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llvm-project/llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp

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//===------ PPCLoopPreIncPrep.cpp - Loop Pre-Inc. AM Prep. Pass -----------===//
//
// 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 file implements a pass to prepare loops for pre-increment addressing
// modes. Additional PHIs are created for loop induction variables used by
// load/store instructions so that the pre-increment forms can be used.
// Generically, this means transforming loops like this:
// for (int i = 0; i < n; ++i)
// array[i] = c;
// to look like this:
// T *p = array[-1];
// for (int i = 0; i < n; ++i)
// *++p = c;
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ppc-loop-preinc-prep"
#include "PPC.h"
#include "PPCSubtarget.h"
#include "PPCTargetMachine.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include <cassert>
#include <iterator>
#include <utility>
using namespace llvm;
// By default, we limit this to creating 16 PHIs (which is a little over half
// of the allocatable register set).
static cl::opt<unsigned> MaxVars("ppc-preinc-prep-max-vars",
cl::Hidden, cl::init(16),
cl::desc("Potential PHI threshold for PPC preinc loop prep"));
STATISTIC(PHINodeAlreadyExists, "PHI node already in pre-increment form");
namespace llvm {
void initializePPCLoopPreIncPrepPass(PassRegistry&);
} // end namespace llvm
namespace {
class PPCLoopPreIncPrep : public FunctionPass {
public:
static char ID; // Pass ID, replacement for typeid
PPCLoopPreIncPrep() : FunctionPass(ID) {
initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
}
PPCLoopPreIncPrep(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequired<ScalarEvolutionWrapperPass>();
}
bool alreadyPrepared(Loop *L, Instruction* MemI,
const SCEV *BasePtrStartSCEV,
const SCEVConstant *BasePtrIncSCEV);
bool runOnFunction(Function &F) override;
bool runOnLoop(Loop *L);
void simplifyLoopLatch(Loop *L);
bool rotateLoop(Loop *L);
private:
PPCTargetMachine *TM = nullptr;
DominatorTree *DT;
LoopInfo *LI;
ScalarEvolution *SE;
bool PreserveLCSSA;
};
} // end anonymous namespace
char PPCLoopPreIncPrep::ID = 0;
static const char *name = "Prepare loop for pre-inc. addressing modes";
INITIALIZE_PASS_BEGIN(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
return new PPCLoopPreIncPrep(TM);
}
namespace {
struct BucketElement {
BucketElement(const SCEVConstant *O, Instruction *I) : Offset(O), Instr(I) {}
BucketElement(Instruction *I) : Offset(nullptr), Instr(I) {}
const SCEVConstant *Offset;
Instruction *Instr;
};
struct Bucket {
Bucket(const SCEV *B, Instruction *I) : BaseSCEV(B),
Elements(1, BucketElement(I)) {}
const SCEV *BaseSCEV;
SmallVector<BucketElement, 16> Elements;
};
} // end anonymous namespace
static bool IsPtrInBounds(Value *BasePtr) {
Value *StrippedBasePtr = BasePtr;
while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr))
StrippedBasePtr = BC->getOperand(0);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr))
return GEP->isInBounds();
return false;
}
static Value *GetPointerOperand(Value *MemI) {
if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) {
return LMemI->getPointerOperand();
} else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) {
return SMemI->getPointerOperand();
} else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) {
if (IMemI->getIntrinsicID() == Intrinsic::prefetch)
return IMemI->getArgOperand(0);
}
return nullptr;
}
bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
DT = DTWP ? &DTWP->getDomTree() : nullptr;
PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
bool MadeChange = false;
for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
MadeChange |= runOnLoop(*L);
return MadeChange;
}
// In order to prepare for the pre-increment a PHI is added.
// This function will check to see if that PHI already exists and will return
// true if it found an existing PHI with the same start and increment as the
// one we wanted to create.
bool PPCLoopPreIncPrep::alreadyPrepared(Loop *L, Instruction* MemI,
const SCEV *BasePtrStartSCEV,
const SCEVConstant *BasePtrIncSCEV) {
BasicBlock *BB = MemI->getParent();
if (!BB)
return false;
BasicBlock *PredBB = L->getLoopPredecessor();
BasicBlock *LatchBB = L->getLoopLatch();
if (!PredBB || !LatchBB)
return false;
// Run through the PHIs and see if we have some that looks like a preparation
iterator_range<BasicBlock::phi_iterator> PHIIter = BB->phis();
for (auto & CurrentPHI : PHIIter) {
PHINode *CurrentPHINode = dyn_cast<PHINode>(&CurrentPHI);
if (!CurrentPHINode)
continue;
if (!SE->isSCEVable(CurrentPHINode->getType()))
continue;
const SCEV *PHISCEV = SE->getSCEVAtScope(CurrentPHINode, L);
const SCEVAddRecExpr *PHIBasePtrSCEV = dyn_cast<SCEVAddRecExpr>(PHISCEV);
if (!PHIBasePtrSCEV)
continue;
const SCEVConstant *PHIBasePtrIncSCEV =
dyn_cast<SCEVConstant>(PHIBasePtrSCEV->getStepRecurrence(*SE));
if (!PHIBasePtrIncSCEV)
continue;
if (CurrentPHINode->getNumIncomingValues() == 2) {
if ( (CurrentPHINode->getIncomingBlock(0) == LatchBB &&
CurrentPHINode->getIncomingBlock(1) == PredBB) ||
(CurrentPHINode->getIncomingBlock(1) == LatchBB &&
CurrentPHINode->getIncomingBlock(0) == PredBB) ) {
if (PHIBasePtrSCEV->getStart() == BasePtrStartSCEV &&
PHIBasePtrIncSCEV == BasePtrIncSCEV) {
// The existing PHI (CurrentPHINode) has the same start and increment
// as the PHI that we wanted to create.
