can replace the use with an undef. That creates
+ // a debug instruction that is a kill.
+ // FIXME: Should it SSAUpdate job to delete debug instructions
+ // instead of replacing the use with undef?
+ UseMI->eraseFromParent();
+ continue;
+ }
+ if (UseMI->getParent() == DefBB && !UseMI->isPHI())
+ continue;
+ SSAUpdate.RewriteUse(UseMO);
+ }
+ }
+
+ SSAUpdateVRs.clear();
+ SSAUpdateVals.clear();
+ }
+
+ // Eliminate some of the copies inserted by tail duplication to maintain
+ // SSA form.
+ for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
+ MachineInstr *Copy = Copies[i];
+ if (!Copy->isCopy())
+ continue;
+ unsigned Dst = Copy->getOperand(0).getReg();
+ unsigned Src = Copy->getOperand(1).getReg();
+ if (MRI->hasOneNonDBGUse(Src) &&
+ MRI->constrainRegClass(Src, MRI->getRegClass(Dst))) {
+ // Copy is the only use. Do trivial copy propagation here.
+ MRI->replaceRegWith(Dst, Src);
+ Copy->eraseFromParent();
+ }
+ }
+
+ if (NewPHIs.size())
+ NumAddedPHIs += NewPHIs.size();
+
+ return true;
+}
+