| //===- StrongPHIElimination.cpp - Eliminate PHI nodes by inserting copies -===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass eliminates PHI instructions by aggressively coalescing the copies |
| // that would be inserted by a naive algorithm and only inserting the copies |
| // that are necessary. The coalescing technique initially assumes that all |
| // registers appearing in a PHI instruction do not interfere. It then eliminates |
| // proven interferences, using dominators to only perform a linear number of |
| // interference tests instead of the quadratic number of interference tests |
| // that this would naively require. This is a technique derived from: |
| // |
| // Budimlic, et al. Fast copy coalescing and live-range identification. |
| // In Proceedings of the ACM SIGPLAN 2002 Conference on Programming Language |
| // Design and Implementation (Berlin, Germany, June 17 - 19, 2002). |
| // PLDI '02. ACM, New York, NY, 25-32. |
| // |
| // The original implementation constructs a data structure they call a dominance |
| // forest for this purpose. The dominance forest was shown to be unnecessary, |
| // as it is possible to emulate the creation and traversal of a dominance forest |
| // by directly using the dominator tree, rather than actually constructing the |
| // dominance forest. This technique is explained in: |
| // |
| // Boissinot, et al. Revisiting Out-of-SSA Translation for Correctness, Code |
| // Quality and Efficiency, |
| // In Proceedings of the 7th annual IEEE/ACM International Symposium on Code |
| // Generation and Optimization (Seattle, Washington, March 22 - 25, 2009). |
| // CGO '09. IEEE, Washington, DC, 114-125. |
| // |
| // Careful implementation allows for all of the dominator forest interference |
| // checks to be performed at once in a single depth-first traversal of the |
| // dominator tree, which is what is implemented here. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "strongphielim" |
| #include "PHIEliminationUtils.h" |
| #include "llvm/CodeGen/Passes.h" |
| #include "llvm/CodeGen/LiveIntervalAnalysis.h" |
| #include "llvm/CodeGen/MachineDominators.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/ADT/DenseSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Support/Debug.h" |
| using namespace llvm; |
| |
| namespace { |
| class StrongPHIElimination : public MachineFunctionPass { |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| StrongPHIElimination() : MachineFunctionPass(ID) { |
| initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| virtual void getAnalysisUsage(AnalysisUsage&) const; |
| bool runOnMachineFunction(MachineFunction&); |
| |
| private: |
| /// This struct represents a single node in the union-find data structure |
| /// representing the variable congruence classes. There is one difference |
| /// from a normal union-find data structure. We steal two bits from the parent |
| /// pointer . One of these bits is used to represent whether the register |
| /// itself has been isolated, and the other is used to represent whether the |
| /// PHI with that register as its destination has been isolated. |
| /// |
| /// Note that this leads to the strange situation where the leader of a |
| /// congruence class may no longer logically be a member, due to being |
| /// isolated. |
| struct Node { |
| enum Flags { |
| kRegisterIsolatedFlag = 1, |
| kPHIIsolatedFlag = 2 |
| }; |
| Node(unsigned v) : value(v), rank(0) { parent.setPointer(this); } |
| |
| Node *getLeader(); |
| |
| PointerIntPair<Node*, 2> parent; |
| unsigned value; |
| unsigned rank; |
| }; |
| |
| /// Add a register in a new congruence class containing only itself. |
| void addReg(unsigned); |
| |
| /// Join the congruence classes of two registers. This function is biased |
| /// towards the left argument, i.e. after |
| /// |
| /// addReg(r2); |
| /// unionRegs(r1, r2); |
| /// |
| /// the leader of the unioned congruence class is the same as the leader of |
| /// r1's congruence class prior to the union. This is actually relied upon |
