1 //===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements bookkeeping for "interesting" users of expressions
11 // computed from induction variables.
12 //
13 //===----------------------------------------------------------------------===//
14
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/Target/TargetData.h"
25 #include "llvm/Assembly/Writer.h"
26 #include "llvm/ADT/STLExtras.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include <algorithm>
30 using namespace llvm;
31
32 char IVUsers::ID = 0;
33 INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
34 "Induction Variable Users", false, true)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)35 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
36 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
37 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
38 INITIALIZE_PASS_END(IVUsers, "iv-users",
39 "Induction Variable Users", false, true)
40
41 Pass *llvm::createIVUsersPass() {
42 return new IVUsers();
43 }
44
45 /// isInteresting - Test whether the given expression is "interesting" when
46 /// used by the given expression, within the context of analyzing the
47 /// given loop.
isInteresting(const SCEV * S,const Instruction * I,const Loop * L,ScalarEvolution * SE,LoopInfo * LI)48 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
49 ScalarEvolution *SE, LoopInfo *LI) {
50 // An addrec is interesting if it's affine or if it has an interesting start.
51 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
52 // Keep things simple. Don't touch loop-variant strides unless they're
53 // only used outside the loop and we can simplify them.
54 if (AR->getLoop() == L)
55 return AR->isAffine() ||
56 (!L->contains(I) &&
57 SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
58 // Otherwise recurse to see if the start value is interesting, and that
59 // the step value is not interesting, since we don't yet know how to
60 // do effective SCEV expansions for addrecs with interesting steps.
61 return isInteresting(AR->getStart(), I, L, SE, LI) &&
62 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
63 }
64
65 // An add is interesting if exactly one of its operands is interesting.
66 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
67 bool AnyInterestingYet = false;
68 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
69 OI != OE; ++OI)
70 if (isInteresting(*OI, I, L, SE, LI)) {
71 if (AnyInterestingYet)
72 return false;
73 AnyInterestingYet = true;
74 }
75 return AnyInterestingYet;
76 }
77
78 // Nothing else is interesting here.
79 return false;
80 }
81
82 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
83 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
84 /// return true. Otherwise, return false.
AddUsersIfInteresting(Instruction * I)85 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
86 if (!SE->isSCEVable(I->getType()))
87 return false; // Void and FP expressions cannot be reduced.
88
89 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
90 // Also avoid creating IVs of non-native types. For example, we don't want a
91 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
92 uint64_t Width = SE->getTypeSizeInBits(I->getType());
93 if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
94 return false;
95
96 if (!Processed.insert(I))
97 return true; // Instruction already handled.
98
99 // Get the symbolic expression for this instruction.
100 const SCEV *ISE = SE->getSCEV(I);
101
102 // If we've come to an uninteresting expression, stop the traversal and
103 // call this a user.
104 if (!isInteresting(ISE, I, L, SE, LI))
105 return false;
106
107 SmallPtrSet<Instruction *, 4> UniqueUsers;
108 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
109 UI != E; ++UI) {
110 Instruction *User = cast<Instruction>(*UI);
111 if (!UniqueUsers.insert(User))
112 continue;
113
114 // Do not infinitely recurse on PHI nodes.
115 if (isa<PHINode>(User) && Processed.count(User))
116 continue;
117
118 // Descend recursively, but not into PHI nodes outside the current loop.
119 // It's important to see the entire expression outside the loop to get
120 // choices that depend on addressing mode use right, although we won't
121 // consider references outside the loop in all cases.
122 // If User is already in Processed, we don't want to recurse into it again,
123 // but do want to record a second reference in the same instruction.
124 bool AddUserToIVUsers = false;
125 if (LI->getLoopFor(User->getParent()) != L) {
126 if (isa<PHINode>(User) || Processed.count(User) ||
127 !AddUsersIfInteresting(User)) {
128 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
129 << " OF SCEV: " << *ISE << '\n');
130 AddUserToIVUsers = true;
131 }
132 } else if (Processed.count(User) || !AddUsersIfInteresting(User)) {
133 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
134 << " OF SCEV: " << *ISE << '\n');
135 AddUserToIVUsers = true;
136 }
137
138 if (AddUserToIVUsers) {
139 // Okay, we found a user that we cannot reduce.
