lib/CodeGen/LiveInterval.cpp - llvm - Git at Google

 //===-- LiveInterval.cpp - Live Interval Representation -------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file was developed by the LLVM research group and is distributed under
 // the University of Illinois Open Source License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the LiveRange and LiveInterval classes.  Given some
 // numbering of each the machine instructions an interval [i, j) is said to be a
 // live interval for register v if there is no instruction with number j' > j
 // such that v is live at j' abd there is no instruction with number i' < i such
 // that v is live at i'. In this implementation intervals can have holes,
 // i.e. an interval might look like [1,20), [50,65), [1000,1001).  Each
 // individual range is represented as an instance of LiveRange, and the whole
 // interval is represented as an instance of LiveInterval.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/CodeGen/LiveInterval.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Streams.h"
 #include "llvm/Target/MRegisterInfo.h"
 #include <algorithm>
 #include <map>
 #include <ostream>
 using namespace llvm;

 // An example for liveAt():
 //
 // this = [1,4), liveAt(0) will return false. The instruction defining this
 // spans slots [0,3]. The interval belongs to an spilled definition of the
 // variable it represents. This is because slot 1 is used (def slot) and spans
 // up to slot 3 (store slot).
 //
 bool LiveInterval::liveAt(unsigned I) const {
   Ranges::const_iterator r = std::upper_bound(ranges.begin(), ranges.end(), I);

   if (r == ranges.begin())
     return false;

   --r;
   return r->contains(I);
 }

 // overlaps - Return true if the intersection of the two live intervals is
 // not empty.
 //
 // An example for overlaps():
 //
 // 0: A = ...
 // 4: B = ...
 // 8: C = A + B ;; last use of A
 //
 // The live intervals should look like:
 //
 // A = [3, 11)
 // B = [7, x)
 // C = [11, y)
 //
 // A->overlaps(C) should return false since we want to be able to join
 // A and C.
 //
 bool LiveInterval::overlapsFrom(const LiveInterval& other,
                                 const_iterator StartPos) const {
   const_iterator i = begin();
   const_iterator ie = end();
   const_iterator j = StartPos;
   const_iterator je = other.end();

   assert((StartPos->start <= i->start || StartPos == other.begin()) &&
          StartPos != other.end() && "Bogus start position hint!");

   if (i->start < j->start) {
     i = std::upper_bound(i, ie, j->start);
     if (i != ranges.begin()) --i;
   } else if (j->start < i->start) {
     ++StartPos;
     if (StartPos != other.end() && StartPos->start <= i->start) {
       assert(StartPos < other.end() && i < end());
       j = std::upper_bound(j, je, i->start);
       if (j != other.ranges.begin()) --j;
     }
   } else {
     return true;
   }

   if (j == je) return false;

   while (i != ie) {
     if (i->start > j->start) {
       std::swap(i, j);
       std::swap(ie, je);
     }

     if (i->end > j->start)
       return true;
     ++i;
   }

   return false;
 }

 /// extendIntervalEndTo - This method is used when we want to extend the range
 /// specified by I to end at the specified endpoint.  To do this, we should
 /// merge and eliminate all ranges that this will overlap with.  The iterator is
 /// not invalidated.
 void LiveInterval::extendIntervalEndTo(Ranges::iterator I, unsigned NewEnd) {
   assert(I != ranges.end() && "Not a valid interval!");
   unsigned ValId = I->ValId;

   // Search for the first interval that we can't merge with.
   Ranges::iterator MergeTo = next(I);
   for (; MergeTo != ranges.end() && NewEnd >= MergeTo->end; ++MergeTo) {
     assert(MergeTo->ValId == ValId && "Cannot merge with differing values!");
   }

   // If NewEnd was in the middle of an interval, make sure to get its endpoint.
   I->end = std::max(NewEnd, prior(MergeTo)->end);

   // Erase any dead ranges.
   ranges.erase(next(I), MergeTo);

   // If the newly formed range now touches the range after it and if they have
   // the same value number, merge the two ranges into one range.
   Ranges::iterator Next = next(I);
   if (Next != ranges.end() && Next->start <= I->end && Next->ValId == ValId) {
     I->end = Next->end;
     ranges.erase(Next);
   }
 }


 /// extendIntervalStartTo - This method is used when we want to extend the range
 /// specified by I to start at the specified endpoint.  To do this, we should
 /// merge and eliminate all ranges that this will overlap with.
 LiveInterval::Ranges::iterator
 LiveInterval::extendIntervalStartTo(Ranges::iterator I, unsigned NewStart) {
   assert(I != ranges.end() && "Not a valid interval!");
   unsigned ValId = I->ValId;

