1 //===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
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 bookkeeping for "interesting" users of expressions
11 // computed from induction variables.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "iv-users"
16 #include "llvm/Analysis/IVUsers.h"
17 #include "llvm/Constants.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Analysis/Dominators.h"
22 #include "llvm/Analysis/LoopPass.h"
23 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
24 #include "llvm/Assembly/AsmAnnotationWriter.h"
25 #include "llvm/ADT/STLExtras.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/raw_ostream.h"
32 static RegisterPass<IVUsers>
33 X("iv-users", "Induction Variable Users", false, true);
35 Pass *llvm::createIVUsersPass() {
39 /// containsAddRecFromDifferentLoop - Determine whether expression S involves a
40 /// subexpression that is an AddRec from a loop other than L. An outer loop
41 /// of L is OK, but not an inner loop nor a disjoint loop.
42 static bool containsAddRecFromDifferentLoop(const SCEV *S, Loop *L) {
43 // This is very common, put it first.
44 if (isa<SCEVConstant>(S))
46 if (const SCEVCommutativeExpr *AE = dyn_cast<SCEVCommutativeExpr>(S)) {
47 for (unsigned int i=0; i< AE->getNumOperands(); i++)
48 if (containsAddRecFromDifferentLoop(AE->getOperand(i), L))
52 if (const SCEVAddRecExpr *AE = dyn_cast<SCEVAddRecExpr>(S)) {
53 if (const Loop *newLoop = AE->getLoop()) {
56 // if newLoop is an outer loop of L, this is OK.
57 if (newLoop->contains(L))
62 if (const SCEVUDivExpr *DE = dyn_cast<SCEVUDivExpr>(S))
63 return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
64 containsAddRecFromDifferentLoop(DE->getRHS(), L);
66 // SCEVSDivExpr has been backed out temporarily, but will be back; we'll
67 // need this when it is.
68 if (const SCEVSDivExpr *DE = dyn_cast<SCEVSDivExpr>(S))
69 return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
70 containsAddRecFromDifferentLoop(DE->getRHS(), L);
72 if (const SCEVCastExpr *CE = dyn_cast<SCEVCastExpr>(S))
73 return containsAddRecFromDifferentLoop(CE->getOperand(), L);
77 /// getSCEVStartAndStride - Compute the start and stride of this expression,
78 /// returning false if the expression is not a start/stride pair, or true if it
79 /// is. The stride must be a loop invariant expression, but the start may be
80 /// a mix of loop invariant and loop variant expressions. The start cannot,
81 /// however, contain an AddRec from a different loop, unless that loop is an
82 /// outer loop of the current loop.
83 static bool getSCEVStartAndStride(const SCEV *&SH, Loop *L, Loop *UseLoop,
84 const SCEV *&Start, const SCEV *&Stride,
85 ScalarEvolution *SE, DominatorTree *DT) {
86 const SCEV *TheAddRec = Start; // Initialize to zero.
88 // If the outer level is an AddExpr, the operands are all start values except
89 // for a nested AddRecExpr.
90 if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
91 for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
92 if (const SCEVAddRecExpr *AddRec =
93 dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
94 if (AddRec->getLoop() == L)
95 TheAddRec = SE->getAddExpr(AddRec, TheAddRec);
97 return false; // Nested IV of some sort?
99 Start = SE->getAddExpr(Start, AE->getOperand(i));
101 } else if (isa<SCEVAddRecExpr>(SH)) {
104 return false; // not analyzable.
107 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
108 if (!AddRec || AddRec->getLoop() != L) return false;
110 // Use getSCEVAtScope to attempt to simplify other loops out of
112 const SCEV *AddRecStart = AddRec->getStart();
113 AddRecStart = SE->getSCEVAtScope(AddRecStart, UseLoop);
114 const SCEV *AddRecStride = AddRec->getStepRecurrence(*SE);
116 // FIXME: If Start contains an SCEVAddRecExpr from a different loop, other
117 // than an outer loop of the current loop, reject it. LSR has no concept of
118 // operating on more than one loop at a time so don't confuse it with such
120 if (containsAddRecFromDifferentLoop(AddRecStart, L))
123 Start = SE->getAddExpr(Start, AddRecStart);
125 // If stride is an instruction, make sure it properly dominates the header.
126 // Otherwise we could end up with a use before def situation.
127 if (!isa<SCEVConstant>(AddRecStride)) {
128 BasicBlock *Header = L->getHeader();
129 if (!AddRecStride->properlyDominates(Header, DT))
133 WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false);
134 dbgs() << "] Variable stride: " << *AddRec << "\n");
137 Stride = AddRecStride;
141 /// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
142 /// and now we need to decide whether the user should use the preinc or post-inc
143 /// value. If this user should use the post-inc version of the IV, return true.
