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llvm-project/polly/lib/Transform/IndependentBlocks.cpp

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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/CodeGen/BlockGenerators.h"
#include "polly/Options.h"
#include "polly/ScopDetection.h"
#include "polly/Support/ScopHelper.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/DominanceFrontier.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/Local.h"
#include <vector>
using namespace polly;
using namespace llvm;
#define DEBUG_TYPE "polly-independent"
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);
//===--------------------------------------------------------------------===//
/// 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;
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() || Inst->mayWriteToMemory())
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()) {
CurInst->insertBefore(InsertPos);
SE->forgetValue(CurInst);
}
WorkStack.pop_back();
} else {
// for each node N,
Instruction *Operand = dyn_cast<Instruction>(*It);
++WorkStack.back().second;
// 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 operands 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");
continue;
}
if (canSynthesize(Operand, LI, SE, R)) {
DEBUG(dbgs() << "is IV.\n");
continue;
}
// We can not move the operand, a non trivial scalar dependence found!
if (!isSafeToMove(Operand)) {
DEBUG(dbgs() << "Can not move!\n");
continue;
}
// Do not need to move instruction if it is 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()));
continue;
}
// 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;
It->set(MovedOp);
SE->forgetValue(MovedOp);
} 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() + ".moved.to." + CurBB->getName());
DEBUG(dbgs() << "Move to " << *NewOp << "\n");
It->set(NewOp);
ReplacedMap.insert(std::make_pair(Operand, NewOp));
SE->forgetValue(Operand);
// 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()));
}
}
}
SE->forgetValue(Inst);
}
bool IndependentBlocks::createIndependentBlocks(BasicBlock *BB,
const Region *R) {
std::vector<Instruction *> WorkList;
for (Instruction &Inst : *BB)
if (!isSafeToMove(&Inst) && !canSynthesize(&Inst, LI, SE, R))
WorkList.push_back(&Inst);
ReplacedMapType ReplacedMap;
Instruction *InsertPos = BB->getFirstNonPHIOrDbg();
for (Instruction *Inst : WorkList)
if (!isa<PHINode>(Inst))
moveOperandTree(Inst, 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 (BasicBlock *BB : R->blocks())
Changed |= createIndependentBlocks(BB, R);
return Changed;
}
bool IndependentBlocks::eliminateDeadCode(const Region *R) {
std::vector<Instruction *> WorkList;
// Find all trivially dead instructions.
for (BasicBlock *BB : R->blocks())
for (Instruction &Inst : *BB)
if (!isIgnoredIntrinsic(&Inst) && isInstructionTriviallyDead(&Inst))
WorkList.push_back(&Inst);
if (WorkList.empty())
return false;
// Delete them so the cross BB scalar dependences come with them will
// also be eliminated.
while (!WorkList.empty()) {
RecursivelyDeleteTriviallyDeadInstructions(WorkList.back());
WorkList.pop_back();
}
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::isIndependentBlock(const Region *R,
BasicBlock *BB) const {
for (Instruction &Inst : *BB) {
if (canSynthesize(&Inst, LI, SE, R))
continue;
if (isIgnoredIntrinsic(&Inst))
continue;
// A value inside the Scop is referenced outside.
for (User *U : Inst.users()) {
if (isEscapeUse(U, R)) {
DEBUG(dbgs() << "Instruction not independent:\n");
DEBUG(dbgs() << "Instruction used outside the Scop!\n");
DEBUG(Inst.print(dbgs()));
DEBUG(dbgs() << "\n");
return false;
}
}
}
return true;
}
bool IndependentBlocks::areAllBlocksIndependent(const Region *R) const {
for (BasicBlock *BB : R->blocks())
if (!isIndependentBlock(R, BB))
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"?
AU.addPreserved<AAResultsWrapperPass>();
AU.addPreserved<BasicAAWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<DominanceFrontier>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<PostDominatorTree>();
AU.addRequired<RegionInfoPass>();
AU.addPreserved<RegionInfoPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addPreserved<ScalarEvolutionWrapperPass>();
AU.addPreserved<SCEVAAWrapperPass>();
AU.addRequired<ScopDetection>();
AU.addPreserved<ScopDetection>();
}
bool IndependentBlocks::runOnFunction(llvm::Function &F) {
bool Changed = false;
RI = &getAnalysis<RegionInfoPass>().getRegionInfo();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
SD = &getAnalysis<ScopDetection>();
SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
AllocaBlock = &F.getEntryBlock();
DEBUG(dbgs() << "Run IndepBlock on " << F.getName() << '\n');
for (const Region *R : *SD) {
Changed |= createIndependentBlocks(R);
Changed |= eliminateDeadCode(R);
}
verifyAnalysis();
return Changed;
}
void IndependentBlocks::verifyAnalysis() const {}
void IndependentBlocks::verifyScop(const Region *R) const {
assert(areAllBlocksIndependent(R) && "Cannot generate independent blocks");
}
char IndependentBlocks::ID = 0;
char &polly::IndependentBlocksID = IndependentBlocks::ID;
Pass *polly::createIndependentBlocksPass() { return new IndependentBlocks(); }
INITIALIZE_PASS_BEGIN(IndependentBlocks, "polly-independent",
"Polly - Create independent blocks", false, false);
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
INITIALIZE_PASS_DEPENDENCY(RegionInfoPass);
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass);
INITIALIZE_PASS_DEPENDENCY(ScopDetection);
INITIALIZE_PASS_END(IndependentBlocks, "polly-independent",
"Polly - Create independent blocks", false, false)
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