   // Search for the first interval that we can't merge with.
   Ranges::iterator MergeTo = I;
   do {
     if (MergeTo == ranges.begin()) {
       I->start = NewStart;
       ranges.erase(MergeTo, I);
       return I;
     }
     assert(MergeTo->ValId == ValId && "Cannot merge with differing values!");
     --MergeTo;
   } while (NewStart <= MergeTo->start);

   // If we start in the middle of another interval, just delete a range and
   // extend that interval.
   if (MergeTo->end >= NewStart && MergeTo->ValId == ValId) {
     MergeTo->end = I->end;
   } else {
     // Otherwise, extend the interval right after.
     ++MergeTo;
     MergeTo->start = NewStart;
     MergeTo->end = I->end;
   }

   ranges.erase(next(MergeTo), next(I));
   return MergeTo;
 }

 LiveInterval::iterator
 LiveInterval::addRangeFrom(LiveRange LR, iterator From) {
   unsigned Start = LR.start, End = LR.end;
   iterator it = std::upper_bound(From, ranges.end(), Start);

   // If the inserted interval starts in the middle or right at the end of
   // another interval, just extend that interval to contain the range of LR.
   if (it != ranges.begin()) {
     iterator B = prior(it);
     if (LR.ValId == B->ValId) {
       if (B->start <= Start && B->end >= Start) {
         extendIntervalEndTo(B, End);
         return B;
       }
     } else {
       // Check to make sure that we are not overlapping two live ranges with
       // different ValId's.
       assert(B->end <= Start &&
              "Cannot overlap two LiveRanges with differing ValID's"
              " (did you def the same reg twice in a MachineInstr?)");
     }
   }

   // Otherwise, if this range ends in the middle of, or right next to, another
   // interval, merge it into that interval.
   if (it != ranges.end())
     if (LR.ValId == it->ValId) {
       if (it->start <= End) {
         it = extendIntervalStartTo(it, Start);

         // If LR is a complete superset of an interval, we may need to grow its
         // endpoint as well.
         if (End > it->end)
           extendIntervalEndTo(it, End);
         return it;
       }
     } else {
       // Check to make sure that we are not overlapping two live ranges with
       // different ValId's.
       assert(it->start >= End &&
              "Cannot overlap two LiveRanges with differing ValID's");
     }

   // Otherwise, this is just a new range that doesn't interact with anything.
   // Insert it.
   return ranges.insert(it, LR);
 }


 /// removeRange - Remove the specified range from this interval.  Note that
 /// the range must already be in this interval in its entirety.
 void LiveInterval::removeRange(unsigned Start, unsigned End) {
   // Find the LiveRange containing this span.
   Ranges::iterator I = std::upper_bound(ranges.begin(), ranges.end(), Start);
   assert(I != ranges.begin() && "Range is not in interval!");
   --I;
   assert(I->contains(Start) && I->contains(End-1) &&
          "Range is not entirely in interval!");

   // If the span we are removing is at the start of the LiveRange, adjust it.
   if (I->start == Start) {
     if (I->end == End)
       ranges.erase(I);  // Removed the whole LiveRange.
     else
       I->start = End;
     return;
   }

   // Otherwise if the span we are removing is at the end of the LiveRange,
   // adjust the other way.
   if (I->end == End) {
     I->end = Start;
     return;
   }

   // Otherwise, we are splitting the LiveRange into two pieces.
   unsigned OldEnd = I->end;
   I->end = Start;   // Trim the old interval.

   // Insert the new one.
   ranges.insert(next(I), LiveRange(End, OldEnd, I->ValId));
 }

 /// getLiveRangeContaining - Return the live range that contains the
 /// specified index, or null if there is none.
 LiveInterval::const_iterator
 LiveInterval::FindLiveRangeContaining(unsigned Idx) const {
   const_iterator It = std::upper_bound(begin(), end(), Idx);
   if (It != ranges.begin()) {
     --It;
     if (It->contains(Idx))
       return It;
   }

   return end();
 }

 LiveInterval::iterator
 LiveInterval::FindLiveRangeContaining(unsigned Idx) {
   iterator It = std::upper_bound(begin(), end(), Idx);
   if (It != begin()) {
     --It;
     if (It->contains(Idx))
       return It;
   }

   return end();
 }

 /// join - Join two live intervals (this, and other) together.  This applies
 /// mappings to the value numbers in the LHS/RHS intervals as specified.  If
 /// the intervals are not joinable, this aborts.
 void LiveInterval::join(LiveInterval &Other, int *LHSValNoAssignments,
                         int *RHSValNoAssignments,
                         SmallVector<std::pair<unsigned,
                                            unsigned>, 16> &NewValueNumberInfo) {

