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diff --git a/lib/CodeGen/LiveIntervalUnion.cpp b/lib/CodeGen/LiveIntervalUnion.cpp
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+//===-- LiveIntervalUnion.cpp - Live interval union data structure --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// LiveIntervalUnion represents a coalesced set of live intervals. This may be
+// used during coalescing to represent a congruence class, or during register
+// allocation to model liveness of a physical register.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "regalloc"
+#include "LiveIntervalUnion.h"
+#include "llvm/ADT/SparseBitVector.h"
+#include "llvm/CodeGen/MachineLoopRanges.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+using namespace llvm;
+
+
+// Merge a LiveInterval's segments. Guarantee no overlaps.
+void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
+  if (VirtReg.empty())
+    return;
+  ++Tag;
+
+  // Insert each of the virtual register's live segments into the map.
+  LiveInterval::iterator RegPos = VirtReg.begin();
+  LiveInterval::iterator RegEnd = VirtReg.end();
+  SegmentIter SegPos = Segments.find(RegPos->start);
+
+  for (;;) {
+    SegPos.insert(RegPos->start, RegPos->end, &VirtReg);
+    if (++RegPos == RegEnd)
+      return;
+    SegPos.advanceTo(RegPos->start);
+  }
+}
+
+// Remove a live virtual register's segments from this union.
+void LiveIntervalUnion::extract(LiveInterval &VirtReg) {
+  if (VirtReg.empty())
+    return;
+  ++Tag;
+
+  // Remove each of the virtual register's live segments from the map.
+  LiveInterval::iterator RegPos = VirtReg.begin();
+  LiveInterval::iterator RegEnd = VirtReg.end();
+  SegmentIter SegPos = Segments.find(RegPos->start);
+
+  for (;;) {
+    assert(SegPos.value() == &VirtReg && "Inconsistent LiveInterval");
+    SegPos.erase();
+    if (!SegPos.valid())
+      return;
+
+    // Skip all segments that may have been coalesced.
+    RegPos = VirtReg.advanceTo(RegPos, SegPos.start());
+    if (RegPos == RegEnd)
+      return;
+
+    SegPos.advanceTo(RegPos->start);
+  }
+}
+
+void
+LiveIntervalUnion::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
+  OS << "LIU " << PrintReg(RepReg, TRI);
+  if (empty()) {
+    OS << " empty\n";
+    return;
+  }
+  for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
+    OS << " [" << SI.start() << ' ' << SI.stop() << "):"
+       << PrintReg(SI.value()->reg, TRI);
+  }
+  OS << '\n';
+}
+
+void LiveIntervalUnion::InterferenceResult::print(raw_ostream &OS,
+                                          const TargetRegisterInfo *TRI) const {
+  OS << '[' << start() << ';' << stop() << "):"
+     << PrintReg(interference()->reg, TRI);
+}
+
+void LiveIntervalUnion::Query::print(raw_ostream &OS,
+                                     const TargetRegisterInfo *TRI) {
+  OS << "Interferences with ";
+  LiveUnion->print(OS, TRI);
+  InterferenceResult IR = firstInterference();
+  while (isInterference(IR)) {
+    OS << "  ";
+    IR.print(OS, TRI);
+    OS << '\n';
+    nextInterference(IR);
+  }
+}
+
+#ifndef NDEBUG
+// Verify the live intervals in this union and add them to the visited set.
+void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
+  for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
+    VisitedVRegs.set(SI.value()->reg);
+}
+#endif //!NDEBUG
+
+// Private interface accessed by Query.
+//
+// Find a pair of segments that intersect, one in the live virtual register
+// (LiveInterval), and the other in this LiveIntervalUnion. The caller (Query)
+// is responsible for advancing the LiveIntervalUnion segments to find a
+// "notable" intersection, which requires query-specific logic.
+//
+// This design assumes only a fast mechanism for intersecting a single live
+// virtual register segment with a set of LiveIntervalUnion segments.  This may
+// be ok since most virtual registers have very few segments.  If we had a data
+// structure that optimizd MxN intersection of segments, then we would bypass
+// the loop that advances within the LiveInterval.
