1
//===- EdgeProfiling.cpp - Insert counters for edge profiling -------------===//
3
// The LLVM Compiler Infrastructure
5
// This file is distributed under the University of Illinois Open Source
6
// License. See LICENSE.TXT for details.
8
//===----------------------------------------------------------------------===//
10
// This pass instruments the specified program with counters for edge profiling.
11
// Edge profiling can give a reasonable approximation of the hot paths through a
12
// program, and is used for a wide variety of program transformations.
14
// Note that this implementation is very naive. We insert a counter for *every*
15
// edge in the program, instead of using control flow information to prune the
16
// number of counters inserted.
18
//===----------------------------------------------------------------------===//
19
#define DEBUG_TYPE "insert-edge-profiling"
20
#include "ProfilingUtils.h"
21
#include "llvm/Module.h"
22
#include "llvm/Pass.h"
23
#include "llvm/Support/raw_ostream.h"
24
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
25
#include "llvm/Transforms/Instrumentation.h"
26
#include "llvm/ADT/Statistic.h"
30
STATISTIC(NumEdgesInserted, "The # of edges inserted.");
33
class EdgeProfiler : public ModulePass {
34
bool runOnModule(Module &M);
36
static char ID; // Pass identification, replacement for typeid
37
EdgeProfiler() : ModulePass(&ID) {}
39
virtual const char *getPassName() const {
40
return "Edge Profiler";
45
char EdgeProfiler::ID = 0;
46
static RegisterPass<EdgeProfiler>
47
X("insert-edge-profiling", "Insert instrumentation for edge profiling");
49
ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
51
bool EdgeProfiler::runOnModule(Module &M) {
52
Function *Main = M.getFunction("main");
54
errs() << "WARNING: cannot insert edge profiling into a module"
55
<< " with no main function!\n";
56
return false; // No main, no instrumentation!
59
std::set<BasicBlock*> BlocksToInstrument;
60
unsigned NumEdges = 0;
61
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
62
if (F->isDeclaration()) continue;
63
// Reserve space for (0,entry) edge.
65
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
66
// Keep track of which blocks need to be instrumented. We don't want to
67
// instrument blocks that are added as the result of breaking critical
69
BlocksToInstrument.insert(BB);
70
NumEdges += BB->getTerminator()->getNumSuccessors();
74
const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), NumEdges);
75
GlobalVariable *Counters =
76
new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
77
Constant::getNullValue(ATy), "EdgeProfCounters");
78
NumEdgesInserted = NumEdges;
80
// Instrument all of the edges...
82
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
83
if (F->isDeclaration()) continue;
84
// Create counter for (0,entry) edge.
85
IncrementCounterInBlock(&F->getEntryBlock(), i++, Counters);
86
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
87
if (BlocksToInstrument.count(BB)) { // Don't instrument inserted blocks
88
// Okay, we have to add a counter of each outgoing edge. If the
89
// outgoing edge is not critical don't split it, just insert the counter
90
// in the source or destination of the edge.
91
TerminatorInst *TI = BB->getTerminator();
92
for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
93
// If the edge is critical, split it.
94
SplitCriticalEdge(TI, s, this);
96
// Okay, we are guaranteed that the edge is no longer critical. If we
97
// only have a single successor, insert the counter in this block,
98
// otherwise insert it in the successor block.
99
if (TI->getNumSuccessors() == 1) {
100
// Insert counter at the start of the block
101
IncrementCounterInBlock(BB, i++, Counters);
103
// Insert counter at the start of the block
104
IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters);
110
// Add the initialization call to main.
111
InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);