++PHINodeAlreadyExists;
return true;
}
}
}
}
return false;
}
bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
bool MadeChange = false;
// Only prep. the inner-most loop
if (!L->empty())
return MadeChange;
LLVM_DEBUG(dbgs() << "PIP: Examining: " << *L << "\n");
BasicBlock *Header = L->getHeader();
const PPCSubtarget *ST =
TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
unsigned HeaderLoopPredCount = pred_size(Header);
// Collect buckets of comparable addresses used by loads and stores.
SmallVector<Bucket, 16> Buckets;
for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
I != IE; ++I) {
for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
J != JE; ++J) {
Value *PtrValue;
Instruction *MemI;
if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
MemI = LMemI;
PtrValue = LMemI->getPointerOperand();
} else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
MemI = SMemI;
PtrValue = SMemI->getPointerOperand();
} else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(J)) {
if (IMemI->getIntrinsicID() == Intrinsic::prefetch) {
MemI = IMemI;
PtrValue = IMemI->getArgOperand(0);
} else continue;
} else continue;
unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
if (PtrAddrSpace)
continue;
// There are no update forms for Altivec vector load/stores.
if (ST && ST->hasAltivec() &&
PtrValue->getType()->getPointerElementType()->isVectorTy())
continue;
if (L->isLoopInvariant(PtrValue))
continue;
const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L);
if (const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV)) {
if (LARSCEV->getLoop() != L)
continue;
// See getPreIndexedAddressParts, the displacement for LDU/STDU has to
// be 4's multiple (DS-form). For i64 loads/stores when the displacement
// fits in a 16-bit signed field but isn't a multiple of 4, it will be
// useless and possible to break some original well-form addressing mode
// to make this pre-inc prep for it.
if (PtrValue->getType()->getPointerElementType()->isIntegerTy(64)) {
if (const SCEVConstant *StepConst =
dyn_cast<SCEVConstant>(LARSCEV->getStepRecurrence(*SE))) {
const APInt &ConstInt = StepConst->getValue()->getValue();
if (ConstInt.isSignedIntN(16) && ConstInt.srem(4) != 0)
continue;
}
}
} else {
continue;
}
bool FoundBucket = false;
for (auto &B : Buckets) {
const SCEV *Diff = SE->getMinusSCEV(LSCEV, B.BaseSCEV);
if (const auto *CDiff = dyn_cast<SCEVConstant>(Diff)) {
B.Elements.push_back(BucketElement(CDiff, MemI));
FoundBucket = true;
break;
}
}
if (!FoundBucket) {
if (Buckets.size() == MaxVars)
return MadeChange;
Buckets.push_back(Bucket(LSCEV, MemI));
}
}
}
if (Buckets.empty())
return MadeChange;
BasicBlock *LoopPredecessor = L->getLoopPredecessor();
// If there is no loop predecessor, or the loop predecessor's terminator
// returns a value (which might contribute to determining the loop's
// iteration space), insert a new preheader for the loop.
if (!LoopPredecessor ||
!LoopPredecessor->getTerminator()->getType()->isVoidTy()) {
LoopPredecessor = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA);
if (LoopPredecessor)
MadeChange = true;
}
if (!LoopPredecessor)
return MadeChange;
LLVM_DEBUG(dbgs() << "PIP: Found " << Buckets.size() << " buckets\n");
SmallSet<BasicBlock *, 16> BBChanged;
for (unsigned i = 0, e = Buckets.size(); i != e; ++i) {
// The base address of each bucket is transformed into a phi and the others
// are rewritten as offsets of that variable.
