Extract live range calculations from SplitKit.

SplitKit will soon need two copies of these data structures, and the
algorithms will also be useful when LiveIntervalAnalysis becomes
independent of LiveVariables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139572 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveRangeCalc.cpp

@@ -0,0 +1,271 @@
+//===---- 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"
+
+using namespace llvm;
+
+void LiveRangeCalc::reset(const MachineFunction *MF) {
+  unsigned N = MF->getNumBlockIDs();
+  Seen.clear();
+  Seen.resize(N);
+  LiveOut.resize(N);
+  LiveIn.clear();
+}
+
+
+// Transfer information from the LiveIn vector to the live ranges.
+void LiveRangeCalc::updateLiveIns(VNInfo *OverrideVNI, SlotIndexes *Indexes) {
+  for (SmallVectorImpl<LiveInBlock>::iterator I = LiveIn.begin(),
+         E = LiveIn.end(); I != E; ++I) {
+    if (!I->DomNode)
+      continue;
+    MachineBasicBlock *MBB = I->DomNode->getBlock();
+
+    VNInfo *VNI = OverrideVNI ? OverrideVNI : I->Value;
+    assert(VNI && "No live-in value found");
+
+    SlotIndex Start, End;
+    tie(Start, End) = Indexes->getMBBRange(MBB);
+
+    if (I->Kill.isValid())
+      I->LI->addRange(LiveRange(Start, I->Kill, VNI));
+    else {
+      I->LI->addRange(LiveRange(Start, End, VNI));
+      // 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(VNI, 0);
+    }
+  }
+  LiveIn.clear();
+}
+
+
+void LiveRangeCalc::extend(LiveInterval *LI,
+                           SlotIndex Kill,
+                           SlotIndexes *Indexes,
+                           MachineDominatorTree *DomTree,
+                           VNInfo::Allocator *Alloc) {
+  assert(LI && "Missing live range");
+  assert(Kill.isValid() && "Invalid SlotIndex");
+  assert(Indexes && "Missing SlotIndexes");
+  assert(DomTree && "Missing dominator tree");
+  SlotIndex LastUse = Kill.getPrevSlot();
+
+  MachineBasicBlock *KillMBB = Indexes->getMBBFromIndex(LastUse);
+  assert(Kill && "No MBB at Kill");
+
+  // Is there a def in the same MBB we can extend?
+  if (LI->extendInBlock(Indexes->getMBBStartIdx(KillMBB), LastUse))
+    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.
+  VNInfo *VNI = findReachingDefs(LI, KillMBB, Kill, Indexes, DomTree);
+
+  // When there were multiple different values, we may need new PHIs.
+  if (!VNI)
+    updateSSA(Indexes, DomTree, Alloc);
+
+  updateLiveIns(VNI, Indexes);
+}
+
+
+// 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(SlotIndexes *Indexes,
+                                    MachineDominatorTree *DomTree,
+                                    VNInfo::Allocator *Alloc) {
+  assert(Indexes && "Missing SlotIndexes");
+  assert(DomTree && "Missing dominator tree");
+  updateSSA(Indexes, DomTree, Alloc);
+  updateLiveIns(0, Indexes);
+}
+
+
+VNInfo *LiveRangeCalc::findReachingDefs(LiveInterval *LI,
+                                        MachineBasicBlock *KillMBB,
+                                        SlotIndex Kill,
+                                        SlotIndexes *Indexes,
+                                        MachineDominatorTree *DomTree) {
+  // Blocks where LI should be live-in.
+  SmallVector<MachineBasicBlock*, 16> WorkList(1, KillMBB);
+
+  // 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 = WorkList[i];
+    assert(!MBB->pred_empty() && "Value live-in to entry block?");
+    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 = LI->extendInBlock(Start, End.getPrevSlot());
+       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);
+       else
+          // Loopback to KillMBB, so value is really live through.
+         Kill = SlotIndex();
+    }
+  }
+
+  // Transfer WorkList to LiveInBlocks in reverse order.
+  // This ordering works best with updateSSA().
+  LiveIn.clear();
+  LiveIn.reserve(WorkList.size());
+  while(!WorkList.empty())
+    addLiveInBlock(LI, DomTree->getNode(WorkList.pop_back_val()));
+
+  // The kill block may not be live-through.
+  assert(LiveIn.back().DomNode->getBlock() == KillMBB);
+  LiveIn.back().Kill = Kill;
+
+  return UniqueVNI ? TheVNI : 0;
+}
+
+
+// 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(SlotIndexes *Indexes,
+                              MachineDominatorTree *DomTree,
+                              VNInfo::Allocator *Alloc) {
+  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);
+        VNInfo *VNI = I->LI->getNextValue(Start, 0, *Alloc);
+        VNI->setIsPHIDef(true);
+        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())
+          I->LI->addRange(LiveRange(Start, I->Kill, VNI));
+        else {
+          I->LI->addRange(LiveRange(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);
+}