+//
+// If no intersection exists, set VirtRegI = VirtRegEnd, and set SI to the first
+// segment whose start point is greater than LiveInterval's end point.
+//
+// Assumes that segments are sorted by start position in both
+// LiveInterval and LiveSegments.
+void LiveIntervalUnion::Query::findIntersection(InterferenceResult &IR) const {
+  // Search until reaching the end of the LiveUnion segments.
+  LiveInterval::iterator VirtRegEnd = VirtReg->end();
+  if (IR.VirtRegI == VirtRegEnd)
+    return;
+  while (IR.LiveUnionI.valid()) {
+    // Slowly advance the live virtual reg iterator until we surpass the next
+    // segment in LiveUnion.
+    //
+    // Note: If this is ever used for coalescing of fixed registers and we have
+    // a live vreg with thousands of segments, then change this code to use
+    // upperBound instead.
+    IR.VirtRegI = VirtReg->advanceTo(IR.VirtRegI, IR.LiveUnionI.start());
+    if (IR.VirtRegI == VirtRegEnd)
+      break; // Retain current (nonoverlapping) LiveUnionI
+
+    // VirtRegI may have advanced far beyond LiveUnionI, catch up.
+    IR.LiveUnionI.advanceTo(IR.VirtRegI->start);
+
+    // Check if no LiveUnionI exists with VirtRegI->Start < LiveUnionI.end
+    if (!IR.LiveUnionI.valid())
+      break;
+    if (IR.LiveUnionI.start() < IR.VirtRegI->end) {
+      assert(overlap(*IR.VirtRegI, IR.LiveUnionI) &&
+             "upperBound postcondition");
+      break;
+    }
+  }
+  if (!IR.LiveUnionI.valid())
+    IR.VirtRegI = VirtRegEnd;
+}
+
+// Find the first intersection, and cache interference info
+// (retain segment iterators into both VirtReg and LiveUnion).
+const LiveIntervalUnion::InterferenceResult &
+LiveIntervalUnion::Query::firstInterference() {
+  if (CheckedFirstInterference)
+    return FirstInterference;
+  CheckedFirstInterference = true;
+  InterferenceResult &IR = FirstInterference;
+
+  // Quickly skip interference check for empty sets.
+  if (VirtReg->empty() || LiveUnion->empty()) {
+    IR.VirtRegI = VirtReg->end();
+  } else if (VirtReg->beginIndex() < LiveUnion->startIndex()) {
+    // VirtReg starts first, perform double binary search.
+    IR.VirtRegI = VirtReg->find(LiveUnion->startIndex());
+    if (IR.VirtRegI != VirtReg->end())
+      IR.LiveUnionI = LiveUnion->find(IR.VirtRegI->start);
+  } else {
+    // LiveUnion starts first, perform double binary search.
+    IR.LiveUnionI = LiveUnion->find(VirtReg->beginIndex());
+    if (IR.LiveUnionI.valid())
+      IR.VirtRegI = VirtReg->find(IR.LiveUnionI.start());
+    else
+      IR.VirtRegI = VirtReg->end();
+  }
+  findIntersection(FirstInterference);
+  assert((IR.VirtRegI == VirtReg->end() || IR.LiveUnionI.valid())
+         && "Uninitialized iterator");
+  return FirstInterference;
+}
+
+// Treat the result as an iterator and advance to the next interfering pair
+// of segments. This is a plain iterator with no filter.
+bool LiveIntervalUnion::Query::nextInterference(InterferenceResult &IR) const {
+  assert(isInterference(IR) && "iteration past end of interferences");
+
+  // Advance either the VirtReg or LiveUnion segment to ensure that we visit all
+  // unique overlapping pairs.
+  if (IR.VirtRegI->end < IR.LiveUnionI.stop()) {
+    if (++IR.VirtRegI == VirtReg->end())
+      return false;
+  }
+  else {
+    if (!(++IR.LiveUnionI).valid()) {
+      IR.VirtRegI = VirtReg->end();
+      return false;
+    }
+  }
+  // Short-circuit findIntersection() if possible.
+  if (overlap(*IR.VirtRegI, IR.LiveUnionI))
+    return true;
+
+  // Find the next intersection.