// We have a choice now of which instruction's memory operand we use as the
// base for the generated PHI. Always picking the first instruction in each
// bucket does not work well, specifically because that instruction might
// be a prefetch (and there are no pre-increment dcbt variants). Otherwise,
// the choice is somewhat arbitrary, because the backend will happily
// generate direct offsets from both the pre-incremented and
// post-incremented pointer values. Thus, we'll pick the first non-prefetch
// instruction in each bucket, and adjust the recurrence and other offsets
// accordingly.
for (int j = 0, je = Buckets[i].Elements.size(); j != je; ++j) {
if (auto *II = dyn_cast<IntrinsicInst>(Buckets[i].Elements[j].Instr))
if (II->getIntrinsicID() == Intrinsic::prefetch)
continue;
// If we'd otherwise pick the first element anyway, there's nothing to do.
if (j == 0)
break;
// If our chosen element has no offset from the base pointer, there's
// nothing to do.
if (!Buckets[i].Elements[j].Offset ||
Buckets[i].Elements[j].Offset->isZero())
break;
const SCEV *Offset = Buckets[i].Elements[j].Offset;
Buckets[i].BaseSCEV = SE->getAddExpr(Buckets[i].BaseSCEV, Offset);
for (auto &E : Buckets[i].Elements) {
if (E.Offset)
E.Offset = cast<SCEVConstant>(SE->getMinusSCEV(E.Offset, Offset));
else
E.Offset = cast<SCEVConstant>(SE->getNegativeSCEV(Offset));
}
std::swap(Buckets[i].Elements[j], Buckets[i].Elements[0]);
break;
}
const SCEVAddRecExpr *BasePtrSCEV =
cast<SCEVAddRecExpr>(Buckets[i].BaseSCEV);
if (!BasePtrSCEV->isAffine())
continue;
LLVM_DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n");
assert(BasePtrSCEV->getLoop() == L &&
"AddRec for the wrong loop?");
// The instruction corresponding to the Bucket's BaseSCEV must be the first
// in the vector of elements.
Instruction *MemI = Buckets[i].Elements.begin()->Instr;
Value *BasePtr = GetPointerOperand(MemI);
assert(BasePtr && "No pointer operand");
Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
BasePtr->getType()->getPointerAddressSpace());
const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
continue;
const SCEVConstant *BasePtrIncSCEV =
dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
if (!BasePtrIncSCEV)
continue;
BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
if (!isSafeToExpand(BasePtrStartSCEV, *SE))
continue;
LLVM_DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
if (alreadyPrepared(L, MemI, BasePtrStartSCEV, BasePtrIncSCEV))
continue;
PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
MemI->hasName() ? MemI->getName() + ".phi" : "",
Header->getFirstNonPHI());
SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
LoopPredecessor->getTerminator());
// Note that LoopPredecessor might occur in the predecessor list multiple
// times, and we need to add it the right number of times.
for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
PI != PE; ++PI) {
if (*PI != LoopPredecessor)
continue;
NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
}
Instruction *InsPoint = &*Header->getFirstInsertionPt();
GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint);
PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
PI != PE; ++PI) {
if (*PI == LoopPredecessor)
continue;
NewPHI->addIncoming(PtrInc, *PI);
}
Instruction *NewBasePtr;
if (PtrInc->getType() != BasePtr->getType())
NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint);
else
NewBasePtr = PtrInc;
if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
BBChanged.insert(IDel->getParent());
BasePtr->replaceAllUsesWith(NewBasePtr);
RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
// Keep track of the replacement pointer values we've inserted so that we
// don't generate more pointer values than necessary.
SmallPtrSet<Value *, 16> NewPtrs;
NewPtrs.insert( NewBasePtr);
for (auto I = std::next(Buckets[i].Elements.begin()),
IE = Buckets[i].Elements.end(); I != IE; ++I) {
Value *Ptr = GetPointerOperand(I->Instr);
assert(Ptr && "No pointer operand");
if (NewPtrs.count(Ptr))
continue;
Instruction *RealNewPtr;
if (!I->Offset || I->Offset->getValue()->isZero()) {
RealNewPtr = NewBasePtr;
} else {
Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
if (PtrIP && isa<Instruction>(NewBasePtr) &&
cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
PtrIP = nullptr;
else if (isa<PHINode>(PtrIP))
PtrIP = &*PtrIP->getParent()->getFirstInsertionPt();
else if (!PtrIP)
PtrIP = I->Instr;
GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
I8Ty, PtrInc, I->Offset->getValue(),
I->Instr->hasName() ? I->Instr->getName() + ".off" : "", PtrIP);
if (!PtrIP)
NewPtr->insertAfter(cast<Instruction>(PtrInc));
NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
RealNewPtr = NewPtr;
}
if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
BBChanged.insert(IDel->getParent());
Instruction *ReplNewPtr;
if (Ptr->getType() != RealNewPtr->getType()) {
ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
Ptr->hasName() ? Ptr->getName() + ".cast" : "");
ReplNewPtr->insertAfter(RealNewPtr);
} else
ReplNewPtr = RealNewPtr;
Ptr->replaceAllUsesWith(ReplNewPtr);
RecursivelyDeleteTriviallyDeadInstructions(Ptr);
NewPtrs.insert(RealNewPtr);
}
MadeChange = true;
}
for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
I != IE; ++I) {
if (BBChanged.count(*I))
DeleteDeadPHIs(*I);
}
return MadeChange;
}
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