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//===- LoopPass.cpp - Loop Pass and Loop Pass Manager ---------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements LoopPass and LPPassManager. All loop optimization
// and transformation passes are derived from LoopPass. LPPassManager is
// responsible for managing LoopPasses.
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/LoopAnalysisManager.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/OptBisect.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PassTimingInfo.h"
#include "llvm/IR/PrintPasses.h"
#include "llvm/IR/StructuralHash.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "loop-pass-manager"
namespace {
/// PrintLoopPass - Print a Function corresponding to a Loop.
class PrintLoopPassWrapper : public LoopPass {
raw_ostream &OS;
std::string Banner;
static char ID;
PrintLoopPassWrapper() : LoopPass(ID), OS(dbgs()) {}
PrintLoopPassWrapper(raw_ostream &OS, const std::string &Banner)
: LoopPass(ID), OS(OS), Banner(Banner) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool runOnLoop(Loop *L, LPPassManager &) override {
auto BBI = llvm::find_if(L->blocks(), [](BasicBlock *BB) { return BB; });
if (BBI != L->blocks().end() &&
isFunctionInPrintList((*BBI)->getParent()->getName())) {
printLoop(*L, OS, Banner);
return false;
StringRef getPassName() const override { return "Print Loop IR"; }
char PrintLoopPassWrapper::ID = 0;
// LPPassManager
char LPPassManager::ID = 0;
: FunctionPass(ID), PMDataManager() {
LI = nullptr;
CurrentLoop = nullptr;
// Insert loop into loop nest (LoopInfo) and loop queue (LQ).
void LPPassManager::addLoop(Loop &L) {
if (L.isOutermost()) {
// This is the top level loop.
// Insert L into the loop queue after the parent loop.
for (auto I = LQ.begin(), E = LQ.end(); I != E; ++I) {
if (*I == L.getParentLoop()) {
// deque does not support insert after.
LQ.insert(I, 1, &L);
// Recurse through all subloops and all loops into LQ.
static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
for (Loop *I : reverse(*L))
addLoopIntoQueue(I, LQ);
/// Pass Manager itself does not invalidate any analysis info.
void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
// LPPassManager needs LoopInfo. In the long term LoopInfo class will
// become part of LPPassManager.
void LPPassManager::markLoopAsDeleted(Loop &L) {
assert((&L == CurrentLoop || CurrentLoop->contains(&L)) &&
"Must not delete loop outside the current loop tree!");
// If this loop appears elsewhere within the queue, we also need to remove it
// there. However, we have to be careful to not remove the back of the queue
// as that is assumed to match the current loop.
assert(LQ.back() == CurrentLoop && "Loop queue back isn't the current loop!");
llvm::erase_value(LQ, &L);
if (&L == CurrentLoop) {
CurrentLoopDeleted = true;
// Add this loop back onto the back of the queue to preserve our invariants.
/// run - Execute all of the passes scheduled for execution. Keep track of
/// whether any of the passes modifies the function, and if so, return true.
bool LPPassManager::runOnFunction(Function &F) {
auto &LIWP = getAnalysis<LoopInfoWrapperPass>();
LI = &LIWP.getLoopInfo();
Module &M = *F.getParent();
#if 0
DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
bool Changed = false;
// Collect inherited analysis from Module level pass manager.
// Populate the loop queue in reverse program order. There is no clear need to
// process sibling loops in either forward or reverse order. There may be some
// advantage in deleting uses in a later loop before optimizing the
// definitions in an earlier loop. If we find a clear reason to process in
// forward order, then a forward variant of LoopPassManager should be created.
// Note that LoopInfo::iterator visits loops in reverse program
// order. Here, reverse_iterator gives us a forward order, and the LoopQueue
// reverses the order a third time by popping from the back.
for (Loop *L : reverse(*LI))
addLoopIntoQueue(L, LQ);
if (LQ.empty()) // No loops, skip calling finalizers
return false;
// Initialization
for (Loop *L : LQ) {
for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
LoopPass *P = getContainedPass(Index);
Changed |= P->doInitialization(L, *this);
// Walk Loops
unsigned InstrCount, FunctionSize = 0;
StringMap<std::pair<unsigned, unsigned>> FunctionToInstrCount;
bool EmitICRemark = M.shouldEmitInstrCountChangedRemark();
// Collect the initial size of the module and the function we're looking at.
if (EmitICRemark) {
InstrCount = initSizeRemarkInfo(M, FunctionToInstrCount);
FunctionSize = F.getInstructionCount();
while (!LQ.empty()) {
CurrentLoopDeleted = false;
CurrentLoop = LQ.back();
// Run all passes on the current Loop.
for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
LoopPass *P = getContainedPass(Index);
llvm::TimeTraceScope LoopPassScope("RunLoopPass", P->getPassName());
bool LocalChanged = false;
PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
TimeRegion PassTimer(getPassTimer(P));
uint64_t RefHash = StructuralHash(F);
LocalChanged = P->runOnLoop(CurrentLoop, *this);
if (!LocalChanged && (RefHash != StructuralHash(F))) {
llvm::errs() << "Pass modifies its input and doesn't report it: "
<< P->getPassName() << "\n";
llvm_unreachable("Pass modifies its input and doesn't report it");
Changed |= LocalChanged;
if (EmitICRemark) {
unsigned NewSize = F.getInstructionCount();
// Update the size of the function, emit a remark, and update the
// size of the module.
