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/Support/CommandLine.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Assembly/Writer.h"
27 #include "llvm/ADT/STLExtras.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
34 INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
35 "Induction Variable Users", false, true)
36 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
37 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
38 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
39 INITIALIZE_PASS_END(IVUsers, "iv-users",
40 "Induction Variable Users", false, true)
42 // IVUsers behavior currently depends on this temporary indvars mode. The
43 // option must be defined upstream from its uses.
45 bool DisableIVRewrite = false;
47 cl::opt<bool, true> DisableIVRewriteOpt(
48 "disable-iv-rewrite", cl::Hidden, cl::location(llvm::DisableIVRewrite),
49 cl::desc("Disable canonical induction variable rewriting"));
51 Pass *llvm::createIVUsersPass() {
55 /// isInteresting - Test whether the given expression is "interesting" when
56 /// used by the given expression, within the context of analyzing the
58 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
59 ScalarEvolution *SE) {
60 // An addrec is interesting if it's affine or if it has an interesting start.
61 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
62 // Keep things simple. Don't touch loop-variant strides.
63 if (AR->getLoop() == L)
64 return AR->isAffine() || !L->contains(I);
65 // Otherwise recurse to see if the start value is interesting, and that
66 // the step value is not interesting, since we don't yet know how to
67 // do effective SCEV expansions for addrecs with interesting steps.
68 return isInteresting(AR->getStart(), I, L, SE) &&
69 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
72 // An add is interesting if exactly one of its operands is interesting.
73 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
74 bool AnyInterestingYet = false;
75 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
77 if (isInteresting(*OI, I, L, SE)) {
78 if (AnyInterestingYet)
80 AnyInterestingYet = true;
82 return AnyInterestingYet;
85 // Nothing else is interesting here.
89 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
90 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
91 /// return true. Otherwise, return false.
92 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
93 if (!SE->isSCEVable(I->getType()))
94 return false; // Void and FP expressions cannot be reduced.
96 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
97 // Also avoid creating IVs of non-native types. For example, we don't want a
98 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
99 uint64_t Width = SE->getTypeSizeInBits(I->getType());
100 if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
103 // We expect Sign/Zero extension to be eliminated from the IR before analyzing
104 // any downstream uses.
105 if (DisableIVRewrite && (isa<SExtInst>(I) || isa<ZExtInst>(I)))
108 if (!Processed.insert(I))
109 return true; // Instruction already handled.
111 // Get the symbolic expression for this instruction.
112 const SCEV *ISE = SE->getSCEV(I);
114 // If we've come to an uninteresting expression, stop the traversal and
116 if (!isInteresting(ISE, I, L, SE))
119 SmallPtrSet<Instruction *, 4> UniqueUsers;
120 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
122 Instruction *User = cast<Instruction>(*UI);
123 if (!UniqueUsers.insert(User))
126 // Do not infinitely recurse on PHI nodes.
127 if (isa<PHINode>(User) && Processed.count(User))
130 // Descend recursively, but not into PHI nodes outside the current loop.
131 // It's important to see the entire expression outside the loop to get
132 // choices that depend on addressing mode use right, although we won't
133 // consider references outside the loop in all cases.
134 // If User is already in Processed, we don't want to recurse into it again,
135 // but do want to record a second reference in the same instruction.
136 bool AddUserToIVUsers = false;
137 if (LI->getLoopFor(User->getParent()) != L) {
138 if (isa<PHINode>(User) || Processed.count(User) ||
139 !AddUsersIfInteresting(User)) {
140 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
141 << " OF SCEV: " << *ISE << '\n');
142 AddUserToIVUsers = true;
144 } else if (Processed.count(User) ||
145 !AddUsersIfInteresting(User)) {
146 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
147 << " OF SCEV: " << *ISE << '\n');
148 AddUserToIVUsers = true;
151 if (AddUserToIVUsers) {
152 // Okay, we found a user that we cannot reduce.
153 IVUses.push_back(new IVStrideUse(this, User, I));
154 IVStrideUse &NewUse = IVUses.back();
155 // Transform the expression into a normalized form.
156 ISE = TransformForPostIncUse(NormalizeAutodetect,
160 DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
166 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
167 IVUses.push_back(new IVStrideUse(this, User, Operand));
168 return IVUses.back();
173 initializeIVUsersPass(*PassRegistry::getPassRegistry());
176 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
177 AU.addRequired<LoopInfo>();
178 AU.addRequired<DominatorTree>();
179 AU.addRequired<ScalarEvolution>();
180 AU.setPreservesAll();
183 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
186 LI = &getAnalysis<LoopInfo>();
187 DT = &getAnalysis<DominatorTree>();
188 SE = &getAnalysis<ScalarEvolution>();
189 TD = getAnalysisIfAvailable<TargetData>();
191 // Find all uses of induction variables in this loop, and categorize
192 // them by stride. Start by finding all of the PHI nodes in the header for
193 // this loop. If they are induction variables, inspect their uses.
194 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
195 (void)AddUsersIfInteresting(I);
200 void IVUsers::print(raw_ostream &OS, const Module *M) const {
201 OS << "IV Users for loop ";
202 WriteAsOperand(OS, L->getHeader(), false);
203 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
204 OS << " with backedge-taken count "
205 << *SE->getBackedgeTakenCount(L);
209 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
210 E = IVUses.end(); UI != E; ++UI) {
212 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
213 OS << " = " << *getReplacementExpr(*UI);
214 for (PostIncLoopSet::const_iterator
215 I = UI->PostIncLoops.begin(),
216 E = UI->PostIncLoops.end(); I != E; ++I) {
217 OS << " (post-inc with loop ";
218 WriteAsOperand(OS, (*I)->getHeader(), false);
222 UI->getUser()->print(OS);
227 void IVUsers::dump() const {
231 void IVUsers::releaseMemory() {
236 /// getReplacementExpr - Return a SCEV expression which computes the
237 /// value of the OperandValToReplace.
238 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
239 return SE->getSCEV(IU.getOperandValToReplace());
242 /// getExpr - Return the expression for the use.
243 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
245 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
246 IU.getUser(), IU.getOperandValToReplace(),
247 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
251 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
252 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
253 if (AR->getLoop() == L)
255 return findAddRecForLoop(AR->getStart(), L);
258 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
259 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
261 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
269 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
270 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
271 return AR->getStepRecurrence(*SE);
275 void IVStrideUse::transformToPostInc(const Loop *L) {
276 PostIncLoops.insert(L);
279 void IVStrideUse::deleted() {
280 // Remove this user from the list.
281 Parent->IVUses.erase(this);