+  findIntersection(IR);
+  return isInterference(IR);
+}
+
+// Scan the vector of interfering virtual registers in this union. Assume it's
+// quite small.
+bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
+  SmallVectorImpl<LiveInterval*>::const_iterator I =
+    std::find(InterferingVRegs.begin(), InterferingVRegs.end(), VirtReg);
+  return I != InterferingVRegs.end();
+}
+
+// Count the number of virtual registers in this union that interfere with this
+// query's live virtual register.
+//
+// The number of times that we either advance IR.VirtRegI or call
+// LiveUnion.upperBound() will be no more than the number of holes in
+// VirtReg. So each invocation of collectInterferingVRegs() takes
+// time proportional to |VirtReg Holes| * time(LiveUnion.upperBound()).
+//
+// For comments on how to speed it up, see Query::findIntersection().
+unsigned LiveIntervalUnion::Query::
+collectInterferingVRegs(unsigned MaxInterferingRegs) {
+  InterferenceResult IR = firstInterference();
+  LiveInterval::iterator VirtRegEnd = VirtReg->end();
+  LiveInterval *RecentInterferingVReg = NULL;
+  if (IR.VirtRegI != VirtRegEnd) while (IR.LiveUnionI.valid()) {
+    // Advance the union's iterator to reach an unseen interfering vreg.
+    do {
+      if (IR.LiveUnionI.value() == RecentInterferingVReg)
+        continue;
+
+      if (!isSeenInterference(IR.LiveUnionI.value()))
+        break;
+
+      // Cache the most recent interfering vreg to bypass isSeenInterference.
+      RecentInterferingVReg = IR.LiveUnionI.value();
+
+    } while ((++IR.LiveUnionI).valid());
+    if (!IR.LiveUnionI.valid())
+      break;
+
+    // Advance the VirtReg iterator until surpassing the next segment in
+    // LiveUnion.
+    IR.VirtRegI = VirtReg->advanceTo(IR.VirtRegI, IR.LiveUnionI.start());
+    if (IR.VirtRegI == VirtRegEnd)
+      break;
+
+    // Check for intersection with the union's segment.
+    if (overlap(*IR.VirtRegI, IR.LiveUnionI)) {
+
+      if (!IR.LiveUnionI.value()->isSpillable())
+        SeenUnspillableVReg = true;
+
+      if (InterferingVRegs.size() == MaxInterferingRegs)
+        // Leave SeenAllInterferences set to false to indicate that at least one
+        // interference exists beyond those we collected.
+        return MaxInterferingRegs;
+
+      InterferingVRegs.push_back(IR.LiveUnionI.value());
+
+      // Cache the most recent interfering vreg to bypass isSeenInterference.
+      RecentInterferingVReg = IR.LiveUnionI.value();
+      ++IR.LiveUnionI;
+      continue;
+    }
+    // VirtRegI may have advanced far beyond LiveUnionI,
+    // do a fast intersection test to "catch up"
+    IR.LiveUnionI.advanceTo(IR.VirtRegI->start);
+  }
+  SeenAllInterferences = true;
+  return InterferingVRegs.size();
+}
+
+bool LiveIntervalUnion::Query::checkLoopInterference(MachineLoopRange *Loop) {
+  // VirtReg is likely live throughout the loop, so start by checking LIU-Loop
+  // overlaps.
+  IntervalMapOverlaps<LiveIntervalUnion::Map, MachineLoopRange::Map>
+    Overlaps(LiveUnion->getMap(), Loop->getMap());
+  if (!Overlaps.valid())
+    return false;
+
+  // The loop is overlapping an LIU assignment. Check VirtReg as well.
+  LiveInterval::iterator VRI = VirtReg->find(Overlaps.start());
+
+  for (;;) {
+    if (VRI == VirtReg->end())
+      return false;
+    if (VRI->start < Overlaps.stop())
+      return true;
+
+    Overlaps.advanceTo(VRI->start);
+    if (!Overlaps.valid())
+      return false;
+    if (Overlaps.start() < VRI->end)
+      return true;
+
+    VRI = VirtReg->advanceTo(VRI, Overlaps.start());
+  }
+}