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comparison lib/Analysis/IVUsers.cpp @ 3:9ad51c7bc036

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1st commit. remove git dir and add all files.
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Wed, 15 May 2013 06:43:32 +0900
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-1:000000000000 3:9ad51c7bc036
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/ADT/STLExtras.h"
18 #include "llvm/Analysis/Dominators.h"
19 #include "llvm/Analysis/LoopPass.h"
20 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
21 #include "llvm/Analysis/ValueTracking.h"
22 #include "llvm/Assembly/Writer.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/Instructions.h"
27 #include "llvm/IR/Type.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include <algorithm>
31 using namespace llvm;
32
33 char IVUsers::ID = 0;
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)
41
42 Pass *llvm::createIVUsersPass() {
43 return new IVUsers();
44 }
45
46 /// isInteresting - Test whether the given expression is "interesting" when
47 /// used by the given expression, within the context of analyzing the
48 /// given loop.
49 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
50 ScalarEvolution *SE, LoopInfo *LI) {
51 // An addrec is interesting if it's affine or if it has an interesting start.
52 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
53 // Keep things simple. Don't touch loop-variant strides unless they're
54 // only used outside the loop and we can simplify them.
55 if (AR->getLoop() == L)
56 return AR->isAffine() ||
57 (!L->contains(I) &&
58 SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
59 // Otherwise recurse to see if the start value is interesting, and that
60 // the step value is not interesting, since we don't yet know how to
61 // do effective SCEV expansions for addrecs with interesting steps.
62 return isInteresting(AR->getStart(), I, L, SE, LI) &&
63 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
64 }
65
66 // An add is interesting if exactly one of its operands is interesting.
67 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
68 bool AnyInterestingYet = false;
69 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
70 OI != OE; ++OI)
71 if (isInteresting(*OI, I, L, SE, LI)) {
72 if (AnyInterestingYet)
73 return false;
74 AnyInterestingYet = true;
75 }
76 return AnyInterestingYet;
77 }
78
79 // Nothing else is interesting here.
80 return false;
81 }
82
83 /// Return true if all loop headers that dominate this block are in simplified
84 /// form.
85 static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
86 const LoopInfo *LI,
87 SmallPtrSet<Loop*,16> &SimpleLoopNests) {
88 Loop *NearestLoop = 0;
89 for (DomTreeNode *Rung = DT->getNode(BB);
90 Rung; Rung = Rung->getIDom()) {
91 BasicBlock *DomBB = Rung->getBlock();
92 Loop *DomLoop = LI->getLoopFor(DomBB);
93 if (DomLoop && DomLoop->getHeader() == DomBB) {
94 // If the domtree walk reaches a loop with no preheader, return false.
95 if (!DomLoop->isLoopSimplifyForm())
96 return false;
97 // If we have already checked this loop nest, stop checking.
98 if (SimpleLoopNests.count(DomLoop))
99 break;
100 // If we have not already checked this loop nest, remember the loop
101 // header nearest to BB. The nearest loop may not contain BB.
102 if (!NearestLoop)
103 NearestLoop = DomLoop;
104 }
105 }
106 if (NearestLoop)
107 SimpleLoopNests.insert(NearestLoop);
108 return true;
109 }
110
111 /// AddUsersImpl - Inspect the specified instruction. If it is a
112 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
113 /// return true. Otherwise, return false.
114 bool IVUsers::AddUsersImpl(Instruction *I,
115 SmallPtrSet<Loop*,16> &SimpleLoopNests) {
116 // Add this IV user to the Processed set before returning false to ensure that
117 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
118 if (!Processed.insert(I))
119 return true; // Instruction already handled.
120
121 if (!SE->isSCEVable(I->getType()))
122 return false; // Void and FP expressions cannot be reduced.
123
124 // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
125 // pass to SCEVExpander. Expressions are not safe to expand if they represent
126 // operations that are not safe to speculate, namely integer division.
127 if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I, TD))
128 return false;
129
130 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
131 // Also avoid creating IVs of non-native types. For example, we don't want a
132 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
133 uint64_t Width = SE->getTypeSizeInBits(I->getType());
134 if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
135 return false;
136
137 // Get the symbolic expression for this instruction.
138 const SCEV *ISE = SE->getSCEV(I);
139
140 // If we've come to an uninteresting expression, stop the traversal and
141 // call this a user.
142 if (!isInteresting(ISE, I, L, SE, LI))
143 return false;
144
145 SmallPtrSet<Instruction *, 4> UniqueUsers;
146 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
147 UI != E; ++UI) {
148 Instruction *User = cast<Instruction>(*UI);
149 if (!UniqueUsers.insert(User))
150 continue;
151
152 // Do not infinitely recurse on PHI nodes.
153 if (isa<PHINode>(User) && Processed.count(User))
154 continue;
155
156 // Only consider IVUsers that are dominated by simplified loop
157 // headers. Otherwise, SCEVExpander will crash.
158 BasicBlock *UseBB = User->getParent();
159 // A phi's use is live out of its predecessor block.
160 if (PHINode *PHI = dyn_cast<PHINode>(User)) {
161 unsigned OperandNo = UI.getOperandNo();
162 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
163 UseBB = PHI->getIncomingBlock(ValNo);
164 }
165 if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
166 return false;
167
168 // Descend recursively, but not into PHI nodes outside the current loop.
