llvm-6502/include/llvm/Analysis/BlockFrequencyImpl.h

380 lines
11 KiB
C++

//===-- BlockFrequencyImpl.h - Block Frequency Implementation --*- C++ -*--===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Shared implementation of BlockFrequency for IR and Machine Instructions.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_BLOCKFREQUENCYIMPL_H
#define LLVM_ANALYSIS_BLOCKFREQUENCYIMPL_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <string>
#include <vector>
namespace llvm {
class BlockFrequencyInfo;
class MachineBlockFrequencyInfo;
/// BlockFrequencyImpl implements block frequency algorithm for IR and
/// Machine Instructions. Algorithm starts with value ENTRY_FREQ
/// for the entry block and then propagates frequencies using branch weights
/// from (Machine)BranchProbabilityInfo. LoopInfo is not required because
/// algorithm can find "backedges" by itself.
template<class BlockT, class FunctionT, class BlockProbInfoT>
class BlockFrequencyImpl {
DenseMap<const BlockT *, BlockFrequency> Freqs;
BlockProbInfoT *BPI;
FunctionT *Fn;
typedef GraphTraits< Inverse<BlockT *> > GT;
static const uint64_t EntryFreq = 1 << 14;
std::string getBlockName(BasicBlock *BB) const {
return BB->getName().str();
}
std::string getBlockName(MachineBasicBlock *MBB) const {
std::string str;
raw_string_ostream ss(str);
ss << "BB#" << MBB->getNumber();
if (const BasicBlock *BB = MBB->getBasicBlock())
ss << " derived from LLVM BB " << BB->getName();
return ss.str();
}
void setBlockFreq(BlockT *BB, BlockFrequency Freq) {
Freqs[BB] = Freq;
DEBUG(dbgs() << "Frequency(" << getBlockName(BB) << ") = ";
printBlockFreq(dbgs(), Freq) << "\n");
}
/// getEdgeFreq - Return edge frequency based on SRC frequency and Src -> Dst
/// edge probability.
BlockFrequency getEdgeFreq(BlockT *Src, BlockT *Dst) const {
BranchProbability Prob = BPI->getEdgeProbability(Src, Dst);
return getBlockFreq(Src) * Prob;
}
/// incBlockFreq - Increase BB block frequency by FREQ.
///
void incBlockFreq(BlockT *BB, BlockFrequency Freq) {
Freqs[BB] += Freq;
DEBUG(dbgs() << "Frequency(" << getBlockName(BB) << ") += ";
printBlockFreq(dbgs(), Freq) << " --> ";
printBlockFreq(dbgs(), Freqs[BB]) << "\n");
}
// All blocks in postorder.
std::vector<BlockT *> POT;
// Map Block -> Position in reverse-postorder list.
DenseMap<BlockT *, unsigned> RPO;
// For each loop header, record the per-iteration probability of exiting the
// loop. This is the reciprocal of the expected number of loop iterations.
typedef DenseMap<BlockT*, BranchProbability> LoopExitProbMap;
LoopExitProbMap LoopExitProb;
// (reverse-)postorder traversal iterators.
typedef typename std::vector<BlockT *>::iterator pot_iterator;
typedef typename std::vector<BlockT *>::reverse_iterator rpot_iterator;
pot_iterator pot_begin() { return POT.begin(); }
pot_iterator pot_end() { return POT.end(); }
rpot_iterator rpot_begin() { return POT.rbegin(); }
rpot_iterator rpot_end() { return POT.rend(); }
rpot_iterator rpot_at(BlockT *BB) {
rpot_iterator I = rpot_begin();
unsigned idx = RPO.lookup(BB);
assert(idx);
std::advance(I, idx - 1);
assert(*I == BB);
return I;
}
/// isBackedge - Return if edge Src -> Dst is a reachable backedge.
///
bool isBackedge(BlockT *Src, BlockT *Dst) const {
unsigned a = RPO.lookup(Src);
if (!a)
return false;
unsigned b = RPO.lookup(Dst);
assert(b && "Destination block should be reachable");
return a >= b;
}
/// getSingleBlockPred - return single BB block predecessor or NULL if
/// BB has none or more predecessors.
