/3rd_party/llvm/lib/CodeGen/LiveRangeCalc.cpp
https://code.google.com/p/softart/ · C++ · 376 lines · 239 code · 54 blank · 83 comment · 87 complexity · 6122c61d236408d7dd018cf21d0ab0e1 MD5 · raw file
- //===---- LiveRangeCalc.cpp - Calculate live ranges -----------------------===//
- //
- // The LLVM Compiler Infrastructure
- //
- // This file is distributed under the University of Illinois Open Source
- // License. See LICENSE.TXT for details.
- //
- //===----------------------------------------------------------------------===//
- //
- // Implementation of the LiveRangeCalc class.
- //
- //===----------------------------------------------------------------------===//
- #define DEBUG_TYPE "regalloc"
- #include "LiveRangeCalc.h"
- #include "llvm/CodeGen/MachineDominators.h"
- #include "llvm/CodeGen/MachineRegisterInfo.h"
- using namespace llvm;
- void LiveRangeCalc::reset(const MachineFunction *mf,
- SlotIndexes *SI,
- MachineDominatorTree *MDT,
- VNInfo::Allocator *VNIA) {
- MF = mf;
- MRI = &MF->getRegInfo();
- Indexes = SI;
- DomTree = MDT;
- Alloc = VNIA;
- unsigned N = MF->getNumBlockIDs();
- Seen.clear();
- Seen.resize(N);
- LiveOut.resize(N);
- LiveIn.clear();
- }
- void LiveRangeCalc::createDeadDefs(LiveRange &LR, unsigned Reg) {
- assert(MRI && Indexes && "call reset() first");
- // Visit all def operands. If the same instruction has multiple defs of Reg,
- // LR.createDeadDef() will deduplicate.
- for (MachineRegisterInfo::def_iterator
- I = MRI->def_begin(Reg), E = MRI->def_end(); I != E; ++I) {
- const MachineInstr *MI = &*I;
- // Find the corresponding slot index.
- SlotIndex Idx;
- if (MI->isPHI())
- // PHI defs begin at the basic block start index.
- Idx = Indexes->getMBBStartIdx(MI->getParent());
- else
- // Instructions are either normal 'r', or early clobber 'e'.
- Idx = Indexes->getInstructionIndex(MI)
- .getRegSlot(I.getOperand().isEarlyClobber());
- // Create the def in LR. This may find an existing def.
- LR.createDeadDef(Idx, *Alloc);
- }
- }
- void LiveRangeCalc::extendToUses(LiveRange &LR, unsigned Reg) {
- assert(MRI && Indexes && "call reset() first");
- // Visit all operands that read Reg. This may include partial defs.
- for (MachineRegisterInfo::reg_nodbg_iterator I = MRI->reg_nodbg_begin(Reg),
- E = MRI->reg_nodbg_end(); I != E; ++I) {
- MachineOperand &MO = I.getOperand();
- // Clear all kill flags. They will be reinserted after register allocation
- // by LiveIntervalAnalysis::addKillFlags().
- if (MO.isUse())
- MO.setIsKill(false);
- if (!MO.readsReg())
- continue;
- // MI is reading Reg. We may have visited MI before if it happens to be
- // reading Reg multiple times. That is OK, extend() is idempotent.
- const MachineInstr *MI = &*I;
- // Find the SlotIndex being read.
- SlotIndex Idx;
- if (MI->isPHI()) {
- assert(!MO.isDef() && "Cannot handle PHI def of partial register.");
- // PHI operands are paired: (Reg, PredMBB).
- // Extend the live range to be live-out from PredMBB.
- Idx = Indexes->getMBBEndIdx(MI->getOperand(I.getOperandNo()+1).getMBB());
- } else {
- // This is a normal instruction.
- Idx = Indexes->getInstructionIndex(MI).getRegSlot();
- // Check for early-clobber redefs.
- unsigned DefIdx;
- if (MO.isDef()) {
- if (MO.isEarlyClobber())
- Idx = Idx.getRegSlot(true);
- } else if (MI->isRegTiedToDefOperand(I.getOperandNo(), &DefIdx)) {
- // FIXME: This would be a lot easier if tied early-clobber uses also
- // had an early-clobber flag.
- if (MI->getOperand(DefIdx).isEarlyClobber())
- Idx = Idx.getRegSlot(true);
- }
- }
- extend(LR, Idx, Reg);
- }
- }
- // Transfer information from the LiveIn vector to the live ranges.
- void LiveRangeCalc::updateLiveIns() {
- LiveRangeUpdater Updater;
- for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
- E = LiveIn.end(); I != E; ++I) {
- if (!I->DomNode)
- continue;
- MachineBasicBlock *MBB = I->DomNode->getBlock();
- assert(I->Value && "No live-in value found");
- SlotIndex Start, End;
- tie(Start, End) = Indexes->getMBBRange(MBB);
- if (I->Kill.isValid())
- // Value is killed inside this block.
