//===- 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 machine instruction PHI nodes by inserting copy // instructions, using an intelligent copy-folding technique based on // dominator information. This is technique is 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. // DOI= http://doi.acm.org/10.1145/512529.512534 // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "strongphielim" #include "llvm/CodeGen/Passes.h" #include "llvm/CodeGen/LiveIntervalAnalysis.h" #include "llvm/CodeGen/MachineDominators.h" #include "llvm/CodeGen/MachineFunctionPass.h" #include "llvm/CodeGen/MachineInstr.h" #include "llvm/CodeGen/MachineLoopInfo.h" #include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/Statistic.h" #include "llvm/Support/Compiler.h" using namespace llvm; namespace { struct VISIBILITY_HIDDEN StrongPHIElimination : public MachineFunctionPass { static char ID; // Pass identification, replacement for typeid StrongPHIElimination() : MachineFunctionPass((intptr_t)&ID) {} // Waiting stores, for each MBB, the set of copies that need to // be inserted into that MBB DenseMap > Waiting; // Stacks holds the renaming stack for each register std::map > Stacks; // Registers in UsedByAnother are PHI nodes that are themselves // used as operands to another another PHI node std::set UsedByAnother; // RenameSets are the sets of operands (and their VNInfo IDs) to a PHI // (the defining instruction of the key) that can be renamed without copies. std::map > RenameSets; // PhiValueNumber holds the ID numbers of the VNs for each phi that we're // eliminating, indexed by the register defined by that phi. std::map PhiValueNumber; // Store the DFS-in number of each block DenseMap preorder; // Store the DFS-out number of each block DenseMap maxpreorder; bool runOnMachineFunction(MachineFunction &Fn); virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired(); AU.addRequired(); // TODO: Actually make this true. AU.addPreserved(); MachineFunctionPass::getAnalysisUsage(AU); } virtual void releaseMemory() { preorder.clear(); maxpreorder.clear(); Waiting.clear(); Stacks.clear(); UsedByAnother.clear(); RenameSets.clear(); } private: /// DomForestNode - Represents a node in the "dominator forest". This is /// a forest in which the nodes represent registers and the edges /// represent a dominance relation in the block defining those registers. struct DomForestNode { private: // Store references to our children std::vector children; // The register we represent unsigned reg; // Add another node as our child void addChild(DomForestNode* DFN) { children.push_back(DFN); } public: typedef std::vector::iterator iterator; // Create a DomForestNode by providing the register it represents, and // the node to be its parent. The virtual root node has register 0 // and a null parent. DomForestNode(unsigned r, DomForestNode* parent) : reg(r) { if (parent) parent->addChild(this); } ~DomForestNode() { for (iterator I = begin(), E = end(); I != E; ++I) delete *I; } /// getReg - Return the regiser that this node represents inline unsigned getReg() { return reg; } // Provide iterator access to our children inline DomForestNode::iterator begin() { return children.begin(); } inline DomForestNode::iterator end() { return children.end(); } }; void computeDFS(MachineFunction& MF); void processBlock(MachineBasicBlock* MBB); std::vector computeDomForest(std::map& instrs, MachineRegisterInfo& MRI); void processPHIUnion(MachineInstr* Inst, std::map& PHIUnion, std::vector& DF, std::vector >& locals); void ScheduleCopies(MachineBasicBlock* MBB, std::set& pushed); void InsertCopies(MachineBasicBlock* MBB, SmallPtrSet& v); void mergeLiveIntervals(unsigned primary, unsigned secondary, unsigned VN); }; char StrongPHIElimination::ID = 0; RegisterPass X("strong-phi-node-elimination", "Eliminate PHI nodes for register allocation, intelligently"); } const PassInfo *llvm::StrongPHIEliminationID = X.getPassInfo(); /// computeDFS - Computes the DFS-in and DFS-out numbers of the dominator tree /// of the given MachineFunction. These