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<ScalarEvolution>();
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(ScalarEvolution)
97 INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
99 FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
100 return new PPCLoopPreIncPrep(TM);
104 struct SCEVLess : std::binary_function<const SCEV *, const SCEV *, bool>
106 SCEVLess(ScalarEvolution *SE) : SE(SE) {}
108 bool operator() (const SCEV *X, const SCEV *Y) const {
109 const SCEV *Diff = SE->getMinusSCEV(X, Y);
110 return cast<SCEVConstant>(Diff)->getValue()->getSExtValue() < 0;
118 static bool IsPtrInBounds(Value *BasePtr) {
119 Value *StrippedBasePtr = BasePtr;
120 while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr))
121 StrippedBasePtr = BC->getOperand(0);
122 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr))
123 return GEP->isInBounds();
128 static Value *GetPointerOperand(Value *MemI) {
129 if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) {
130 return LMemI->getPointerOperand();
131 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) {
132 return SMemI->getPointerOperand();
133 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) {
134 if (IMemI->getIntrinsicID() == Intrinsic::prefetch)
135 return IMemI->getArgOperand(0);
141 bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
142 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
143 SE = &getAnalysis<ScalarEvolution>();
145 bool MadeChange = false;
150 for (auto I = df_begin(*LI->begin()), E = df_end(*LI->begin()); I != E; ++I) {
152 MadeChange |= runOnLoop(L);
158 bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
159 bool MadeChange = false;
161 // Only prep. the inner-most loop
165 DEBUG(dbgs() << "PIP: Examining: " << *L << "\n");
167 BasicBlock *Header = L->getHeader();
169 const PPCSubtarget *ST =
170 TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
172 unsigned HeaderLoopPredCount =
173 std::distance(pred_begin(Header), pred_end(Header));
175 // Collect buckets of comparable addresses used by loads and stores.
176 typedef std::multimap<const SCEV *, Instruction *, SCEVLess> Bucket;
177 SmallVector<Bucket, 16> Buckets;
178 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
180 for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
185 if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
187 PtrValue = LMemI->getPointerOperand();
188 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
190 PtrValue = SMemI->getPointerOperand();
191 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(J)) {
192 if (IMemI->getIntrinsicID() == Intrinsic::prefetch) {
194 PtrValue = IMemI->getArgOperand(0);
198 unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
202 // There are no update forms for Altivec vector load/stores.
203 if (ST && ST->hasAltivec() &&
204 PtrValue->getType()->getPointerElementType()->isVectorTy())
207 if (L->isLoopInvariant(PtrValue))
210 const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L);
211 if (const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV)) {
212 if (LARSCEV->getLoop() != L)
218 bool FoundBucket = false;
219 for (unsigned i = 0, e = Buckets.size(); i != e; ++i)
220 for (Bucket::iterator K = Buckets[i].begin(), KE = Buckets[i].end();
222 const SCEV *Diff = SE->getMinusSCEV(K->first, LSCEV);
223 if (isa<SCEVConstant>(Diff)) {
224 Buckets[i].insert(std::make_pair(LSCEV, MemI));
231 Buckets.push_back(Bucket(SCEVLess(SE)));
232 Buckets[Buckets.size()-1].insert(std::make_pair(LSCEV, MemI));
237 if (Buckets.empty() || Buckets.size() > MaxVars)
240 BasicBlock *LoopPredecessor = L->getLoopPredecessor();
241 // If there is no loop predecessor, or the loop predecessor's terminator
242 // returns a value (which might contribute to determining the loop's
243 // iteration space), insert a new preheader for the loop.
244 if (!LoopPredecessor ||
245 !LoopPredecessor->getTerminator()->getType()->isVoidTy()) {
246 LoopPredecessor = InsertPreheaderForLoop(L, this);
250 if (!LoopPredecessor)
253 DEBUG(dbgs() << "PIP: Found " << Buckets.size() << " buckets\n");
255 SmallSet<BasicBlock *, 16> BBChanged;
256 for (unsigned i = 0, e = Buckets.size(); i != e; ++i) {
257 // The base address of each bucket is transformed into a phi and the others
258 // are rewritten as offsets of that variable.
260 const SCEVAddRecExpr *BasePtrSCEV =
261 cast<SCEVAddRecExpr>(Buckets[i].begin()->first);
262 if (!BasePtrSCEV->isAffine())
265 DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n");
266 assert(BasePtrSCEV->getLoop() == L &&
267 "AddRec for the wrong loop?");
269 Instruction *MemI = Buckets[i].begin()->second;
270 Value *BasePtr = GetPointerOperand(MemI);
271 assert(BasePtr && "No pointer operand");
273 Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
274 Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
275 BasePtr->getType()->getPointerAddressSpace());
277 const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
278 if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
281 const SCEVConstant *BasePtrIncSCEV =
282 dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
285 BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
286 if (!isSafeToExpand(BasePtrStartSCEV, *SE))
289 DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
291 PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
292 MemI->hasName() ? MemI->getName() + ".phi" : "",
293 Header->getFirstNonPHI());
295 SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
296 Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
297 LoopPredecessor->getTerminator());
299 // Note that LoopPredecessor might occur in the predecessor list multiple
300 // times, and we need to add it the right number of times.
301 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
303 if (*PI != LoopPredecessor)
306 NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
309 Instruction *InsPoint = Header->getFirstInsertionPt();
310 GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
311 I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
312 MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint);
313 PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
314 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
316 if (*PI == LoopPredecessor)
319 NewPHI->addIncoming(PtrInc, *PI);
322 Instruction *NewBasePtr;
323 if (PtrInc->getType() != BasePtr->getType())
324 NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
325 PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint);
329 if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
330 BBChanged.insert(IDel->getParent());
331 BasePtr->replaceAllUsesWith(NewBasePtr);
332 RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
334 Value *LastNewPtr = NewBasePtr;
335 for (Bucket::iterator I = std::next(Buckets[i].begin()),
336 IE = Buckets[i].end(); I != IE; ++I) {
337 Value *Ptr = GetPointerOperand(I->second);
338 assert(Ptr && "No pointer operand");
339 if (Ptr == LastNewPtr)
342 Instruction *RealNewPtr;
343 const SCEVConstant *Diff =
344 cast<SCEVConstant>(SE->getMinusSCEV(I->first, BasePtrSCEV));
345 if (Diff->isZero()) {
346 RealNewPtr = NewBasePtr;
348 Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
349 if (PtrIP && isa<Instruction>(NewBasePtr) &&
350 cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
352 else if (isa<PHINode>(PtrIP))
353 PtrIP = PtrIP->getParent()->getFirstInsertionPt();
357 GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
358 I8Ty, PtrInc, Diff->getValue(),
359 I->second->hasName() ? I->second->getName() + ".off" : "", PtrIP);
361 NewPtr->insertAfter(cast<Instruction>(PtrInc));
362 NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
366 if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
367 BBChanged.insert(IDel->getParent());
369 Instruction *ReplNewPtr;
370 if (Ptr->getType() != RealNewPtr->getType()) {
371 ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
372 Ptr->hasName() ? Ptr->getName() + ".cast" : "");
373 ReplNewPtr->insertAfter(RealNewPtr);
375 ReplNewPtr = RealNewPtr;
377 Ptr->replaceAllUsesWith(ReplNewPtr);
378 RecursivelyDeleteTriviallyDeadInstructions(Ptr);
380 LastNewPtr = RealNewPtr;
386 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
388 if (BBChanged.count(*I))