169 // It's important to see the entire expression outside the loop to get
170 // choices that depend on addressing mode use right, although we won't
171 // consider references outside the loop in all cases.
172 // If User is already in Processed, we don't want to recurse into it again,
173 // but do want to record a second reference in the same instruction.
174 bool AddUserToIVUsers = false;
175 if (LI->getLoopFor(User->getParent()) != L) {
176 if (isa<PHINode>(User) || Processed.count(User) ||
177 !AddUsersImpl(User, SimpleLoopNests)) {
178 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
179 << " OF SCEV: " << *ISE << '\n');
180 AddUserToIVUsers = true;
181 }
182 } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
183 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
184 << " OF SCEV: " << *ISE << '\n');
185 AddUserToIVUsers = true;
186 }
187
188 if (AddUserToIVUsers) {
189 // Okay, we found a user that we cannot reduce.
190 IVUses.push_back(new IVStrideUse(this, User, I));
191 IVStrideUse &NewUse = IVUses.back();
192 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
193 // The regular return value here is discarded; instead of recording
194 // it, we just recompute it when we need it.
195 ISE = TransformForPostIncUse(NormalizeAutodetect,
196 ISE, User, I,
197 NewUse.PostIncLoops,
198 *SE, *DT);
199 DEBUG(if (SE->getSCEV(I) != ISE)
200 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
201 }
202 }
203 return true;
204 }
205
206 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
207 // SCEVExpander can only handle users that are dominated by simplified loop
208 // entries. Keep track of all loops that are only dominated by other simple
209 // loops so we don't traverse the domtree for each user.
210 SmallPtrSet<Loop*,16> SimpleLoopNests;
211
212 return AddUsersImpl(I, SimpleLoopNests);
213 }
214
215 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
216 IVUses.push_back(new IVStrideUse(this, User, Operand));
217 return IVUses.back();
218 }
219
220 IVUsers::IVUsers()
221 : LoopPass(ID) {
222 initializeIVUsersPass(*PassRegistry::getPassRegistry());
223 }
224
225 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
226 AU.addRequired<LoopInfo>();
227 AU.addRequired<DominatorTree>();
228 AU.addRequired<ScalarEvolution>();
229 AU.setPreservesAll();
230 }
231
232 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
233
234 L = l;
235 LI = &getAnalysis<LoopInfo>();
236 DT = &getAnalysis<DominatorTree>();
237 SE = &getAnalysis<ScalarEvolution>();
238 TD = getAnalysisIfAvailable<DataLayout>();
239
240 // Find all uses of induction variables in this loop, and categorize
241 // them by stride. Start by finding all of the PHI nodes in the header for
242 // this loop. If they are induction variables, inspect their uses.
243 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
244 (void)AddUsersIfInteresting(I);
245
246 return false;
247 }
248
249 void IVUsers::print(raw_ostream &OS, const Module *M) const {
250 OS << "IV Users for loop ";
251 WriteAsOperand(OS, L->getHeader(), false);
252 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
253 OS << " with backedge-taken count "
254 << *SE->getBackedgeTakenCount(L);
255 }
256 OS << ":\n";
257
258 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
259 E = IVUses.end(); UI != E; ++UI) {
260 OS << " ";
261 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
262 OS << " = " << *getReplacementExpr(*UI);
263 for (PostIncLoopSet::const_iterator
264 I = UI->PostIncLoops.begin(),
265 E = UI->PostIncLoops.end(); I != E; ++I) {
266 OS << " (post-inc with loop ";
267 WriteAsOperand(OS, (*I)->getHeader(), false);
268 OS << ")";
269 }
270 OS << " in ";
271 UI->getUser()->print(OS);
272 OS << '\n';
273 }
274 }
275
276 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
277 void IVUsers::dump() const {
278 print(dbgs());
279 }
280 #endif
281
282 void IVUsers::releaseMemory() {
283 Processed.clear();
284 IVUses.clear();
285 }
286
287 /// getReplacementExpr - Return a SCEV expression which computes the
288 /// value of the OperandValToReplace.
289 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
290 return SE->getSCEV(IU.getOperandValToReplace());
291 }
292
293 /// getExpr - Return the expression for the use.
294 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
295 return
296 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
297 IU.getUser(), IU.getOperandValToReplace(),
298 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
299 *SE, *DT);
300 }
301
302 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
303 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
304 if (AR->getLoop() == L)
305 return AR;
306 return findAddRecForLoop(AR->getStart(), L);
307 }
308
309 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
310 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
311 I != E; ++I)
312 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
313 return AR;
314 return 0;
315 }
316
317 return 0;
318 }
319
320 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
321 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
322 return AR->getStepRecurrence(*SE);
323 return 0;
324 }
325
326 void IVStrideUse::transformToPostInc(const Loop *L) {
327 PostIncLoops.insert(L);
328 }
329
330 void IVStrideUse::deleted() {
331 // Remove this user from the list.
332 Parent->Processed.erase(this->getUser());
333 Parent->IVUses.erase(this);
334 // this now dangles!
335 }