BlockT *getSingleBlockPred(BlockT *BB) {
typename GT::ChildIteratorType
PI = GraphTraits< Inverse<BlockT *> >::child_begin(BB),
PE = GraphTraits< Inverse<BlockT *> >::child_end(BB);
if (PI == PE)
return 0;
BlockT *Pred = *PI;
++PI;
if (PI != PE)
return 0;
return Pred;
}
void doBlock(BlockT *BB, BlockT *LoopHead,
SmallPtrSet<BlockT *, 8> &BlocksInLoop) {
DEBUG(dbgs() << "doBlock(" << getBlockName(BB) << ")\n");
setBlockFreq(BB, 0);
if (BB == LoopHead) {
setBlockFreq(BB, EntryFreq);
return;
}
if(BlockT *Pred = getSingleBlockPred(BB)) {
if (BlocksInLoop.count(Pred))
setBlockFreq(BB, getEdgeFreq(Pred, BB));
// TODO: else? irreducible, ignore it for now.
return;
}
bool isInLoop = false;
bool isLoopHead = false;
for (typename GT::ChildIteratorType
PI = GraphTraits< Inverse<BlockT *> >::child_begin(BB),
PE = GraphTraits< Inverse<BlockT *> >::child_end(BB);
PI != PE; ++PI) {
BlockT *Pred = *PI;
if (isBackedge(Pred, BB)) {
isLoopHead = true;
} else if (BlocksInLoop.count(Pred)) {
incBlockFreq(BB, getEdgeFreq(Pred, BB));
isInLoop = true;
}
// TODO: else? irreducible.
}
if (!isInLoop)
return;
if (!isLoopHead)
return;
// This block is a loop header, so boost its frequency by the expected
// number of loop iterations. The loop blocks will be revisited so they all
// get this boost.
typename LoopExitProbMap::const_iterator I = LoopExitProb.find(BB);
assert(I != LoopExitProb.end() && "Loop header missing from table");
Freqs[BB] /= I->second;
DEBUG(dbgs() << "Loop header scaled to ";
printBlockFreq(dbgs(), Freqs[BB]) << ".\n");
}
/// doLoop - Propagate block frequency down through the loop.
void doLoop(BlockT *Head, BlockT *Tail) {
DEBUG(dbgs() << "doLoop(" << getBlockName(Head) << ", "
<< getBlockName(Tail) << ")\n");
SmallPtrSet<BlockT *, 8> BlocksInLoop;
for (rpot_iterator I = rpot_at(Head), E = rpot_at(Tail); ; ++I) {
BlockT *BB = *I;
doBlock(BB, Head, BlocksInLoop);
BlocksInLoop.insert(BB);
if (I == E)
break;
}
// Compute loop's cyclic probability using backedges probabilities.
BlockFrequency BackFreq;
for (typename GT::ChildIteratorType
PI = GraphTraits< Inverse<BlockT *> >::child_begin(Head),
PE = GraphTraits< Inverse<BlockT *> >::child_end(Head);
PI != PE; ++PI) {
BlockT *Pred = *PI;
assert(Pred);
if (isBackedge(Pred, Head))
BackFreq += getEdgeFreq(Pred, Head);
}
// The cyclic probability is freq(BackEdges) / freq(Head), where freq(Head)
// only counts edges entering the loop, not the loop backedges.
// The probability of leaving the loop on each iteration is:
//
// ExitProb = 1 - CyclicProb
//
// The Expected number of loop iterations is:
//
// Iterations = 1 / ExitProb
//
uint64_t D = std::max(getBlockFreq(Head).getFrequency(), UINT64_C(1));
uint64_t N = std::max(BackFreq.getFrequency(), UINT64_C(1));
if (N < D)
N = D - N;
else
// We'd expect N < D, but rounding and saturation means that can't be
// guaranteed.
