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llvm-project/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp

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//===- BlockFrequencyImplInfo.cpp - Block Frequency Info Implementation ---===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Loops should be simplified before this analysis.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h"
#include <numeric>
using namespace llvm;
using namespace llvm::bfi_detail;
#define DEBUG_TYPE "block-freq"
ScaledNumber<uint64_t> BlockMass::toScaled() const {
if (isFull())
return ScaledNumber<uint64_t>(1, 0);
return ScaledNumber<uint64_t>(getMass() + 1, -64);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void BlockMass::dump() const { print(dbgs()); }
#endif
static char getHexDigit(int N) {
assert(N < 16);
if (N < 10)
return '0' + N;
return 'a' + N - 10;
}
raw_ostream &BlockMass::print(raw_ostream &OS) const {
for (int Digits = 0; Digits < 16; ++Digits)
OS << getHexDigit(Mass >> (60 - Digits * 4) & 0xf);
return OS;
}
namespace {
typedef BlockFrequencyInfoImplBase::BlockNode BlockNode;
typedef BlockFrequencyInfoImplBase::Distribution Distribution;
typedef BlockFrequencyInfoImplBase::Distribution::WeightList WeightList;
typedef BlockFrequencyInfoImplBase::Scaled64 Scaled64;
typedef BlockFrequencyInfoImplBase::LoopData LoopData;
typedef BlockFrequencyInfoImplBase::Weight Weight;
typedef BlockFrequencyInfoImplBase::FrequencyData FrequencyData;
/// \brief Dithering mass distributer.
///
/// This class splits up a single mass into portions by weight, dithering to
/// spread out error. No mass is lost. The dithering precision depends on the
/// precision of the product of \a BlockMass and \a BranchProbability.
///
/// The distribution algorithm follows.
///
/// 1. Initialize by saving the sum of the weights in \a RemWeight and the
/// mass to distribute in \a RemMass.
///
/// 2. For each portion:
///
/// 1. Construct a branch probability, P, as the portion's weight divided
/// by the current value of \a RemWeight.
/// 2. Calculate the portion's mass as \a RemMass times P.
/// 3. Update \a RemWeight and \a RemMass at each portion by subtracting
/// the current portion's weight and mass.
struct DitheringDistributer {
uint32_t RemWeight;
BlockMass RemMass;
DitheringDistributer(Distribution &Dist, const BlockMass &Mass);
BlockMass takeMass(uint32_t Weight);
};
} // end anonymous namespace
DitheringDistributer::DitheringDistributer(Distribution &Dist,
const BlockMass &Mass) {
Dist.normalize();
RemWeight = Dist.Total;
RemMass = Mass;
}
BlockMass DitheringDistributer::takeMass(uint32_t Weight) {
assert(Weight && "invalid weight");
assert(Weight <= RemWeight);
BlockMass Mass = RemMass * BranchProbability(Weight, RemWeight);
// Decrement totals (dither).
RemWeight -= Weight;
RemMass -= Mass;
return Mass;
}
void Distribution::add(const BlockNode &Node, uint64_t Amount,
Weight::DistType Type) {
assert(Amount && "invalid weight of 0");
uint64_t NewTotal = Total + Amount;
// Check for overflow. It should be impossible to overflow twice.
bool IsOverflow = NewTotal < Total;
assert(!(DidOverflow && IsOverflow) && "unexpected repeated overflow");
DidOverflow |= IsOverflow;
// Update the total.
Total = NewTotal;
// Save the weight.
Weights.push_back(Weight(Type, Node, Amount));
}
static void combineWeight(Weight &W, const Weight &OtherW) {
assert(OtherW.TargetNode.isValid());
if (!W.Amount) {
W = OtherW;
return;
}
assert(W.Type == OtherW.Type);
assert(W.TargetNode == OtherW.TargetNode);
assert(OtherW.Amount && "Expected non-zero weight");
if (W.Amount > W.Amount + OtherW.Amount)
// Saturate on overflow.