| /// in the copy insertion code. |
| void unionRegs(unsigned, unsigned); |
| |
| /// Get the color of a register. The color is 0 if the register has been |
| /// isolated. |
| unsigned getRegColor(unsigned); |
| |
| // Isolate a register. |
| void isolateReg(unsigned); |
| |
| /// Get the color of a PHI. The color of a PHI is 0 if the PHI has been |
| /// isolated. Otherwise, it is the original color of its destination and |
| /// all of its operands (before they were isolated, if they were). |
| unsigned getPHIColor(MachineInstr*); |
| |
| /// Isolate a PHI. |
| void isolatePHI(MachineInstr*); |
| |
| /// Traverses a basic block, splitting any interferences found between |
| /// registers in the same congruence class. It takes two DenseMaps as |
| /// arguments that it also updates: CurrentDominatingParent, which maps |
| /// a color to the register in that congruence class whose definition was |
| /// most recently seen, and ImmediateDominatingParent, which maps a register |
| /// to the register in the same congruence class that most immediately |
| /// dominates it. |
| /// |
| /// This function assumes that it is being called in a depth-first traversal |
| /// of the dominator tree. |
| void SplitInterferencesForBasicBlock( |
| MachineBasicBlock&, |
| DenseMap<unsigned, unsigned> &CurrentDominatingParent, |
| DenseMap<unsigned, unsigned> &ImmediateDominatingParent); |
| |
| // Lowers a PHI instruction, inserting copies of the source and destination |
| // registers as necessary. |
| void InsertCopiesForPHI(MachineInstr*, MachineBasicBlock*); |
| |
| // Merges the live interval of Reg into NewReg and renames Reg to NewReg |
| // everywhere that Reg appears. Requires Reg and NewReg to have non- |
| // overlapping lifetimes. |
| void MergeLIsAndRename(unsigned Reg, unsigned NewReg); |
| |
| MachineRegisterInfo *MRI; |
| const TargetInstrInfo *TII; |
| MachineDominatorTree *DT; |
| LiveIntervals *LI; |
| |
| BumpPtrAllocator Allocator; |
| |
| DenseMap<unsigned, Node*> RegNodeMap; |
| |
| // Maps a basic block to a list of its defs of registers that appear as PHI |
| // sources. |
| DenseMap<MachineBasicBlock*, std::vector<MachineInstr*> > PHISrcDefs; |
| |
| // Maps a color to a pair of a MachineInstr* and a virtual register, which |
| // is the operand of that PHI corresponding to the current basic block. |
| DenseMap<unsigned, std::pair<MachineInstr*, unsigned> > CurrentPHIForColor; |
| |
| // FIXME: Can these two data structures be combined? Would a std::multimap |
| // be any better? |
| |
| // Stores pairs of predecessor basic blocks and the source registers of |
| // inserted copy instructions. |
| typedef DenseSet<std::pair<MachineBasicBlock*, unsigned> > SrcCopySet; |
| SrcCopySet InsertedSrcCopySet; |
| |
| // Maps pairs of predecessor basic blocks and colors to their defining copy |
| // instructions. |
| typedef DenseMap<std::pair<MachineBasicBlock*, unsigned>, MachineInstr*> |
| SrcCopyMap; |
| SrcCopyMap InsertedSrcCopyMap; |
| |
| // Maps inserted destination copy registers to their defining copy |
| // instructions. |
| typedef DenseMap<unsigned, MachineInstr*> DestCopyMap; |
| DestCopyMap InsertedDestCopies; |
| }; |
| |
| struct MIIndexCompare { |
| MIIndexCompare(LiveIntervals *LiveIntervals) : LI(LiveIntervals) { } |
| |
| bool operator()(const MachineInstr *LHS, const MachineInstr *RHS) const { |
| return LI->getInstructionIndex(LHS) < LI->getInstructionIndex(RHS); |
| } |
| |
| LiveIntervals *LI; |
| }; |
| } // namespace |
| |
| STATISTIC(NumPHIsLowered, "Number of PHIs lowered"); |
| STATISTIC(NumDestCopiesInserted, "Number of destination copies inserted"); |
| STATISTIC(NumSrcCopiesInserted, "Number of source copies inserted"); |
| |
| char StrongPHIElimination::ID = 0; |
| INITIALIZE_PASS_BEGIN(StrongPHIElimination, "strong-phi-node-elimination", |
| "Eliminate PHI nodes for register allocation, intelligently", false, false) |
| INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) |