   // Try to do the least amount of work possible.  In particular, if there are
   // more liverange chunks in the other set than there are in the 'this' set,
   // swap sets to merge the fewest chunks in possible.
   //
   // Also, if one range is a physreg and one is a vreg, we always merge from the
   // vreg into the physreg, which leaves the vreg intervals pristine.
   if ((Other.ranges.size() > ranges.size() &&
       MRegisterInfo::isVirtualRegister(reg)) ||
       MRegisterInfo::isPhysicalRegister(Other.reg)) {
     swap(Other);
     std::swap(LHSValNoAssignments, RHSValNoAssignments);
   }

   // Determine if any of our live range values are mapped.  This is uncommon, so
   // we want to avoid the interval scan if not.
   bool MustMapCurValNos = false;
   for (unsigned i = 0, e = getNumValNums(); i != e; ++i) {
     if (ValueNumberInfo[i].first == ~2U) continue;  // tombstone value #
     if (i != (unsigned)LHSValNoAssignments[i]) {
       MustMapCurValNos = true;
       break;
     }
   }

   // If we have to apply a mapping to our base interval assignment, rewrite it
   // now.
   if (MustMapCurValNos) {
     // Map the first live range.
     iterator OutIt = begin();
     OutIt->ValId = LHSValNoAssignments[OutIt->ValId];
     ++OutIt;
     for (iterator I = OutIt, E = end(); I != E; ++I) {
       OutIt->ValId = LHSValNoAssignments[I->ValId];

       // If this live range has the same value # as its immediate predecessor,
       // and if they are neighbors, remove one LiveRange.  This happens when we
       // have [0,3:0)[4,7:1) and map 0/1 onto the same value #.
       if (OutIt->ValId == (OutIt-1)->ValId && (OutIt-1)->end == OutIt->start) {
         (OutIt-1)->end = OutIt->end;
       } else {
         if (I != OutIt) {
           OutIt->start = I->start;
           OutIt->end = I->end;
         }

         // Didn't merge, on to the next one.
         ++OutIt;
       }
     }

     // If we merge some live ranges, chop off the end.
     ranges.erase(OutIt, end());
   }

   // Okay, now insert the RHS live ranges into the LHS.
   iterator InsertPos = begin();
   for (iterator I = Other.begin(), E = Other.end(); I != E; ++I) {
     // Map the ValId in the other live range to the current live range.
     I->ValId = RHSValNoAssignments[I->ValId];
     InsertPos = addRangeFrom(*I, InsertPos);
   }

   ValueNumberInfo.clear();
   ValueNumberInfo.append(NewValueNumberInfo.begin(), NewValueNumberInfo.end());
   weight += Other.weight;
   if (Other.preference && !preference)
     preference = Other.preference;
 }

 /// MergeRangesInAsValue - Merge all of the intervals in RHS into this live
 /// interval as the specified value number.  The LiveRanges in RHS are
 /// allowed to overlap with LiveRanges in the current interval, but only if
 /// the overlapping LiveRanges have the specified value number.
 void LiveInterval::MergeRangesInAsValue(const LiveInterval &RHS,
                                         unsigned LHSValNo) {
   // TODO: Make this more efficient.
   iterator InsertPos = begin();
   for (const_iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
     // Map the ValId in the other live range to the current live range.
     LiveRange Tmp = *I;
     Tmp.ValId = LHSValNo;
     InsertPos = addRangeFrom(Tmp, InsertPos);
   }
 }


 /// MergeInClobberRanges - For any live ranges that are not defined in the
 /// current interval, but are defined in the Clobbers interval, mark them
 /// used with an unknown definition value.
 void LiveInterval::MergeInClobberRanges(const LiveInterval &Clobbers) {
   if (Clobbers.begin() == Clobbers.end()) return;

   // Find a value # to use for the clobber ranges.  If there is already a value#
   // for unknown values, use it.
   // FIXME: Use a single sentinal number for these!
   unsigned ClobberValNo = getNextValue(~0U, 0);

   iterator IP = begin();
   for (const_iterator I = Clobbers.begin(), E = Clobbers.end(); I != E; ++I) {
     unsigned Start = I->start, End = I->end;
     IP = std::upper_bound(IP, end(), Start);

