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//===- HexagonVectorLoopCarriedReuse.cpp ----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass removes the computation of provably redundant expressions that have
// been computed earlier in a previous iteration. It relies on the use of PHIs
// to identify loop carried dependences. This is scalar replacement for vector
// types.
//
//===----------------------------------------------------------------------===//
#include "HexagonVectorLoopCarriedReuse.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/IntrinsicsHexagon.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <map>
#include <memory>
#include <set>
using namespace llvm;
#define DEBUG_TYPE "hexagon-vlcr"
STATISTIC(HexagonNumVectorLoopCarriedReuse,
"Number of values that were reused from a previous iteration.");
static cl::opt<int> HexagonVLCRIterationLim(
"hexagon-vlcr-iteration-lim", cl::Hidden,
cl::desc("Maximum distance of loop carried dependences that are handled"),
cl::init(2));
namespace llvm {
void initializeHexagonVectorLoopCarriedReuseLegacyPassPass(PassRegistry &);
Pass *createHexagonVectorLoopCarriedReuseLegacyPass();
} // end namespace llvm
namespace {
// See info about DepChain in the comments at the top of this file.
using ChainOfDependences = SmallVector<Instruction *, 4>;
class DepChain {
ChainOfDependences Chain;
public:
bool isIdentical(DepChain &Other) const {
if (Other.size() != size())
return false;
ChainOfDependences &OtherChain = Other.getChain();
for (int i = 0; i < size(); ++i) {
if (Chain[i] != OtherChain[i])
return false;
}
return true;
}
ChainOfDependences &getChain() {
return Chain;
}
int size() const {
return Chain.size();
}
void clear() {
Chain.clear();
}
void push_back(Instruction *I) {
Chain.push_back(I);
}
int iterations() const {
return size() - 1;
}
Instruction *front() const {
return Chain.front();
}
Instruction *back() const {
return Chain.back();
}
Instruction *&operator[](const int index) {
return Chain[index];
}
friend raw_ostream &operator<< (raw_ostream &OS, const DepChain &D);
};
LLVM_ATTRIBUTE_UNUSED
raw_ostream &operator<<(raw_ostream &OS, const DepChain &D) {
const ChainOfDependences &CD = D.Chain;
int ChainSize = CD.size();
OS << "**DepChain Start::**\n";
for (int i = 0; i < ChainSize -1; ++i) {
OS << *(CD[i]) << " -->\n";
}
OS << *CD[ChainSize-1] << "\n";
return OS;
}
struct ReuseValue {
Instruction *Inst2Replace = nullptr;
// In the new PHI node that we'll construct this is the value that'll be
// used over the backedge. This is the value that gets reused from a
// previous iteration.
Instruction *BackedgeInst = nullptr;
std::map<Instruction *, DepChain *> DepChains;
int Iterations = -1;
ReuseValue() = default;
void reset() {
Inst2Replace = nullptr;
BackedgeInst = nullptr;
DepChains.clear();
Iterations = -1;
}
bool isDefined() { return Inst2Replace != nullptr; }
};
LLVM_ATTRIBUTE_UNUSED
raw_ostream &operator<<(raw_ostream &OS, const ReuseValue &RU) {
OS << "** ReuseValue ***\n";
OS << "Instruction to Replace: " << *(RU.Inst2Replace) << "\n";
OS << "Backedge Instruction: " << *(RU.BackedgeInst) << "\n";
return OS;
}
class HexagonVectorLoopCarriedReuseLegacyPass : public LoopPass {
public:
static char ID;
explicit HexagonVectorLoopCarriedReuseLegacyPass() : LoopPass(ID) {
PassRegistry *PR = PassRegistry::getPassRegistry();
initializeHexagonVectorLoopCarriedReuseLegacyPassPass(*PR);
}
StringRef getPassName() const override {
return "Hexagon-specific loop carried reuse for HVX vectors";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
AU.setPreservesCFG();
}
bool runOnLoop(Loop *L, LPPassManager &LPM) override;
};
class HexagonVectorLoopCarriedReuse {
public:
HexagonVectorLoopCarriedReuse(Loop *L) : CurLoop(L){};
bool run();
private:
SetVector<DepChain *> Dependences;
std::set<Instruction *> ReplacedInsts;
Loop *CurLoop;
ReuseValue ReuseCandidate;
bool doVLCR();
void findLoopCarriedDeps();
void findValueToReuse();
void findDepChainFromPHI(Instruction *I, DepChain &D);
void reuseValue();
Value *findValueInBlock(Value *Op, BasicBlock *BB);