W.Amount = UINT64_MAX;
else
W.Amount += OtherW.Amount;
}
static void combineWeightsBySorting(WeightList &Weights) {
// Sort so edges to the same node are adjacent.
std::sort(Weights.begin(), Weights.end(),
[](const Weight &L,
const Weight &R) { return L.TargetNode < R.TargetNode; });
// Combine adjacent edges.
WeightList::iterator O = Weights.begin();
for (WeightList::const_iterator I = O, L = O, E = Weights.end(); I != E;
++O, (I = L)) {
*O = *I;
// Find the adjacent weights to the same node.
for (++L; L != E && I->TargetNode == L->TargetNode; ++L)
combineWeight(*O, *L);
}
// Erase extra entries.
Weights.erase(O, Weights.end());
}
static void combineWeightsByHashing(WeightList &Weights) {
// Collect weights into a DenseMap.
typedef DenseMap<BlockNode::IndexType, Weight> HashTable;
HashTable Combined(NextPowerOf2(2 * Weights.size()));
for (const Weight &W : Weights)
combineWeight(Combined[W.TargetNode.Index], W);
// Check whether anything changed.
if (Weights.size() == Combined.size())
return;
// Fill in the new weights.
Weights.clear();
Weights.reserve(Combined.size());
for (const auto &I : Combined)
Weights.push_back(I.second);
}
static void combineWeights(WeightList &Weights) {
// Use a hash table for many successors to keep this linear.
if (Weights.size() > 128) {
combineWeightsByHashing(Weights);
return;
}
combineWeightsBySorting(Weights);
}
static uint64_t shiftRightAndRound(uint64_t N, int Shift) {
assert(Shift >= 0);
assert(Shift < 64);
if (!Shift)
return N;
return (N >> Shift) + (UINT64_C(1) & N >> (Shift - 1));
}
void Distribution::normalize() {
// Early exit for termination nodes.
if (Weights.empty())
return;
// Only bother if there are multiple successors.
if (Weights.size() > 1)
combineWeights(Weights);
// Early exit when combined into a single successor.
if (Weights.size() == 1) {
Total = 1;
Weights.front().Amount = 1;
return;
}
// Determine how much to shift right so that the total fits into 32-bits.
//
// If we shift at all, shift by 1 extra. Otherwise, the lower limit of 1
// for each weight can cause a 32-bit overflow.
int Shift = 0;
if (DidOverflow)
Shift = 33;
else if (Total > UINT32_MAX)
Shift = 33 - countLeadingZeros(Total);
// Early exit if nothing needs to be scaled.
if (!Shift) {
// If we didn't overflow then combineWeights() shouldn't have changed the
// sum of the weights, but let's double-check.
assert(Total == std::accumulate(Weights.begin(), Weights.end(), UINT64_C(0),
[](uint64_t Sum, const Weight &W) {
return Sum + W.Amount;
}) &&
"Expected total to be correct");
return;
}
// Recompute the total through accumulation (rather than shifting it) so that
// it's accurate after shifting and any changes combineWeights() made above.
Total = 0;
// Sum the weights to each node and shift right if necessary.
for (Weight &W : Weights) {
// Scale down below UINT32_MAX. Since Shift is larger than necessary, we
// can round here without concern about overflow.
assert(W.TargetNode.isValid());
W.Amount = std::max(UINT64_C(1), shiftRightAndRound(W.Amount, Shift));
assert(W.Amount <= UINT32_MAX);
// Update the total.
Total += W.Amount;
}
assert(Total <= UINT32_MAX);
}
void BlockFrequencyInfoImplBase::clear() {
// Swap with a default-constructed std::vector, since std::vector<>::clear()
// does not actually clear heap storage.
std::vector<FrequencyData>().swap(Freqs);
std::vector<WorkingData>().swap(Working);
Loops.clear();
}
/// \brief Clear all memory not needed downstream.
