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//===- LoopExtractor.cpp - Extract each loop into a new function ----------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// A pass wrapper around the ExtractLoop() scalar transformation to extract each
// top-level loop into its own new function. If the loop is the ONLY loop in a
// given function, it is not touched. This is a pass most useful for debugging
// via bugpoint.
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/CodeExtractor.h"
#include <fstream>
#include <set>
using namespace llvm;
#define DEBUG_TYPE "loop-extract"
STATISTIC(NumExtracted, "Number of loops extracted");
namespace {
struct LoopExtractor : public LoopPass {
static char ID; // Pass identification, replacement for typeid
unsigned NumLoops;
explicit LoopExtractor(unsigned numLoops = ~0)
: LoopPass(ID), NumLoops(numLoops) {
bool runOnLoop(Loop *L, LPPassManager &) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
char LoopExtractor::ID = 0;
INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract",
"Extract loops into new functions", false, false)
INITIALIZE_PASS_END(LoopExtractor, "loop-extract",
"Extract loops into new functions", false, false)
namespace {
/// SingleLoopExtractor - For bugpoint.
struct SingleLoopExtractor : public LoopExtractor {
static char ID; // Pass identification, replacement for typeid
SingleLoopExtractor() : LoopExtractor(1) {}
} // End anonymous namespace
char SingleLoopExtractor::ID = 0;
INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single",
"Extract at most one loop into a new function", false, false)
// createLoopExtractorPass - This pass extracts all natural loops from the
// program into a function if it can.
Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &LPM) {
if (skipLoop(L))
return false;
// Only visit top-level loops.
if (L->getParentLoop())
return false;
// If LoopSimplify form is not available, stay out of trouble.
if (!L->isLoopSimplifyForm())
return false;
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
bool Changed = false;
// If there is more than one top-level loop in this function, extract all of
// the loops. Otherwise there is exactly one top-level loop; in this case if
// this function is more than a minimal wrapper around the loop, extract
// the loop.
bool ShouldExtractLoop = false;
// Extract the loop if the entry block doesn't branch to the loop header.
TerminatorInst *EntryTI =
if (!isa<BranchInst>(EntryTI) ||
!cast<BranchInst>(EntryTI)->isUnconditional() ||
EntryTI->getSuccessor(0) != L->getHeader()) {
ShouldExtractLoop = true;
} else {
// Check to see if any exits from the loop are more than just return
// blocks.
SmallVector<BasicBlock*, 8> ExitBlocks;
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
ShouldExtractLoop = true;
if (ShouldExtractLoop) {
// We must omit EH pads. EH pads must accompany the invoke
// instruction. But this would result in a loop in the extracted
// function. An infinite cycle occurs when it tries to extract that loop as
// well.
SmallVector<BasicBlock*, 8> ExitBlocks;
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
if (ExitBlocks[i]->isEHPad()) {
ShouldExtractLoop = false;
if (ShouldExtractLoop) {
if (NumLoops == 0) return Changed;
CodeExtractor Extractor(DT, *L);
if (Extractor.extractCodeRegion() != nullptr) {
Changed = true;
// After extraction, the loop is replaced by a function call, so
// we shouldn't try to run any more loop passes on it.
return Changed;
// createSingleLoopExtractorPass - This pass extracts one natural loop from the
// program into a function if it can. This is used by bugpoint.
Pass *llvm::createSingleLoopExtractorPass() {
return new SingleLoopExtractor();
// BlockFile - A file which contains a list of blocks that should not be
// extracted.
static cl::opt<std::string>
BlockFile("extract-blocks-file", cl::value_desc("filename"),
cl::desc("A file containing list of basic blocks to not extract"),
namespace {
/// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
/// from the module into their own functions except for those specified by the
/// BlocksToNotExtract list.
class BlockExtractorPass : public ModulePass {
void LoadFile(const char *Filename);
void SplitLandingPadPreds(Function *F);
std::vector<BasicBlock*> BlocksToNotExtract;
std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
static char ID; // Pass identification, replacement for typeid
BlockExtractorPass() : ModulePass(ID) {
if (!BlockFile.empty())
bool runOnModule(Module &M) override;
char BlockExtractorPass::ID = 0;
INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
"Extract Basic Blocks From Module (for bugpoint use)",
false, false)
// createBlockExtractorPass - This pass extracts all blocks (except those
// specified in the argument list) from the functions in the module.
ModulePass *llvm::createBlockExtractorPass() {
return new BlockExtractorPass();
void BlockExtractorPass::LoadFile(const char *Filename) {
// Load the BlockFile...
std::ifstream In(Filename);
if (!In.good()) {
errs() << "WARNING: BlockExtractor couldn't load file '" << Filename
<< "'!\n";
while (In) {
std::string FunctionName, BlockName;
In >> FunctionName;
In >> BlockName;
if (!BlockName.empty())
std::make_pair(FunctionName, BlockName));
/// SplitLandingPadPreds - The landing pad needs to be extracted with the invoke
/// instruction. The critical edge breaker will refuse to break critical edges
/// to a landing pad. So do them here. After this method runs, all landing pads
/// should have only one predecessor.
void BlockExtractorPass::SplitLandingPadPreds(Function *F) {
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
InvokeInst *II = dyn_cast<InvokeInst>(I);
if (!II) continue;
BasicBlock *Parent = II->getParent();
BasicBlock *LPad = II->getUnwindDest();
// Look through the landing pad's predecessors. If one of them ends in an
// 'invoke', then we want to split the landing pad.
bool Split = false;
for (pred_iterator
PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ++PI) {
BasicBlock *BB = *PI;
if (BB->isLandingPad() && BB != Parent &&
isa<InvokeInst>(Parent->getTerminator())) {
Split = true;
if (!Split) continue;
SmallVector<BasicBlock*, 2> NewBBs;
SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", NewBBs);
bool BlockExtractorPass::runOnModule(Module &M) {
if (skipModule(M))
return false;
std::set<BasicBlock*> TranslatedBlocksToNotExtract;
for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
BasicBlock *BB = BlocksToNotExtract[i];
Function *F = BB->getParent();
// Map the corresponding function in this module.
Function *MF = M.getFunction(F->getName());
assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
// Figure out which index the basic block is in its function.
Function::iterator BBI = MF->begin();
std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
while (!BlocksToNotExtractByName.empty()) {
// There's no way to find BBs by name without looking at every BB inside
// every Function. Fortunately, this is always empty except when used by
// bugpoint in which case correctness is more important than performance.
std::string &FuncName = BlocksToNotExtractByName.back().first;
std::string &BlockName = BlocksToNotExtractByName.back().second;
for (Function &F : M) {
if (F.getName() != FuncName) continue;
for (BasicBlock &BB : F) {
if (BB.getName() != BlockName) continue;
// Now that we know which blocks to not extract, figure out which ones we WANT
// to extract.
std::vector<BasicBlock*> BlocksToExtract;
for (Function &F : M) {
for (BasicBlock &BB : F)
if (!TranslatedBlocksToNotExtract.count(&BB))
for (BasicBlock *BlockToExtract : BlocksToExtract) {
SmallVector<BasicBlock*, 2> BlocksToExtractVec;
if (const InvokeInst *II =
return !BlocksToExtract.empty();