DepChain *getDepChainBtwn(Instruction *I1, Instruction *I2, int Iters);
bool isEquivalentOperation(Instruction *I1, Instruction *I2);
bool canReplace(Instruction *I);
bool isCallInstCommutative(CallInst *C);
};
} // end anonymous namespace
char HexagonVectorLoopCarriedReuseLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(HexagonVectorLoopCarriedReuseLegacyPass, "hexagon-vlcr",
"Hexagon-specific predictive commoning for HVX vectors",
false, false)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass)
INITIALIZE_PASS_END(HexagonVectorLoopCarriedReuseLegacyPass, "hexagon-vlcr",
"Hexagon-specific predictive commoning for HVX vectors",
false, false)
PreservedAnalyses
HexagonVectorLoopCarriedReusePass::run(Loop &L, LoopAnalysisManager &LAM,
LoopStandardAnalysisResults &AR,
LPMUpdater &U) {
HexagonVectorLoopCarriedReuse Vlcr(&L);
if (!Vlcr.run())
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
bool HexagonVectorLoopCarriedReuseLegacyPass::runOnLoop(Loop *L,
LPPassManager &LPM) {
if (skipLoop(L))
return false;
HexagonVectorLoopCarriedReuse Vlcr(L);
return Vlcr.run();
}
bool HexagonVectorLoopCarriedReuse::run() {
if (!CurLoop->getLoopPreheader())
return false;
// Work only on innermost loops.
if (!CurLoop->getSubLoops().empty())
return false;
// Work only on single basic blocks loops.
if (CurLoop->getNumBlocks() != 1)
return false;
return doVLCR();
}
bool HexagonVectorLoopCarriedReuse::isCallInstCommutative(CallInst *C) {
switch (C->getCalledFunction()->getIntrinsicID()) {
case Intrinsic::hexagon_V6_vaddb:
case Intrinsic::hexagon_V6_vaddb_128B:
case Intrinsic::hexagon_V6_vaddh:
case Intrinsic::hexagon_V6_vaddh_128B:
case Intrinsic::hexagon_V6_vaddw:
case Intrinsic::hexagon_V6_vaddw_128B:
case Intrinsic::hexagon_V6_vaddubh:
case Intrinsic::hexagon_V6_vaddubh_128B:
case Intrinsic::hexagon_V6_vadduhw:
case Intrinsic::hexagon_V6_vadduhw_128B:
case Intrinsic::hexagon_V6_vaddhw:
case Intrinsic::hexagon_V6_vaddhw_128B:
case Intrinsic::hexagon_V6_vmaxb:
case Intrinsic::hexagon_V6_vmaxb_128B:
case Intrinsic::hexagon_V6_vmaxh:
case Intrinsic::hexagon_V6_vmaxh_128B:
case Intrinsic::hexagon_V6_vmaxw:
case Intrinsic::hexagon_V6_vmaxw_128B:
case Intrinsic::hexagon_V6_vmaxub:
case Intrinsic::hexagon_V6_vmaxub_128B:
case Intrinsic::hexagon_V6_vmaxuh:
case Intrinsic::hexagon_V6_vmaxuh_128B:
case Intrinsic::hexagon_V6_vminub:
case Intrinsic::hexagon_V6_vminub_128B:
case Intrinsic::hexagon_V6_vminuh:
case Intrinsic::hexagon_V6_vminuh_128B:
case Intrinsic::hexagon_V6_vminb:
case Intrinsic::hexagon_V6_vminb_128B:
case Intrinsic::hexagon_V6_vminh:
case Intrinsic::hexagon_V6_vminh_128B:
case Intrinsic::hexagon_V6_vminw:
case Intrinsic::hexagon_V6_vminw_128B:
case Intrinsic::hexagon_V6_vmpyub:
case Intrinsic::hexagon_V6_vmpyub_128B:
case Intrinsic::hexagon_V6_vmpyuh:
case Intrinsic::hexagon_V6_vmpyuh_128B:
case Intrinsic::hexagon_V6_vavgub:
case Intrinsic::hexagon_V6_vavgub_128B:
case Intrinsic::hexagon_V6_vavgh:
case Intrinsic::hexagon_V6_vavgh_128B:
case Intrinsic::hexagon_V6_vavguh:
case Intrinsic::hexagon_V6_vavguh_128B:
case Intrinsic::hexagon_V6_vavgw:
case Intrinsic::hexagon_V6_vavgw_128B:
case Intrinsic::hexagon_V6_vavgb:
case Intrinsic::hexagon_V6_vavgb_128B:
case Intrinsic::hexagon_V6_vavguw:
case Intrinsic::hexagon_V6_vavguw_128B:
case Intrinsic::hexagon_V6_vabsdiffh:
case Intrinsic::hexagon_V6_vabsdiffh_128B:
case Intrinsic::hexagon_V6_vabsdiffub:
case Intrinsic::hexagon_V6_vabsdiffub_128B:
case Intrinsic::hexagon_V6_vabsdiffuh:
case Intrinsic::hexagon_V6_vabsdiffuh_128B:
case Intrinsic::hexagon_V6_vabsdiffw:
case Intrinsic::hexagon_V6_vabsdiffw_128B:
return true;
default:
return false;
}
}
bool HexagonVectorLoopCarriedReuse::isEquivalentOperation(Instruction *I1,
Instruction *I2) {
if (!I1->isSameOperationAs(I2))
return false;
// This check is in place specifically for intrinsics. isSameOperationAs will
// return two for any two hexagon intrinsics because they are essentially the
// same instruciton (CallInst). We need to scratch the surface to see if they
// are calls to the same function.
