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/STLExtras.h"
26 #include "llvm/ADT/SmallSet.h"
27 #include "llvm/ADT/Statistic.h"
28 #include "llvm/Analysis/CodeMetrics.h"
29 #include "llvm/Analysis/InstructionSimplify.h"
30 #include "llvm/Analysis/LoopInfo.h"
31 #include "llvm/Analysis/ScalarEvolution.h"
32 #include "llvm/Analysis/ScalarEvolutionExpander.h"
33 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
34 #include "llvm/Analysis/ValueTracking.h"
35 #include "llvm/IR/CFG.h"
36 #include "llvm/IR/Dominators.h"
37 #include "llvm/IR/Function.h"
38 #include "llvm/IR/IntrinsicInst.h"
39 #include "llvm/IR/Module.h"
40 #include "llvm/Support/CommandLine.h"
41 #include "llvm/Support/Debug.h"
42 #include "llvm/Transforms/Scalar.h"
43 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
44 #include "llvm/Transforms/Utils/Local.h"
45 #include "llvm/Transforms/Utils/LoopUtils.h"
46 #include "llvm/Transforms/Utils/ValueMapper.h"
49 // By default, we limit this to creating 16 PHIs (which is a little over half
50 // of the allocatable register set).
51 static cl::opt<unsigned> MaxVars("ppc-preinc-prep-max-vars",
52 cl::Hidden, cl::init(16),
53 cl::desc("Potential PHI threshold for PPC preinc loop prep"));
56 void initializePPCLoopPreIncPrepPass(PassRegistry&);
61 class PPCLoopPreIncPrep : public FunctionPass {
63 static char ID; // Pass ID, replacement for typeid
64 PPCLoopPreIncPrep() : FunctionPass(ID), TM(nullptr) {
65 initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
67 PPCLoopPreIncPrep(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
68 initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
71 void getAnalysisUsage(AnalysisUsage &AU) const override {
72 AU.addPreserved<DominatorTreeWrapperPass>();
73 AU.addRequired<LoopInfoWrapperPass>();
74 AU.addPreserved<LoopInfoWrapperPass>();
75 AU.addRequired<ScalarEvolution>();
78 bool runOnFunction(Function &F) override;
80 bool runOnLoop(Loop *L);
81 void simplifyLoopLatch(Loop *L);
82 bool rotateLoop(Loop *L);
91 char PPCLoopPreIncPrep::ID = 0;
92 static const char *name = "Prepare loop for pre-inc. addressing modes";
93 INITIALIZE_PASS_BEGIN(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
94 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
95 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
96 INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
98 FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
99 return new PPCLoopPreIncPrep(TM);
103 struct SCEVLess : std::binary_function<const SCEV *, const SCEV *, bool>
105 SCEVLess(ScalarEvolution *SE) : SE(SE) {}
107 bool operator() (const SCEV *X, const SCEV *Y) const {
108 const SCEV *Diff = SE->getMinusSCEV(X, Y);
109 return cast<SCEVConstant>(Diff)->getValue()->getSExtValue() < 0;
117 static bool IsPtrInBounds(Value *BasePtr) {
118 Value *StrippedBasePtr = BasePtr;
119 while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr))
120 StrippedBasePtr = BC->getOperand(0);
121 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr))
122 return GEP->isInBounds();
127 static Value *GetPointerOperand(Value *MemI) {
128 if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) {
129 return LMemI->getPointerOperand();
130 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) {
131 return SMemI->getPointerOperand();
132 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) {
133 if (IMemI->getIntrinsicID() == Intrinsic::prefetch)
134 return IMemI->getArgOperand(0);
140 bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
141 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
142 SE = &getAnalysis<ScalarEvolution>();
144 bool MadeChange = false;
146 for (LoopInfo::iterator I = LI->begin(), E = LI->end();
149 MadeChange |= runOnLoop(L);
155 bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
156 bool MadeChange = false;
158 // Only prep. the inner-most loop
162 BasicBlock *Header = L->getHeader();
164 const PPCSubtarget *ST =
165 TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
167 unsigned HeaderLoopPredCount = 0;
168 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
170 ++HeaderLoopPredCount;
173 // Collect buckets of comparable addresses used by loads and stores.
