1 //===------ PPCLoopPreIncPrep.cpp - Loop Pre-Inc. AM Prep. Pass -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements a pass to prepare loops for pre-increment addressing
11 // modes. Additional PHIs are created for loop induction variables used by
12 // load/store instructions so that the pre-increment forms can be used.
13 // Generically, this means transforming loops like this:
14 // for (int i = 0; i < n; ++i)
18 // for (int i = 0; i < n; ++i)
20 //===----------------------------------------------------------------------===//
22 #define DEBUG_TYPE "ppc-loop-preinc-prep"
24 #include "PPCTargetMachine.h"
25 #include "llvm/ADT/DepthFirstIterator.h"
26 #include "llvm/ADT/STLExtras.h"
27 #include "llvm/ADT/SmallSet.h"
28 #include "llvm/ADT/Statistic.h"
29 #include "llvm/Analysis/CodeMetrics.h"
30 #include "llvm/Analysis/InstructionSimplify.h"
31 #include "llvm/Analysis/LoopInfo.h"
32 #include "llvm/Analysis/ScalarEvolution.h"
33 #include "llvm/Analysis/ScalarEvolutionExpander.h"
34 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
35 #include "llvm/Analysis/ValueTracking.h"
36 #include "llvm/IR/CFG.h"
37 #include "llvm/IR/Dominators.h"
38 #include "llvm/IR/Function.h"
39 #include "llvm/IR/IntrinsicInst.h"
40 #include "llvm/IR/Module.h"
41 #include "llvm/Support/CommandLine.h"
42 #include "llvm/Support/Debug.h"
43 #include "llvm/Transforms/Scalar.h"
44 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
45 #include "llvm/Transforms/Utils/Local.h"
46 #include "llvm/Transforms/Utils/LoopUtils.h"
47 #include "llvm/Transforms/Utils/ValueMapper.h"
50 // By default, we limit this to creating 16 PHIs (which is a little over half
51 // of the allocatable register set).
52 static cl::opt<unsigned> MaxVars("ppc-preinc-prep-max-vars",
53 cl::Hidden, cl::init(16),
54 cl::desc("Potential PHI threshold for PPC preinc loop prep"));
57 void initializePPCLoopPreIncPrepPass(PassRegistry&);
62 class PPCLoopPreIncPrep : public FunctionPass {
64 static char ID; // Pass ID, replacement for typeid
65 PPCLoopPreIncPrep() : FunctionPass(ID), TM(nullptr) {
66 initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
68 PPCLoopPreIncPrep(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
69 initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
72 void getAnalysisUsage(AnalysisUsage &AU) const override {
73 AU.addPreserved<DominatorTreeWrapperPass>();
74 AU.addRequired<LoopInfoWrapperPass>();
75 AU.addPreserved<LoopInfoWrapperPass>();
76 AU.addRequired<ScalarEvolutionWrapperPass>();
79 bool runOnFunction(Function &F) override;
81 bool runOnLoop(Loop *L);
82 void simplifyLoopLatch(Loop *L);
83 bool rotateLoop(Loop *L);
94 char PPCLoopPreIncPrep::ID = 0;
95 static const char *name = "Prepare loop for pre-inc. addressing modes";
96 INITIALIZE_PASS_BEGIN(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
97 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
98 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
99 INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
101 FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
102 return new PPCLoopPreIncPrep(TM);
106 struct BucketElement {
107 BucketElement(const SCEVConstant *O, Instruction *I) : Offset(O), Instr(I) {}
108 BucketElement(Instruction *I) : Offset(nullptr), Instr(I) {}
110 const SCEVConstant *Offset;
115 Bucket(const SCEV *B, Instruction *I) : BaseSCEV(B),
116 Elements(1, BucketElement(I)) {}
118 const SCEV *BaseSCEV;
119 SmallVector<BucketElement, 16> Elements;
123 static bool IsPtrInBounds(Value *BasePtr) {
124 Value *StrippedBasePtr = BasePtr;
125 while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr))
126 StrippedBasePtr = BC->getOperand(0);
127 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr))
128 return GEP->isInBounds();
133 static Value *GetPointerOperand(Value *MemI) {
134 if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) {
135 return LMemI->getPointerOperand();
136 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) {
137 return SMemI->getPointerOperand();
138 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) {
139 if (IMemI->getIntrinsicID() == Intrinsic::prefetch)
140 return IMemI->getArgOperand(0);
146 bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
147 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
148 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
149 auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
150 DT = DTWP ? &DTWP->getDomTree() : nullptr;
151 PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
153 bool MadeChange = false;
155 for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
156 for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
157 MadeChange |= runOnLoop(*L);
162 bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
163 bool MadeChange = false;
165 // Only prep. the inner-most loop
169 DEBUG(dbgs() << "PIP: Examining: " << *L << "\n");
171 BasicBlock *Header = L->getHeader();
173 const PPCSubtarget *ST =
174 TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
176 unsigned HeaderLoopPredCount =
177 std::distance(pred_begin(Header), pred_end(Header));
179 // Collect buckets of comparable addresses used by loads and stores.