numbers are then used in other parts /// of the PHI elimination process. void StrongPHIElimination::computeDFS(MachineFunction& MF) { SmallPtrSet frontier; SmallPtrSet visited; unsigned time = 0; MachineDominatorTree& DT = getAnalysis(); MachineDomTreeNode* node = DT.getRootNode(); std::vector worklist; worklist.push_back(node); while (!worklist.empty()) { MachineDomTreeNode* currNode = worklist.back(); if (!frontier.count(currNode)) { frontier.insert(currNode); ++time; preorder.insert(std::make_pair(currNode->getBlock(), time)); } bool inserted = false; for (MachineDomTreeNode::iterator I = node->begin(), E = node->end(); I != E; ++I) if (!frontier.count(*I) && !visited.count(*I)) { worklist.push_back(*I); inserted = true; break; } if (!inserted) { frontier.erase(currNode); visited.insert(currNode); maxpreorder.insert(std::make_pair(currNode->getBlock(), time)); worklist.pop_back(); } } } /// PreorderSorter - a helper class that is used to sort registers /// according to the preorder number of their defining blocks class PreorderSorter { private: DenseMap& preorder; MachineRegisterInfo& MRI; public: PreorderSorter(DenseMap& p, MachineRegisterInfo& M) : preorder(p), MRI(M) { } bool operator()(unsigned A, unsigned B) { if (A == B) return false; MachineBasicBlock* ABlock = MRI.getVRegDef(A)->getParent(); MachineBasicBlock* BBlock = MRI.getVRegDef(B)->getParent(); if (preorder[ABlock] < preorder[BBlock]) return true; else if (preorder[ABlock] > preorder[BBlock]) return false; return false; } }; /// computeDomForest - compute the subforest of the DomTree corresponding /// to the defining blocks of the registers in question std::vector StrongPHIElimination::computeDomForest(std::map& regs, MachineRegisterInfo& MRI) { // Begin by creating a virtual root node, since the actual results // may well be a forest. Assume this node has maximum DFS-out number. DomForestNode* VirtualRoot = new DomForestNode(0, 0); maxpreorder.insert(std::make_pair((MachineBasicBlock*)0, ~0UL)); // Populate a worklist with the registers std::vector worklist; worklist.reserve(regs.size()); for (std::map::iterator I = regs.begin(), E = regs.end(); I != E; ++I) worklist.push_back(I->first); // Sort the registers by the DFS-in number of their defining block PreorderSorter PS(preorder, MRI); std::sort(worklist.begin(), worklist.end(), PS); // Create a "current parent" stack, and put the virtual root on top of it DomForestNode* CurrentParent = VirtualRoot; std::vector stack; stack.push_back(VirtualRoot); // Iterate over all the registers in the previously computed order for (std::vector::iterator I = worklist.begin(), E = worklist.end(); I != E; ++I) { unsigned pre = preorder[MRI.getVRegDef(*I)->getParent()]; MachineBasicBlock* parentBlock = CurrentParent->getReg() ? MRI.getVRegDef(CurrentParent->getReg())->getParent() : 0; // If the DFS-in number of the register is greater than the DFS-out number // of the current parent, repeatedly pop the parent stack until it isn't. while (pre > maxpreorder[parentBlock]) { stack.pop_back(); CurrentParent = stack.back(); parentBlock = CurrentParent->getReg() ? MRI.getVRegDef(CurrentParent->getReg())->getParent() : 0; } // Now that we've found the appropriate parent, create a DomForestNode for // this register and attach it to the forest DomForestNode* child = new DomForestNode(*I, CurrentParent); // Push this new node on the "current parent" stack stack.push_back(child); CurrentParent = child; } // Return a vector containing the children of the virtual root node std::vector ret; ret.insert(ret.end(), VirtualRoot->begin(), VirtualRoot->end()); return ret; } /// isLiveIn - helper method that determines, from a regno, if a register /// is live into a block static bool isLiveIn(unsigned r, MachineBasicBlock* MBB, LiveIntervals& LI) { LiveInterval& I = LI.getOrCreateInterval(r); unsigned idx = LI.getMBBStartIdx(MBB); return I.liveBeforeAndAt(idx); } /// isLiveOut - help method that determines, from a regno, if a register is /// live out of a block. static bool isLiveOut(unsigned r, MachineBasicBlock* MBB, LiveIntervals& LI) { for (MachineBasicBlock::succ_iterator PI = MBB->succ_begin(), E = MBB->succ_end(); PI != E; ++PI) { if (isLiveIn(r, *PI, LI)) return true; } return false; } /// interferes - checks for local interferences by scanning a block. The only /// trick parameter is 'mode' which tells it the relationship of the two /// registers. 