N = 1;
// Now ExitProb = N / D, make sure it fits in an i32/i32 fraction.
assert(N <= D);
if (D > UINT32_MAX) {
unsigned Shift = 32 - countLeadingZeros(D);
D >>= Shift;
N >>= Shift;
if (N == 0)
N = 1;
}
BranchProbability LEP = BranchProbability(N, D);
LoopExitProb.insert(std::make_pair(Head, LEP));
DEBUG(dbgs() << "LoopExitProb[" << getBlockName(Head) << "] = " << LEP
<< " from 1 - ";
printBlockFreq(dbgs(), BackFreq) << " / ";
printBlockFreq(dbgs(), getBlockFreq(Head)) << ".\n");
}
friend class BlockFrequencyInfo;
friend class MachineBlockFrequencyInfo;
BlockFrequencyImpl() { }
void doFunction(FunctionT *fn, BlockProbInfoT *bpi) {
Fn = fn;
BPI = bpi;
// Clear everything.
RPO.clear();
POT.clear();
LoopExitProb.clear();
Freqs.clear();
BlockT *EntryBlock = fn->begin();
std::copy(po_begin(EntryBlock), po_end(EntryBlock), std::back_inserter(POT));
unsigned RPOidx = 0;
for (rpot_iterator I = rpot_begin(), E = rpot_end(); I != E; ++I) {
BlockT *BB = *I;
RPO[BB] = ++RPOidx;
DEBUG(dbgs() << "RPO[" << getBlockName(BB) << "] = " << RPO[BB] << "\n");
}
// Travel over all blocks in postorder.
for (pot_iterator I = pot_begin(), E = pot_end(); I != E; ++I) {
BlockT *BB = *I;
BlockT *LastTail = 0;
DEBUG(dbgs() << "POT: " << getBlockName(BB) << "\n");
for (typename GT::ChildIteratorType
PI = GraphTraits< Inverse<BlockT *> >::child_begin(BB),
PE = GraphTraits< Inverse<BlockT *> >::child_end(BB);
PI != PE; ++PI) {
BlockT *Pred = *PI;
if (isBackedge(Pred, BB) && (!LastTail || RPO[Pred] > RPO[LastTail]))
LastTail = Pred;
}
if (LastTail)
doLoop(BB, LastTail);
}
// At the end assume the whole function as a loop, and travel over it once
// again.
doLoop(*(rpot_begin()), *(pot_begin()));
}
public:
uint64_t getEntryFreq() { return EntryFreq; }
/// getBlockFreq - Return block frequency. Return 0 if we don't have it.
BlockFrequency getBlockFreq(const BlockT *BB) const {
typename DenseMap<const BlockT *, BlockFrequency>::const_iterator
I = Freqs.find(BB);
if (I != Freqs.end())
return I->second;
return 0;
}
void print(raw_ostream &OS) const {
OS << "\n\n---- Block Freqs ----\n";
for (typename FunctionT::iterator I = Fn->begin(), E = Fn->end(); I != E;) {
BlockT *BB = I++;
OS << " " << getBlockName(BB) << " = ";
printBlockFreq(OS, getBlockFreq(BB)) << "\n";
for (typename GraphTraits<BlockT *>::ChildIteratorType
SI = GraphTraits<BlockT *>::child_begin(BB),
SE = GraphTraits<BlockT *>::child_end(BB); SI != SE; ++SI) {
BlockT *Succ = *SI;
OS << " " << getBlockName(BB) << " -> " << getBlockName(Succ)
<< " = "; printBlockFreq(OS, getEdgeFreq(BB, Succ)) << "\n";
}
}
}
void dump() const {
print(dbgs());
}
// Utility method that looks up the block frequency associated with BB and
// prints it to OS.
raw_ostream &printBlockFreq(raw_ostream &OS,
const BlockT *BB) {
return printBlockFreq(OS, getBlockFreq(BB));
}
raw_ostream &printBlockFreq(raw_ostream &OS,
const BlockFrequency &Freq) const {
// Convert fixed-point number to decimal.
uint64_t Frequency = Freq.getFrequency();
OS << Frequency / EntryFreq << ".";
uint64_t Rem = Frequency % EntryFreq;
uint64_t Eps = 1;
do {
Rem *= 10;
Eps *= 10;
OS << Rem / EntryFreq;
Rem = Rem % EntryFreq;
} while (Rem >= Eps/2);
return OS;
}
};
}
#endif