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//===- OptimalEdgeProfiling.cpp - Insert counters for opt. edge profiling -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass instruments the specified program with counters for edge profiling.
// Edge profiling can give a reasonable approximation of the hot paths through a
// program, and is used for a wide variety of program transformations.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "insert-optimal-edge-profiling"
#include "llvm/Transforms/Instrumentation.h"
#include "MaximumSpanningTree.h"
#include "ProfilingUtils.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Analysis/ProfileInfoLoader.h"
#include "llvm/Constants.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
STATISTIC(NumEdgesInserted, "The # of edges inserted.");
namespace {
class OptimalEdgeProfiler : public ModulePass {
bool runOnModule(Module &M);
public:
static char ID; // Pass identification, replacement for typeid
OptimalEdgeProfiler() : ModulePass(ID) {
initializeOptimalEdgeProfilerPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(ProfileEstimatorPassID);
AU.addRequired<ProfileInfo>();
}
virtual const char *getPassName() const {
return "Optimal Edge Profiler";
}
};
}
char OptimalEdgeProfiler::ID = 0;
INITIALIZE_PASS_BEGIN(OptimalEdgeProfiler, "insert-optimal-edge-profiling",
"Insert optimal instrumentation for edge profiling",
false, false)
INITIALIZE_PASS_DEPENDENCY(ProfileEstimatorPass)
INITIALIZE_AG_DEPENDENCY(ProfileInfo)
INITIALIZE_PASS_END(OptimalEdgeProfiler, "insert-optimal-edge-profiling",
"Insert optimal instrumentation for edge profiling",
false, false)
ModulePass *llvm::createOptimalEdgeProfilerPass() {
return new OptimalEdgeProfiler();
}
inline static void printEdgeCounter(ProfileInfo::Edge e,
BasicBlock* b,
unsigned i) {
DEBUG(dbgs() << "--Edge Counter for " << (e) << " in " \
<< ((b)?(b)->getName():"0") << " (# " << (i) << ")\n");
}
bool OptimalEdgeProfiler::runOnModule(Module &M) {
Function *Main = M.getFunction("main");
if (Main == 0) {
M.getContext().emitWarning("cannot insert edge profiling into a module"
" with no main function");
return false; // No main, no instrumentation!
}
// NumEdges counts all the edges that may be instrumented. Later on its
// decided which edges to actually instrument, to achieve optimal profiling.
// For the entry block a virtual edge (0,entry) is reserved, for each block
// with no successors an edge (BB,0) is reserved. These edges are necessary
// to calculate a truly optimal maximum spanning tree and thus an optimal
// instrumentation.
unsigned NumEdges = 0;
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (F->isDeclaration()) continue;
// Reserve space for (0,entry) edge.
++NumEdges;
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
// Keep track of which blocks need to be instrumented. We don't want to
// instrument blocks that are added as the result of breaking critical
// edges!
if (BB->getTerminator()->getNumSuccessors() == 0) {
// Reserve space for (BB,0) edge.
++NumEdges;
} else {
NumEdges += BB->getTerminator()->getNumSuccessors();
}
}
}
// In the profiling output a counter for each edge is reserved, but only few
// are used. This is done to be able to read back in the profile without
// calulating the maximum spanning tree again, instead each edge counter that
// is not used is initialised with -1 to signal that this edge counter has to
// be calculated from other edge counters on reading the profile info back
// in.
Type *Int32 = Type::getInt32Ty(M.getContext());
ArrayType *ATy = ArrayType::get(Int32, NumEdges);
GlobalVariable *Counters =
new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
Constant::getNullValue(ATy), "OptEdgeProfCounters");
NumEdgesInserted = 0;
std::vector<Constant*> Initializer(NumEdges);
Constant *Zero = ConstantInt::get(Int32, 0);
Constant *Uncounted = ConstantInt::get(Int32, ProfileInfoLoader::Uncounted);
// Instrument all of the edges not in MST...
unsigned i = 0;
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (F->isDeclaration()) continue;
DEBUG(dbgs() << "Working on " << F->getName() << "\n");
// Calculate a Maximum Spanning Tree with the edge weights determined by
// ProfileEstimator. ProfileEstimator also assign weights to the virtual
// edges (0,entry) and (BB,0) (for blocks with no successors) and this
// edges also participate in the maximum spanning tree calculation.
// The third parameter of MaximumSpanningTree() has the effect that not the
// actual MST is returned but the edges _not_ in the MST.
ProfileInfo::EdgeWeights ECs =
getAnalysis<ProfileInfo>(*F).getEdgeWeights(F);
std::vector<ProfileInfo::EdgeWeight> EdgeVector(ECs.begin(), ECs.end());
MaximumSpanningTree<BasicBlock> MST(EdgeVector);
std::stable_sort(MST.begin(), MST.end());
// Check if (0,entry) not in the MST. If not, instrument edge
// (IncrementCounterInBlock()) and set the counter initially to zero, if
// the edge is in the MST the counter is initialised to -1.
BasicBlock *entry = &(F->getEntryBlock());
ProfileInfo::Edge edge = ProfileInfo::getEdge(0, entry);
if (!std::binary_search(MST.begin(), MST.end(), edge)) {
printEdgeCounter(edge, entry, i);
IncrementCounterInBlock(entry, i, Counters); ++NumEdgesInserted;
Initializer[i++] = (Zero);
} else{
Initializer[i++] = (Uncounted);
}
// InsertedBlocks contains all blocks that were inserted for splitting an
// edge, this blocks do not have to be instrumented.
DenseSet<BasicBlock*> InsertedBlocks;
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
// Check if block was not inserted and thus does not have to be
// instrumented.
if (InsertedBlocks.count(BB)) continue;
// Okay, we have to add a counter of each outgoing edge not in MST. If
// the outgoing edge is not critical don't split it, just insert the
// counter in the source or destination of the edge. Also, if the block
// has no successors, the virtual edge (BB,0) is processed.
TerminatorInst *TI = BB->getTerminator();
if (TI->getNumSuccessors() == 0) {
ProfileInfo::Edge edge = ProfileInfo::getEdge(BB, 0);
if (!std::binary_search(MST.begin(), MST.end(), edge)) {
printEdgeCounter(edge, BB, i);
IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted;
Initializer[i++] = (Zero);
} else{
Initializer[i++] = (Uncounted);
}
}
for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
BasicBlock *Succ = TI->getSuccessor(s);
ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,Succ);
if (!std::binary_search(MST.begin(), MST.end(), edge)) {
// If the edge is critical, split it.
bool wasInserted = SplitCriticalEdge(TI, s, this);
Succ = TI->getSuccessor(s);
if (wasInserted)
InsertedBlocks.insert(Succ);
// Okay, we are guaranteed that the edge is no longer critical. If
// we only have a single successor, insert the counter in this block,
// otherwise insert it in the successor block.
if (TI->getNumSuccessors() == 1) {
// Insert counter at the start of the block
printEdgeCounter(edge, BB, i);
IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted;
} else {
// Insert counter at the start of the block
printEdgeCounter(edge, Succ, i);
IncrementCounterInBlock(Succ, i, Counters); ++NumEdgesInserted;
}
Initializer[i++] = (Zero);
} else {
Initializer[i++] = (Uncounted);
}
}
}
}
// Check if the number of edges counted at first was the number of edges we
// considered for instrumentation.
assert(i == NumEdges && "the number of edges in counting array is wrong");
// Assign the now completely defined initialiser to the array.
Constant *init = ConstantArray::get(ATy, Initializer);
Counters->setInitializer(init);
// Add the initialization call to main.
InsertProfilingInitCall(Main, "llvm_start_opt_edge_profiling", Counters);
return true;
}
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