0 - defined in the same block, 1 - first properly dominates /// second, 2 - second properly dominates first static bool interferes(unsigned a, unsigned b, MachineBasicBlock* scan, LiveIntervals& LV, unsigned mode) { MachineInstr* def = 0; MachineInstr* kill = 0; // The code is still in SSA form at this point, so there is only one // definition per VReg. Thus we can safely use MRI->getVRegDef(). const MachineRegisterInfo* MRI = &scan->getParent()->getRegInfo(); bool interference = false; // Wallk the block, checking for interferences for (MachineBasicBlock::iterator MBI = scan->begin(), MBE = scan->end(); MBI != MBE; ++MBI) { MachineInstr* curr = MBI; // Same defining block... if (mode == 0) { if (curr == MRI->getVRegDef(a)) { // If we find our first definition, save it if (!def) { def = curr; // If there's already an unkilled definition, then // this is an interference } else if (!kill) { interference = true; break; // If there's a definition followed by a KillInst, then // they can't interfere } else { interference = false; break; } // Symmetric with the above } else if (curr == MRI->getVRegDef(b)) { if (!def) { def = curr; } else if (!kill) { interference = true; break; } else { interference = false; break; } // Store KillInsts if they match up with the definition } else if (curr->killsRegister(a)) { if (def == MRI->getVRegDef(a)) { kill = curr; } else if (curr->killsRegister(b)) { if (def == MRI->getVRegDef(b)) { kill = curr; } } } // First properly dominates second... } else if (mode == 1) { if (curr == MRI->getVRegDef(b)) { // Definition of second without kill of first is an interference if (!kill) { interference = true; break; // Definition after a kill is a non-interference } else { interference = false; break; } // Save KillInsts of First } else if (curr->killsRegister(a)) { kill = curr; } // Symmetric with the above } else if (mode == 2) { if (curr == MRI->getVRegDef(a)) { if (!kill) { interference = true; break; } else { interference = false; break; } } else if (curr->killsRegister(b)) { kill = curr; } } } return interference; } /// processBlock - Determine how to break up PHIs in the current block. Each /// PHI is broken up by some combination of renaming its operands and inserting /// copies. This method is responsible for determining which operands receive /// which treatment. void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) { LiveIntervals& LI = getAnalysis(); MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo(); // Holds names that have been added to a set in any PHI within this block // before the current one. std::set ProcessedNames; MachineBasicBlock::iterator FirstNonPHI = MBB->begin(); while (FirstNonPHI->getOpcode() == TargetInstrInfo::PHI) FirstNonPHI++; // Iterate over all the PHI nodes in this block MachineBasicBlock::iterator P = MBB->begin(); while (P != FirstNonPHI && P->getOpcode() == TargetInstrInfo::PHI) { unsigned DestReg = P->getOperand(0).getReg(); // Don't both doing PHI elimination for dead PHI's. if (P->registerDefIsDead(DestReg)) { ++P; continue; } LiveInterval& PI = LI.getOrCreateInterval(DestReg); unsigned pIdx = LI.getInstructionIndex(FirstNonPHI); VNInfo* PVN = PI.getLiveRangeContaining(pIdx)->valno; PhiValueNumber.insert(std::make_pair(DestReg, PVN->id)); // PHIUnion is the set of incoming registers to the PHI node that // are going to be renames rather than having copies inserted. This set // is refinded over the course of this function. UnionedBlocks is the set // of corresponding MBBs. std::map PHIUnion; SmallPtrSet UnionedBlocks; // Iterate over the operands of the PHI node for (int i = P->getNumOperands() - 1; i >= 2; i-=2) { unsigned SrcReg = P->getOperand(i-1).getReg(); // Check for trivial interferences via liveness information, allowing us // to avoid extra work later. Any registers that interfere cannot both // be in the renaming set, so choose one and add copies for it instead. // The conditions are: // 1) if the operand is live into the PHI node's block OR // 2) if the PHI node is live out of the operand's defining block OR // 3) if the operand is itself a PHI node and the original PHI is // live into the operand's defining block OR // 4) if the operand is already being renamed for another PHI node // in this block OR // 5) if any two operands are defined in the same block, insert copies // for one of them if (isLiveIn(SrcReg, P->getParent(), LI) || isLiveOut(P->getOperand(0).getReg(), MRI.getVRegDef(SrcReg)->getParent(), LI) || ( MRI.getVRegDef(SrcReg)->getOpcode() == TargetInstrInfo::PHI && isLiveIn(P->getOperand(0).getReg(), MRI.getVRegDef(SrcReg)->getParent(), LI) ) || ProcessedNames.count(SrcReg) || UnionedBlocks.count(MRI.getVRegDef(SrcReg)->getParent())) { // Add a copy for the selected register MachineBasicBlock* From = P->getOperand(i).getMBB(); Waiting[From].insert(std::make_pair(SrcReg, DestReg)); UsedByAnother.insert(SrcReg); } else { // Otherwise, add it to the renaming set LiveInterval& I = LI.getOrCreateInterval(SrcReg); unsigned idx = LI.getMBBEndIdx(P->getOperand(i).getMBB()); VNInfo* VN = I.getLiveRangeContaining(idx)->valno; assert(VN && "No VNInfo for register?"); PHIUnion.insert(std::make_pair(SrcReg, VN->id)); UnionedBlocks.insert(MRI.getVRegDef(SrcReg)->getParent()); } } // Compute the dominator forest for the renaming set. This is a forest // where the nodes are the registers and the edges represent dominance // relations between the defining blocks of the registers std::vector DF = computeDomForest(PHIUnion, MRI); // Walk DomForest to resolve interferences at an inter-block level. This // will remove registers from the renaming set (and insert copies for them) // if interferences are found. std::vector > localInterferences; processPHIUnion(P, PHIUnion, DF, localInterferences); // The dominator forest walk may have returned some register pairs whose // interference cannot be determines from dominator analysis. We now // examine these pairs for local interferences. for (std::vector >::iterator I = localInterferences.begin(), E = localInterferences.end(); I != E; ++I) { std::pair p = *I; MachineDominatorTree& MDT = getAnalysis(); // Determine the block we need to scan and the relationship between // the two registers MachineBasicBlock* scan = 0; unsigned mode = 0; if (MRI.getVRegDef(p.first)->getParent() == MRI.getVRegDef(p.second)->getParent()) { scan = MRI.getVRegDef(p.first)->getParent(); mode = 0; // Same block } else if (MDT.dominates(MRI.getVRegDef(p.first)->getParent(), MRI.getVRegDef(p.second)->getParent())) { scan = MRI.getVRegDef(p.second)->getParent(); mode = 1; // First dominates second } else { scan = MRI.getVRegDef(p.first)->getParent(); mode = 2; // Second dominates first } // If there's an interference, we need to insert copies if (interferes(p.first, p.second, scan, LI, mode)) { // Insert copies for First for (int i = P->getNumOperands() - 1; i >= 2; i-=2) { if (P->getOperand(i-1).getReg() == p.first) { unsigned SrcReg = p.first; MachineBasicBlock* From = P->getOperand(i).getMBB(); Waiting[From].insert(std::make_pair(SrcReg, P->getOperand(0).getReg())); UsedByAnother.insert(SrcReg); PHIUnion.erase(SrcReg); } } } } // Add the renaming set for this PHI node to our overal renaming information RenameSets.insert(std::make_pair(P->getOperand(0).getReg(), PHIUnion)); // Remember which registers are already renamed, so that we don't try to // rename them for another PHI node in this block for (std::map::iterator I = PHIUnion.begin(), E = PHIUnion.end(); I != E; ++I) ProcessedNames.insert(I->first); ++P; } } /// processPHIUnion - Take a set of candidate registers to be coalesced when /// decomposing the PHI instruction. Use the DominanceForest to remove the ones /// that are known to interfere, and