| INITIALIZE_PASS_DEPENDENCY(SlotIndexes) |
| INITIALIZE_PASS_DEPENDENCY(LiveIntervals) |
| INITIALIZE_PASS_END(StrongPHIElimination, "strong-phi-node-elimination", |
| "Eliminate PHI nodes for register allocation, intelligently", false, false) |
| |
| char &llvm::StrongPHIEliminationID = StrongPHIElimination::ID; |
| |
| void StrongPHIElimination::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesCFG(); |
| AU.addRequired<MachineDominatorTree>(); |
| AU.addRequired<SlotIndexes>(); |
| AU.addPreserved<SlotIndexes>(); |
| AU.addRequired<LiveIntervals>(); |
| AU.addPreserved<LiveIntervals>(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| static MachineOperand *findLastUse(MachineBasicBlock *MBB, unsigned Reg) { |
| // FIXME: This only needs to check from the first terminator, as only the |
| // first terminator can use a virtual register. |
| for (MachineBasicBlock::reverse_iterator RI = MBB->rbegin(); ; ++RI) { |
| assert (RI != MBB->rend()); |
| MachineInstr *MI = &*RI; |
| |
| for (MachineInstr::mop_iterator OI = MI->operands_begin(), |
| OE = MI->operands_end(); OI != OE; ++OI) { |
| MachineOperand &MO = *OI; |
| if (MO.isReg() && MO.isUse() && MO.getReg() == Reg) |
| return &MO; |
| } |
| } |
| return NULL; |
| } |
| |
| bool StrongPHIElimination::runOnMachineFunction(MachineFunction &MF) { |
| MRI = &MF.getRegInfo(); |
| TII = MF.getTarget().getInstrInfo(); |
| DT = &getAnalysis<MachineDominatorTree>(); |
| LI = &getAnalysis<LiveIntervals>(); |
| |
| for (MachineFunction::iterator I = MF.begin(), E = MF.end(); |
| I != E; ++I) { |
| for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end(); |
| BBI != BBE && BBI->isPHI(); ++BBI) { |
| unsigned DestReg = BBI->getOperand(0).getReg(); |
| addReg(DestReg); |
| PHISrcDefs[I].push_back(BBI); |
| |
| for (unsigned i = 1; i < BBI->getNumOperands(); i += 2) { |
| MachineOperand &SrcMO = BBI->getOperand(i); |
| unsigned SrcReg = SrcMO.getReg(); |
| addReg(SrcReg); |
| unionRegs(DestReg, SrcReg); |
| |
| MachineInstr *DefMI = MRI->getVRegDef(SrcReg); |
| if (DefMI) |
| PHISrcDefs[DefMI->getParent()].push_back(DefMI); |
| } |
| } |
| } |
| |
| // Perform a depth-first traversal of the dominator tree, splitting |
| // interferences amongst PHI-congruence classes. |
| DenseMap<unsigned, unsigned> CurrentDominatingParent; |
| DenseMap<unsigned, unsigned> ImmediateDominatingParent; |
| for (df_iterator<MachineDomTreeNode*> DI = df_begin(DT->getRootNode()), |
| DE = df_end(DT->getRootNode()); DI != DE; ++DI) { |
| SplitInterferencesForBasicBlock(*DI->getBlock(), |
| CurrentDominatingParent, |
| ImmediateDominatingParent); |
| } |
| |
| // Insert copies for all PHI source and destination registers. |
| for (MachineFunction::iterator I = MF.begin(), E = MF.end(); |
| I != E; ++I) { |
| for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end(); |
| BBI != BBE && BBI->isPHI(); ++BBI) { |
| InsertCopiesForPHI(BBI, I); |
| } |
| } |
| |
| // FIXME: Preserve the equivalence classes during copy insertion and use |
| // the preversed equivalence classes instead of recomputing them. |
| RegNodeMap.clear(); |
| for (MachineFunction::iterator I = MF.begin(), E = MF.end(); |
| I != E; ++I) { |
| for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end(); |
| BBI != BBE && BBI->isPHI(); ++BBI) { |
| unsigned DestReg = BBI->getOperand(0).getReg(); |
| addReg(DestReg); |
| |
| for (unsigned i = 1; i < BBI->getNumOperands(); i += 2) { |
| unsigned SrcReg = BBI->getOperand(i).getReg(); |
| addReg(SrcReg); |
| unionRegs(DestReg, SrcReg); |
| } |
| } |
| } |
| |
| DenseMap<unsigned, unsigned> RegRenamingMap; |
| bool Changed = false; |
| for (MachineFunction::iterator I = MF.begin(), E = MF.end(); |
| I != E; ++I) { |
| MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end(); |
| while (BBI != BBE && BBI->isPHI()) { |
| MachineInstr *PHI = BBI; |
| |
| assert(PHI->getNumOperands() > 0); |
| |
| unsigned SrcReg = PHI->getOperand(1).getReg(); |
| unsigned SrcColor = getRegColor(SrcReg); |
| unsigned NewReg = RegRenamingMap[SrcColor]; |