174 typedef std::multimap<const SCEV *, Instruction *, SCEVLess> Bucket;
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->getSCEV(PtrValue);
209 if (!isa<SCEVAddRecExpr>(LSCEV))
212 bool FoundBucket = false;
213 for (unsigned i = 0, e = Buckets.size(); i != e; ++i)
214 for (Bucket::iterator K = Buckets[i].begin(), KE = Buckets[i].end();
216 const SCEV *Diff = SE->getMinusSCEV(K->first, LSCEV);
217 if (isa<SCEVConstant>(Diff)) {
218 Buckets[i].insert(std::make_pair(LSCEV, MemI));
225 Buckets.push_back(Bucket(SCEVLess(SE)));
226 Buckets[Buckets.size()-1].insert(std::make_pair(LSCEV, MemI));
231 if (Buckets.empty() || Buckets.size() > MaxVars)
234 BasicBlock *LoopPredecessor = L->getLoopPredecessor();
235 // If there is no loop predecessor, or the loop predecessor's terminator
236 // returns a value (which might contribute to determining the loop's
237 // iteration space), insert a new preheader for the loop.
238 if (!LoopPredecessor ||
239 !LoopPredecessor->getTerminator()->getType()->isVoidTy())
240 LoopPredecessor = InsertPreheaderForLoop(L, this);
241 if (!LoopPredecessor)
244 SmallSet<BasicBlock *, 16> BBChanged;
245 for (unsigned i = 0, e = Buckets.size(); i != e; ++i) {
246 // The base address of each bucket is transformed into a phi and the others
247 // are rewritten as offsets of that variable.
249 const SCEVAddRecExpr *BasePtrSCEV =
250 cast<SCEVAddRecExpr>(Buckets[i].begin()->first);
251 if (!BasePtrSCEV->isAffine())
254 Instruction *MemI = Buckets[i].begin()->second;
255 Value *BasePtr = GetPointerOperand(MemI);
256 assert(BasePtr && "No pointer operand");
258 Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
259 Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
260 BasePtr->getType()->getPointerAddressSpace());
262 const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
263 if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
266 const SCEVConstant *BasePtrIncSCEV =
267 dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
270 BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
271 if (!isSafeToExpand(BasePtrStartSCEV, *SE))
274 PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
275 MemI->hasName() ? MemI->getName() + ".phi" : "",
276 Header->getFirstNonPHI());
278 SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
279 Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
280 LoopPredecessor->getTerminator());
282 // Note that LoopPredecessor might occur in the predecessor list multiple
283 // times, and we need to add it the right number of times.
284 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
286 if (*PI != LoopPredecessor)
289 NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
292 Instruction *InsPoint = Header->getFirstInsertionPt();
293 GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
294 I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
295 MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint);
296 PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
297 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
299 if (*PI == LoopPredecessor)
302 NewPHI->addIncoming(PtrInc, *PI);
305 Instruction *NewBasePtr;
306 if (PtrInc->getType() != BasePtr->getType())
307 NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
308 PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint);
312 if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
313 BBChanged.insert(IDel->getParent());
314 BasePtr->replaceAllUsesWith(NewBasePtr);
315 RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
317 Value *LastNewPtr = NewBasePtr;
318 for (Bucket::iterator I = std::next(Buckets[i].begin()),
319 IE = Buckets[i].end(); I != IE; ++I) {
320 Value *Ptr = GetPointerOperand(I->second);
321 assert(Ptr && "No pointer operand");
322 if (Ptr == LastNewPtr)
325 Instruction *RealNewPtr;
326 const SCEVConstant *Diff =
327 cast<SCEVConstant>(SE->getMinusSCEV(I->first, BasePtrSCEV));
328 if (Diff->isZero()) {
329 RealNewPtr = NewBasePtr;
331 Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
332 if (PtrIP && isa<Instruction>(NewBasePtr) &&
333 cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
335 else if (isa<PHINode>(PtrIP))
336 PtrIP = PtrIP->getParent()->getFirstInsertionPt();
340 GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
341 I8Ty, PtrInc, Diff->getValue(),
342 I->second->hasName() ? I->second->getName() + ".off" : "", PtrIP);
344 NewPtr->insertAfter(cast<Instruction>(PtrInc));
345 NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
349 if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
350 BBChanged.insert(IDel->getParent());
352 Instruction *ReplNewPtr;
353 if (Ptr->getType() != RealNewPtr->getType()) {
354 ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
355 Ptr->hasName() ? Ptr->getName() + ".cast" : "");
356 ReplNewPtr->insertAfter(RealNewPtr);
358 ReplNewPtr = RealNewPtr;
360 Ptr->replaceAllUsesWith(ReplNewPtr);
361 RecursivelyDeleteTriviallyDeadInstructions(Ptr);
363 LastNewPtr = RealNewPtr;
369 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
371 if (BBChanged.count(*I))