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//===------ IndependentBlocks.cpp - Create Independent Blocks in Regions --===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// Create independent blocks in the regions detected by ScopDetection.
#include "polly/LinkAllPasses.h"
#include "polly/ScopDetection.h"
#include "polly/Support/ScopHelper.h"
#include "polly/CodeGen/Cloog.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/RegionPass.h"
#include "llvm/Analysis/RegionIterator.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/Assembly/Writer.h"
#define DEBUG_TYPE "polly-independent"
#include "llvm/Support/Debug.h"
#include <vector>
using namespace polly;
using namespace llvm;
namespace {
struct IndependentBlocks : public FunctionPass {
RegionInfo *RI;
ScalarEvolution *SE;
ScopDetection *SD;
LoopInfo *LI;
BasicBlock *AllocaBlock;
static char ID;
IndependentBlocks() : FunctionPass(ID) {}
// Create new code for every instruction operator that can be expressed by a
// SCEV. Like this there are just two types of instructions left:
// 1. Instructions that only reference loop ivs or parameters outside the
// region.
// 2. Instructions that are not used for any memory modification. (These
// will be ignored later on.)
// Blocks containing only these kind of instructions are called independent
// blocks as they can be scheduled arbitrarily.
bool createIndependentBlocks(BasicBlock *BB, const Region *R);
bool createIndependentBlocks(const Region *R);
// Elimination on the Scop to eliminate the scalar dependences come with
// trivially dead instructions.
bool eliminateDeadCode(const Region *R);
/// Non trivial scalar dependences checking functions.
/// Non trivial scalar dependences occur when the def and use are located in
/// different BBs and we can not move them into the same one. This will
/// prevent use from schedule BBs arbitrarily.
/// @brief This function checks if a scalar value that is part of the
/// Scop is used outside of the Scop.
/// @param Use The use of the instruction.
/// @param R The maximum region in the Scop.
/// @return Return true if the Use of an instruction and the instruction
/// itself form a non trivial scalar dependence.
static bool isEscapeUse(const Value *Use, const Region *R);
/// @brief This function just checks if a Value is either defined in the same
/// basic block or outside the region, such that there are no scalar
/// dependences between basic blocks that are both part of the same
/// region.
/// @param Operand The operand of the instruction.
/// @param CurBB The BasicBlock that contains the instruction.
/// @param R The maximum region in the Scop.
/// @return Return true if the Operand of an instruction and the instruction
/// itself form a non trivial scalar (true) dependence.
bool isEscapeOperand(const Value *Operand, const BasicBlock *CurBB,
const Region *R) const;
/// Operand tree moving functions.
/// Trivial scalar dependences can eliminate by move the def to the same BB
/// that containing use.
/// @brief Check if the instruction can be moved to another place safely.
/// @param Inst The instruction.
/// @return Return true if the instruction can be moved safely, false
/// otherwise.
static bool isSafeToMove(Instruction *Inst);
typedef std::map<Instruction*, Instruction*> ReplacedMapType;
/// @brief Move all safe to move instructions in the Operand Tree (DAG) to
/// eliminate trivial scalar dependences.
/// @param Inst The root of the operand Tree.
/// @param R The maximum region in the Scop.
/// @param ReplacedMap The map that mapping original instruction to the moved
/// instruction.
/// @param InsertPos The insert position of the moved instructions.
void moveOperandTree(Instruction *Inst, const Region *R,
ReplacedMapType &ReplacedMap,
Instruction *InsertPos);
bool isIndependentBlock(const Region *R, BasicBlock *BB) const;
bool areAllBlocksIndependent(const Region *R) const;
// Split the exit block to hold load instructions.
bool splitExitBlock(Region *R);
bool translateScalarToArray(BasicBlock *BB, const Region *R);
bool translateScalarToArray(Instruction *Inst, const Region *R);
bool translateScalarToArray(const Region *R);
bool runOnFunction(Function &F);
void verifyAnalysis() const;
void verifyScop(const Region *R) const;
void getAnalysisUsage(AnalysisUsage &AU) const;
bool IndependentBlocks::isSafeToMove(Instruction *Inst) {
if (Inst->mayReadFromMemory() ||
return false;
return isSafeToSpeculativelyExecute(Inst);
void IndependentBlocks::moveOperandTree(Instruction *Inst, const Region *R,
ReplacedMapType &ReplacedMap,
Instruction *InsertPos) {
BasicBlock *CurBB = Inst->getParent();
// Depth first traverse the operand tree (or operand dag, because we will
// stop at PHINodes, so there are no cycle).