| if (!NewReg) { |
| NewReg = SrcReg; |
| RegRenamingMap[SrcColor] = SrcReg; |
| } |
| MergeLIsAndRename(SrcReg, NewReg); |
| |
| unsigned DestReg = PHI->getOperand(0).getReg(); |
| if (!InsertedDestCopies.count(DestReg)) |
| MergeLIsAndRename(DestReg, NewReg); |
| |
| for (unsigned i = 3; i < PHI->getNumOperands(); i += 2) { |
| unsigned SrcReg = PHI->getOperand(i).getReg(); |
| MergeLIsAndRename(SrcReg, NewReg); |
| } |
| |
| ++BBI; |
| LI->RemoveMachineInstrFromMaps(PHI); |
| PHI->eraseFromParent(); |
| Changed = true; |
| } |
| } |
| |
| // Due to the insertion of copies to split live ranges, the live intervals are |
| // guaranteed to not overlap, except in one case: an original PHI source and a |
| // PHI destination copy. In this case, they have the same value and thus don't |
| // truly intersect, so we merge them into the value live at that point. |
| // FIXME: Is there some better way we can handle this? |
| for (DestCopyMap::iterator I = InsertedDestCopies.begin(), |
| E = InsertedDestCopies.end(); I != E; ++I) { |
| unsigned DestReg = I->first; |
| unsigned DestColor = getRegColor(DestReg); |
| unsigned NewReg = RegRenamingMap[DestColor]; |
| |
| LiveInterval &DestLI = LI->getInterval(DestReg); |
| LiveInterval &NewLI = LI->getInterval(NewReg); |
| |
| assert(DestLI.ranges.size() == 1 |
| && "PHI destination copy's live interval should be a single live " |
| "range from the beginning of the BB to the copy instruction."); |
| LiveRange *DestLR = DestLI.begin(); |
| VNInfo *NewVNI = NewLI.getVNInfoAt(DestLR->start); |
| if (!NewVNI) { |
| NewVNI = NewLI.createValueCopy(DestLR->valno, LI->getVNInfoAllocator()); |
| MachineInstr *CopyInstr = I->second; |
| CopyInstr->getOperand(1).setIsKill(true); |
| } |
| |
| LiveRange NewLR(DestLR->start, DestLR->end, NewVNI); |
| NewLI.addRange(NewLR); |
| |
| LI->removeInterval(DestReg); |
| MRI->replaceRegWith(DestReg, NewReg); |
| } |
| |
| // Adjust the live intervals of all PHI source registers to handle the case |
| // where the PHIs in successor blocks were the only later uses of the source |
| // register. |
| for (SrcCopySet::iterator I = InsertedSrcCopySet.begin(), |
| E = InsertedSrcCopySet.end(); I != E; ++I) { |
| MachineBasicBlock *MBB = I->first; |
| unsigned SrcReg = I->second; |
| if (unsigned RenamedRegister = RegRenamingMap[getRegColor(SrcReg)]) |
| SrcReg = RenamedRegister; |
| |
| LiveInterval &SrcLI = LI->getInterval(SrcReg); |
| |
| bool isLiveOut = false; |
| for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(), |
| SE = MBB->succ_end(); SI != SE; ++SI) { |
| if (SrcLI.liveAt(LI->getMBBStartIdx(*SI))) { |
| isLiveOut = true; |
| break; |
| } |
| } |
| |
| if (isLiveOut) |
| continue; |
| |
| MachineOperand *LastUse = findLastUse(MBB, SrcReg); |
| assert(LastUse); |
| SlotIndex LastUseIndex = LI->getInstructionIndex(LastUse->getParent()); |
| SrcLI.removeRange(LastUseIndex.getDefIndex(), LI->getMBBEndIdx(MBB)); |
| LastUse->setIsKill(true); |
| } |
| |
| LI->renumber(); |
| |
| Allocator.Reset(); |
| RegNodeMap.clear(); |
| PHISrcDefs.clear(); |
| InsertedSrcCopySet.clear(); |
| InsertedSrcCopyMap.clear(); |
| InsertedDestCopies.clear(); |
| |
| return Changed; |
| } |
| |
| void StrongPHIElimination::addReg(unsigned Reg) { |
| if (RegNodeMap.count(Reg)) |
| return; |
| RegNodeMap[Reg] = new (Allocator) Node(Reg); |
| } |
| |
| StrongPHIElimination::Node* |
| StrongPHIElimination::Node::getLeader() { |
| Node *N = this; |
| Node *Parent = parent.getPointer(); |
| Node *Grandparent = Parent->parent.getPointer(); |
| |
| while (Parent != Grandparent) { |
| N->parent.setPointer(Grandparent); |
| N = Grandparent; |
| Parent = Parent->parent.getPointer(); |
| Grandparent = Parent->parent.getPointer(); |
| } |
| |
| return Parent; |
| } |
| |
| unsigned StrongPHIElimination::getRegColor(unsigned Reg) { |
| DenseMap<unsigned, Node*>::iterator RI = RegNodeMap.find(Reg); |
| if (RI == RegNodeMap.end()) |
| return 0; |
| Node *Node = RI->second; |