- End = I->Kill;
- else {
- // The value is live-through, update LiveOut as well.
- // Defer the Domtree lookup until it is needed.
- assert(Seen.test(MBB->getNumber()));
- LiveOut[MBB] = LiveOutPair(I->Value, (MachineDomTreeNode *)0);
- }
- Updater.setDest(&I->LR);
- Updater.add(Start, End, I->Value);
- }
- LiveIn.clear();
- }
- void LiveRangeCalc::extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg) {
- assert(Kill.isValid() && "Invalid SlotIndex");
- assert(Indexes && "Missing SlotIndexes");
- assert(DomTree && "Missing dominator tree");
- MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(Kill.getPrevSlot());
- assert(KillMBB && "No MBB at Kill");
- // Is there a def in the same MBB we can extend?
- if (LR.extendInBlock(Indexes->getMBBStartIdx(KillMBB), Kill))
- return;
- // Find the single reaching def, or determine if Kill is jointly dominated by
- // multiple values, and we may need to create even more phi-defs to preserve
- // VNInfo SSA form. Perform a search for all predecessor blocks where we
- // know the dominating VNInfo.
- if (findReachingDefs(LR, *KillMBB, Kill, PhysReg))
- return;
- // When there were multiple different values, we may need new PHIs.
- calculateValues();
- }
- // This function is called by a client after using the low-level API to add
- // live-out and live-in blocks. The unique value optimization is not
- // available, SplitEditor::transferValues handles that case directly anyway.
- void LiveRangeCalc::calculateValues() {
- assert(Indexes && "Missing SlotIndexes");
- assert(DomTree && "Missing dominator tree");
- updateSSA();
- updateLiveIns();
- }
- bool LiveRangeCalc::findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
- SlotIndex Kill, unsigned PhysReg) {
- unsigned KillMBBNum = KillMBB.getNumber();
- // Block numbers where LR should be live-in.
- SmallVector<unsigned, 16> WorkList(1, KillMBBNum);
- // Remember if we have seen more than one value.
- bool UniqueVNI = true;
- VNInfo *TheVNI = 0;
- // Using Seen as a visited set, perform a BFS for all reaching defs.
- for (unsigned i = 0; i != WorkList.size(); ++i) {
- MachineBasicBlock *MBB = MF->getBlockNumbered(WorkList[i]);
- #ifndef NDEBUG
- if (MBB->pred_empty()) {
- MBB->getParent()->verify();
- llvm_unreachable("Use not jointly dominated by defs.");
- }
- if (TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
- !MBB->isLiveIn(PhysReg)) {
- MBB->getParent()->verify();
- errs() << "The register needs to be live in to BB#" << MBB->getNumber()
- << ", but is missing from the live-in list.\n";
- llvm_unreachable("Invalid global physical register");
- }
- #endif
- for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
- PE = MBB->pred_end(); PI != PE; ++PI) {
- MachineBasicBlock *Pred = *PI;
- // Is this a known live-out block?
- if (Seen.test(Pred->getNumber())) {
- if (VNInfo *VNI = LiveOut[Pred].first) {
- if (TheVNI && TheVNI != VNI)
- UniqueVNI = false;
- TheVNI = VNI;
- }
- continue;
- }
- SlotIndex Start, End;
- tie(Start, End) = Indexes->getMBBRange(Pred);
- // First time we see Pred. Try to determine the live-out value, but set
- // it as null if Pred is live-through with an unknown value.
- VNInfo *VNI = LR.extendInBlock(Start, End);
- setLiveOutValue(Pred, VNI);
- if (VNI) {
- if (TheVNI && TheVNI != VNI)
- UniqueVNI = false;
- TheVNI = VNI;
- continue;
- }
- // No, we need a live-in value for Pred as well
- if (Pred != &KillMBB)
- WorkList.push_back(Pred->getNumber());
- else
- // Loopback to KillMBB, so value is really live through.
- Kill = SlotIndex();
- }
- }
- LiveIn.clear();
- // Both updateSSA() and LiveRangeUpdater benefit from ordered blocks, but
- // neither require it. Skip the sorting overhead for small updates.
- if (WorkList.size() > 4)
- array_pod_sort(WorkList.begin(), WorkList.end());
- // If a unique reaching def was found, blit in the live ranges immediately.
- if (UniqueVNI) {
- LiveRangeUpdater Updater(&LR);
- for (SmallVectorImpl<unsigned>::const_iterator I = WorkList.begin(),
- E = WorkList.end(); I != E; ++I) {
- SlotIndex Start, End;
- tie(Start, End) = Indexes->getMBBRange(*I);
- // Trim the live range in KillMBB.