if (NewSize != FunctionSize) {
int64_t Delta = static_cast<int64_t>(NewSize) -
emitInstrCountChangedRemark(P, M, Delta, InstrCount,
FunctionToInstrCount, &F);
InstrCount = static_cast<int64_t>(InstrCount) + Delta;
FunctionSize = NewSize;
if (LocalChanged)
CurrentLoopDeleted ? "<deleted loop>"
: CurrentLoop->getName());
if (!CurrentLoopDeleted) {
// Manually check that this loop is still healthy. This is done
// instead of relying on LoopInfo::verifyLoop since LoopInfo
// is a function pass and it's really expensive to verify every
// loop in the function every time. That level of checking can be
// enabled with the -verify-loop-info option.
TimeRegion PassTimer(getPassTimer(&LIWP));
// Here we apply same reasoning as in the above case. Only difference
// is that LPPassManager might run passes which do not require LCSSA
// form (LoopPassPrinter for example). We should skip verification for
// such passes.
// FIXME: Loop-sink currently break LCSSA. Fix it and reenable the
// verification!
#if 0
if (mustPreserveAnalysisID(LCSSAVerificationPass::ID))
assert(CurrentLoop->isRecursivelyLCSSAForm(*DT, *LI));
// Then call the regular verifyAnalysis functions.
if (LocalChanged)
CurrentLoopDeleted ? "<deleted>"
: CurrentLoop->getHeader()->getName(),
if (CurrentLoopDeleted)
// Do not run other passes on this loop.
// If the loop was deleted, release all the loop passes. This frees up
// some memory, and avoids trouble with the pass manager trying to call
// verifyAnalysis on them.
if (CurrentLoopDeleted) {
for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
Pass *P = getContainedPass(Index);
freePass(P, "<deleted>", ON_LOOP_MSG);
// Pop the loop from queue after running all passes.
// Finalization
for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
LoopPass *P = getContainedPass(Index);
Changed |= P->doFinalization();
return Changed;
/// Print passes managed by this manager
void LPPassManager::dumpPassStructure(unsigned Offset) {
errs().indent(Offset*2) << "Loop Pass Manager\n";
for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
Pass *P = getContainedPass(Index);
P->dumpPassStructure(Offset + 1);
dumpLastUses(P, Offset+1);
// LoopPass
Pass *LoopPass::createPrinterPass(raw_ostream &O,
const std::string &Banner) const {
return new PrintLoopPassWrapper(O, Banner);
// Check if this pass is suitable for the current LPPassManager, if
// available. This pass P is not suitable for a LPPassManager if P
// is not preserving higher level analysis info used by other
// LPPassManager passes. In such case, pop LPPassManager from the
// stack. This will force assignPassManager() to create new
// LPPassManger as expected.
void LoopPass::preparePassManager(PMStack &PMS) {
// Find LPPassManager
while (!PMS.empty() &&>getPassManagerType() > PMT_LoopPassManager)
// If this pass is destroying high level information that is used
// by other passes that are managed by LPM then do not insert
// this pass in current LPM. Use new LPPassManager.
if (>getPassManagerType() == PMT_LoopPassManager &&
/// Assign pass manager to manage this pass.
void LoopPass::assignPassManager(PMStack &PMS,
PassManagerType PreferredType) {
// Find LPPassManager
while (!PMS.empty() &&>getPassManagerType() > PMT_LoopPassManager)
LPPassManager *LPPM;
if (>getPassManagerType() == PMT_LoopPassManager)
LPPM = (LPPassManager*);
else {
// Create new Loop Pass Manager if it does not exist.
assert (!PMS.empty() && "Unable to create Loop Pass Manager");
PMDataManager *PMD =;
// [1] Create new Loop Pass Manager
LPPM = new LPPassManager();
// [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 = LPPM->getAsPass();
// [4] Push new manager into PMS
static std::string getDescription(const Loop &L) {
return "loop";
bool LoopPass::skipLoop(const Loop *L) const {
const Function *F = L->getHeader()->getParent();
if (!F)
return false;
// Check the opt bisect limit.
OptPassGate &Gate = F->getContext().getOptPassGate();
if (Gate.isEnabled() && !Gate.shouldRunPass(this, getDescription(*L)))
return true;
// Check for the OptimizeNone attribute.
if (F->hasOptNone()) {
// FIXME: Report this to dbgs() only once per function.
LLVM_DEBUG(dbgs() << "Skipping pass '" << getPassName() << "' in function "
<< F->getName() << "\n");
// FIXME: Delete loop from pass manager's queue?
return true;
return false;
LCSSAVerificationPass::LCSSAVerificationPass() : FunctionPass(ID) {
char LCSSAVerificationPass::ID = 0;
INITIALIZE_PASS(LCSSAVerificationPass, "lcssa-verification", "LCSSA Verifier",
false, false)