| if (Node->parent.getInt() & Node::kRegisterIsolatedFlag) |
| return 0; |
| return Node->getLeader()->value; |
| } |
| |
| void StrongPHIElimination::unionRegs(unsigned Reg1, unsigned Reg2) { |
| Node *Node1 = RegNodeMap[Reg1]->getLeader(); |
| Node *Node2 = RegNodeMap[Reg2]->getLeader(); |
| |
| if (Node1->rank > Node2->rank) { |
| Node2->parent.setPointer(Node1->getLeader()); |
| } else if (Node1->rank < Node2->rank) { |
| Node1->parent.setPointer(Node2->getLeader()); |
| } else if (Node1 != Node2) { |
| Node2->parent.setPointer(Node1->getLeader()); |
| Node1->rank++; |
| } |
| } |
| |
| void StrongPHIElimination::isolateReg(unsigned Reg) { |
| Node *Node = RegNodeMap[Reg]; |
| Node->parent.setInt(Node->parent.getInt() | Node::kRegisterIsolatedFlag); |
| } |
| |
| unsigned StrongPHIElimination::getPHIColor(MachineInstr *PHI) { |
| assert(PHI->isPHI()); |
| |
| unsigned DestReg = PHI->getOperand(0).getReg(); |
| Node *DestNode = RegNodeMap[DestReg]; |
| if (DestNode->parent.getInt() & Node::kPHIIsolatedFlag) |
| return 0; |
| |
| for (unsigned i = 1; i < PHI->getNumOperands(); i += 2) { |
| unsigned SrcColor = getRegColor(PHI->getOperand(i).getReg()); |
| if (SrcColor) |
| return SrcColor; |
| } |
| return 0; |
| } |
| |
| void StrongPHIElimination::isolatePHI(MachineInstr *PHI) { |
| assert(PHI->isPHI()); |
| Node *Node = RegNodeMap[PHI->getOperand(0).getReg()]; |
| Node->parent.setInt(Node->parent.getInt() | Node::kPHIIsolatedFlag); |
| } |
| |
| /// SplitInterferencesForBasicBlock - traverses a basic block, splitting any |
| /// interferences found between registers in the same congruence class. It |
| /// takes two DenseMaps as arguments that it also updates: |
| /// |
| /// 1) CurrentDominatingParent, which maps a color to the register in that |
| /// congruence class whose definition was most recently seen. |
| /// |
| /// 2) ImmediateDominatingParent, which maps a register to the register in the |
| /// same congruence class that most immediately dominates it. |
| /// |
| /// This function assumes that it is being called in a depth-first traversal |
| /// of the dominator tree. |
| /// |
| /// The algorithm used here is a generalization of the dominance-based SSA test |
| /// for two variables. If there are variables a_1, ..., a_n such that |
| /// |
| /// def(a_1) dom ... dom def(a_n), |
| /// |
| /// then we can test for an interference between any two a_i by only using O(n) |
| /// interference tests between pairs of variables. If i < j and a_i and a_j |
| /// interfere, then a_i is alive at def(a_j), so it is also alive at def(a_i+1). |
| /// Thus, in order to test for an interference involving a_i, we need only check |
| /// for a potential interference with a_i+1. |
| /// |
| /// This method can be generalized to arbitrary sets of variables by performing |
| /// a depth-first traversal of the dominator tree. As we traverse down a branch |
| /// of the dominator tree, we keep track of the current dominating variable and |
| /// only perform an interference test with that variable. However, when we go to |
| /// another branch of the dominator tree, the definition of the current dominating |
| /// variable may no longer dominate the current block. In order to correct this, |
| /// we need to use a stack of past choices of the current dominating variable |
| /// and pop from this stack until we find a variable whose definition actually |
| /// dominates the current block. |
| /// |
| /// There will be one push on this stack for each variable that has become the |
| /// current dominating variable, so instead of using an explicit stack we can |
| /// simply associate the previous choice for a current dominating variable with |
| /// the new choice. This works better in our implementation, where we test for |
| /// interference in multiple distinct sets at once. |
| void |
| StrongPHIElimination::SplitInterferencesForBasicBlock( |
| MachineBasicBlock &MBB, |
| DenseMap<unsigned, unsigned> &CurrentDominatingParent, |
| DenseMap<unsigned, unsigned> &ImmediateDominatingParent) { |
