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llvm-mirror/lib/Target/Hexagon/HexagonVectorLoopCarriedReuse.cpp
Pengxuan Zheng acbb48020d [Hexagon] Make HexagonVLCR compatibile with New PM 
The patch modifies HexagonVectorLoopCarriedReuse pass to make it compatible with both Legacy Pass Manager through HexagonVectorLoopCarriedReuseLegacyPass and with New Pass Manager through HexagonVectorLoopCarriedReusePass.

Reviewed By: pzheng

Differential Revision: https://reviews.llvm.org/D86955
2020-09-21 13:45:12 -07:00

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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), cl::ZeroOrMore);
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 (auto UI = PN->use_begin(), E = PN->use_end(); UI != E; ++UI) {
Use &U = *UI;
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 (auto UI = BEInst->use_begin(), E = BEInst->use_end(); UI != E;
++UI) {
Use &U = *UI;
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->getFirstNonPHI());
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 (size_t i = 0; i < Dependences.size();
++i) { dbgs() << *Dependences[i] << "\n"; });
}
Pass *llvm::createHexagonVectorLoopCarriedReuseLegacyPass() {
return new HexagonVectorLoopCarriedReuseLegacyPass();
}
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