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);
92 char PPCLoopPreIncPrep::ID = 0;
93 static const char *name = "Prepare loop for pre-inc. addressing modes";
94 INITIALIZE_PASS_BEGIN(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
95 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
96 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
97 INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
99 FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
100 return new PPCLoopPreIncPrep(TM);
104 struct BucketElement {
105 BucketElement(const SCEVConstant *O, Instruction *I) : Offset(O), Instr(I) {}
106 BucketElement(Instruction *I) : Offset(nullptr), Instr(I) {}
108 const SCEVConstant *Offset;
113 Bucket(const SCEV *B, Instruction *I) : BaseSCEV(B),
114 Elements(1, BucketElement(I)) {}
116 const SCEV *BaseSCEV;
117 SmallVector<BucketElement, 16> Elements;
121 static bool IsPtrInBounds(Value *BasePtr) {
122 Value *StrippedBasePtr = BasePtr;
123 while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr))
124 StrippedBasePtr = BC->getOperand(0);
125 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr))
126 return GEP->isInBounds();
131 static Value *GetPointerOperand(Value *MemI) {
132 if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) {
133 return LMemI->getPointerOperand();
134 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) {
135 return SMemI->getPointerOperand();
136 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) {
137 if (IMemI->getIntrinsicID() == Intrinsic::prefetch)
138 return IMemI->getArgOperand(0);
144 bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
145 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
146 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
148 bool MadeChange = false;
150 for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
151 for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
152 MadeChange |= runOnLoop(*L);
157 bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
158 bool MadeChange = false;
160 // Only prep. the inner-most loop
164 DEBUG(dbgs() << "PIP: Examining: " << *L << "\n");
166 BasicBlock *Header = L->getHeader();
168 const PPCSubtarget *ST =
169 TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
171 unsigned HeaderLoopPredCount =
172 std::distance(pred_begin(Header), pred_end(Header));
174 // Collect buckets of comparable addresses used by loads and stores.
175 SmallVector<Bucket, 16> Buckets;
176 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
178 for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
183 if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
185 PtrValue = LMemI->getPointerOperand();
186 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
188 PtrValue = SMemI->getPointerOperand();
189 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(J)) {
190 if (IMemI->getIntrinsicID() == Intrinsic::prefetch) {
192 PtrValue = IMemI->getArgOperand(0);
196 unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
200 // There are no update forms for Altivec vector load/stores.
201 if (ST && ST->hasAltivec() &&
202 PtrValue->getType()->getPointerElementType()->isVectorTy())
205 if (L->isLoopInvariant(PtrValue))
208 const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L);
209 if (const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV)) {
210 if (LARSCEV->getLoop() != L)
216 bool FoundBucket = false;
217 for (auto &B : Buckets) {
218 const SCEV *Diff = SE->getMinusSCEV(LSCEV, B.BaseSCEV);
219 if (const auto *CDiff = dyn_cast<SCEVConstant>(Diff)) {
220 B.Elements.push_back(BucketElement(CDiff, MemI));
227 if (Buckets.size() == MaxVars)
229 Buckets.push_back(Bucket(LSCEV, MemI));
237 BasicBlock *LoopPredecessor = L->getLoopPredecessor();
238 // If there is no loop predecessor, or the loop predecessor's terminator
239 // returns a value (which might contribute to determining the loop's
240 // iteration space), insert a new preheader for the loop.
241 if (!LoopPredecessor ||
242 !LoopPredecessor->getTerminator()->getType()->isVoidTy()) {
243 LoopPredecessor = InsertPreheaderForLoop(L, this);
247 if (!LoopPredecessor)
250 DEBUG(dbgs() << "PIP: Found " << Buckets.size() << " buckets\n");
252 SmallSet<BasicBlock *, 16> BBChanged;
253 for (unsigned i = 0, e = Buckets.size(); i != e; ++i) {
254 // The base address of each bucket is transformed into a phi and the others
255 // are rewritten as offsets of that variable.
257 // We have a choice now of which instruction's memory operand we use as the
258 // base for the generated PHI. Always picking the first instruction in each
259 // bucket does not work well, specifically because that instruction might
260 // be a prefetch (and there are no pre-increment dcbt variants). Otherwise,
261 // the choice is somewhat arbitrary, because the backend will happily
262 // generate direct offsets from both the pre-incremented and
263 // post-incremented pointer values. Thus, we'll pick the first non-prefetch
264 // instruction in each bucket, and adjust the recurrence and other offsets
266 for (int j = 0, je = Buckets[i].Elements.size(); j != je; ++j) {
267 if (auto *II = dyn_cast<IntrinsicInst>(Buckets[i].Elements[j].Instr))
268 if (II->getIntrinsicID() == Intrinsic::prefetch)
271 // If we'd otherwise pick the first element anyway, there's nothing to do.