| // Sort defs by their order in the original basic block, as the code below |
| // assumes that it is processing definitions in dominance order. |
| std::vector<MachineInstr*> &DefInstrs = PHISrcDefs[&MBB]; |
| std::sort(DefInstrs.begin(), DefInstrs.end(), MIIndexCompare(LI)); |
| |
| for (std::vector<MachineInstr*>::const_iterator BBI = DefInstrs.begin(), |
| BBE = DefInstrs.end(); BBI != BBE; ++BBI) { |
| for (MachineInstr::const_mop_iterator I = (*BBI)->operands_begin(), |
| E = (*BBI)->operands_end(); I != E; ++I) { |
| const MachineOperand &MO = *I; |
| |
| // FIXME: This would be faster if it were possible to bail out of checking |
| // an instruction's operands after the explicit defs, but this is incorrect |
| // for variadic instructions, which may appear before register allocation |
| // in the future. |
| if (!MO.isReg() || !MO.isDef()) |
| continue; |
| |
| unsigned DestReg = MO.getReg(); |
| if (!DestReg || !TargetRegisterInfo::isVirtualRegister(DestReg)) |
| continue; |
| |
| // If the virtual register being defined is not used in any PHI or has |
| // already been isolated, then there are no more interferences to check. |
| unsigned DestColor = getRegColor(DestReg); |
| if (!DestColor) |
| continue; |
| |
| // The input to this pass sometimes is not in SSA form in every basic |
| // block, as some virtual registers have redefinitions. We could eliminate |
| // this by fixing the passes that generate the non-SSA code, or we could |
| // handle it here by tracking defining machine instructions rather than |
| // virtual registers. For now, we just handle the situation conservatively |
| // in a way that will possibly lead to false interferences. |
| unsigned &CurrentParent = CurrentDominatingParent[DestColor]; |
| unsigned NewParent = CurrentParent; |
| if (NewParent == DestReg) |
| continue; |
| |
| // Pop registers from the stack represented by ImmediateDominatingParent |
| // until we find a parent that dominates the current instruction. |
| while (NewParent && (!DT->dominates(MRI->getVRegDef(NewParent), *BBI) |
| || !getRegColor(NewParent))) |
| NewParent = ImmediateDominatingParent[NewParent]; |
| |
| // If NewParent is nonzero, then its definition dominates the current |
| // instruction, so it is only necessary to check for the liveness of |
| // NewParent in order to check for an interference. |
| if (NewParent |
| && LI->getInterval(NewParent).liveAt(LI->getInstructionIndex(*BBI))) { |
| // If there is an interference, always isolate the new register. This |
| // could be improved by using a heuristic that decides which of the two |
| // registers to isolate. |
| isolateReg(DestReg); |
| CurrentParent = NewParent; |
| } else { |
| // If there is no interference, update ImmediateDominatingParent and set |
| // the CurrentDominatingParent for this color to the current register. |
| ImmediateDominatingParent[DestReg] = NewParent; |
| CurrentParent = DestReg; |
| } |
| } |
| } |
| |
| // We now walk the PHIs in successor blocks and check for interferences. This |
| // is necessary because the use of a PHI's operands are logically contained in |
| // the predecessor block. The def of a PHI's destination register is processed |
| // along with the other defs in a basic block. |
| |
| CurrentPHIForColor.clear(); |
| |
| for (MachineBasicBlock::succ_iterator SI = MBB.succ_begin(), |
| SE = MBB.succ_end(); SI != SE; ++SI) { |
| for (MachineBasicBlock::iterator BBI = (*SI)->begin(), BBE = (*SI)->end(); |
| BBI != BBE && BBI->isPHI(); ++BBI) { |
| MachineInstr *PHI = BBI; |
| |
| // If a PHI is already isolated, either by being isolated directly or |
| // having all of its operands isolated, ignore it. |
| unsigned Color = getPHIColor(PHI); |
| if (!Color) |
| continue; |
| |
| // Find the index of the PHI operand that corresponds to this basic block. |
| unsigned PredIndex; |
| for (PredIndex = 1; PredIndex < PHI->getNumOperands(); PredIndex += 2) { |
| if (PHI->getOperand(PredIndex + 1).getMBB() == &MBB) |
| break; |
| } |