     // If the start of this range overlaps with an existing liverange, trim it.
     if (IP != begin() && IP[-1].end > Start) {
       Start = IP[-1].end;
       // Trimmed away the whole range?
       if (Start >= End) continue;
     }
     // If the end of this range overlaps with an existing liverange, trim it.
     if (IP != end() && End > IP->start) {
       End = IP->start;
       // If this trimmed away the whole range, ignore it.
       if (Start == End) continue;
     }

     // Insert the clobber interval.
     IP = addRangeFrom(LiveRange(Start, End, ClobberValNo), IP);
   }
 }

 /// MergeValueNumberInto - This method is called when two value nubmers
 /// are found to be equivalent.  This eliminates V1, replacing all
 /// LiveRanges with the V1 value number with the V2 value number.  This can
 /// cause merging of V1/V2 values numbers and compaction of the value space.
 void LiveInterval::MergeValueNumberInto(unsigned V1, unsigned V2) {
   assert(V1 != V2 && "Identical value#'s are always equivalent!");

   // This code actually merges the (numerically) larger value number into the
   // smaller value number, which is likely to allow us to compactify the value
   // space.  The only thing we have to be careful of is to preserve the
   // instruction that defines the result value.

   // Make sure V2 is smaller than V1.
   if (V1 < V2) {
     setValueNumberInfo(V1, getValNumInfo(V2));
     std::swap(V1, V2);
   }

   // Merge V1 live ranges into V2.
   for (iterator I = begin(); I != end(); ) {
     iterator LR = I++;
     if (LR->ValId != V1) continue;  // Not a V1 LiveRange.

     // Okay, we found a V1 live range.  If it had a previous, touching, V2 live
     // range, extend it.
     if (LR != begin()) {
       iterator Prev = LR-1;
       if (Prev->ValId == V2 && Prev->end == LR->start) {
         Prev->end = LR->end;

         // Erase this live-range.
         ranges.erase(LR);
         I = Prev+1;
         LR = Prev;
       }
     }

     // Okay, now we have a V1 or V2 live range that is maximally merged forward.
     // Ensure that it is a V2 live-range.
     LR->ValId = V2;

     // If we can merge it into later V2 live ranges, do so now.  We ignore any
     // following V1 live ranges, as they will be merged in subsequent iterations
     // of the loop.
     if (I != end()) {
       if (I->start == LR->end && I->ValId == V2) {
         LR->end = I->end;
         ranges.erase(I);
         I = LR+1;
       }
     }
   }

   // Now that V1 is dead, remove it.  If it is the largest value number, just
   // nuke it (and any other deleted values neighboring it), otherwise mark it as
   // ~1U so it can be nuked later.
   if (V1 == getNumValNums()-1) {
     do {
       ValueNumberInfo.pop_back();
     } while (ValueNumberInfo.back().first == ~1U);
   } else {
     ValueNumberInfo[V1].first = ~1U;
   }
 }

 unsigned LiveInterval::getSize() const {
   unsigned Sum = 0;
   for (const_iterator I = begin(), E = end(); I != E; ++I)
     Sum += I->end - I->start;
   return Sum;
 }

 std::ostream& llvm::operator<<(std::ostream& os, const LiveRange &LR) {
   return os << '[' << LR.start << ',' << LR.end << ':' << LR.ValId << ")";
 }

 void LiveRange::dump() const {
   cerr << *this << "\n";
 }

 void LiveInterval::print(std::ostream &OS, const MRegisterInfo *MRI) const {
   if (MRI && MRegisterInfo::isPhysicalRegister(reg))
     OS << MRI->getName(reg);
   else
     OS << "%reg" << reg;

   OS << ',' << weight;

   if (empty())
     OS << "EMPTY";
   else {
     OS << " = ";
     for (LiveInterval::Ranges::const_iterator I = ranges.begin(),
            E = ranges.end(); I != E; ++I)
     OS << *I;
   }

