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llvm-mirror/lib/CodeGen/LiveInterval.cpp
Owen Anderson 9d2293f7ad MergeValueInto is too smart: it might choose to do the merge the opposite direction. 
Live interval reconstruction needs to account for this, and scour its maps to
prevent dangling references.

llvm-svn: 63558
2009-02-02 22:42:01 +00:00

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//===-- LiveInterval.cpp - Live Interval Representation -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file 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/SmallSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Streams.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include <algorithm>
#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);
}
// liveBeforeAndAt - Check if the interval is live at the index and the index
// just before it. If index is liveAt, check if it starts a new live range.
// If it does, then check if the previous live range ends at index-1.
bool LiveInterval::liveBeforeAndAt(unsigned I) const {
Ranges::const_iterator r = std::upper_bound(ranges.begin(), ranges.end(), I);
if (r == ranges.begin())
return false;
--r;
if (!r->contains(I))
return false;
if (I != r->start)
return true;
// I is the start of a live range. Check if the previous live range ends
// at I-1.
if (r == ranges.begin())
return false;
return r->end == 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!");
VNInfo *ValNo = I->valno;
unsigned OldEnd = I->end;
// 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->valno == ValNo && "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);
// Update kill info.
removeKills(ValNo, OldEnd, I->end-1);
// 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->valno == ValNo) {
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!");
VNInfo *ValNo = I->valno;
// 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->valno == ValNo && "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->valno == ValNo) {
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.valno == B->valno) {
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 valno'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.valno == it->valno) {
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);
else if (End < it->end)
// Overlapping intervals, there might have been a kill here.
removeKill(it->valno, End);
return it;
}
} else {
// Check to make sure that we are not overlapping two live ranges with
// different valno'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);
}
/// isInOneLiveRange - Return true if the range specified is entirely in the
/// a single LiveRange of the live interval.
bool LiveInterval::isInOneLiveRange(unsigned Start, unsigned End) {
Ranges::iterator I = std::upper_bound(ranges.begin(), ranges.end(), Start);
if (I == ranges.begin())
return false;
--I;
return I->contains(Start) && I->contains(End-1);
}
/// removeRange - Remove the specified range from this interval. Note that
/// the range must be in a single LiveRange in its entirety.
void LiveInterval::removeRange(unsigned Start, unsigned End,
bool RemoveDeadValNo) {
// 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.
VNInfo *ValNo = I->valno;
if (I->start == Start) {
if (I->end == End) {
removeKills(I->valno, Start, End);
if (RemoveDeadValNo) {
// Check if val# is dead.
bool isDead = true;
for (const_iterator II = begin(), EE = end(); II != EE; ++II)
if (II != I && II->valno == ValNo) {
isDead = false;
break;
}
if (isDead) {
// Now that ValNo 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 (ValNo->id == getNumValNums()-1) {
do {
VNInfo *VNI = valnos.back();
valnos.pop_back();
VNI->~VNInfo();
} while (!valnos.empty() && valnos.back()->def == ~1U);
} else {
ValNo->def = ~1U;
}
}
}
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) {
removeKills(ValNo, Start, 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, ValNo));
}
/// removeValNo - Remove all the ranges defined by the specified value#.
/// Also remove the value# from value# list.
void LiveInterval::removeValNo(VNInfo *ValNo) {
if (empty()) return;
Ranges::iterator I = ranges.end();
Ranges::iterator E = ranges.begin();
do {
--I;
if (I->valno == ValNo)
ranges.erase(I);
} while (I != E);
// Now that ValNo 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 (ValNo->id == getNumValNums()-1) {
do {
VNInfo *VNI = valnos.back();
valnos.pop_back();
VNI->~VNInfo();
} while (!valnos.empty() && valnos.back()->def == ~1U);
} else {
ValNo->def = ~1U;
}
}
/// 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();
}
/// findDefinedVNInfo - Find the VNInfo that's defined at the specified index
/// (register interval) or defined by the specified register (stack inteval).
VNInfo *LiveInterval::findDefinedVNInfo(unsigned DefIdxOrReg) const {
VNInfo *VNI = NULL;
for (LiveInterval::const_vni_iterator i = vni_begin(), e = vni_end();
i != e; ++i)
if ((*i)->def == DefIdxOrReg) {
VNI = *i;
break;
}
return VNI;
}
/// 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, const int *LHSValNoAssignments,
const int *RHSValNoAssignments,
SmallVector<VNInfo*, 16> &NewVNInfo) {
// 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;
unsigned NumVals = getNumValNums();
unsigned NumNewVals = NewVNInfo.size();
for (unsigned i = 0; i != NumVals; ++i) {
unsigned LHSValID = LHSValNoAssignments[i];
if (i != LHSValID ||
(NewVNInfo[LHSValID] && NewVNInfo[LHSValID] != getValNumInfo(i)))
MustMapCurValNos = true;
}
// 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->valno = NewVNInfo[LHSValNoAssignments[OutIt->valno->id]];
++OutIt;
for (iterator I = OutIt, E = end(); I != E; ++I) {
OutIt->valno = NewVNInfo[LHSValNoAssignments[I->valno->id]];
// 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->valno == (OutIt-1)->valno && (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());
}
// Remember assignements because val# ids are changing.
SmallVector<unsigned, 16> OtherAssignments;
for (iterator I = Other.begin(), E = Other.end(); I != E; ++I)
OtherAssignments.push_back(RHSValNoAssignments[I->valno->id]);
// Update val# info. Renumber them and make sure they all belong to this
// LiveInterval now. Also remove dead val#'s.
unsigned NumValNos = 0;
for (unsigned i = 0; i < NumNewVals; ++i) {
VNInfo *VNI = NewVNInfo[i];
if (VNI) {
if (i >= NumVals)
valnos.push_back(VNI);
else
valnos[NumValNos] = VNI;
VNI->id = NumValNos++; // Renumber val#.