///
/// Releases all memory not used downstream. In particular, saves Freqs.
static void cleanup(BlockFrequencyInfoImplBase &BFI) {
std::vector<FrequencyData> SavedFreqs(std::move(BFI.Freqs));
BFI.clear();
BFI.Freqs = std::move(SavedFreqs);
}
bool BlockFrequencyInfoImplBase::addToDist(Distribution &Dist,
const LoopData *OuterLoop,
const BlockNode &Pred,
const BlockNode &Succ,
uint64_t Weight) {
if (!Weight)
Weight = 1;
auto isLoopHeader = [&OuterLoop](const BlockNode &Node) {
return OuterLoop && OuterLoop->isHeader(Node);
};
BlockNode Resolved = Working[Succ.Index].getResolvedNode();
#ifndef NDEBUG
auto debugSuccessor = [&](const char *Type) {
dbgs() << " =>"
<< " [" << Type << "] weight = " << Weight;
if (!isLoopHeader(Resolved))
dbgs() << ", succ = " << getBlockName(Succ);
if (Resolved != Succ)
dbgs() << ", resolved = " << getBlockName(Resolved);
dbgs() << "\n";
};
(void)debugSuccessor;
#endif
if (isLoopHeader(Resolved)) {
DEBUG(debugSuccessor("backedge"));
Dist.addBackedge(Resolved, Weight);
return true;
}
if (Working[Resolved.Index].getContainingLoop() != OuterLoop) {
DEBUG(debugSuccessor(" exit "));
Dist.addExit(Resolved, Weight);
return true;
}
if (Resolved < Pred) {
if (!isLoopHeader(Pred)) {
// If OuterLoop is an irreducible loop, we can't actually handle this.
assert((!OuterLoop || !OuterLoop->isIrreducible()) &&
"unhandled irreducible control flow");
// Irreducible backedge. Abort.
DEBUG(debugSuccessor("abort!!!"));
return false;
}
// If "Pred" is a loop header, then this isn't really a backedge; rather,
// OuterLoop must be irreducible. These false backedges can come only from
// secondary loop headers.
assert(OuterLoop && OuterLoop->isIrreducible() && !isLoopHeader(Resolved) &&
"unhandled irreducible control flow");
}
DEBUG(debugSuccessor(" local "));
Dist.addLocal(Resolved, Weight);
return true;
}
bool BlockFrequencyInfoImplBase::addLoopSuccessorsToDist(
const LoopData *OuterLoop, LoopData &Loop, Distribution &Dist) {
// Copy the exit map into Dist.
for (const auto &I : Loop.Exits)
if (!addToDist(Dist, OuterLoop, Loop.getHeader(), I.first,
I.second.getMass()))
// Irreducible backedge.
return false;
return true;
}
/// \brief Compute the loop scale for a loop.
void BlockFrequencyInfoImplBase::computeLoopScale(LoopData &Loop) {
// Compute loop scale.
DEBUG(dbgs() << "compute-loop-scale: " << getLoopName(Loop) << "\n");
// Infinite loops need special handling. If we give the back edge an infinite
// mass, they may saturate all the other scales in the function down to 1,
// making all the other region temperatures look exactly the same. Choose an
// arbitrary scale to avoid these issues.
//
// FIXME: An alternate way would be to select a symbolic scale which is later
// replaced to be the maximum of all computed scales plus 1. This would
// appropriately describe the loop as having a large scale, without skewing
// the final frequency computation.
const Scaled64 InfiniteLoopScale(1, 12);
// LoopScale == 1 / ExitMass
// ExitMass == HeadMass - BackedgeMass
BlockMass TotalBackedgeMass;
for (auto &Mass : Loop.BackedgeMass)
TotalBackedgeMass += Mass;
BlockMass ExitMass = BlockMass::getFull() - TotalBackedgeMass;
// Block scale stores the inverse of the scale. If this is an infinite loop,
// its exit mass will be zero. In this case, use an arbitrary scale for the
// loop scale.