140 IVUses.push_back(new IVStrideUse(this, User, I));
141 IVStrideUse &NewUse = IVUses.back();
142 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
143 // The regular return value here is discarded; instead of recording
144 // it, we just recompute it when we need it.
145 ISE = TransformForPostIncUse(NormalizeAutodetect,
146 ISE, User, I,
147 NewUse.PostIncLoops,
148 *SE, *DT);
149 DEBUG(if (SE->getSCEV(I) != ISE)
150 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
151 }
152 }
153 return true;
154 }
155
AddUser(Instruction * User,Value * Operand)156 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
157 IVUses.push_back(new IVStrideUse(this, User, Operand));
158 return IVUses.back();
159 }
160
IVUsers()161 IVUsers::IVUsers()
162 : LoopPass(ID) {
163 initializeIVUsersPass(*PassRegistry::getPassRegistry());
164 }
165
getAnalysisUsage(AnalysisUsage & AU) const166 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
167 AU.addRequired<LoopInfo>();
168 AU.addRequired<DominatorTree>();
169 AU.addRequired<ScalarEvolution>();
170 AU.setPreservesAll();
171 }
172
runOnLoop(Loop * l,LPPassManager & LPM)173 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
174
175 L = l;
176 LI = &getAnalysis<LoopInfo>();
177 DT = &getAnalysis<DominatorTree>();
178 SE = &getAnalysis<ScalarEvolution>();
179 TD = getAnalysisIfAvailable<TargetData>();
180
181 // Find all uses of induction variables in this loop, and categorize
182 // them by stride. Start by finding all of the PHI nodes in the header for
183 // this loop. If they are induction variables, inspect their uses.
184 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
185 (void)AddUsersIfInteresting(I);
186
187 return false;
188 }
189
print(raw_ostream & OS,const Module * M) const190 void IVUsers::print(raw_ostream &OS, const Module *M) const {
191 OS << "IV Users for loop ";
192 WriteAsOperand(OS, L->getHeader(), false);
193 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
194 OS << " with backedge-taken count "
195 << *SE->getBackedgeTakenCount(L);
196 }
197 OS << ":\n";
198
199 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
200 E = IVUses.end(); UI != E; ++UI) {
201 OS << " ";
202 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
203 OS << " = " << *getReplacementExpr(*UI);
204 for (PostIncLoopSet::const_iterator
205 I = UI->PostIncLoops.begin(),
206 E = UI->PostIncLoops.end(); I != E; ++I) {
207 OS << " (post-inc with loop ";
208 WriteAsOperand(OS, (*I)->getHeader(), false);
209 OS << ")";
210 }
211 OS << " in ";
212 UI->getUser()->print(OS);
213 OS << '\n';
214 }
215 }
216
dump() const217 void IVUsers::dump() const {
218 print(dbgs());
219 }
220
releaseMemory()221 void IVUsers::releaseMemory() {
222 Processed.clear();
223 IVUses.clear();
224 }
225
226 /// getReplacementExpr - Return a SCEV expression which computes the
227 /// value of the OperandValToReplace.
getReplacementExpr(const IVStrideUse & IU) const228 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
229 return SE->getSCEV(IU.getOperandValToReplace());
230 }
231
232 /// getExpr - Return the expression for the use.
getExpr(const IVStrideUse & IU) const233 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
234 return
235 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
236 IU.getUser(), IU.getOperandValToReplace(),
237 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
238 *SE, *DT);
239 }
240
findAddRecForLoop(const SCEV * S,const Loop * L)241 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
242 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
243 if (AR->getLoop() == L)
244 return AR;
245 return findAddRecForLoop(AR->getStart(), L);
246 }
247
248 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
249 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
250 I != E; ++I)
251 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
252 return AR;
253 return 0;
254 }
255
256 return 0;
257 }
258
getStride(const IVStrideUse & IU,const Loop * L) const259 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
260 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
261 return AR->getStepRecurrence(*SE);
262 return 0;
263 }
264
transformToPostInc(const Loop * L)265 void IVStrideUse::transformToPostInc(const Loop *L) {
266 PostIncLoops.insert(L);
267 }
268
deleted()269 void IVStrideUse::deleted() {
270 // Remove this user from the list.
271 Parent->IVUses.erase(this);
272 // this now dangles!
273 }
274