typedef Instruction::op_iterator ChildIt;
std::vector<std::pair<Instruction*, ChildIt> > WorkStack;
WorkStack.push_back(std::make_pair(Inst, Inst->op_begin()));
DenseSet<Instruction*> VisitedSet;
while (!WorkStack.empty()) {
Instruction *CurInst = WorkStack.back().first;
ChildIt It = WorkStack.back().second;
DEBUG(dbgs() << "Checking Operand of Node:\n" << *CurInst << "\n------>\n");
if (It == CurInst->op_end()) {
// Insert the new instructions in topological order.
if (!CurInst->getParent())
} else {
// for each node N,
Instruction *Operand = dyn_cast<Instruction>(*It);
// Can not move no instruction value.
if (Operand == 0) continue;
DEBUG(dbgs() << "For Operand:\n" << *Operand << "\n--->");
// If the Scop Region does not contain N, skip it and all its operand and
// continue. because we reach a "parameter".
// FIXME: we must keep the predicate instruction inside the Scop, otherwise
// it will be translated to a load instruction, and we can not handle load
// as affine predicate at this moment.
if (!R->contains(Operand) && !isa<TerminatorInst>(CurInst)) {
DEBUG(dbgs() << "Out of region.\n");
// No need to move induction variable.
if (isIndVar(Operand, LI)) {
DEBUG(dbgs() << "is IV.\n");
// We can not move the operand, a non trivial scalar dependence found!
if (!isSafeToMove(Operand)) {
DEBUG(dbgs() << "Can not move!\n");
// Do not need to move instruction if it contained in the same BB with
// the root instruction.
if (Operand->getParent() == CurBB) {
DEBUG(dbgs() << "No need to move.\n");
// Try to move its operand, but do not visit an instuction twice.
if (VisitedSet.insert(Operand).second)
WorkStack.push_back(std::make_pair(Operand, Operand->op_begin()));
// Now we need to move Operand to CurBB.
// Check if we already moved it.
ReplacedMapType::iterator At = ReplacedMap.find(Operand);
if (At != ReplacedMap.end()) {
DEBUG(dbgs() << "Moved.\n");
Instruction *MovedOp = At->second;
// Skip all its children as we already processed them.
} else {
// Note that NewOp is not inserted in any BB now, we will insert it when
// it popped form the work stack, so it will be inserted in topological
// order.
Instruction *NewOp = Operand->clone();
NewOp->setName(Operand->getName() + "" + CurBB->getName());
DEBUG(dbgs() << "Move to " << *NewOp << "\n");
ReplacedMap.insert(std::make_pair(Operand, NewOp));
// Process its operands, but do not visit an instuction twice.
if (VisitedSet.insert(NewOp).second)
WorkStack.push_back(std::make_pair(NewOp, NewOp->op_begin()));
bool IndependentBlocks::createIndependentBlocks(BasicBlock *BB,
const Region *R) {
std::vector<Instruction*> WorkList;
for (BasicBlock::iterator II = BB->begin(), IE = BB->end(); II != IE; ++II)
if (!isSafeToMove(II) && !isIndVar(II, LI))
ReplacedMapType ReplacedMap;
Instruction *InsertPos = BB->getFirstNonPHIOrDbg();
for (std::vector<Instruction*>::iterator I = WorkList.begin(),
E = WorkList.end(); I != E; ++I)
moveOperandTree(*I, R, ReplacedMap, InsertPos);
// The BB was changed if we replaced any operand.