Loop.Scale =
ExitMass.isEmpty() ? InfiniteLoopScale : ExitMass.toScaled().inverse();
DEBUG(dbgs() << " - exit-mass = " << ExitMass << " (" << BlockMass::getFull()
<< " - " << TotalBackedgeMass << ")\n"
<< " - scale = " << Loop.Scale << "\n");
}
/// \brief Package up a loop.
void BlockFrequencyInfoImplBase::packageLoop(LoopData &Loop) {
DEBUG(dbgs() << "packaging-loop: " << getLoopName(Loop) << "\n");
// Clear the subloop exits to prevent quadratic memory usage.
for (const BlockNode &M : Loop.Nodes) {
if (auto *Loop = Working[M.Index].getPackagedLoop())
Loop->Exits.clear();
DEBUG(dbgs() << " - node: " << getBlockName(M.Index) << "\n");
}
Loop.IsPackaged = true;
}
#ifndef NDEBUG
static void debugAssign(const BlockFrequencyInfoImplBase &BFI,
const DitheringDistributer &D, const BlockNode &T,
const BlockMass &M, const char *Desc) {
dbgs() << " => assign " << M << " (" << D.RemMass << ")";
if (Desc)
dbgs() << " [" << Desc << "]";
if (T.isValid())
dbgs() << " to " << BFI.getBlockName(T);
dbgs() << "\n";
}
#endif
void BlockFrequencyInfoImplBase::distributeMass(const BlockNode &Source,
LoopData *OuterLoop,
Distribution &Dist) {
BlockMass Mass = Working[Source.Index].getMass();
DEBUG(dbgs() << " => mass: " << Mass << "\n");
// Distribute mass to successors as laid out in Dist.
DitheringDistributer D(Dist, Mass);
for (const Weight &W : Dist.Weights) {
// Check for a local edge (non-backedge and non-exit).
BlockMass Taken = D.takeMass(W.Amount);
if (W.Type == Weight::Local) {
Working[W.TargetNode.Index].getMass() += Taken;
DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
continue;
}
// Backedges and exits only make sense if we're processing a loop.
assert(OuterLoop && "backedge or exit outside of loop");
// Check for a backedge.
if (W.Type == Weight::Backedge) {
OuterLoop->BackedgeMass[OuterLoop->getHeaderIndex(W.TargetNode)] += Taken;
DEBUG(debugAssign(*this, D, W.TargetNode, Taken, "back"));
continue;
}
// This must be an exit.
assert(W.Type == Weight::Exit);
OuterLoop->Exits.push_back(std::make_pair(W.TargetNode, Taken));
DEBUG(debugAssign(*this, D, W.TargetNode, Taken, "exit"));
}
}
static void convertFloatingToInteger(BlockFrequencyInfoImplBase &BFI,
const Scaled64 &Min, const Scaled64 &Max) {
// Scale the Factor to a size that creates integers. Ideally, integers would
// be scaled so that Max == UINT64_MAX so that they can be best
// differentiated. However, in the presence of large frequency values, small
// frequencies are scaled down to 1, making it impossible to differentiate
// small, unequal numbers. When the spread between Min and Max frequencies
// fits well within MaxBits, we make the scale be at least 8.
const unsigned MaxBits = 64;
const unsigned SpreadBits = (Max / Min).lg();
Scaled64 ScalingFactor;
if (SpreadBits <= MaxBits - 3) {
// If the values are small enough, make the scaling factor at least 8 to
// allow distinguishing small values.
ScalingFactor = Min.inverse();
ScalingFactor <<= 3;
} else {
// If the values need more than MaxBits to be represented, saturate small
// frequency values down to 1 by using a scaling factor that benefits large
// frequency values.
ScalingFactor = Scaled64(1, MaxBits) / Max;
}
// Translate the floats to integers.
DEBUG(dbgs() << "float-to-int: min = " << Min << ", max = " << Max
<< ", factor = " << ScalingFactor << "\n");
for (size_t Index = 0; Index < BFI.Freqs.size(); ++Index) {
Scaled64 Scaled = BFI.Freqs[Index].Scaled * ScalingFactor;
BFI.Freqs[Index].Integer = std::max(UINT64_C(1), Scaled.toInt<uint64_t>());
DEBUG(dbgs() << " - " << BFI.getBlockName(Index) << ": float = "
<< BFI.Freqs[Index].Scaled << ", scaled = " << Scaled
<< ", int = " << BFI.Freqs[Index].Integer << "\n");
}
}
/// \brief Unwrap a loop package.