180 SmallVector<Bucket, 16> Buckets;
181 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
183 for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
188 if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
190 PtrValue = LMemI->getPointerOperand();
191 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
193 PtrValue = SMemI->getPointerOperand();
194 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(J)) {
195 if (IMemI->getIntrinsicID() == Intrinsic::prefetch) {
197 PtrValue = IMemI->getArgOperand(0);
201 unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
205 // There are no update forms for Altivec vector load/stores.
206 if (ST && ST->hasAltivec() &&
207 PtrValue->getType()->getPointerElementType()->isVectorTy())
210 if (L->isLoopInvariant(PtrValue))
213 const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L);
214 if (const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV)) {
215 if (LARSCEV->getLoop() != L)
221 bool FoundBucket = false;
222 for (auto &B : Buckets) {
223 const SCEV *Diff = SE->getMinusSCEV(LSCEV, B.BaseSCEV);
224 if (const auto *CDiff = dyn_cast<SCEVConstant>(Diff)) {
225 B.Elements.push_back(BucketElement(CDiff, MemI));
232 if (Buckets.size() == MaxVars)
234 Buckets.push_back(Bucket(LSCEV, MemI));
242 BasicBlock *LoopPredecessor = L->getLoopPredecessor();
243 // If there is no loop predecessor, or the loop predecessor's terminator
244 // returns a value (which might contribute to determining the loop's
245 // iteration space), insert a new preheader for the loop.
246 if (!LoopPredecessor ||
247 !LoopPredecessor->getTerminator()->getType()->isVoidTy()) {
248 LoopPredecessor = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA);
252 if (!LoopPredecessor)
255 DEBUG(dbgs() << "PIP: Found " << Buckets.size() << " buckets\n");
257 SmallSet<BasicBlock *, 16> BBChanged;
258 for (unsigned i = 0, e = Buckets.size(); i != e; ++i) {
259 // The base address of each bucket is transformed into a phi and the others
260 // are rewritten as offsets of that variable.
262 // We have a choice now of which instruction's memory operand we use as the
263 // base for the generated PHI. Always picking the first instruction in each
264 // bucket does not work well, specifically because that instruction might
265 // be a prefetch (and there are no pre-increment dcbt variants). Otherwise,
266 // the choice is somewhat arbitrary, because the backend will happily
267 // generate direct offsets from both the pre-incremented and
268 // post-incremented pointer values. Thus, we'll pick the first non-prefetch
269 // instruction in each bucket, and adjust the recurrence and other offsets
271 for (int j = 0, je = Buckets[i].Elements.size(); j != je; ++j) {
272 if (auto *II = dyn_cast<IntrinsicInst>(Buckets[i].Elements[j].Instr))
273 if (II->getIntrinsicID() == Intrinsic::prefetch)
276 // If we'd otherwise pick the first element anyway, there's nothing to do.