- if (*I == KillMBBNum && Kill.isValid())
- End = Kill;
- else
- LiveOut[MF->getBlockNumbered(*I)] =
- LiveOutPair(TheVNI, (MachineDomTreeNode *)0);
- Updater.add(Start, End, TheVNI);
- }
- return true;
- }
- // Multiple values were found, so transfer the work list to the LiveIn array
- // where UpdateSSA will use it as a work list.
- LiveIn.reserve(WorkList.size());
- for (SmallVectorImpl<unsigned>::const_iterator
- I = WorkList.begin(), E = WorkList.end(); I != E; ++I) {
- MachineBasicBlock *MBB = MF->getBlockNumbered(*I);
- addLiveInBlock(LR, DomTree->getNode(MBB));
- if (MBB == &KillMBB)
- LiveIn.back().Kill = Kill;
- }
- return false;
- }
- // This is essentially the same iterative algorithm that SSAUpdater uses,
- // except we already have a dominator tree, so we don't have to recompute it.
- void LiveRangeCalc::updateSSA() {
- assert(Indexes && "Missing SlotIndexes");
- assert(DomTree && "Missing dominator tree");
- // Interate until convergence.
- unsigned Changes;
- do {
- Changes = 0;
- // Propagate live-out values down the dominator tree, inserting phi-defs
- // when necessary.
- for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
- E = LiveIn.end(); I != E; ++I) {
- MachineDomTreeNode *Node = I->DomNode;
- // Skip block if the live-in value has already been determined.
- if (!Node)
- continue;
- MachineBasicBlock *MBB = Node->getBlock();
- MachineDomTreeNode *IDom = Node->getIDom();
- LiveOutPair IDomValue;
- // We need a live-in value to a block with no immediate dominator?
- // This is probably an unreachable block that has survived somehow.
- bool needPHI = !IDom || !Seen.test(IDom->getBlock()->getNumber());
- // IDom dominates all of our predecessors, but it may not be their
- // immediate dominator. Check if any of them have live-out values that are
- // properly dominated by IDom. If so, we need a phi-def here.
- if (!needPHI) {
- IDomValue = LiveOut[IDom->getBlock()];
- // Cache the DomTree node that defined the value.
- if (IDomValue.first && !IDomValue.second)
- LiveOut[IDom->getBlock()].second = IDomValue.second =
- DomTree->getNode(Indexes->getMBBFromIndex(IDomValue.first->def));
- for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
- PE = MBB->pred_end(); PI != PE; ++PI) {
- LiveOutPair &Value = LiveOut[*PI];
- if (!Value.first || Value.first == IDomValue.first)
- continue;
- // Cache the DomTree node that defined the value.
- if (!Value.second)
- Value.second =
- DomTree->getNode(Indexes->getMBBFromIndex(Value.first->def));
- // This predecessor is carrying something other than IDomValue.
- // It could be because IDomValue hasn't propagated yet, or it could be
- // because MBB is in the dominance frontier of that value.
- if (DomTree->dominates(IDom, Value.second)) {
- needPHI = true;
- break;
- }
- }
- }
- // The value may be live-through even if Kill is set, as can happen when
- // we are called from extendRange. In that case LiveOutSeen is true, and
- // LiveOut indicates a foreign or missing value.
- LiveOutPair &LOP = LiveOut[MBB];
- // Create a phi-def if required.
- if (needPHI) {
- ++Changes;
- assert(Alloc && "Need VNInfo allocator to create PHI-defs");
- SlotIndex Start, End;
- tie(Start, End) = Indexes->getMBBRange(MBB);
- LiveRange &LR = I->LR;
- VNInfo *VNI = LR.getNextValue(Start, *Alloc);
- I->Value = VNI;
- // This block is done, we know the final value.
- I->DomNode = 0;
- // Add liveness since updateLiveIns now skips this node.
- if (I->Kill.isValid())
- LR.addSegment(LiveInterval::Segment(Start, I->Kill, VNI));
- else {
- LR.addSegment(LiveInterval::Segment(Start, End, VNI));
- LOP = LiveOutPair(VNI, Node);
- }
- } else if (IDomValue.first) {
- // No phi-def here. Remember incoming value.
- I->Value = IDomValue.first;
- // If the IDomValue is killed in the block, don't propagate through.
- if (I->Kill.isValid())
- continue;
- // Propagate IDomValue if it isn't killed:
- // MBB is live-out and doesn't define its own value.
- if (LOP.first == IDomValue.first)
- continue;
- ++Changes;
- LOP = IDomValue;
- }
- }
- } while (Changes);
- }