///
/// Visits all the members of a loop, adjusting their BlockData according to
/// the loop's pseudo-node.
static void unwrapLoop(BlockFrequencyInfoImplBase &BFI, LoopData &Loop) {
DEBUG(dbgs() << "unwrap-loop-package: " << BFI.getLoopName(Loop)
<< ": mass = " << Loop.Mass << ", scale = " << Loop.Scale
<< "\n");
Loop.Scale *= Loop.Mass.toScaled();
Loop.IsPackaged = false;
DEBUG(dbgs() << " => combined-scale = " << Loop.Scale << "\n");
// Propagate the head scale through the loop. Since members are visited in
// RPO, the head scale will be updated by the loop scale first, and then the
// final head scale will be used for updated the rest of the members.
for (const BlockNode &N : Loop.Nodes) {
const auto &Working = BFI.Working[N.Index];
Scaled64 &F = Working.isAPackage() ? Working.getPackagedLoop()->Scale
: BFI.Freqs[N.Index].Scaled;
Scaled64 New = Loop.Scale * F;
DEBUG(dbgs() << " - " << BFI.getBlockName(N) << ": " << F << " => " << New
<< "\n");
F = New;
}
}
void BlockFrequencyInfoImplBase::unwrapLoops() {
// Set initial frequencies from loop-local masses.
for (size_t Index = 0; Index < Working.size(); ++Index)
Freqs[Index].Scaled = Working[Index].Mass.toScaled();
for (LoopData &Loop : Loops)
unwrapLoop(*this, Loop);
}
void BlockFrequencyInfoImplBase::finalizeMetrics() {
// Unwrap loop packages in reverse post-order, tracking min and max
// frequencies.
auto Min = Scaled64::getLargest();
auto Max = Scaled64::getZero();
for (size_t Index = 0; Index < Working.size(); ++Index) {
// Update min/max scale.
Min = std::min(Min, Freqs[Index].Scaled);
Max = std::max(Max, Freqs[Index].Scaled);
}
// Convert to integers.
convertFloatingToInteger(*this, Min, Max);
// Clean up data structures.
cleanup(*this);
// Print out the final stats.
DEBUG(dump());
}
BlockFrequency
BlockFrequencyInfoImplBase::getBlockFreq(const BlockNode &Node) const {
if (!Node.isValid())
return 0;
return Freqs[Node.Index].Integer;
}
Optional<uint64_t>
BlockFrequencyInfoImplBase::getBlockProfileCount(const Function &F,
const BlockNode &Node) const {
return getProfileCountFromFreq(F, getBlockFreq(Node).getFrequency());
}
Optional<uint64_t>
BlockFrequencyInfoImplBase::getProfileCountFromFreq(const Function &F,
uint64_t Freq) const {
auto EntryCount = F.getEntryCount();
if (!EntryCount)
return None;
// Use 128 bit APInt to do the arithmetic to avoid overflow.
APInt BlockCount(128, EntryCount.getValue());
APInt BlockFreq(128, Freq);
APInt EntryFreq(128, getEntryFreq());
BlockCount *= BlockFreq;
BlockCount = BlockCount.udiv(EntryFreq);
return BlockCount.getLimitedValue();
}
Scaled64
BlockFrequencyInfoImplBase::getFloatingBlockFreq(const BlockNode &Node) const {
if (!Node.isValid())
return Scaled64::getZero();
return Freqs[Node.Index].Scaled;
}
void BlockFrequencyInfoImplBase::setBlockFreq(const BlockNode &Node,
uint64_t Freq) {
assert(Node.isValid() && "Expected valid node");
assert(Node.Index < Freqs.size() && "Expected legal index");
Freqs[Node.Index].Integer = Freq;
}
std::string
BlockFrequencyInfoImplBase::getBlockName(const BlockNode &Node) const {
return std::string();
}
std::string
BlockFrequencyInfoImplBase::getLoopName(const LoopData &Loop) const {
return getBlockName(Loop.getHeader()) + (Loop.isIrreducible() ? "**" : "*");
}
raw_ostream &
BlockFrequencyInfoImplBase::printBlockFreq(raw_ostream &OS,