if (CallInst *C1 = dyn_cast<CallInst>(I1)) {
if (CallInst *C2 = dyn_cast<CallInst>(I2)) {
if (C1->getCalledFunction() != C2->getCalledFunction())
return false;
}
}
// If both the Instructions are of Vector Type and any of the element
// is integer constant, check their values too for equivalence.
if (I1->getType()->isVectorTy() && I2->getType()->isVectorTy()) {
unsigned NumOperands = I1->getNumOperands();
for (unsigned i = 0; i < NumOperands; ++i) {
ConstantInt *C1 = dyn_cast<ConstantInt>(I1->getOperand(i));
ConstantInt *C2 = dyn_cast<ConstantInt>(I2->getOperand(i));
if(!C1) continue;
assert(C2);
if (C1->getSExtValue() != C2->getSExtValue())
return false;
}
}
return true;
}
bool HexagonVectorLoopCarriedReuse::canReplace(Instruction *I) {
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
if (!II)
return true;
switch (II->getIntrinsicID()) {
case Intrinsic::hexagon_V6_hi:
case Intrinsic::hexagon_V6_lo:
case Intrinsic::hexagon_V6_hi_128B:
case Intrinsic::hexagon_V6_lo_128B:
LLVM_DEBUG(dbgs() << "Not considering for reuse: " << *II << "\n");
return false;
default:
return true;
}
}
void HexagonVectorLoopCarriedReuse::findValueToReuse() {
for (auto *D : Dependences) {
LLVM_DEBUG(dbgs() << "Processing dependence " << *(D->front()) << "\n");
if (D->iterations() > HexagonVLCRIterationLim) {
LLVM_DEBUG(
dbgs()
<< ".. Skipping because number of iterations > than the limit\n");
continue;
}
PHINode *PN = cast<PHINode>(D->front());
Instruction *BEInst = D->back();
int Iters = D->iterations();
BasicBlock *BB = PN->getParent();
LLVM_DEBUG(dbgs() << "Checking if any uses of " << *PN
<< " can be reused\n");
SmallVector<Instruction *, 4> PNUsers;
for (Use &U : PN->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
if (User->getParent() != BB)
continue;
if (ReplacedInsts.count(User)) {
LLVM_DEBUG(dbgs() << *User
<< " has already been replaced. Skipping...\n");
continue;
}
if (isa<PHINode>(User))
continue;
if (User->mayHaveSideEffects())
continue;
if (!canReplace(User))
continue;
PNUsers.push_back(User);
}
LLVM_DEBUG(dbgs() << PNUsers.size() << " use(s) of the PHI in the block\n");
// For each interesting use I of PN, find an Instruction BEUser that
// performs the same operation as I on BEInst and whose other operands,
// if any, can also be rematerialized in OtherBB. We stop when we find the
// first such Instruction BEUser. This is because once BEUser is
// rematerialized in OtherBB, we may find more such "fixup" opportunities
// in this block. So, we'll start over again.
for (Instruction *I : PNUsers) {
for (Use &U : BEInst->uses()) {
Instruction *BEUser = cast<Instruction>(U.getUser());
if (BEUser->getParent() != BB)
continue;
if (!isEquivalentOperation(I, BEUser))
continue;
int NumOperands = I->getNumOperands();
// Take operands of each PNUser one by one and try to find DepChain
// with every operand of the BEUser. If any of the operands of BEUser
// has DepChain with current operand of the PNUser, break the matcher
// loop. Keep doing this for Every PNUser operand. If PNUser operand
// does not have DepChain with any of the BEUser operand, break the
// outer matcher loop, mark the BEUser as null and reset the ReuseCandidate.
