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;
147 for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
148 for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
149 MadeChange |= runOnLoop(*L);
154 bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
155 bool MadeChange = false;
157 // Only prep. the inner-most loop
161 DEBUG(dbgs() << "PIP: Examining: " << *L << "\n");
163 BasicBlock *Header = L->getHeader();
165 const PPCSubtarget *ST =
166 TM ? TM->getSubtargetImpl(*Header->getParent()) : nullptr;
168 unsigned HeaderLoopPredCount =
169 std::distance(pred_begin(Header), pred_end(Header));
171 // Collect buckets of comparable addresses used by loads and stores.
172 typedef std::multimap<const SCEV *, Instruction *, SCEVLess> Bucket;
173 SmallVector<Bucket, 16> Buckets;
174 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
176 for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
181 if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
183 PtrValue = LMemI->getPointerOperand();
184 } else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
186 PtrValue = SMemI->getPointerOperand();
187 } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(J)) {
188 if (IMemI->getIntrinsicID() == Intrinsic::prefetch) {
190 PtrValue = IMemI->getArgOperand(0);
194 unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
198 // There are no update forms for Altivec vector load/stores.
199 if (ST && ST->hasAltivec() &&
200 PtrValue->getType()->getPointerElementType()->isVectorTy())
203 if (L->isLoopInvariant(PtrValue))
206 const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L);
207 if (const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV)) {
208 if (LARSCEV->getLoop() != L)
214 bool FoundBucket = false;
215 for (unsigned i = 0, e = Buckets.size(); i != e; ++i)
216 for (Bucket::iterator K = Buckets[i].begin(), KE = Buckets[i].end();
218 const SCEV *Diff = SE->getMinusSCEV(K->first, LSCEV);
219 if (isa<SCEVConstant>(Diff)) {
220 Buckets[i].insert(std::make_pair(LSCEV, MemI));
227 Buckets.push_back(Bucket(SCEVLess(SE)));
228 Buckets[Buckets.size()-1].insert(std::make_pair(LSCEV, MemI));
233 if (Buckets.empty() || Buckets.size() > MaxVars)
236 BasicBlock *LoopPredecessor = L->getLoopPredecessor();
237 // If there is no loop predecessor, or the loop predecessor's terminator
238 // returns a value (which might contribute to determining the loop's
239 // iteration space), insert a new preheader for the loop.
240 if (!LoopPredecessor ||
241 !LoopPredecessor->getTerminator()->getType()->isVoidTy()) {
242 LoopPredecessor = InsertPreheaderForLoop(L, this);
246 if (!LoopPredecessor)
249 DEBUG(dbgs() << "PIP: Found " << Buckets.size() << " buckets\n");
251 SmallSet<BasicBlock *, 16> BBChanged;
252 for (unsigned i = 0, e = Buckets.size(); i != e; ++i) {
253 // The base address of each bucket is transformed into a phi and the others
254 // are rewritten as offsets of that variable.
256 const SCEVAddRecExpr *BasePtrSCEV =
257 cast<SCEVAddRecExpr>(Buckets[i].begin()->first);
258 if (!BasePtrSCEV->isAffine())
261 DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n");
262 assert(BasePtrSCEV->getLoop() == L &&
263 "AddRec for the wrong loop?");
265 Instruction *MemI = Buckets[i].begin()->second;
266 Value *BasePtr = GetPointerOperand(MemI);
267 assert(BasePtr && "No pointer operand");
269 Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
270 Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
271 BasePtr->getType()->getPointerAddressSpace());
273 const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
274 if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
277 const SCEVConstant *BasePtrIncSCEV =
278 dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
281 BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
282 if (!isSafeToExpand(BasePtrStartSCEV, *SE))
285 DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
287 PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
288 MemI->hasName() ? MemI->getName() + ".phi" : "",
289 Header->getFirstNonPHI());
291 SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
292 Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
293 LoopPredecessor->getTerminator());
295 // Note that LoopPredecessor might occur in the predecessor list multiple
296 // times, and we need to add it the right number of times.
297 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
299 if (*PI != LoopPredecessor)
302 NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
305 Instruction *InsPoint = Header->getFirstInsertionPt();
306 GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
307 I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
308 MemI->hasName() ? MemI->getName() + ".inc" : "", InsPoint);
309 PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
310 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
312 if (*PI == LoopPredecessor)
315 NewPHI->addIncoming(PtrInc, *PI);
318 Instruction *NewBasePtr;
319 if (PtrInc->getType() != BasePtr->getType())
320 NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
321 PtrInc->hasName() ? PtrInc->getName() + ".cast" : "", InsPoint);
325 if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
326 BBChanged.insert(IDel->getParent());
327 BasePtr->replaceAllUsesWith(NewBasePtr);
328 RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
330 Value *LastNewPtr = NewBasePtr;
331 for (Bucket::iterator I = std::next(Buckets[i].begin()),
332 IE = Buckets[i].end(); I != IE; ++I) {
333 Value *Ptr = GetPointerOperand(I->second);
334 assert(Ptr && "No pointer operand");
335 if (Ptr == LastNewPtr)
338 Instruction *RealNewPtr;
339 const SCEVConstant *Diff =
340 cast<SCEVConstant>(SE->getMinusSCEV(I->first, BasePtrSCEV));
341 if (Diff->isZero()) {
342 RealNewPtr = NewBasePtr;
344 Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
345 if (PtrIP && isa<Instruction>(NewBasePtr) &&
346 cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
348 else if (isa<PHINode>(PtrIP))
349 PtrIP = PtrIP->getParent()->getFirstInsertionPt();
353 GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
354 I8Ty, PtrInc, Diff->getValue(),
355 I->second->hasName() ? I->second->getName() + ".off" : "", PtrIP);
357 NewPtr->insertAfter(cast<Instruction>(PtrInc));
358 NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
362 if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
363 BBChanged.insert(IDel->getParent());
365 Instruction *ReplNewPtr;
366 if (Ptr->getType() != RealNewPtr->getType()) {
367 ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
368 Ptr->hasName() ? Ptr->getName() + ".cast" : "");
369 ReplNewPtr->insertAfter(RealNewPtr);
371 ReplNewPtr = RealNewPtr;
373 Ptr->replaceAllUsesWith(ReplNewPtr);
374 RecursivelyDeleteTriviallyDeadInstructions(Ptr);
376 LastNewPtr = RealNewPtr;
382 for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
384 if (BBChanged.count(*I))