const BlockNode &Node) const {
return OS << getFloatingBlockFreq(Node);
}
raw_ostream &
BlockFrequencyInfoImplBase::printBlockFreq(raw_ostream &OS,
const BlockFrequency &Freq) const {
Scaled64 Block(Freq.getFrequency(), 0);
Scaled64 Entry(getEntryFreq(), 0);
return OS << Block / Entry;
}
void IrreducibleGraph::addNodesInLoop(const BFIBase::LoopData &OuterLoop) {
Start = OuterLoop.getHeader();
Nodes.reserve(OuterLoop.Nodes.size());
for (auto N : OuterLoop.Nodes)
addNode(N);
indexNodes();
}
void IrreducibleGraph::addNodesInFunction() {
Start = 0;
for (uint32_t Index = 0; Index < BFI.Working.size(); ++Index)
if (!BFI.Working[Index].isPackaged())
addNode(Index);
indexNodes();
}
void IrreducibleGraph::indexNodes() {
for (auto &I : Nodes)
Lookup[I.Node.Index] = &I;
}
void IrreducibleGraph::addEdge(IrrNode &Irr, const BlockNode &Succ,
const BFIBase::LoopData *OuterLoop) {
if (OuterLoop && OuterLoop->isHeader(Succ))
return;
auto L = Lookup.find(Succ.Index);
if (L == Lookup.end())
return;
IrrNode &SuccIrr = *L->second;
Irr.Edges.push_back(&SuccIrr);
SuccIrr.Edges.push_front(&Irr);
++SuccIrr.NumIn;
}
namespace llvm {
template <> struct GraphTraits<IrreducibleGraph> {
typedef bfi_detail::IrreducibleGraph GraphT;
typedef const GraphT::IrrNode *NodeRef;
typedef GraphT::IrrNode::iterator ChildIteratorType;
static NodeRef getEntryNode(const GraphT &G) { return G.StartIrr; }
static ChildIteratorType child_begin(NodeRef N) { return N->succ_begin(); }
static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); }
};
} // end namespace llvm
/// \brief Find extra irreducible headers.
///
/// Find entry blocks and other blocks with backedges, which exist when \c G
/// contains irreducible sub-SCCs.
static void findIrreducibleHeaders(
const BlockFrequencyInfoImplBase &BFI,
const IrreducibleGraph &G,
const std::vector<const IrreducibleGraph::IrrNode *> &SCC,
LoopData::NodeList &Headers, LoopData::NodeList &Others) {
// Map from nodes in the SCC to whether it's an entry block.
SmallDenseMap<const IrreducibleGraph::IrrNode *, bool, 8> InSCC;
// InSCC also acts the set of nodes in the graph. Seed it.
for (const auto *I : SCC)
InSCC[I] = false;
for (auto I = InSCC.begin(), E = InSCC.end(); I != E; ++I) {
auto &Irr = *I->first;
for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
if (InSCC.count(P))
continue;
// This is an entry block.
I->second = true;
Headers.push_back(Irr.Node);
DEBUG(dbgs() << " => entry = " << BFI.getBlockName(Irr.Node) << "\n");
break;
}
}
assert(Headers.size() >= 2 &&
"Expected irreducible CFG; -loop-info is likely invalid");
if (Headers.size() == InSCC.size()) {
// Every block is a header.
std::sort(Headers.begin(), Headers.end());
return;
}
// Look for extra headers from irreducible sub-SCCs.
for (const auto &I : InSCC) {
// Entry blocks are already headers.
if (I.second)
continue;
auto &Irr = *I.first;
for (const auto *P : make_range(Irr.pred_begin(), Irr.pred_end())) {
// Skip forward edges.
if (P->Node < Irr.Node)
continue;
// Skip predecessors from entry blocks. These can have inverted
// ordering.
if (InSCC.lookup(P))
continue;
// Store the extra header.
Headers.push_back(Irr.Node);
DEBUG(dbgs() << " => extra = " << BFI.getBlockName(Irr.Node) << "\n");
break;
}
if (Headers.back() == Irr.Node)
// Added this as a header.
continue;
// This is not a header.