// This ensures that DepChain exist for all the PNUser operand with
// BEUser operand. This also ensures that DepChains are independent of
// the positions in PNUser and BEUser.
std::map<Instruction *, DepChain *> DepChains;
CallInst *C1 = dyn_cast<CallInst>(I);
if ((I && I->isCommutative()) || (C1 && isCallInstCommutative(C1))) {
bool Found = false;
for (int OpNo = 0; OpNo < NumOperands; ++OpNo) {
Value *Op = I->getOperand(OpNo);
Instruction *OpInst = dyn_cast<Instruction>(Op);
Found = false;
for (int T = 0; T < NumOperands; ++T) {
Value *BEOp = BEUser->getOperand(T);
Instruction *BEOpInst = dyn_cast<Instruction>(BEOp);
if (!OpInst && !BEOpInst) {
if (Op == BEOp) {
Found = true;
break;
}
}
if ((OpInst && !BEOpInst) || (!OpInst && BEOpInst))
continue;
DepChain *D = getDepChainBtwn(OpInst, BEOpInst, Iters);
if (D) {
Found = true;
DepChains[OpInst] = D;
break;
}
}
if (!Found) {
BEUser = nullptr;
break;
}
}
} else {
for (int OpNo = 0; OpNo < NumOperands; ++OpNo) {
Value *Op = I->getOperand(OpNo);
Value *BEOp = BEUser->getOperand(OpNo);
Instruction *OpInst = dyn_cast<Instruction>(Op);
if (!OpInst) {
if (Op == BEOp)
continue;
// Do not allow reuse to occur when the operands may be different
// values.
BEUser = nullptr;
break;
}
Instruction *BEOpInst = dyn_cast<Instruction>(BEOp);
DepChain *D = getDepChainBtwn(OpInst, BEOpInst, Iters);
if (D) {
DepChains[OpInst] = D;
} else {
BEUser = nullptr;
break;
}
}
}
if (BEUser) {
LLVM_DEBUG(dbgs() << "Found Value for reuse.\n");
ReuseCandidate.Inst2Replace = I;
ReuseCandidate.BackedgeInst = BEUser;
ReuseCandidate.DepChains = DepChains;
ReuseCandidate.Iterations = Iters;
return;
}
ReuseCandidate.reset();
}
}
}
ReuseCandidate.reset();
}
Value *HexagonVectorLoopCarriedReuse::findValueInBlock(Value *Op,
BasicBlock *BB) {
PHINode *PN = dyn_cast<PHINode>(Op);
assert(PN);
Value *ValueInBlock = PN->getIncomingValueForBlock(BB);
return ValueInBlock;
}
void HexagonVectorLoopCarriedReuse::reuseValue() {
LLVM_DEBUG(dbgs() << ReuseCandidate);
Instruction *Inst2Replace = ReuseCandidate.Inst2Replace;
Instruction *BEInst = ReuseCandidate.BackedgeInst;
int NumOperands = Inst2Replace->getNumOperands();
std::map<Instruction *, DepChain *> &DepChains = ReuseCandidate.DepChains;
int Iterations = ReuseCandidate.Iterations;
BasicBlock *LoopPH = CurLoop->getLoopPreheader();
assert(!DepChains.empty() && "No DepChains");
LLVM_DEBUG(dbgs() << "reuseValue is making the following changes\n");
SmallVector<Instruction *, 4> InstsInPreheader;
for (int i = 0; i < Iterations; ++i) {
Instruction *InstInPreheader = Inst2Replace->clone();
SmallVector<Value *, 4> Ops;
for (int j = 0; j < NumOperands; ++j) {
Instruction *I = dyn_cast<Instruction>(Inst2Replace->getOperand(j));
if (!I)
continue;
// Get the DepChain corresponding to this operand.
DepChain &D = *DepChains[I];
// Get the PHI for the iteration number and find
// the incoming value from the Loop Preheader for
// that PHI.