   // Print value number info.
   if (getNumValNums()) {
     OS << "  ";
     for (unsigned i = 0; i != getNumValNums(); ++i) {
       if (i) OS << " ";
       OS << i << "@";
       if (ValueNumberInfo[i].first == ~0U) {
         OS << "?";
       } else {
         OS << ValueNumberInfo[i].first;
       }
     }
   }
 }

 void LiveInterval::dump() const {
   cerr << *this << "\n";
 }


 void LiveRange::print(std::ostream &os) const {
   os << *this;
 }
	//===-- LiveInterval.cpp - Live Interval Representation -------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file was developed by the LLVM research group and is distributed under
	// the University of Illinois Open Source License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements the LiveRange and LiveInterval classes. Given some
	// numbering of each the machine instructions an interval [i, j) is said to be a
	// live interval for register v if there is no instruction with number j' > j
	// such that v is live at j' abd there is no instruction with number i' < i such
	// that v is live at i'. In this implementation intervals can have holes,
	// i.e. an interval might look like [1,20), [50,65), [1000,1001). Each
	// individual range is represented as an instance of LiveRange, and the whole
	// interval is represented as an instance of LiveInterval.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/CodeGen/LiveInterval.h"
	#include "llvm/ADT/STLExtras.h"
	#include "llvm/Support/Streams.h"
	#include "llvm/Target/MRegisterInfo.h"
	#include <algorithm>
	#include <map>
	#include <ostream>
	using namespace llvm;

	// An example for liveAt():
	//
	// this = [1,4), liveAt(0) will return false. The instruction defining this
	// spans slots [0,3]. The interval belongs to an spilled definition of the
	// variable it represents. This is because slot 1 is used (def slot) and spans
	// up to slot 3 (store slot).
	//
	bool LiveInterval::liveAt(unsigned I) const {
	Ranges::const_iterator r = std::upper_bound(ranges.begin(), ranges.end(), I);

	if (r == ranges.begin())
	return false;

	--r;
	return r->contains(I);
	}

	// overlaps - Return true if the intersection of the two live intervals is
	// not empty.
	//
	// An example for overlaps():
	//
	// 0: A = ...
	// 4: B = ...
	// 8: C = A + B ;; last use of A
	//
	// The live intervals should look like:
	//
	// A = [3, 11)
	// B = [7, x)
	// C = [11, y)
	//
	// A->overlaps(C) should return false since we want to be able to join
	// A and C.
	//
	bool LiveInterval::overlapsFrom(const LiveInterval& other,
	const_iterator StartPos) const {
	const_iterator i = begin();
	const_iterator ie = end();
	const_iterator j = StartPos;
	const_iterator je = other.end();

	assert((StartPos->start <= i->start \|\| StartPos == other.begin()) &&
	StartPos != other.end() && "Bogus start position hint!");

	if (i->start < j->start) {
	i = std::upper_bound(i, ie, j->start);
	if (i != ranges.begin()) --i;
	} else if (j->start < i->start) {
	++StartPos;
	if (StartPos != other.end() && StartPos->start <= i->start) {
	assert(StartPos < other.end() && i < end());
	j = std::upper_bound(j, je, i->start);
	if (j != other.ranges.begin()) --j;
	}
	} else {
	return true;
	}

	if (j == je) return false;

	while (i != ie) {
	if (i->start > j->start) {
	std::swap(i, j);
	std::swap(ie, je);
	}

	if (i->end > j->start)
	return true;
	++i;
	}

	return false;
	}

	/// extendIntervalEndTo - This method is used when we want to extend the range
	/// specified by I to end at the specified endpoint. To do this, we should
	/// merge and eliminate all ranges that this will overlap with. The iterator is
	/// not invalidated.
	void LiveInterval::extendIntervalEndTo(Ranges::iterator I, unsigned NewEnd) {
	assert(I != ranges.end() && "Not a valid interval!");
	unsigned ValId = I->ValId;

	// Search for the first interval that we can't merge with.
	Ranges::iterator MergeTo = next(I);
	for (; MergeTo != ranges.end() && NewEnd >= MergeTo->end; ++MergeTo) {
	assert(MergeTo->ValId == ValId && "Cannot merge with differing values!");
	}

	// If NewEnd was in the middle of an interval, make sure to get its endpoint.
	I->end = std::max(NewEnd, prior(MergeTo)->end);

	// Erase any dead ranges.
	ranges.erase(next(I), MergeTo);

	// If the newly formed range now touches the range after it and if they have
	// the same value number, merge the two ranges into one range.
	Ranges::iterator Next = next(I);
	if (Next != ranges.end() && Next->start <= I->end && Next->ValId == ValId) {
	I->end = Next->end;
	ranges.erase(Next);
	}
	}


	/// extendIntervalStartTo - This method is used when we want to extend the range
	/// specified by I to start at the specified endpoint. To do this, we should
	/// merge and eliminate all ranges that this will overlap with.
	LiveInterval::Ranges::iterator
	LiveInterval::extendIntervalStartTo(Ranges::iterator I, unsigned NewStart) {
	assert(I != ranges.end() && "Not a valid interval!");
	unsigned ValId = I->ValId;