}
}
if (NumNewVals < NumVals)
valnos.resize(NumNewVals); // shrinkify
// Okay, now insert the RHS live ranges into the LHS.
iterator InsertPos = begin();
unsigned RangeNo = 0;
for (iterator I = Other.begin(), E = Other.end(); I != E; ++I, ++RangeNo) {
// Map the valno in the other live range to the current live range.
I->valno = NewVNInfo[OtherAssignments[RangeNo]];
assert(I->valno && "Adding a dead range?");
InsertPos = addRangeFrom(*I, InsertPos);
}
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,
VNInfo *LHSValNo) {
// TODO: Make this more efficient.
iterator InsertPos = begin();
for (const_iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
// Map the valno in the other live range to the current live range.
LiveRange Tmp = *I;
Tmp.valno = LHSValNo;
InsertPos = addRangeFrom(Tmp, InsertPos);
}
}
/// MergeValueInAsValue - Merge all of the live ranges of a specific val#
/// 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, it will replace the value numbers of the overlaped
/// live ranges with the specified value number.
void LiveInterval::MergeValueInAsValue(const LiveInterval &RHS,
const VNInfo *RHSValNo, VNInfo *LHSValNo) {
SmallVector<VNInfo*, 4> ReplacedValNos;
iterator IP = begin();
for (const_iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
if (I->valno != RHSValNo)
continue;
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) {
if (IP[-1].valno != LHSValNo) {
ReplacedValNos.push_back(IP[-1].valno);
IP[-1].valno = LHSValNo; // Update val#.
}
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) {
if (IP->valno != LHSValNo) {
ReplacedValNos.push_back(IP->valno);
IP->valno = LHSValNo; // Update val#.
}
End = IP->start;
// If this trimmed away the whole range, ignore it.
if (Start == End) continue;
}
// Map the valno in the other live range to the current live range.
IP = addRangeFrom(LiveRange(Start, End, LHSValNo), IP);
}
SmallSet<VNInfo*, 4> Seen;
for (unsigned i = 0, e = ReplacedValNos.size(); i != e; ++i) {
VNInfo *V1 = ReplacedValNos[i];
if (Seen.insert(V1)) {
bool isDead = true;
for (const_iterator I = begin(), E = end(); I != E; ++I)
if (I->valno == V1) {
isDead = false;
break;
}
if (isDead) {
// 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->id == getNumValNums()-1) {
do {
VNInfo *VNI = valnos.back();
valnos.pop_back();
VNI->~VNInfo();
} while (!valnos.empty() && valnos.back()->def == ~1U);
} else {
V1->def = ~1U;
}
}
}
}
}
/// 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,
BumpPtrAllocator &VNInfoAllocator) {
if (Clobbers.empty()) 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!
VNInfo *ClobberValNo = getNextValue(~0U, 0, VNInfoAllocator);
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.
VNInfo* LiveInterval::MergeValueNumberInto(VNInfo *V1, VNInfo *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->id < V2->id) {
copyValNumInfo(V1, V2);
std::swap(V1, V2);
}
// Merge V1 live ranges into V2.
for (iterator I = begin(); I != end(); ) {
iterator LR = I++;
if (LR->valno != 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->valno == 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->valno = 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->valno == 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->id == getNumValNums()-1) {
do {
VNInfo *VNI = valnos.back();
valnos.pop_back();
VNI->~VNInfo();
} while (valnos.back()->def == ~1U);
} else {
V1->def = ~1U;
}
return V2;
}
void LiveInterval::Copy(const LiveInterval &RHS,
BumpPtrAllocator &VNInfoAllocator) {
ranges.clear();
valnos.clear();
preference = RHS.preference;
weight = RHS.weight;
for (unsigned i = 0, e = RHS.getNumValNums(); i != e; ++i) {
const VNInfo *VNI = RHS.getValNumInfo(i);
VNInfo *NewVNI = getNextValue(~0U, 0, VNInfoAllocator);
copyValNumInfo(NewVNI, VNI);
}
for (unsigned i = 0, e = RHS.ranges.size(); i != e; ++i) {
const LiveRange &LR = RHS.ranges[i];
addRange(LiveRange(LR.start, LR.end, getValNumInfo(LR.valno->id)));
}
}
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.valno->id << ")";
}
void LiveRange::dump() const {
cerr << *this << "\n";
}
void LiveInterval::print(std::ostream &OS,
const TargetRegisterInfo *TRI) const {
if (isStackSlot())
OS << "SS#" << getStackSlotIndex();
else if (TRI && TargetRegisterInfo::isPhysicalRegister(reg))
OS << TRI->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 << " ";
unsigned vnum = 0;
for (const_vni_iterator i = vni_begin(), e = vni_end(); i != e;
++i, ++vnum) {
const VNInfo *vni = *i;
if (vnum) OS << " ";
OS << vnum << "@";
if (vni->def == ~1U) {
OS << "x";
} else {
if (vni->def == ~0U)
OS << "?";
else
OS << vni->def;
unsigned ee = vni->kills.size();
if (ee || vni->hasPHIKill) {
OS << "-(";
for (unsigned j = 0; j != ee; ++j) {
OS << vni->kills[j];
if (j != ee-1)
OS << " ";
}
if (vni->hasPHIKill) {
if (ee)
OS << " ";
OS << "phi";
}
OS << ")";
}
}
}
}
}
void LiveInterval::dump() const {
cerr << *this << "\n";
}
void LiveRange::print(std::ostream &os) const {
os << *this;
}
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