| assert(PredIndex < PHI->getNumOperands()); |
| unsigned PredOperandReg = PHI->getOperand(PredIndex).getReg(); |
| |
| // Pop registers from the stack represented by ImmediateDominatingParent |
| // until we find a parent that dominates the current instruction. |
| unsigned &CurrentParent = CurrentDominatingParent[Color]; |
| unsigned NewParent = CurrentParent; |
| while (NewParent |
| && (!DT->dominates(MRI->getVRegDef(NewParent)->getParent(), &MBB) |
| || !getRegColor(NewParent))) |
| NewParent = ImmediateDominatingParent[NewParent]; |
| CurrentParent = NewParent; |
| |
| // If there is an interference with a register, always isolate the |
| // register rather than the PHI. It is also possible to isolate the |
| // PHI, but that introduces copies for all of the registers involved |
| // in that PHI. |
| if (NewParent && LI->isLiveOutOfMBB(LI->getInterval(NewParent), &MBB) |
| && NewParent != PredOperandReg) |
| isolateReg(NewParent); |
| |
| std::pair<MachineInstr*, unsigned> |
| &CurrentPHI = CurrentPHIForColor[Color]; |
| |
| // If two PHIs have the same operand from every shared predecessor, then |
| // they don't actually interfere. Otherwise, isolate the current PHI. This |
| // could possibly be improved, e.g. we could isolate the PHI with the |
| // fewest operands. |
| if (CurrentPHI.first && CurrentPHI.second != PredOperandReg) |
| isolatePHI(PHI); |
| else |
| CurrentPHI = std::make_pair(PHI, PredOperandReg); |
| } |
| } |
| } |
| |
| void StrongPHIElimination::InsertCopiesForPHI(MachineInstr *PHI, |
| MachineBasicBlock *MBB) { |
| assert(PHI->isPHI()); |
| ++NumPHIsLowered; |
| unsigned PHIColor = getPHIColor(PHI); |
| |
| for (unsigned i = 1; i < PHI->getNumOperands(); i += 2) { |
| MachineOperand &SrcMO = PHI->getOperand(i); |
| |
| // If a source is defined by an implicit def, there is no need to insert a |
| // copy in the predecessor. |
| if (SrcMO.isUndef()) |
| continue; |
| |
| unsigned SrcReg = SrcMO.getReg(); |
| assert(TargetRegisterInfo::isVirtualRegister(SrcReg) && |
| "Machine PHI Operands must all be virtual registers!"); |
| |
| MachineBasicBlock *PredBB = PHI->getOperand(i + 1).getMBB(); |
| unsigned SrcColor = getRegColor(SrcReg); |
| |
| // If neither the PHI nor the operand were isolated, then we only need to |
| // set the phi-kill flag on the VNInfo at this PHI. |
| if (PHIColor && SrcColor == PHIColor) { |
| LiveInterval &SrcInterval = LI->getInterval(SrcReg); |
| SlotIndex PredIndex = LI->getMBBEndIdx(PredBB); |
| VNInfo *SrcVNI = SrcInterval.getVNInfoBefore(PredIndex); |
| assert(SrcVNI); |
| SrcVNI->setHasPHIKill(true); |
| continue; |
| } |
| |
| unsigned CopyReg = 0; |
| if (PHIColor) { |
| SrcCopyMap::const_iterator I |
| = InsertedSrcCopyMap.find(std::make_pair(PredBB, PHIColor)); |
| CopyReg |
| = I != InsertedSrcCopyMap.end() ? I->second->getOperand(0).getReg() : 0; |
| } |
| |
| if (!CopyReg) { |
| const TargetRegisterClass *RC = MRI->getRegClass(SrcReg); |
| CopyReg = MRI->createVirtualRegister(RC); |
| |
| MachineBasicBlock::iterator |
| CopyInsertPoint = findPHICopyInsertPoint(PredBB, MBB, SrcReg); |
| unsigned SrcSubReg = SrcMO.getSubReg(); |
| MachineInstr *CopyInstr = BuildMI(*PredBB, |
| CopyInsertPoint, |
| PHI->getDebugLoc(), |
| TII->get(TargetOpcode::COPY), |
| CopyReg).addReg(SrcReg, 0, SrcSubReg); |
| LI->InsertMachineInstrInMaps(CopyInstr); |
| ++NumSrcCopiesInserted; |
| |
| // addLiveRangeToEndOfBlock() also adds the phikill flag to the VNInfo for |
| // the newly added range. |
| LI->addLiveRangeToEndOfBlock(CopyReg, CopyInstr); |
| InsertedSrcCopySet.insert(std::make_pair(PredBB, SrcReg)); |
| |
| addReg(CopyReg); |
| if (PHIColor) { |
| unionRegs(PHIColor, CopyReg); |
| assert(getRegColor(CopyReg) != CopyReg); |
| } else { |
| PHIColor = CopyReg; |
| assert(getRegColor(CopyReg) == CopyReg); |
| } |
| |
| if (!InsertedSrcCopyMap.count(std::make_pair(PredBB, PHIColor))) |
| InsertedSrcCopyMap[std::make_pair(PredBB, PHIColor)] = CopyInstr; |
| } |
| |
| SrcMO.setReg(CopyReg); |
| |