	// Search for the first interval that we can't merge with.
	Ranges::iterator MergeTo = I;
	do {
	if (MergeTo == ranges.begin()) {
	I->start = NewStart;
	ranges.erase(MergeTo, I);
	return I;
	}
	assert(MergeTo->ValId == ValId && "Cannot merge with differing values!");
	--MergeTo;
	} while (NewStart <= MergeTo->start);

	// If we start in the middle of another interval, just delete a range and
	// extend that interval.
	if (MergeTo->end >= NewStart && MergeTo->ValId == ValId) {
	MergeTo->end = I->end;
	} else {
	// Otherwise, extend the interval right after.
	++MergeTo;
	MergeTo->start = NewStart;
	MergeTo->end = I->end;
	}

	ranges.erase(next(MergeTo), next(I));
	return MergeTo;
	}

	LiveInterval::iterator
	LiveInterval::addRangeFrom(LiveRange LR, iterator From) {
	unsigned Start = LR.start, End = LR.end;
	iterator it = std::upper_bound(From, ranges.end(), Start);

	// If the inserted interval starts in the middle or right at the end of
	// another interval, just extend that interval to contain the range of LR.
	if (it != ranges.begin()) {
	iterator B = prior(it);
	if (LR.ValId == B->ValId) {
	if (B->start <= Start && B->end >= Start) {
	extendIntervalEndTo(B, End);
	return B;
	}
	} else {
	// Check to make sure that we are not overlapping two live ranges with
	// different ValId's.
	assert(B->end <= Start &&
	"Cannot overlap two LiveRanges with differing ValID's"
	" (did you def the same reg twice in a MachineInstr?)");
	}
	}

	// Otherwise, if this range ends in the middle of, or right next to, another
	// interval, merge it into that interval.
	if (it != ranges.end())
	if (LR.ValId == it->ValId) {
	if (it->start <= End) {
	it = extendIntervalStartTo(it, Start);

	// If LR is a complete superset of an interval, we may need to grow its
	// endpoint as well.
	if (End > it->end)
	extendIntervalEndTo(it, End);
	return it;
	}
	} else {
	// Check to make sure that we are not overlapping two live ranges with
	// different ValId's.
	assert(it->start >= End &&
	"Cannot overlap two LiveRanges with differing ValID's");
	}

	// Otherwise, this is just a new range that doesn't interact with anything.
	// Insert it.
	return ranges.insert(it, LR);
	}


	/// removeRange - Remove the specified range from this interval. Note that
	/// the range must already be in this interval in its entirety.
	void LiveInterval::removeRange(unsigned Start, unsigned End) {
	// Find the LiveRange containing this span.
	Ranges::iterator I = std::upper_bound(ranges.begin(), ranges.end(), Start);
	assert(I != ranges.begin() && "Range is not in interval!");
	--I;
	assert(I->contains(Start) && I->contains(End-1) &&
	"Range is not entirely in interval!");

	// If the span we are removing is at the start of the LiveRange, adjust it.
	if (I->start == Start) {
	if (I->end == End)
	ranges.erase(I); // Removed the whole LiveRange.
	else
	I->start = End;
	return;
	}

	// Otherwise if the span we are removing is at the end of the LiveRange,
	// adjust the other way.
	if (I->end == End) {
	I->end = Start;
	return;
	}

	// Otherwise, we are splitting the LiveRange into two pieces.
	unsigned OldEnd = I->end;
	I->end = Start; // Trim the old interval.

	// Insert the new one.
	ranges.insert(next(I), LiveRange(End, OldEnd, I->ValId));
	}

	/// getLiveRangeContaining - Return the live range that contains the
	/// specified index, or null if there is none.
	LiveInterval::const_iterator
	LiveInterval::FindLiveRangeContaining(unsigned Idx) const {
	const_iterator It = std::upper_bound(begin(), end(), Idx);
	if (It != ranges.begin()) {
	--It;
	if (It->contains(Idx))
	return It;
	}

	return end();
	}

	LiveInterval::iterator
	LiveInterval::FindLiveRangeContaining(unsigned Idx) {
	iterator It = std::upper_bound(begin(), end(), Idx);
	if (It != begin()) {
	--It;
	if (It->contains(Idx))
	return It;
	}

	return end();
	}

	/// join - Join two live intervals (this, and other) together. This applies
	/// mappings to the value numbers in the LHS/RHS intervals as specified. If
	/// the intervals are not joinable, this aborts.
	void LiveInterval::join(LiveInterval &Other, int *LHSValNoAssignments,
	int *RHSValNoAssignments,
	SmallVector<std::pair<unsigned,
	unsigned>, 16> &NewValueNumberInfo) {

