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

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//===------ PPCLoopPreIncPrep.cpp - Loop Pre-Inc. AM Prep. Pass -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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 "PPCTargetMachine.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
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"));
namespace llvm {
void initializePPCLoopPreIncPrepPass(PassRegistry&);
}
namespace {
class PPCLoopPreIncPrep : public FunctionPass {
public:
static char ID; // Pass ID, replacement for typeid
PPCLoopPreIncPrep() : FunctionPass(ID), TM(nullptr) {
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<ScalarEvolution>();
}
bool runOnFunction(Function &F) override;
bool runOnLoop(Loop *L);
void simplifyLoopLatch(Loop *L);
bool rotateLoop(Loop *L);
private:
PPCTargetMachine *TM;
LoopInfo *LI;
ScalarEvolution *SE;
};
}
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(ScalarEvolution)
INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
return new PPCLoopPreIncPrep(TM);
}
namespace {
struct SCEVLess : std::binary_function<const SCEV *, const SCEV *, bool>
{
SCEVLess(ScalarEvolution *SE) : SE(SE) {}
bool operator() (const SCEV *X, const SCEV *Y) const {
const SCEV *Diff = SE->getMinusSCEV(X, Y);
return cast<SCEVConstant>(Diff)->getValue()->getSExtValue() < 0;
}
protected:
ScalarEvolution *SE;
};
}
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 0;
}
bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
SE = &getAnalysis<ScalarEvolution>();
bool MadeChange = false;
for (LoopInfo::iterator I = LI->begin(), E = LI->end();
I != E; ++I) {
Loop *L = *I;
MadeChange |= runOnLoop(L);
}
return MadeChange;
}
bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
bool MadeChange = false;
// Only prep. the inner-most loop
if (!L->empty())
return MadeChange;
BasicBlock *Header = L->getHeader();
const PPCSubtarget *ST =
TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
unsigned HeaderLoopPredCount = 0;
for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
PI != PE; ++PI) {
++HeaderLoopPredCount;
}
// Collect buckets of comparable addresses used by loads and stores.
typedef std::multimap<const SCEV *, Instruction *, SCEVLess> Bucket;
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->getSCEV(PtrValue);
if (!isa<SCEVAddRecExpr>(LSCEV))
continue;
bool FoundBucket = false;
for (unsigned i = 0, e = Buckets.size(); i != e; ++i)
for (Bucket::iterator K = Buckets[i].begin(), KE = Buckets[i].end();
K != KE; ++K) {
const SCEV *Diff = SE->getMinusSCEV(K->first, LSCEV);
if (isa<SCEVConstant>(Diff)) {
Buckets[i].insert(std::make_pair(LSCEV, MemI));
FoundBucket = true;
break;
}
}
if (!FoundBucket) {
Buckets.push_back(Bucket(SCEVLess(SE)));
Buckets[Buckets.size()-1].insert(std::make_pair(LSCEV, MemI));
}
}
}
if (Buckets.empty() || Buckets.size() > MaxVars)
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, this);
if (!LoopPredecessor)
return MadeChange;
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.
const SCEVAddRecExpr *BasePtrSCEV =
cast<SCEVAddRecExpr>(Buckets[i].begin()->first);
if (!BasePtrSCEV->isAffine())
continue;
Instruction *MemI = Buckets[i].begin()->second;
Value *BasePtr = GetPointerOperand(MemI);
assert(BasePtr && "No pointer operand");
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;
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(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);
Value *LastNewPtr = NewBasePtr;
for (Bucket::iterator I = std::next(Buckets[i].begin()),
IE = Buckets[i].end(); I != IE; ++I) {
Value *Ptr = GetPointerOperand(I->second);
assert(Ptr && "No pointer operand");
if (Ptr == LastNewPtr)
continue;
Instruction *RealNewPtr;
const SCEVConstant *Diff =
cast<SCEVConstant>(SE->getMinusSCEV(I->first, BasePtrSCEV));
if (Diff->isZero()) {
RealNewPtr = NewBasePtr;
} else {
Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
if (PtrIP && isa<Instruction>(NewBasePtr) &&
cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
PtrIP = 0;
else if (isa<PHINode>(PtrIP))
PtrIP = PtrIP->getParent()->getFirstInsertionPt();
else if (!PtrIP)
PtrIP = I->second;
GetElementPtrInst *NewPtr =
GetElementPtrInst::Create(PtrInc, Diff->getValue(),
I->second->hasName() ? I->second->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);
LastNewPtr = 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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