flag others that need to be checked for /// local interferences. void StrongPHIElimination::processPHIUnion(MachineInstr* Inst, std::map& PHIUnion, std::vector& DF, std::vector >& locals) { std::vector worklist(DF.begin(), DF.end()); SmallPtrSet visited; // Code is still in SSA form, so we can use MRI::getVRegDef() MachineRegisterInfo& MRI = Inst->getParent()->getParent()->getRegInfo(); LiveIntervals& LI = getAnalysis(); unsigned DestReg = Inst->getOperand(0).getReg(); // DF walk on the DomForest while (!worklist.empty()) { DomForestNode* DFNode = worklist.back(); visited.insert(DFNode); bool inserted = false; for (DomForestNode::iterator CI = DFNode->begin(), CE = DFNode->end(); CI != CE; ++CI) { DomForestNode* child = *CI; // If the current node is live-out of the defining block of one of its // children, insert a copy for it. NOTE: The paper actually calls for // a more elaborate heuristic for determining whether to insert copies // for the child or the parent. In the interest of simplicity, we're // just always choosing the parent. if (isLiveOut(DFNode->getReg(), MRI.getVRegDef(child->getReg())->getParent(), LI)) { // Insert copies for parent for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) { if (Inst->getOperand(i-1).getReg() == DFNode->getReg()) { unsigned SrcReg = DFNode->getReg(); MachineBasicBlock* From = Inst->getOperand(i).getMBB(); Waiting[From].insert(std::make_pair(SrcReg, DestReg)); UsedByAnother.insert(SrcReg); PHIUnion.erase(SrcReg); } } // If a node is live-in to the defining block of one of its children, but // not live-out, then we need to scan that block for local interferences. } else if (isLiveIn(DFNode->getReg(), MRI.getVRegDef(child->getReg())->getParent(), LI) || MRI.getVRegDef(DFNode->getReg())->getParent() == MRI.getVRegDef(child->getReg())->getParent()) { // Add (p, c) to possible local interferences locals.push_back(std::make_pair(DFNode->getReg(), child->getReg())); } if (!visited.count(child)) { worklist.push_back(child); inserted = true; } } if (!inserted) worklist.pop_back(); } } /// ScheduleCopies - Insert copies into predecessor blocks, scheduling /// them properly so as to avoid the 'lost copy' and the 'virtual swap' /// problems. /// /// Based on "Practical Improvements to the Construction and Destruction /// of Static Single Assignment Form" by Briggs, et al. void StrongPHIElimination::ScheduleCopies(MachineBasicBlock* MBB, std::set& pushed) { // FIXME: This function needs to update LiveVariables std::map& copy_set= Waiting[MBB]; std::map worklist; std::map map; // Setup worklist of initial copies for (std::map::iterator I = copy_set.begin(), E = copy_set.end(); I != E; ) { map.insert(std::make_pair(I->first, I->first)); map.insert(std::make_pair(I->second, I->second)); if (!UsedByAnother.count(I->first)) { worklist.insert(*I); // Avoid iterator invalidation unsigned first = I->first; ++I; copy_set.erase(first); } else { ++I; } } LiveIntervals& LI = getAnalysis(); MachineFunction* MF = MBB->getParent(); MachineRegisterInfo& MRI = MF->getRegInfo(); const TargetInstrInfo *TII = MF->getTarget().getInstrInfo(); // Iterate over the worklist, inserting copies while (!worklist.empty() || !copy_set.empty()) { while (!worklist.empty()) { std::pair curr = *worklist.begin(); worklist.erase(curr.first); const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first); if (isLiveOut(curr.second, MBB, LI)) { // Create a temporary unsigned t = MF->getRegInfo().createVirtualRegister(RC); // Insert copy from curr.second to a temporary at // the Phi defining curr.second MachineBasicBlock::iterator PI = MRI.getVRegDef(curr.second); TII->copyRegToReg(*PI->getParent(), PI, t, curr.second, RC, RC); // Push temporary on Stacks Stacks[curr.second].push_back(t); // Insert curr.second in pushed pushed.insert(curr.second); } // Insert copy from map[curr.first] to curr.second TII->copyRegToReg(*MBB, MBB->getFirstTerminator(), curr.second, map[curr.first], RC, RC); map[curr.first] = curr.second; // If curr.first is a destination in copy_set... for (std::map::iterator I = copy_set.begin(), E = copy_set.end(); I != E; ) if (curr.first == I->second) { std::pair temp = *I; // Avoid iterator invalidation ++I; copy_set.erase(temp.first); worklist.insert(temp); break; } else { ++I; } } if (!copy_set.empty()) { std::pair curr = *copy_set.begin(); copy_set.erase(curr.first); const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first); // Insert a copy from dest to a new temporary t at the end of b unsigned t = MF->getRegInfo().createVirtualRegister(RC); TII->copyRegToReg(*MBB, MBB->getFirstTerminator(), t, curr.second, RC, RC); map[curr.second] = t; worklist.insert(curr); } } } /// InsertCopies - insert copies into MBB and all of its successors void StrongPHIElimination::InsertCopies(MachineBasicBlock* MBB, SmallPtrSet& visited) { visited.insert(MBB); std::set pushed; // Rewrite register uses from Stacks for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; ++I) for (unsigned i = 0; i < I->getNumOperands(); ++i) if (I->getOperand(i).isRegister() && Stacks[I->getOperand(i).getReg()].size()) { I->getOperand(i).setReg(Stacks[I->getOperand(i).getReg()].back()); } // Schedule the copies for this block ScheduleCopies(MBB, pushed); // Recur to our successors for (GraphTraits::ChildIteratorType I = GraphTraits::child_begin(MBB), E = GraphTraits::child_end(MBB); I != E; ++I) if (!visited.count(*I)) InsertCopies(*I, visited); // As we exit this block, pop the names we pushed while processing it for (std::set::iterator I = pushed.begin(), E = pushed.end(); I != E; ++I) Stacks[*I].pop_back(); } /// ComputeUltimateVN - Assuming we are going to join two live intervals, /// compute what the resultant value numbers for each value in the input two /// ranges will be. This is complicated by copies between the two which can /// and will commonly cause multiple value numbers to be merged into one. /// /// VN is the value number that we're trying to resolve. InstDefiningValue /// keeps track of the new InstDefiningValue assignment for the result /// LiveInterval. ThisFromOther/OtherFromThis are sets that keep track of /// whether a value in this or other is a copy from the opposite set. /// ThisValNoAssignments/OtherValNoAssignments keep track of value #'s that have /// already been assigned. /// /// ThisFromOther[x] - If x is defined as a copy from the other interval, this /// contains the value number the copy is from. /// static unsigned ComputeUltimateVN(VNInfo *VNI, SmallVector &NewVNInfo, DenseMap &ThisFromOther, DenseMap &OtherFromThis, SmallVector &ThisValNoAssignments, SmallVector &OtherValNoAssignments) { unsigned VN = VNI->id; // If the VN has already been computed, just return it. if (ThisValNoAssignments[VN] >= 0) return ThisValNoAssignments[VN]; // assert(ThisValNoAssignments[VN] != -2 && "Cyclic case?"); // If this val is not a copy from the other val, then it must be a new value // number in the destination. DenseMap::iterator I = ThisFromOther.find(VNI); if (I == ThisFromOther.end()) { NewVNInfo.push_back(VNI); return ThisValNoAssignments[VN] = NewVNInfo.size()-1; } VNInfo *OtherValNo = I->second; // Otherwise, this *is* a copy from the RHS. If the other side has already // been computed, return it. if (OtherValNoAssignments[OtherValNo->id] >= 0) return ThisValNoAssignments[VN] = OtherValNoAssignments[OtherValNo->id]; // Mark this value number as currently being computed, then ask what the // ultimate value # of the other value is. ThisValNoAssignments[VN] = -2; unsigned UltimateVN = ComputeUltimateVN(OtherValNo, NewVNInfo, OtherFromThis, ThisFromOther, OtherValNoAssignments, ThisValNoAssignments); return ThisValNoAssignments[VN] = UltimateVN; } void StrongPHIElimination::mergeLiveIntervals(unsigned primary, unsigned secondary, unsigned secondaryVN) { LiveIntervals& LI = getAnalysis(); LiveInterval& LHS = LI.getOrCreateInterval(primary); LiveInterval& RHS = LI.getOrCreateInterval(secondary); // Compute the final value assignment, assuming that the live ranges can be // coalesced. SmallVector LHSValNoAssignments; SmallVector