return !ReplacedMap.empty();
bool IndependentBlocks::createIndependentBlocks(const Region *R) {
bool Changed = false;
for (Region::const_block_iterator SI = R->block_begin(), SE = R->block_end();
SI != SE; ++SI)
Changed |= createIndependentBlocks(*SI, R);
return Changed;
bool IndependentBlocks::eliminateDeadCode(const Region *R) {
std::vector<Instruction*> WorkList;
// Find all trivially dead instructions.
for (Region::const_block_iterator SI = R->block_begin(), SE = R->block_end();
SI != SE; ++SI)
for (BasicBlock::iterator I = (*SI)->begin(), E = (*SI)->end(); I != E; ++I)
if (isInstructionTriviallyDead(I))
if (WorkList.empty()) return false;
// Delete them so the cross BB scalar dependences come with them will
// also be eliminated.
while (!WorkList.empty()) {
return true;
bool IndependentBlocks::isEscapeUse(const Value *Use, const Region *R) {
// Non-instruction user will never escape.
if (!isa<Instruction>(Use)) return false;
return !R->contains(cast<Instruction>(Use));
bool IndependentBlocks::isEscapeOperand(const Value *Operand,
const BasicBlock *CurBB,
const Region *R) const {
const Instruction *OpInst = dyn_cast<Instruction>(Operand);
// Non-instruction operand will never escape.
if (OpInst == 0) return false;
// Induction variables are valid operands.
if (isIndVar(OpInst, LI)) return false;
// A value from a different BB is used in the same region.
return R->contains(OpInst) && (OpInst->getParent() != CurBB);
bool IndependentBlocks::splitExitBlock(Region *R) {
// Split the exit BB to place the load instruction of escaped users.
BasicBlock *ExitBB = R->getExit();
Region *ExitRegion = RI->getRegionFor(ExitBB);
if (ExitBB != ExitRegion->getEntry())
return false;
BasicBlock *NewExit = createSingleExitEdge(R, this);
std::vector<Region*> toUpdate;
while (!toUpdate.empty()) {
Region *Reg = toUpdate.back();
for (Region::iterator I = Reg->begin(), E = Reg->end(); I != E; ++I) {
Region *SubR = *I;
if (SubR->getExit() == ExitBB)
RI->setRegionFor(NewExit, R->getParent());
return true;
bool IndependentBlocks::translateScalarToArray(const Region *R) {
bool Changed = false;
for (Region::const_block_iterator SI = R->block_begin(), SE = R->block_end();
SI != SE; ++SI)
Changed |= translateScalarToArray(*SI, R);
return Changed;
bool IndependentBlocks::translateScalarToArray(Instruction *Inst,
const Region *R) {
if (isIndVar(Inst, LI))
return false;
SmallVector<Instruction*, 4> LoadInside, LoadOutside;
for (Instruction::use_iterator UI = Inst->use_begin(),
UE = Inst->use_end(); UI != UE; ++UI)
// Inst is referenced outside or referenced as an escaped operand.
if (Instruction *U = dyn_cast<Instruction>(*UI)) {
BasicBlock *UParent = U->getParent();
if (isEscapeUse(U, R))
if (isIndVar(U, LI))
if (R->contains(UParent) && isEscapeOperand(Inst, UParent, R))
if (LoadOutside.empty() && LoadInside.empty())
return false;
// Create the alloca.
AllocaInst *Slot = new AllocaInst(Inst->getType(), 0,
Inst->getName() + ".s2a",
assert(!isa<InvokeInst>(Inst) && "Unexpect Invoke in Scop!");
// Store right after Inst.
