--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/CodeGen/LiveRangeCalc.cpp	Thu Dec 12 13:56:28 2013 +0900
@@ -0,0 +1,376 @@
+//===---- 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);
+}