275 // If our chosen element has no offset from the base pointer, there's
277 if (!Buckets[i].Elements[j].Offset ||
278 Buckets[i].Elements[j].Offset->isZero())
281 const SCEV *Offset = Buckets[i].Elements[j].Offset;
282 Buckets[i].BaseSCEV = SE->getAddExpr(Buckets[i].BaseSCEV, Offset);
283 for (auto &E : Buckets[i].Elements) {
285 E.Offset = cast<SCEVConstant>(SE->getMinusSCEV(E.Offset, Offset));
287 E.Offset = cast<SCEVConstant>(SE->getNegativeSCEV(Offset));
290 std::swap(Buckets[i].Elements[j], Buckets[i].Elements[0]);
294 const SCEVAddRecExpr *BasePtrSCEV =
295 cast<SCEVAddRecExpr>(Buckets[i].BaseSCEV);
296 if (!BasePtrSCEV->isAffine())
299 DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n");
300 assert(BasePtrSCEV->getLoop() == L &&
301 "AddRec for the wrong loop?");
303 // The instruction corresponding to the Bucket's BaseSCEV must be the first
304 // in the vector of elements.
305 Instruction *MemI = Buckets[i].Elements.begin()->Instr;
306 Value *BasePtr = GetPointerOperand(MemI);
307 assert(BasePtr && "No pointer operand");
309 Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
310 Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
311 BasePtr->getType()->getPointerAddressSpace());
313 const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
314 if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
317 const SCEVConstant *BasePtrIncSCEV =
318 dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
321 BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
322 if (!isSafeToExpand(BasePtrStartSCEV, *SE))
325 DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
327 PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
328 MemI->hasName() ? MemI->getName() + ".phi" : "",
329 Header->getFirstNonPHI());
331 SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
332 Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
333 LoopPredecessor->getTerminator());
335 // Note that LoopPredecessor might occur in the predecessor list multiple
336 // times, and we need to add it the right number of times.
337 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
339 if (*PI != LoopPredecessor)
342 NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
345 Instruction *InsPoint = &*Header->getFirstInsertionPt();
346 GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
347 I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
348 MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint);
349 PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
350 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
352 if (*PI == LoopPredecessor)
355 NewPHI->addIncoming(PtrInc, *PI);
358 Instruction *NewBasePtr;
359 if (PtrInc->getType() != BasePtr->getType())
360 NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
361 PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint);
365 if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
366 BBChanged.insert(IDel->getParent());
367 BasePtr->replaceAllUsesWith(NewBasePtr);
368 RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
370 // Keep track of the replacement pointer values we've inserted so that we
371 // don't generate more pointer values than necessary.
372 SmallPtrSet<Value *, 16> NewPtrs;
373 NewPtrs.insert( NewBasePtr);
375 for (auto I = std::next(Buckets[i].Elements.begin()),
376 IE = Buckets[i].Elements.end(); I != IE; ++I) {
377 Value *Ptr = GetPointerOperand(I->Instr);
378 assert(Ptr && "No pointer operand");
379 if (NewPtrs.count(Ptr))
382 Instruction *RealNewPtr;
383 if (!I->Offset || I->Offset->getValue()->isZero()) {
384 RealNewPtr = NewBasePtr;
386 Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
387 if (PtrIP && isa<Instruction>(NewBasePtr) &&
388 cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
390 else if (isa<PHINode>(PtrIP))
391 PtrIP = &*PtrIP->getParent()->getFirstInsertionPt();
395 GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
396 I8Ty, PtrInc, I->Offset->getValue(),
397 I->Instr->hasName() ? I->Instr->getName() + ".off" : "", PtrIP);
399 NewPtr->insertAfter(cast<Instruction>(PtrInc));
400 NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
404 if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
405 BBChanged.insert(IDel->getParent());
407 Instruction *ReplNewPtr;
408 if (Ptr->getType() != RealNewPtr->getType()) {
409 ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
410 Ptr->hasName() ? Ptr->getName() + ".cast" : "");
411 ReplNewPtr->insertAfter(RealNewPtr);
413 ReplNewPtr = RealNewPtr;
415 Ptr->replaceAllUsesWith(ReplNewPtr);
416 RecursivelyDeleteTriviallyDeadInstructions(Ptr);
418 NewPtrs.insert(RealNewPtr);
424 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
426 if (BBChanged.count(*I))