BasicBlock::iterator StorePos = Inst;
(void) new StoreInst(Inst, Slot, ++StorePos);
if (!LoadOutside.empty()) {
LoadInst *ExitLoad = new LoadInst(Slot, Inst->getName()+".loadoutside",
false, R->getExit()->getFirstNonPHI());
while (!LoadOutside.empty()) {
Instruction *U = LoadOutside.pop_back_val();
assert(!isa<PHINode>(U) && "Can not handle PHI node outside!");
U->replaceUsesOfWith(Inst, ExitLoad);
while (!LoadInside.empty()) {
Instruction *U = LoadInside.pop_back_val();
assert(!isa<PHINode>(U) && "Can not handle PHI node outside!");
LoadInst *L = new LoadInst(Slot, Inst->getName()+".loadarray",
false, U);
U->replaceUsesOfWith(Inst, L);
return true;
bool IndependentBlocks::translateScalarToArray(BasicBlock *BB,
const Region *R) {
bool changed = false;
SmallVector<Instruction*, 32> Insts;
for (BasicBlock::iterator II = BB->begin(), IE = --BB->end();
II != IE; ++II)
while (!Insts.empty()) {
Instruction *Inst = Insts.pop_back_val();
changed |= translateScalarToArray(Inst, R);
return changed;
bool IndependentBlocks::isIndependentBlock(const Region *R,
BasicBlock *BB) const {
for (BasicBlock::iterator II = BB->begin(), IE = --BB->end();
II != IE; ++II) {
Instruction *Inst = &*II;
if (isIndVar(Inst, LI))
// A value inside the Scop is referenced outside.
for (Instruction::use_iterator UI = Inst->use_begin(),
UE = Inst->use_end(); UI != UE; ++UI) {
if (isEscapeUse(*UI, R)) {
DEBUG(dbgs() << "Instruction not independent:\n");
DEBUG(dbgs() << "Instruction used outside the Scop!\n");
DEBUG(dbgs() << "\n");
return false;
for (Instruction::op_iterator OI = Inst->op_begin(),
OE = Inst->op_end(); OI != OE; ++OI) {
if (isEscapeOperand(*OI, BB, R)) {
DEBUG(dbgs() << "Instruction in function '";
WriteAsOperand(dbgs(), BB->getParent(), false);
dbgs() << "' not independent:\n");
DEBUG(dbgs() << "Uses invalid operator\n");
DEBUG(dbgs() << "\n");
DEBUG(dbgs() << "Invalid operator is: ";
WriteAsOperand(dbgs(), *OI, false);
dbgs() << "\n");
return false;
return true;
bool IndependentBlocks::areAllBlocksIndependent(const Region *R) const {
for (Region::const_block_iterator SI = R->block_begin(), SE = R->block_end();
SI != SE; ++SI)
if (!isIndependentBlock(R, *SI))
return false;
return true;
void IndependentBlocks::getAnalysisUsage(AnalysisUsage &AU) const {
// FIXME: If we set preserves cfg, the cfg only passes do not need to
// be "addPreserved"?
bool IndependentBlocks::runOnFunction(llvm::Function &F) {
bool Changed = false;
RI = &getAnalysis<RegionInfo>();
LI = &getAnalysis<LoopInfo>();
SD = &getAnalysis<ScopDetection>();
SE = &getAnalysis<ScalarEvolution>();
AllocaBlock = &F.getEntryBlock();
DEBUG(dbgs() << "Run IndepBlock on " << F.getName() << '\n');
for (ScopDetection::iterator I = SD->begin(), E = SD->end(); I != E; ++I) {
const Region *R = *I;
Changed |= createIndependentBlocks(R);
Changed |= eliminateDeadCode(R);
// This may change the RegionTree.
Changed |= splitExitBlock(const_cast<Region*>(R));
DEBUG(dbgs() << "Before Scalar to Array------->\n");
for (ScopDetection::iterator I = SD->begin(), E = SD->end(); I != E; ++I)
Changed |= translateScalarToArray(*I);
DEBUG(dbgs() << "After Independent Blocks------------->\n");
return Changed;
void IndependentBlocks::verifyAnalysis() const {
for (ScopDetection::const_iterator I = SD->begin(), E = SD->end();I != E;++I)
void IndependentBlocks::verifyScop(const Region *R) const {
assert (areAllBlocksIndependent(R) && "Cannot generate independent blocks");
char IndependentBlocks::ID = 0;
char &polly::IndependentBlocksID = IndependentBlocks::ID;
INITIALIZE_PASS_BEGIN(IndependentBlocks, "polly-independent",
"Polly - Create independent blocks", false, false)
INITIALIZE_PASS_END(IndependentBlocks, "polly-independent",
"Polly - Create independent blocks", false, false)
Pass *polly::createIndependentBlocksPass() {
return new IndependentBlocks();