+/// isProfitableToCSE - Return true if it's profitable to eliminate MI with a
+/// common expression that defines Reg.
+bool MachineCSE::isProfitableToCSE(unsigned CSReg, unsigned Reg,
+ MachineInstr *CSMI, MachineInstr *MI) {
+ // FIXME: Heuristics that works around the lack the live range splitting.
+
+ // Heuristics #1: Don't cse "cheap" computating if the def is not local or in an
+ // immediate predecessor. We don't want to increase register pressure and end up
+ // causing other computation to be spilled.
+ if (MI->getDesc().isAsCheapAsAMove()) {
+ MachineBasicBlock *CSBB = CSMI->getParent();
+ MachineBasicBlock *BB = MI->getParent();
+ if (CSBB != BB &&
+ find(CSBB->succ_begin(), CSBB->succ_end(), BB) == CSBB->succ_end())
+ return false;
+ }
+
+ // Heuristics #2: If the expression doesn't not use a vr and the only use
+ // of the redundant computation are copies, do not cse.
+ bool HasVRegUse = false;
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (MO.isReg() && MO.isUse() && MO.getReg() &&
+ TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
+ HasVRegUse = true;
+ break;
+ }
+ }
+ if (!HasVRegUse) {
+ bool HasNonCopyUse = false;
+ for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(Reg),
+ E = MRI->use_nodbg_end(); I != E; ++I) {
+ MachineInstr *Use = &*I;
+ // Ignore copies.
+ if (!isCopy(Use, TII)) {
+ HasNonCopyUse = true;
+ break;
+ }
+ }
+ if (!HasNonCopyUse)
+ return false;
+ }
+
+ // Heuristics #3: If the common subexpression is used by PHIs, do not reuse
+ // it unless the defined value is already used in the BB of the new use.
+ bool HasPHI = false;
+ SmallPtrSet<MachineBasicBlock*, 4> CSBBs;
+ for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(CSReg),
+ E = MRI->use_nodbg_end(); I != E; ++I) {
+ MachineInstr *Use = &*I;
+ HasPHI |= Use->isPHI();
+ CSBBs.insert(Use->getParent());
+ }
+
+ if (!HasPHI)
+ return true;
+ return CSBBs.count(MI->getParent());
+}
+
+void MachineCSE::EnterScope(MachineBasicBlock *MBB) {
+ DEBUG(dbgs() << "Entering: " << MBB->getName() << '\n');
+ ScopeType *Scope = new ScopeType(VNT);
+ ScopeMap[MBB] = Scope;
+}
+
+void MachineCSE::ExitScope(MachineBasicBlock *MBB) {
+ DEBUG(dbgs() << "Exiting: " << MBB->getName() << '\n');
+ DenseMap<MachineBasicBlock*, ScopeType*>::iterator SI = ScopeMap.find(MBB);
+ assert(SI != ScopeMap.end());
+ ScopeMap.erase(SI);
+ delete SI->second;
+}
+
+bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {