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//===- CallGraphSCCPass.cpp - Pass that operates BU on call graph ---------===//
// 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 CallGraphSCCPass class, which is used for passes
// which are implemented as bottom-up traversals on the call graph. Because
// there may be cycles in the call graph, passes of this type operate on the
// call-graph in SCC order: that is, they process function bottom-up, except for
// recursive functions, which they process all at once.
#include "llvm/Analysis/CallGraphSCCPass.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/LegacyPassManagers.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/OptBisect.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <string>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "cgscc-passmgr"
static cl::opt<unsigned>
MaxIterations("max-cg-scc-iterations", cl::ReallyHidden, cl::init(4));
STATISTIC(MaxSCCIterations, "Maximum CGSCCPassMgr iterations on one SCC");
// CGPassManager
/// CGPassManager manages FPPassManagers and CallGraphSCCPasses.
namespace {
class CGPassManager : public ModulePass, public PMDataManager {
static char ID;
explicit CGPassManager() : ModulePass(ID), PMDataManager() {}
/// Execute all of the passes scheduled for execution. Keep track of
/// whether any of the passes modifies the module, and if so, return true.
bool runOnModule(Module &M) override;
using ModulePass::doInitialization;
using ModulePass::doFinalization;
bool doInitialization(CallGraph &CG);
bool doFinalization(CallGraph &CG);
/// Pass Manager itself does not invalidate any analysis info.
void getAnalysisUsage(AnalysisUsage &Info) const override {
// CGPassManager walks SCC and it needs CallGraph.
StringRef getPassName() const override { return "CallGraph Pass Manager"; }
PMDataManager *getAsPMDataManager() override { return this; }
Pass *getAsPass() override { return this; }
// Print passes managed by this manager
void dumpPassStructure(unsigned Offset) override {
errs().indent(Offset*2) << "Call Graph SCC Pass Manager\n";
for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
Pass *P = getContainedPass(Index);
P->dumpPassStructure(Offset + 1);
dumpLastUses(P, Offset+1);
Pass *getContainedPass(unsigned N) {
assert(N < PassVector.size() && "Pass number out of range!");
return static_cast<Pass *>(PassVector[N]);
PassManagerType getPassManagerType() const override {
return PMT_CallGraphPassManager;
bool RunAllPassesOnSCC(CallGraphSCC &CurSCC, CallGraph &CG,
bool &DevirtualizedCall);
bool RunPassOnSCC(Pass *P, CallGraphSCC &CurSCC,
CallGraph &CG, bool &CallGraphUpToDate,
bool &DevirtualizedCall);
bool RefreshCallGraph(const CallGraphSCC &CurSCC, CallGraph &CG,
bool IsCheckingMode);
} // end anonymous namespace.
char CGPassManager::ID = 0;
bool CGPassManager::RunPassOnSCC(Pass *P, CallGraphSCC &CurSCC,
CallGraph &CG, bool &CallGraphUpToDate,
bool &DevirtualizedCall) {
bool Changed = false;
PMDataManager *PM = P->getAsPMDataManager();
Module &M = CG.getModule();
if (!PM) {
CallGraphSCCPass *CGSP = (CallGraphSCCPass*)P;
if (!CallGraphUpToDate) {
DevirtualizedCall |= RefreshCallGraph(CurSCC, CG, false);
CallGraphUpToDate = true;
unsigned InstrCount = 0;
bool EmitICRemark = M.shouldEmitInstrCountChangedRemark();
TimeRegion PassTimer(getPassTimer(CGSP));
if (EmitICRemark)
InstrCount = initSizeRemarkInfo(M);
Changed = CGSP->runOnSCC(CurSCC);
// If the pass modified the module, it may have modified the instruction
// count of the module. Try emitting a remark.
if (EmitICRemark)
emitInstrCountChangedRemark(P, M, InstrCount);
// After the CGSCCPass is done, when assertions are enabled, use
// RefreshCallGraph to verify that the callgraph was correctly updated.
#ifndef NDEBUG
if (Changed)
RefreshCallGraph(CurSCC, CG, true);
return Changed;
assert(PM->getPassManagerType() == PMT_FunctionPassManager &&
"Invalid CGPassManager member");
FPPassManager *FPP = (FPPassManager*)P;
// Run pass P on all functions in the current SCC.
for (CallGraphNode *CGN : CurSCC) {
if (Function *F = CGN->getFunction()) {
dumpPassInfo(P, EXECUTION_MSG, ON_FUNCTION_MSG, F->getName());
TimeRegion PassTimer(getPassTimer(FPP));
Changed |= FPP->runOnFunction(*F);
// The function pass(es) modified the IR, they may have clobbered the
// callgraph.
if (Changed && CallGraphUpToDate) {
LLVM_DEBUG(dbgs() << "CGSCCPASSMGR: Pass Dirtied SCC: " << P->getPassName()
<< '\n');
CallGraphUpToDate = false;
return Changed;
/// Scan the functions in the specified CFG and resync the
/// callgraph with the call sites found in it. This is used after
/// FunctionPasses have potentially munged the callgraph, and can be used after
/// CallGraphSCC passes to verify that they correctly updated the callgraph.
/// This function returns true if it devirtualized an existing function call,
/// meaning it turned an indirect call into a direct call. This happens when
/// a function pass like GVN optimizes away stuff feeding the indirect call.
/// This never happens in checking mode.
bool CGPassManager::RefreshCallGraph(const CallGraphSCC &CurSCC, CallGraph &CG,
bool CheckingMode) {
DenseMap<Value*, CallGraphNode*> CallSites;
LLVM_DEBUG(dbgs() << "CGSCCPASSMGR: Refreshing SCC with " << CurSCC.size()
<< " nodes:\n";
for (CallGraphNode *CGN
: CurSCC) CGN->dump(););
bool MadeChange = false;
bool DevirtualizedCall = false;
// Scan all functions in the SCC.
unsigned FunctionNo = 0;
for (CallGraphSCC::iterator SCCIdx = CurSCC.begin(), E = CurSCC.end();
SCCIdx != E; ++SCCIdx, ++FunctionNo) {
CallGraphNode *CGN = *SCCIdx;
Function *F = CGN->getFunction();
if (!F || F->isDeclaration()) continue;
// Walk the function body looking for call sites. Sync up the call sites in
// CGN with those actually in the function.
// Keep track of the number of direct and indirect calls that were
// invalidated and removed.
unsigned NumDirectRemoved = 0, NumIndirectRemoved = 0;
// Get the set of call sites currently in the function.
for (CallGraphNode::iterator I = CGN->begin(), E = CGN->end(); I != E; ) {
// If this call site is null, then the function pass deleted the call
// entirely and the WeakTrackingVH nulled it out.
if (!I->first ||
// If we've already seen this call site, then the FunctionPass RAUW'd
// one call with another, which resulted in two "uses" in the edge
// list of the same call.
CallSites.count(I->first) ||
// If the call edge is not from a call or invoke, or it is a
// instrinsic call, then the function pass RAUW'd a call with
// another value. This can happen when constant folding happens
// of well known functions etc.
!CallSite(I->first) ||
(CallSite(I->first).getCalledFunction() &&
CallSite(I->first).getCalledFunction()->isIntrinsic() &&
CallSite(I->first).getCalledFunction()->getIntrinsicID()))) {
assert(!CheckingMode &&
"CallGraphSCCPass did not update the CallGraph correctly!");
// If this was an indirect call site, count it.
if (!I->second->getFunction())
// Just remove the edge from the set of callees, keep track of whether
// I points to the last element of the vector.
bool WasLast = I + 1 == E;
// If I pointed to the last element of the vector, we have to bail out:
// iterator checking rejects comparisons of the resultant pointer with
// end.
if (WasLast)
E = CGN->end();
assert(!CallSites.count(I->first) &&
"Call site occurs in node multiple times");
CallSite CS(I->first);
if (CS) {
Function *Callee = CS.getCalledFunction();
// Ignore intrinsics because they're not really function calls.
if (!Callee || !(Callee->isIntrinsic()))
CallSites.insert(std::make_pair(I->first, I->second));
// Loop over all of the instructions in the function, getting the callsites.
// Keep track of the number of direct/indirect calls added.
unsigned NumDirectAdded = 0, NumIndirectAdded = 0;
for (BasicBlock &BB : *F)
for (Instruction &I : BB) {
CallSite CS(&I);
if (!CS) continue;
Function *Callee = CS.getCalledFunction();
if (Callee && Callee->isIntrinsic()) continue;
// If this call site already existed in the callgraph, just verify it
// matches up to expectations and remove it from CallSites.
DenseMap<Value*, CallGraphNode*>::iterator ExistingIt =
if (ExistingIt != CallSites.end()) {
CallGraphNode *ExistingNode = ExistingIt->second;
// Remove from CallSites since we have now seen it.
// Verify that the callee is right.
if (ExistingNode->getFunction() == CS.getCalledFunction())
// If we are in checking mode, we are not allowed to actually mutate
// the callgraph. If this is a case where we can infer that the
// callgraph is less precise than it could be (e.g. an indirect call
// site could be turned direct), don't reject it in checking mode, and
// don't tweak it to be more precise.
if (CheckingMode && CS.getCalledFunction() &&
ExistingNode->getFunction() == nullptr)
assert(!CheckingMode &&
"CallGraphSCCPass did not update the CallGraph correctly!");
// If not, we either went from a direct call to indirect, indirect to
// direct, or direct to different direct.
CallGraphNode *CalleeNode;
if (Function *Callee = CS.getCalledFunction()) {
CalleeNode = CG.getOrInsertFunction(Callee);
// Keep track of whether we turned an indirect call into a direct
// one.
if (!ExistingNode->getFunction()) {
DevirtualizedCall = true;
LLVM_DEBUG(dbgs() << " CGSCCPASSMGR: Devirtualized call to '"
<< Callee->getName() << "'\n");
} else {
CalleeNode = CG.getCallsExternalNode();
// Update the edge target in CGN.
CGN->replaceCallEdge(CS, CS, CalleeNode);
MadeChange = true;
assert(!CheckingMode &&
"CallGraphSCCPass did not update the CallGraph correctly!");
// If the call site didn't exist in the CGN yet, add it.
CallGraphNode *CalleeNode;
if (Function *Callee = CS.getCalledFunction()) {
CalleeNode = CG.getOrInsertFunction(Callee);
} else {
CalleeNode = CG.getCallsExternalNode();
CGN->addCalledFunction(CS, CalleeNode);
MadeChange = true;
// We scanned the old callgraph node, removing invalidated call sites and
// then added back newly found call sites. One thing that can happen is
// that an old indirect call site was deleted and replaced with a new direct
// call. In this case, we have devirtualized a call, and CGSCCPM would like
// to iteratively optimize the new code. Unfortunately, we don't really
// have a great way to detect when this happens. As an approximation, we
// just look at whether the number of indirect calls is reduced and the
// number of direct calls is increased. There are tons of ways to fool this
// (e.g. DCE'ing an indirect call and duplicating an unrelated block with a
// direct call) but this is close enough.
if (NumIndirectRemoved > NumIndirectAdded &&
NumDirectRemoved < NumDirectAdded)
DevirtualizedCall = true;
// After scanning this function, if we still have entries in callsites, then
// they are dangling pointers. WeakTrackingVH should save us for this, so
// abort if
// this happens.
assert(CallSites.empty() && "Dangling pointers found in call sites map");
// Periodically do an explicit clear to remove tombstones when processing
// large scc's.
if ((FunctionNo & 15) == 15)
LLVM_DEBUG(if (MadeChange) {
dbgs() << "CGSCCPASSMGR: Refreshed SCC is now:\n";
for (CallGraphNode *CGN : CurSCC)
if (DevirtualizedCall)
dbgs() << "CGSCCPASSMGR: Refresh devirtualized a call!\n";
} else {
dbgs() << "CGSCCPASSMGR: SCC Refresh didn't change call graph.\n";
return DevirtualizedCall;
/// Execute the body of the entire pass manager on the specified SCC.
/// This keeps track of whether a function pass devirtualizes
/// any calls and returns it in DevirtualizedCall.
bool CGPassManager::RunAllPassesOnSCC(CallGraphSCC &CurSCC, CallGraph &CG,
bool &DevirtualizedCall) {
bool Changed = false;
// Keep track of whether the callgraph is known to be up-to-date or not.
// The CGSSC pass manager runs two types of passes:
// CallGraphSCC Passes and other random function passes. Because other
// random function passes are not CallGraph aware, they may clobber the
// call graph by introducing new calls or deleting other ones. This flag
// is set to false when we run a function pass so that we know to clean up
// the callgraph when we need to run a CGSCCPass again.
bool CallGraphUpToDate = true;
// Run all passes on current SCC.
for (unsigned PassNo = 0, e = getNumContainedPasses();
PassNo != e; ++PassNo) {
Pass *P = getContainedPass(PassNo);
// If we're in -debug-pass=Executions mode, construct the SCC node list,
// otherwise avoid constructing this string as it is expensive.
if (isPassDebuggingExecutionsOrMore()) {
std::string Functions;
#ifndef NDEBUG
raw_string_ostream OS(Functions);
for (CallGraphSCC::iterator I = CurSCC.begin(), E = CurSCC.end();
I != E; ++I) {
if (I != CurSCC.begin()) OS << ", ";
dumpPassInfo(P, EXECUTION_MSG, ON_CG_MSG, Functions);
// Actually run this pass on the current SCC.
Changed |= RunPassOnSCC(P, CurSCC, CG,
CallGraphUpToDate, DevirtualizedCall);
if (Changed)
removeDeadPasses(P, "", ON_CG_MSG);
// If the callgraph was left out of date (because the last pass run was a
// functionpass), refresh it before we move on to the next SCC.
if (!CallGraphUpToDate)
DevirtualizedCall |= RefreshCallGraph(CurSCC, CG, false);
return Changed;
/// Execute all of the passes scheduled for execution. Keep track of
/// whether any of the passes modifies the module, and if so, return true.
bool CGPassManager::runOnModule(Module &M) {
CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
bool Changed = doInitialization(CG);
// Walk the callgraph in bottom-up SCC order.
scc_iterator<CallGraph*> CGI = scc_begin(&CG);
CallGraphSCC CurSCC(CG, &CGI);
while (!CGI.isAtEnd()) {
// Copy the current SCC and increment past it so that the pass can hack
// on the SCC if it wants to without invalidating our iterator.
const std::vector<CallGraphNode *> &NodeVec = *CGI;
// At the top level, we run all the passes in this pass manager on the
// functions in this SCC. However, we support iterative compilation in the
// case where a function pass devirtualizes a call to a function. For
// example, it is very common for a function pass (often GVN or instcombine)
// to eliminate the addressing that feeds into a call. With that improved
// information, we would like the call to be an inline candidate, infer
// mod-ref information etc.
// Because of this, we allow iteration up to a specified iteration count.
// This only happens in the case of a devirtualized call, so we only burn
// compile time in the case that we're making progress. We also have a hard
// iteration count limit in case there is crazy code.
unsigned Iteration = 0;
bool DevirtualizedCall = false;
do {
LLVM_DEBUG(if (Iteration) dbgs()
<< " SCCPASSMGR: Re-visiting SCC, iteration #" << Iteration
<< '\n');
DevirtualizedCall = false;
Changed |= RunAllPassesOnSCC(CurSCC, CG, DevirtualizedCall);
} while (Iteration++ < MaxIterations && DevirtualizedCall);
if (DevirtualizedCall)
LLVM_DEBUG(dbgs() << " CGSCCPASSMGR: Stopped iteration after "
<< Iteration
<< " times, due to -max-cg-scc-iterations\n");
Changed |= doFinalization(CG);
return Changed;
/// Initialize CG
bool CGPassManager::doInitialization(CallGraph &CG) {
bool Changed = false;
for (unsigned i = 0, e = getNumContainedPasses(); i != e; ++i) {
if (PMDataManager *PM = getContainedPass(i)->getAsPMDataManager()) {
assert(PM->getPassManagerType() == PMT_FunctionPassManager &&
"Invalid CGPassManager member");
Changed |= ((FPPassManager*)PM)->doInitialization(CG.getModule());
} else {
Changed |= ((CallGraphSCCPass*)getContainedPass(i))->doInitialization(CG);
return Changed;
/// Finalize CG
bool CGPassManager::doFinalization(CallGraph &CG) {
bool Changed = false;
for (unsigned i = 0, e = getNumContainedPasses(); i != e; ++i) {
if (PMDataManager *PM = getContainedPass(i)->getAsPMDataManager()) {
assert(PM->getPassManagerType() == PMT_FunctionPassManager &&
"Invalid CGPassManager member");
Changed |= ((FPPassManager*)PM)->doFinalization(CG.getModule());
} else {
Changed |= ((CallGraphSCCPass*)getContainedPass(i))->doFinalization(CG);
return Changed;
// CallGraphSCC Implementation
/// This informs the SCC and the pass manager that the specified
/// Old node has been deleted, and New is to be used in its place.
void CallGraphSCC::ReplaceNode(CallGraphNode *Old, CallGraphNode *New) {
assert(Old != New && "Should not replace node with self");
for (unsigned i = 0; ; ++i) {
assert(i != Nodes.size() && "Node not in SCC");
if (Nodes[i] != Old) continue;
Nodes[i] = New;
// Update the active scc_iterator so that it doesn't contain dangling
// pointers to the old CallGraphNode.
scc_iterator<CallGraph*> *CGI = (scc_iterator<CallGraph*>*)Context;
CGI->ReplaceNode(Old, New);
// CallGraphSCCPass Implementation
/// Assign pass manager to manage this pass.
void CallGraphSCCPass::assignPassManager(PMStack &PMS,
PassManagerType PreferredType) {
// Find CGPassManager
while (!PMS.empty() &&>getPassManagerType() > PMT_CallGraphPassManager)
assert(!PMS.empty() && "Unable to handle Call Graph Pass");
CGPassManager *CGP;
if (>getPassManagerType() == PMT_CallGraphPassManager)
CGP = (CGPassManager*);
else {
// Create new Call Graph SCC Pass Manager if it does not exist.
assert(!PMS.empty() && "Unable to create Call Graph Pass Manager");
PMDataManager *PMD =;
// [1] Create new Call Graph Pass Manager
CGP = new CGPassManager();
// [2] Set up new manager's top level manager
PMTopLevelManager *TPM = PMD->getTopLevelManager();
// [3] Assign manager to manage this new manager. This may create
// and push new managers into PMS
Pass *P = CGP;
// [4] Push new manager into PMS
/// For this class, we declare that we require and preserve the call graph.
/// If the derived class implements this method, it should
/// always explicitly call the implementation here.
void CallGraphSCCPass::getAnalysisUsage(AnalysisUsage &AU) const {
// PrintCallGraphPass Implementation
namespace {
/// PrintCallGraphPass - Print a Module corresponding to a call graph.
class PrintCallGraphPass : public CallGraphSCCPass {
std::string Banner;
raw_ostream &OS; // raw_ostream to print on.
static char ID;
PrintCallGraphPass(const std::string &B, raw_ostream &OS)
: CallGraphSCCPass(ID), Banner(B), OS(OS) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool runOnSCC(CallGraphSCC &SCC) override {
bool BannerPrinted = false;
auto PrintBannerOnce = [&] () {
if (BannerPrinted)
OS << Banner;
BannerPrinted = true;
for (CallGraphNode *CGN : SCC) {
if (Function *F = CGN->getFunction()) {
if (!F->isDeclaration() && isFunctionInPrintList(F->getName())) {
} else if (isFunctionInPrintList("*")) {
OS << "\nPrinting <null> Function\n";
return false;
StringRef getPassName() const override { return "Print CallGraph IR"; }
} // end anonymous namespace.
char PrintCallGraphPass::ID = 0;
Pass *CallGraphSCCPass::createPrinterPass(raw_ostream &OS,
const std::string &Banner) const {
return new PrintCallGraphPass(Banner, OS);
bool CallGraphSCCPass::skipSCC(CallGraphSCC &SCC) const {
return !SCC.getCallGraph().getModule()
.shouldRunPass(this, SCC);
char DummyCGSCCPass::ID = 0;
INITIALIZE_PASS(DummyCGSCCPass, "DummyCGSCCPass", "DummyCGSCCPass", false,