	// Try to do the least amount of work possible. In particular, if there are
	// more liverange chunks in the other set than there are in the 'this' set,
	// swap sets to merge the fewest chunks in possible.
	//
	// Also, if one range is a physreg and one is a vreg, we always merge from the
	// vreg into the physreg, which leaves the vreg intervals pristine.
	if ((Other.ranges.size() > ranges.size() &&
	MRegisterInfo::isVirtualRegister(reg)) \|\|
	MRegisterInfo::isPhysicalRegister(Other.reg)) {
	swap(Other);
	std::swap(LHSValNoAssignments, RHSValNoAssignments);
	}

	// Determine if any of our live range values are mapped. This is uncommon, so
	// we want to avoid the interval scan if not.
	bool MustMapCurValNos = false;
	for (unsigned i = 0, e = getNumValNums(); i != e; ++i) {
	if (ValueNumberInfo[i].first == ~2U) continue; // tombstone value #
	if (i != (unsigned)LHSValNoAssignments[i]) {
	MustMapCurValNos = true;
	break;
	}
	}

	// If we have to apply a mapping to our base interval assignment, rewrite it
	// now.
	if (MustMapCurValNos) {
	// Map the first live range.
	iterator OutIt = begin();
	OutIt->ValId = LHSValNoAssignments[OutIt->ValId];
	++OutIt;
	for (iterator I = OutIt, E = end(); I != E; ++I) {
	OutIt->ValId = LHSValNoAssignments[I->ValId];

	// If this live range has the same value # as its immediate predecessor,
	// and if they are neighbors, remove one LiveRange. This happens when we
	// have [0,3:0)[4,7:1) and map 0/1 onto the same value #.
	if (OutIt->ValId == (OutIt-1)->ValId && (OutIt-1)->end == OutIt->start) {
	(OutIt-1)->end = OutIt->end;
	} else {
	if (I != OutIt) {
	OutIt->start = I->start;
	OutIt->end = I->end;
	}

	// Didn't merge, on to the next one.
	++OutIt;
	}
	}

	// If we merge some live ranges, chop off the end.
	ranges.erase(OutIt, end());
	}

	// Okay, now insert the RHS live ranges into the LHS.
	iterator InsertPos = begin();
	for (iterator I = Other.begin(), E = Other.end(); I != E; ++I) {
	// Map the ValId in the other live range to the current live range.
	I->ValId = RHSValNoAssignments[I->ValId];
	InsertPos = addRangeFrom(*I, InsertPos);
	}

	ValueNumberInfo.clear();
	ValueNumberInfo.append(NewValueNumberInfo.begin(), NewValueNumberInfo.end());
	weight += Other.weight;
	if (Other.preference && !preference)
	preference = Other.preference;
	}

	/// MergeRangesInAsValue - Merge all of the intervals in RHS into this live
	/// interval as the specified value number. The LiveRanges in RHS are
	/// allowed to overlap with LiveRanges in the current interval, but only if
	/// the overlapping LiveRanges have the specified value number.
	void LiveInterval::MergeRangesInAsValue(const LiveInterval &RHS,
	unsigned LHSValNo) {
	// TODO: Make this more efficient.
	iterator InsertPos = begin();
	for (const_iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
	// Map the ValId in the other live range to the current live range.
	LiveRange Tmp = *I;
	Tmp.ValId = LHSValNo;
	InsertPos = addRangeFrom(Tmp, InsertPos);
	}
	}


	/// MergeInClobberRanges - For any live ranges that are not defined in the
	/// current interval, but are defined in the Clobbers interval, mark them
	/// used with an unknown definition value.
	void LiveInterval::MergeInClobberRanges(const LiveInterval &Clobbers) {
	if (Clobbers.begin() == Clobbers.end()) return;

	// Find a value # to use for the clobber ranges. If there is already a value#
	// for unknown values, use it.
	// FIXME: Use a single sentinal number for these!
	unsigned ClobberValNo = getNextValue(~0U, 0);

	iterator IP = begin();
	for (const_iterator I = Clobbers.begin(), E = Clobbers.end(); I != E; ++I) {
	unsigned Start = I->start, End = I->end;
	IP = std::upper_bound(IP, end(), Start);