| // If SrcReg is not live beyond the PHI, trim its interval so that it is no |
| // longer live-in to MBB. Note that SrcReg may appear in other PHIs that are |
| // processed later, but this is still correct to do at this point because we |
| // never rely on LiveIntervals being correct while inserting copies. |
| // FIXME: Should this just count uses at PHIs like the normal PHIElimination |
| // pass does? |
| LiveInterval &SrcLI = LI->getInterval(SrcReg); |
| SlotIndex MBBStartIndex = LI->getMBBStartIdx(MBB); |
| SlotIndex PHIIndex = LI->getInstructionIndex(PHI); |
| SlotIndex NextInstrIndex = PHIIndex.getNextIndex(); |
| if (SrcLI.liveAt(MBBStartIndex) && SrcLI.expiredAt(NextInstrIndex)) |
| SrcLI.removeRange(MBBStartIndex, PHIIndex, true); |
| } |
| |
| unsigned DestReg = PHI->getOperand(0).getReg(); |
| unsigned DestColor = getRegColor(DestReg); |
| |
| if (PHIColor && DestColor == PHIColor) { |
| LiveInterval &DestLI = LI->getInterval(DestReg); |
| |
| // Set the phi-def flag for the VN at this PHI. |
| SlotIndex PHIIndex = LI->getInstructionIndex(PHI); |
| VNInfo *DestVNI = DestLI.getVNInfoAt(PHIIndex.getDefIndex()); |
| assert(DestVNI); |
| DestVNI->setIsPHIDef(true); |
| |
| // Prior to PHI elimination, the live ranges of PHIs begin at their defining |
| // instruction. After PHI elimination, PHI instructions are replaced by VNs |
| // with the phi-def flag set, and the live ranges of these VNs start at the |
| // beginning of the basic block. |
| SlotIndex MBBStartIndex = LI->getMBBStartIdx(MBB); |
| DestVNI->def = MBBStartIndex; |
| DestLI.addRange(LiveRange(MBBStartIndex, |
| PHIIndex.getDefIndex(), |
| DestVNI)); |
| return; |
| } |
| |
| const TargetRegisterClass *RC = MRI->getRegClass(DestReg); |
| unsigned CopyReg = MRI->createVirtualRegister(RC); |
| |
| MachineInstr *CopyInstr = BuildMI(*MBB, |
| MBB->SkipPHIsAndLabels(MBB->begin()), |
| PHI->getDebugLoc(), |
| TII->get(TargetOpcode::COPY), |
| DestReg).addReg(CopyReg); |
| LI->InsertMachineInstrInMaps(CopyInstr); |
| PHI->getOperand(0).setReg(CopyReg); |
| ++NumDestCopiesInserted; |
| |
| // Add the region from the beginning of MBB to the copy instruction to |
| // CopyReg's live interval, and give the VNInfo the phidef flag. |
| LiveInterval &CopyLI = LI->getOrCreateInterval(CopyReg); |
| SlotIndex MBBStartIndex = LI->getMBBStartIdx(MBB); |
| SlotIndex DestCopyIndex = LI->getInstructionIndex(CopyInstr); |
| VNInfo *CopyVNI = CopyLI.getNextValue(MBBStartIndex, |
| CopyInstr, |
| LI->getVNInfoAllocator()); |
| CopyVNI->setIsPHIDef(true); |
| CopyLI.addRange(LiveRange(MBBStartIndex, |
| DestCopyIndex.getDefIndex(), |
| CopyVNI)); |
| |
| // Adjust DestReg's live interval to adjust for its new definition at |
| // CopyInstr. |
| LiveInterval &DestLI = LI->getOrCreateInterval(DestReg); |
| SlotIndex PHIIndex = LI->getInstructionIndex(PHI); |
| DestLI.removeRange(PHIIndex.getDefIndex(), DestCopyIndex.getDefIndex()); |
| |
| VNInfo *DestVNI = DestLI.getVNInfoAt(DestCopyIndex.getDefIndex()); |
| assert(DestVNI); |
| DestVNI->def = DestCopyIndex.getDefIndex(); |
| |
| InsertedDestCopies[CopyReg] = CopyInstr; |
| } |
| |
| void StrongPHIElimination::MergeLIsAndRename(unsigned Reg, unsigned NewReg) { |
| if (Reg == NewReg) |
| return; |
| |
| LiveInterval &OldLI = LI->getInterval(Reg); |
| LiveInterval &NewLI = LI->getInterval(NewReg); |
| |
| // Merge the live ranges of the two registers. |
| DenseMap<VNInfo*, VNInfo*> VNMap; |
| for (LiveInterval::iterator LRI = OldLI.begin(), LRE = OldLI.end(); |
| LRI != LRE; ++LRI) { |
| LiveRange OldLR = *LRI; |
| VNInfo *OldVN = OldLR.valno; |
| |
| VNInfo *&NewVN = VNMap[OldVN]; |
| if (!NewVN) { |
| NewVN = NewLI.createValueCopy(OldVN, LI->getVNInfoAllocator()); |
| VNMap[OldVN] = NewVN; |
| } |
| |
| LiveRange LR(OldLR.start, OldLR.end, NewVN); |
| NewLI.addRange(LR); |
| } |
| |
| // Remove the LiveInterval for the register being renamed and replace all |
| // of its defs and uses with the new register. |
| LI->removeInterval(Reg); |
| MRI->replaceRegWith(Reg, NewReg); |
| } |