145 /// Choosing wrong here can break dominance properties (if we choose to use the
146 /// post-inc value when we cannot) or it can end up adding extra live-ranges to
147 /// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
148 /// should use the post-inc value).
149 static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
150 Loop *L, LoopInfo *LI, DominatorTree *DT,
152 // If the user is in the loop, use the preinc value.
153 if (L->contains(User)) return false;
155 BasicBlock *LatchBlock = L->getLoopLatch();
159 // Ok, the user is outside of the loop. If it is dominated by the latch
160 // block, use the post-inc value.
161 if (DT->dominates(LatchBlock, User->getParent()))
164 // There is one case we have to be careful of: PHI nodes. These little guys
165 // can live in blocks that are not dominated by the latch block, but (since
166 // their uses occur in the predecessor block, not the block the PHI lives in)
167 // should still use the post-inc value. Check for this case now.
168 PHINode *PN = dyn_cast<PHINode>(User);
169 if (!PN) return false; // not a phi, not dominated by latch block.
171 // Look at all of the uses of IV by the PHI node. If any use corresponds to
172 // a block that is not dominated by the latch block, give up and use the
173 // preincremented value.
174 unsigned NumUses = 0;
175 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
176 if (PN->getIncomingValue(i) == IV) {
178 if (!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
182 // Okay, all uses of IV by PN are in predecessor blocks that really are
183 // dominated by the latch block. Use the post-incremented value.
187 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
188 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
189 /// return true. Otherwise, return false.
190 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
191 if (!SE->isSCEVable(I->getType()))
192 return false; // Void and FP expressions cannot be reduced.
194 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
195 if (SE->getTypeSizeInBits(I->getType()) > 64)
198 if (!Processed.insert(I))
199 return true; // Instruction already handled.
201 // Get the symbolic expression for this instruction.
202 const SCEV *ISE = SE->getSCEV(I);
203 if (isa<SCEVCouldNotCompute>(ISE)) return false;
205 // Get the start and stride for this expression.
206 Loop *UseLoop = LI->getLoopFor(I->getParent());
207 const SCEV *Start = SE->getIntegerSCEV(0, ISE->getType());
208 const SCEV *Stride = Start;
210 if (!getSCEVStartAndStride(ISE, L, UseLoop, Start, Stride, SE, DT))
211 return false; // Non-reducible symbolic expression, bail out.
213 // Keep things simple. Don't touch loop-variant strides.
214 if (!Stride->isLoopInvariant(L) && L->contains(I))
217 SmallPtrSet<Instruction *, 4> UniqueUsers;
218 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
220 Instruction *User = cast<Instruction>(*UI);
221 if (!UniqueUsers.insert(User))
224 // Do not infinitely recurse on PHI nodes.
225 if (isa<PHINode>(User) && Processed.count(User))
228 // Descend recursively, but not into PHI nodes outside the current loop.
229 // It's important to see the entire expression outside the loop to get
230 // choices that depend on addressing mode use right, although we won't
231 // consider references ouside the loop in all cases.
232 // If User is already in Processed, we don't want to recurse into it again,
233 // but do want to record a second reference in the same instruction.
234 bool AddUserToIVUsers = false;
235 if (LI->getLoopFor(User->getParent()) != L) {
236 if (isa<PHINode>(User) || Processed.count(User) ||
237 !AddUsersIfInteresting(User)) {
238 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
239 << " OF SCEV: " << *ISE << '\n');
240 AddUserToIVUsers = true;
242 } else if (Processed.count(User) ||
243 !AddUsersIfInteresting(User)) {
244 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
245 << " OF SCEV: " << *ISE << '\n');
246 AddUserToIVUsers = true;
249 if (AddUserToIVUsers) {
250 IVUsersOfOneStride *StrideUses = IVUsesByStride[Stride];
251 if (!StrideUses) { // First occurrence of this stride?
252 StrideOrder.push_back(Stride);
253 StrideUses = new IVUsersOfOneStride(Stride);
254 IVUses.push_back(StrideUses);
255 IVUsesByStride[Stride] = StrideUses;
258 // Okay, we found a user that we cannot reduce. Analyze the instruction
259 // and decide what to do with it. If we are a use inside of the loop, use
260 // the value before incrementation, otherwise use it after incrementation.
261 if (IVUseShouldUsePostIncValue(User, I, L, LI, DT, this)) {
262 // The value used will be incremented by the stride more than we are
263 // expecting, so subtract this off.