	// If the start of this range overlaps with an existing liverange, trim it.
	if (IP != begin() && IP[-1].end > Start) {
	Start = IP[-1].end;
	// Trimmed away the whole range?
	if (Start >= End) continue;
	}
	// If the end of this range overlaps with an existing liverange, trim it.
	if (IP != end() && End > IP->start) {
	End = IP->start;
	// If this trimmed away the whole range, ignore it.
	if (Start == End) continue;
	}

	// Insert the clobber interval.
	IP = addRangeFrom(LiveRange(Start, End, ClobberValNo), IP);
	}
	}

	/// MergeValueNumberInto - This method is called when two value nubmers
	/// are found to be equivalent. This eliminates V1, replacing all
	/// LiveRanges with the V1 value number with the V2 value number. This can
	/// cause merging of V1/V2 values numbers and compaction of the value space.
	void LiveInterval::MergeValueNumberInto(unsigned V1, unsigned V2) {
	assert(V1 != V2 && "Identical value#'s are always equivalent!");

	// This code actually merges the (numerically) larger value number into the
	// smaller value number, which is likely to allow us to compactify the value
	// space. The only thing we have to be careful of is to preserve the
	// instruction that defines the result value.

	// Make sure V2 is smaller than V1.
	if (V1 < V2) {
	setValueNumberInfo(V1, getValNumInfo(V2));
	std::swap(V1, V2);
	}

	// Merge V1 live ranges into V2.
	for (iterator I = begin(); I != end(); ) {
	iterator LR = I++;
	if (LR->ValId != V1) continue; // Not a V1 LiveRange.

	// Okay, we found a V1 live range. If it had a previous, touching, V2 live
	// range, extend it.
	if (LR != begin()) {
	iterator Prev = LR-1;
	if (Prev->ValId == V2 && Prev->end == LR->start) {
	Prev->end = LR->end;

	// Erase this live-range.
	ranges.erase(LR);
	I = Prev+1;
	LR = Prev;
	}
	}

	// Okay, now we have a V1 or V2 live range that is maximally merged forward.
	// Ensure that it is a V2 live-range.
	LR->ValId = V2;

	// If we can merge it into later V2 live ranges, do so now. We ignore any
	// following V1 live ranges, as they will be merged in subsequent iterations
	// of the loop.
	if (I != end()) {
	if (I->start == LR->end && I->ValId == V2) {
	LR->end = I->end;
	ranges.erase(I);
	I = LR+1;
	}
	}
	}

	// Now that V1 is dead, remove it. If it is the largest value number, just
	// nuke it (and any other deleted values neighboring it), otherwise mark it as
	// ~1U so it can be nuked later.
	if (V1 == getNumValNums()-1) {
	do {
	ValueNumberInfo.pop_back();
	} while (ValueNumberInfo.back().first == ~1U);
	} else {
	ValueNumberInfo[V1].first = ~1U;
	}
	}

	unsigned LiveInterval::getSize() const {
	unsigned Sum = 0;
	for (const_iterator I = begin(), E = end(); I != E; ++I)
	Sum += I->end - I->start;
	return Sum;
	}

	std::ostream& llvm::operator<<(std::ostream& os, const LiveRange &LR) {
	return os << '[' << LR.start << ',' << LR.end << ':' << LR.ValId << ")";
	}

	void LiveRange::dump() const {
	cerr << *this << "\n";
	}

	void LiveInterval::print(std::ostream &OS, const MRegisterInfo *MRI) const {
	if (MRI && MRegisterInfo::isPhysicalRegister(reg))
	OS << MRI->getName(reg);
	else
	OS << "%reg" << reg;

	OS << ',' << weight;

	if (empty())
	OS << "EMPTY";
	else {
	OS << " = ";
	for (LiveInterval::Ranges::const_iterator I = ranges.begin(),
	E = ranges.end(); I != E; ++I)
	OS << *I;
	}

	// Print value number info.
	if (getNumValNums()) {
	OS << " ";
	for (unsigned i = 0; i != getNumValNums(); ++i) {
	if (i) OS << " ";
	OS << i << "@";
	if (ValueNumberInfo[i].first == ~0U) {
	OS << "?";
	} else {
	OS << ValueNumberInfo[i].first;
	}
	}
	}
	}

	void LiveInterval::dump() const {
	cerr << *this << "\n";
	}


	void LiveRange::print(std::ostream &os) const {
	os << *this;
	}