RHSValNoAssignments; DenseMap LHSValsDefinedFromRHS; DenseMap RHSValsDefinedFromLHS; SmallVector NewVNInfo; LHSValNoAssignments.resize(LHS.getNumValNums(), -1); RHSValNoAssignments.resize(RHS.getNumValNums(), -1); NewVNInfo.reserve(LHS.getNumValNums() + RHS.getNumValNums()); for (LiveInterval::vni_iterator I = LHS.vni_begin(), E = LHS.vni_end(); I != E; ++I) { VNInfo *VNI = *I; unsigned VN = VNI->id; if (LHSValNoAssignments[VN] >= 0 || VNI->def == ~1U) continue; ComputeUltimateVN(VNI, NewVNInfo, LHSValsDefinedFromRHS, RHSValsDefinedFromLHS, LHSValNoAssignments, RHSValNoAssignments); } for (LiveInterval::vni_iterator I = RHS.vni_begin(), E = RHS.vni_end(); I != E; ++I) { VNInfo *VNI = *I; unsigned VN = VNI->id; if (RHSValNoAssignments[VN] >= 0 || VNI->def == ~1U) continue; // If this value number isn't a copy from the LHS, it's a new number. if (RHSValsDefinedFromLHS.find(VNI) == RHSValsDefinedFromLHS.end()) { NewVNInfo.push_back(VNI); RHSValNoAssignments[VN] = NewVNInfo.size()-1; continue; } ComputeUltimateVN(VNI, NewVNInfo, RHSValsDefinedFromLHS, LHSValsDefinedFromRHS, RHSValNoAssignments, LHSValNoAssignments); } // Update kill info. Some live ranges are extended due to copy coalescing. for (DenseMap::iterator I = LHSValsDefinedFromRHS.begin(), E = LHSValsDefinedFromRHS.end(); I != E; ++I) { VNInfo *VNI = I->first; unsigned LHSValID = LHSValNoAssignments[VNI->id]; LiveInterval::removeKill(NewVNInfo[LHSValID], VNI->def); NewVNInfo[LHSValID]->hasPHIKill |= VNI->hasPHIKill; RHS.addKills(NewVNInfo[LHSValID], VNI->kills); } // Update kill info. Some live ranges are extended due to copy coalescing. for (DenseMap::iterator I = RHSValsDefinedFromLHS.begin(), E = RHSValsDefinedFromLHS.end(); I != E; ++I) { VNInfo *VNI = I->first; unsigned RHSValID = RHSValNoAssignments[VNI->id]; LiveInterval::removeKill(NewVNInfo[RHSValID], VNI->def); NewVNInfo[RHSValID]->hasPHIKill |= VNI->hasPHIKill; LHS.addKills(NewVNInfo[RHSValID], VNI->kills); } // Use the VNInfo we collected earlier to ensure that the phi copy is // merged correctly. // FIXME: This is not working correctly yet. // RHSValNoAssignments[secondaryVN] = primaryVN; // If we get here, we know that we can coalesce the live ranges. Ask the // intervals to coalesce themselves now. LHS.join(RHS, &LHSValNoAssignments[0], &RHSValNoAssignments[0], NewVNInfo); LI.removeInterval(secondary); } bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) { // Compute DFS numbers of each block computeDFS(Fn); // Determine which phi node operands need copies for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) if (!I->empty() && I->begin()->getOpcode() == TargetInstrInfo::PHI) processBlock(I); // Insert copies // FIXME: This process should probably preserve LiveVariables SmallPtrSet visited; InsertCopies(Fn.begin(), visited); // Perform renaming typedef std::map > RenameSetType; for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end(); I != E; ++I) for (std::map::iterator SI = I->second.begin(), SE = I->second.end(); SI != SE; ++SI) { mergeLiveIntervals(I->first, SI->first, SI->second); Fn.getRegInfo().replaceRegWith(SI->first, I->first); } // FIXME: Insert last-minute copies // Remove PHIs std::vector phis; for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { for (MachineBasicBlock::iterator BI = I->begin(), BE = I->end(); BI != BE; ++BI) if (BI->getOpcode() == TargetInstrInfo::PHI) phis.push_back(BI); } LiveIntervals& LI = getAnalysis(); for (std::vector::iterator I = phis.begin(), E = phis.end(); I != E; ++I) { // If this is a dead PHI node, then remove it from LiveIntervals. unsigned DestReg = (*I)->getOperand(0).getReg(); if ((*I)->registerDefIsDead(DestReg)) { LiveInterval& PI = LI.getInterval(DestReg); if (PI.containsOneValue()) { LI.removeInterval(DestReg); } else { MachineBasicBlock::iterator PIter = *I; while (PIter->getOpcode() == TargetInstrInfo::PHI) ++PIter; unsigned idx = LI.getInstructionIndex(PIter); PI.removeRange(*PI.getLiveRangeContaining(idx), true); } } LI.RemoveMachineInstrFromMaps(*I); (*I)->eraseFromParent(); } return false; }