Value *ValInPreheader = findValueInBlock(D[i], LoopPH);
InstInPreheader->setOperand(j, ValInPreheader);
}
InstsInPreheader.push_back(InstInPreheader);
InstInPreheader->setName(Inst2Replace->getName() + ".hexagon.vlcr");
InstInPreheader->insertBefore(LoopPH->getTerminator());
LLVM_DEBUG(dbgs() << "Added " << *InstInPreheader << " to "
<< LoopPH->getName() << "\n");
}
BasicBlock *BB = BEInst->getParent();
IRBuilder<> IRB(BB);
IRB.SetInsertPoint(BB, BB->getFirstNonPHIIt());
Value *BEVal = BEInst;
PHINode *NewPhi;
for (int i = Iterations-1; i >=0 ; --i) {
Instruction *InstInPreheader = InstsInPreheader[i];
NewPhi = IRB.CreatePHI(InstInPreheader->getType(), 2);
NewPhi->addIncoming(InstInPreheader, LoopPH);
NewPhi->addIncoming(BEVal, BB);
LLVM_DEBUG(dbgs() << "Adding " << *NewPhi << " to " << BB->getName()
<< "\n");
BEVal = NewPhi;
}
// We are in LCSSA form. So, a value defined inside the Loop is used only
// inside the loop. So, the following is safe.
Inst2Replace->replaceAllUsesWith(NewPhi);
ReplacedInsts.insert(Inst2Replace);
++HexagonNumVectorLoopCarriedReuse;
}
bool HexagonVectorLoopCarriedReuse::doVLCR() {
assert(CurLoop->getSubLoops().empty() &&
"Can do VLCR on the innermost loop only");
assert((CurLoop->getNumBlocks() == 1) &&
"Can do VLCR only on single block loops");
bool Changed = false;
bool Continue;
LLVM_DEBUG(dbgs() << "Working on Loop: " << *CurLoop->getHeader() << "\n");
do {
// Reset datastructures.
Dependences.clear();
Continue = false;
findLoopCarriedDeps();
findValueToReuse();
if (ReuseCandidate.isDefined()) {
reuseValue();
Changed = true;
Continue = true;
}
llvm::for_each(Dependences, std::default_delete<DepChain>());
} while (Continue);
return Changed;
}
void HexagonVectorLoopCarriedReuse::findDepChainFromPHI(Instruction *I,
DepChain &D) {
PHINode *PN = dyn_cast<PHINode>(I);
if (!PN) {
D.push_back(I);
return;
} else {
auto NumIncomingValues = PN->getNumIncomingValues();
if (NumIncomingValues != 2) {
D.clear();
return;
}
BasicBlock *BB = PN->getParent();
if (BB != CurLoop->getHeader()) {
D.clear();
return;
}
Value *BEVal = PN->getIncomingValueForBlock(BB);
Instruction *BEInst = dyn_cast<Instruction>(BEVal);
// This is a single block loop with a preheader, so at least
// one value should come over the backedge.
assert(BEInst && "There should be a value over the backedge");
Value *PreHdrVal =
PN->getIncomingValueForBlock(CurLoop->getLoopPreheader());
if(!PreHdrVal || !isa<Instruction>(PreHdrVal)) {
D.clear();
return;
}
D.push_back(PN);
findDepChainFromPHI(BEInst, D);
}
}
DepChain *HexagonVectorLoopCarriedReuse::getDepChainBtwn(Instruction *I1,
Instruction *I2,
int Iters) {
for (auto *D : Dependences) {
if (D->front() == I1 && D->back() == I2 && D->iterations() == Iters)
return D;
}
return nullptr;
}
void HexagonVectorLoopCarriedReuse::findLoopCarriedDeps() {
BasicBlock *BB = CurLoop->getHeader();
for (auto I = BB->begin(), E = BB->end(); I != E && isa<PHINode>(I); ++I) {
auto *PN = cast<PHINode>(I);
if (!isa<VectorType>(PN->getType()))
continue;
DepChain *D = new DepChain();
findDepChainFromPHI(PN, *D);
if (D->size() != 0)
Dependences.insert(D);
else
delete D;
}
LLVM_DEBUG(dbgs() << "Found " << Dependences.size() << " dependences\n");
LLVM_DEBUG(for (const DepChain *D : Dependences) dbgs() << *D << "\n";);
}
Pass *llvm::createHexagonVectorLoopCarriedReuseLegacyPass() {
return new HexagonVectorLoopCarriedReuseLegacyPass();
}