Others.push_back(Irr.Node);
DEBUG(dbgs() << " => other = " << BFI.getBlockName(Irr.Node) << "\n");
}
std::sort(Headers.begin(), Headers.end());
std::sort(Others.begin(), Others.end());
}
static void createIrreducibleLoop(
BlockFrequencyInfoImplBase &BFI, const IrreducibleGraph &G,
LoopData *OuterLoop, std::list<LoopData>::iterator Insert,
const std::vector<const IrreducibleGraph::IrrNode *> &SCC) {
// Translate the SCC into RPO.
DEBUG(dbgs() << " - found-scc\n");
LoopData::NodeList Headers;
LoopData::NodeList Others;
findIrreducibleHeaders(BFI, G, SCC, Headers, Others);
auto Loop = BFI.Loops.emplace(Insert, OuterLoop, Headers.begin(),
Headers.end(), Others.begin(), Others.end());
// Update loop hierarchy.
for (const auto &N : Loop->Nodes)
if (BFI.Working[N.Index].isLoopHeader())
BFI.Working[N.Index].Loop->Parent = &*Loop;
else
BFI.Working[N.Index].Loop = &*Loop;
}
iterator_range<std::list<LoopData>::iterator>
BlockFrequencyInfoImplBase::analyzeIrreducible(
const IrreducibleGraph &G, LoopData *OuterLoop,
std::list<LoopData>::iterator Insert) {
assert((OuterLoop == nullptr) == (Insert == Loops.begin()));
auto Prev = OuterLoop ? std::prev(Insert) : Loops.end();
for (auto I = scc_begin(G); !I.isAtEnd(); ++I) {
if (I->size() < 2)
continue;
// Translate the SCC into RPO.
createIrreducibleLoop(*this, G, OuterLoop, Insert, *I);
}
if (OuterLoop)
return make_range(std::next(Prev), Insert);
return make_range(Loops.begin(), Insert);
}
void
BlockFrequencyInfoImplBase::updateLoopWithIrreducible(LoopData &OuterLoop) {
OuterLoop.Exits.clear();
for (auto &Mass : OuterLoop.BackedgeMass)
Mass = BlockMass::getEmpty();
auto O = OuterLoop.Nodes.begin() + 1;
for (auto I = O, E = OuterLoop.Nodes.end(); I != E; ++I)
if (!Working[I->Index].isPackaged())
*O++ = *I;
OuterLoop.Nodes.erase(O, OuterLoop.Nodes.end());
}
void BlockFrequencyInfoImplBase::adjustLoopHeaderMass(LoopData &Loop) {
assert(Loop.isIrreducible() && "this only makes sense on irreducible loops");
// Since the loop has more than one header block, the mass flowing back into
// each header will be different. Adjust the mass in each header loop to
// reflect the masses flowing through back edges.
//
// To do this, we distribute the initial mass using the backedge masses
// as weights for the distribution.
BlockMass LoopMass = BlockMass::getFull();
Distribution Dist;
DEBUG(dbgs() << "adjust-loop-header-mass:\n");
for (uint32_t H = 0; H < Loop.NumHeaders; ++H) {
auto &HeaderNode = Loop.Nodes[H];
auto &BackedgeMass = Loop.BackedgeMass[Loop.getHeaderIndex(HeaderNode)];
DEBUG(dbgs() << " - Add back edge mass for node "
<< getBlockName(HeaderNode) << ": " << BackedgeMass << "\n");
if (BackedgeMass.getMass() > 0)
Dist.addLocal(HeaderNode, BackedgeMass.getMass());
else
DEBUG(dbgs() << " Nothing added. Back edge mass is zero\n");
}
DitheringDistributer D(Dist, LoopMass);
DEBUG(dbgs() << " Distribute loop mass " << LoopMass
<< " to headers using above weights\n");
for (const Weight &W : Dist.Weights) {
BlockMass Taken = D.takeMass(W.Amount);
assert(W.Type == Weight::Local && "all weights should be local");
Working[W.TargetNode.Index].getMass() = Taken;
DEBUG(debugAssign(*this, D, W.TargetNode, Taken, nullptr));
}
}
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