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clang-p2996/llvm/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
Chandler Carruth 2946cd7010 Update the file headers across all of the LLVM projects in the monorepo
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
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llvm-svn: 351636
2019-01-19 08:50:56 +00:00

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18 KiB
C++

//===------ 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;
}