264 const SCEV *NewStart = SE->getMinusSCEV(Start, Stride);
265 StrideUses->addUser(NewStart, User, I);
266 StrideUses->Users.back().setIsUseOfPostIncrementedValue(true);
267 DEBUG(dbgs() << " USING POSTINC SCEV, START=" << *NewStart<< "\n");
269 StrideUses->addUser(Start, User, I);
276 void IVUsers::AddUser(const SCEV *Stride, const SCEV *Offset,
277 Instruction *User, Value *Operand) {
278 IVUsersOfOneStride *StrideUses = IVUsesByStride[Stride];
279 if (!StrideUses) { // First occurrence of this stride?
280 StrideOrder.push_back(Stride);
281 StrideUses = new IVUsersOfOneStride(Stride);
282 IVUses.push_back(StrideUses);
283 IVUsesByStride[Stride] = StrideUses;
285 IVUsesByStride[Stride]->addUser(Offset, User, Operand);
292 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
293 AU.addRequired<LoopInfo>();
294 AU.addRequired<DominatorTree>();
295 AU.addRequired<ScalarEvolution>();
296 AU.setPreservesAll();
299 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
302 LI = &getAnalysis<LoopInfo>();
303 DT = &getAnalysis<DominatorTree>();
304 SE = &getAnalysis<ScalarEvolution>();
306 // Find all uses of induction variables in this loop, and categorize
307 // them by stride. Start by finding all of the PHI nodes in the header for
308 // this loop. If they are induction variables, inspect their uses.
309 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
310 AddUsersIfInteresting(I);
315 /// getReplacementExpr - Return a SCEV expression which computes the
316 /// value of the OperandValToReplace of the given IVStrideUse.
317 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &U) const {
319 const SCEV *RetVal = SE->getIntegerSCEV(0, U.getParent()->Stride->getType());
320 // Create the basic add recurrence.
321 RetVal = SE->getAddRecExpr(RetVal, U.getParent()->Stride, L);
322 // Add the offset in a separate step, because it may be loop-variant.
323 RetVal = SE->getAddExpr(RetVal, U.getOffset());
324 // For uses of post-incremented values, add an extra stride to compute
325 // the actual replacement value.
326 if (U.isUseOfPostIncrementedValue())
327 RetVal = SE->getAddExpr(RetVal, U.getParent()->Stride);
331 /// getCanonicalExpr - Return a SCEV expression which computes the
332 /// value of the SCEV of the given IVStrideUse, ignoring the
333 /// isUseOfPostIncrementedValue flag.
334 const SCEV *IVUsers::getCanonicalExpr(const IVStrideUse &U) const {
336 const SCEV *RetVal = SE->getIntegerSCEV(0, U.getParent()->Stride->getType());
337 // Create the basic add recurrence.
338 RetVal = SE->getAddRecExpr(RetVal, U.getParent()->Stride, L);
339 // Add the offset in a separate step, because it may be loop-variant.
340 RetVal = SE->getAddExpr(RetVal, U.getOffset());
346 // Suppress extraneous comments.
347 class IVUsersAsmAnnotator : public AssemblyAnnotationWriter {};
351 void IVUsers::print(raw_ostream &OS, const Module *M) const {
352 OS << "IV Users for loop ";
353 WriteAsOperand(OS, L->getHeader(), false);
354 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
355 OS << " with backedge-taken count "
356 << *SE->getBackedgeTakenCount(L);
360 IVUsersAsmAnnotator Annotator;
361 for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; ++Stride) {
362 std::map<const SCEV *, IVUsersOfOneStride*>::const_iterator SI =
363 IVUsesByStride.find(StrideOrder[Stride]);
364 assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
365 OS << " Stride " << *SI->first->getType() << " " << *SI->first << ":\n";
367 for (ilist<IVStrideUse>::const_iterator UI = SI->second->Users.begin(),
368 E = SI->second->Users.end(); UI != E; ++UI) {
370 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
372 OS << *getReplacementExpr(*UI);
373 if (UI->isUseOfPostIncrementedValue())
376 UI->getUser()->print(OS, &Annotator);
382 void IVUsers::dump() const {
386 void IVUsers::releaseMemory() {
387 IVUsesByStride.clear();
393 void IVStrideUse::deleted() {
394 // Remove this user from the list.
395 Parent->Users.erase(this);
399 void IVUsersOfOneStride::print(raw_ostream &OS) const {
400 OS << "IV Users of one stride:\n";
403 OS << " Stride: " << *Stride << '\n';
409 for (ilist<IVStrideUse>::const_iterator
410 I = Users.begin(), E = Users.end(); I != E; ++I) {
411 const IVStrideUse &SU = *I;
412 OS << " " << Count++ << '\n';
413 OS << " Offset: " << *SU.getOffset() << '\n';
414 OS << " Instr: " << *SU << '\n';
418 void IVUsersOfOneStride::dump() const {