280 // If our chosen element has no offset from the base pointer, there's
282 if (!Buckets[i].Elements[j].Offset ||
283 Buckets[i].Elements[j].Offset->isZero())
286 const SCEV *Offset = Buckets[i].Elements[j].Offset;
287 Buckets[i].BaseSCEV = SE->getAddExpr(Buckets[i].BaseSCEV, Offset);
288 for (auto &E : Buckets[i].Elements) {
290 E.Offset = cast<SCEVConstant>(SE->getMinusSCEV(E.Offset, Offset));
292 E.Offset = cast<SCEVConstant>(SE->getNegativeSCEV(Offset));
295 std::swap(Buckets[i].Elements[j], Buckets[i].Elements[0]);
299 const SCEVAddRecExpr *BasePtrSCEV =
300 cast<SCEVAddRecExpr>(Buckets[i].BaseSCEV);
301 if (!BasePtrSCEV->isAffine())
304 DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n");
305 assert(BasePtrSCEV->getLoop() == L &&
306 "AddRec for the wrong loop?");
308 // The instruction corresponding to the Bucket's BaseSCEV must be the first
309 // in the vector of elements.
310 Instruction *MemI = Buckets[i].Elements.begin()->Instr;
311 Value *BasePtr = GetPointerOperand(MemI);
312 assert(BasePtr && "No pointer operand");
314 Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
315 Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
316 BasePtr->getType()->getPointerAddressSpace());
318 const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
319 if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
322 const SCEVConstant *BasePtrIncSCEV =
323 dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
326 BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
327 if (!isSafeToExpand(BasePtrStartSCEV, *SE))
330 DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
332 PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
333 MemI->hasName() ? MemI->getName() + ".phi" : "",
334 Header->getFirstNonPHI());
336 SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
337 Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
338 LoopPredecessor->getTerminator());
340 // Note that LoopPredecessor might occur in the predecessor list multiple
341 // times, and we need to add it the right number of times.
342 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
344 if (*PI != LoopPredecessor)
347 NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
350 Instruction *InsPoint = &*Header->getFirstInsertionPt();
351 GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
352 I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
353 MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint);
354 PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
355 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
357 if (*PI == LoopPredecessor)
360 NewPHI->addIncoming(PtrInc, *PI);
363 Instruction *NewBasePtr;
364 if (PtrInc->getType() != BasePtr->getType())
365 NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
366 PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint);
370 if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
371 BBChanged.insert(IDel->getParent());
372 BasePtr->replaceAllUsesWith(NewBasePtr);
373 RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
375 // Keep track of the replacement pointer values we've inserted so that we
376 // don't generate more pointer values than necessary.
377 SmallPtrSet<Value *, 16> NewPtrs;
378 NewPtrs.insert( NewBasePtr);
380 for (auto I = std::next(Buckets[i].Elements.begin()),
381 IE = Buckets[i].Elements.end(); I != IE; ++I) {
382 Value *Ptr = GetPointerOperand(I->Instr);
383 assert(Ptr && "No pointer operand");
384 if (NewPtrs.count(Ptr))
387 Instruction *RealNewPtr;
388 if (!I->Offset || I->Offset->getValue()->isZero()) {
389 RealNewPtr = NewBasePtr;
391 Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
392 if (PtrIP && isa<Instruction>(NewBasePtr) &&
393 cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
395 else if (isa<PHINode>(PtrIP))
396 PtrIP = &*PtrIP->getParent()->getFirstInsertionPt();
400 GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
401 I8Ty, PtrInc, I->Offset->getValue(),
402 I->Instr->hasName() ? I->Instr->getName() + ".off" : "", PtrIP);
404 NewPtr->insertAfter(cast<Instruction>(PtrInc));
405 NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
409 if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
410 BBChanged.insert(IDel->getParent());
412 Instruction *ReplNewPtr;
413 if (Ptr->getType() != RealNewPtr->getType()) {
414 ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
415 Ptr->hasName() ? Ptr->getName() + ".cast" : "");
416 ReplNewPtr->insertAfter(RealNewPtr);
418 ReplNewPtr = RealNewPtr;
420 Ptr->replaceAllUsesWith(ReplNewPtr);
421 RecursivelyDeleteTriviallyDeadInstructions(Ptr);
423 NewPtrs.insert(RealNewPtr);
429 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
431 if (BBChanged.count(*I))