summaryrefslogtreecommitdiff
path: root/lib/Analysis/IVUsers.cpp
blob: b33e2cb9999e86236494f60ac2e9a99fb08a2913 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
//===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements bookkeeping for "interesting" users of expressions
// computed from induction variables.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "iv-users"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;

char IVUsers::ID = 0;
INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
                      "Induction Variable Users", false, true)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_END(IVUsers, "iv-users",
                      "Induction Variable Users", false, true)

Pass *llvm::createIVUsersPass() {
  return new IVUsers();
}

/// isInteresting - Test whether the given expression is "interesting" when
/// used by the given expression, within the context of analyzing the
/// given loop.
static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
                          ScalarEvolution *SE, LoopInfo *LI) {
  // An addrec is interesting if it's affine or if it has an interesting start.
  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
    // Keep things simple. Don't touch loop-variant strides unless they're
    // only used outside the loop and we can simplify them.
    if (AR->getLoop() == L)
      return AR->isAffine() ||
             (!L->contains(I) &&
              SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
    // Otherwise recurse to see if the start value is interesting, and that
    // the step value is not interesting, since we don't yet know how to
    // do effective SCEV expansions for addrecs with interesting steps.
    return isInteresting(AR->getStart(), I, L, SE, LI) &&
          !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
  }

  // An add is interesting if exactly one of its operands is interesting.
  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
    bool AnyInterestingYet = false;
    for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
         OI != OE; ++OI)
      if (isInteresting(*OI, I, L, SE, LI)) {
        if (AnyInterestingYet)
          return false;
        AnyInterestingYet = true;
      }
    return AnyInterestingYet;
  }

  // Nothing else is interesting here.
  return false;
}

/// Return true if all loop headers that dominate this block are in simplified
/// form.
static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
                                 const LoopInfo *LI,
                                 SmallPtrSet<Loop*,16> &SimpleLoopNests) {
  Loop *NearestLoop = 0;
  for (DomTreeNode *Rung = DT->getNode(BB);
       Rung; Rung = Rung->getIDom()) {
    BasicBlock *DomBB = Rung->getBlock();
    Loop *DomLoop = LI->getLoopFor(DomBB);
    if (DomLoop && DomLoop->getHeader() == DomBB) {
      // If the domtree walk reaches a loop with no preheader, return false.
      if (!DomLoop->isLoopSimplifyForm())
        return false;
      // If we have already checked this loop nest, stop checking.
      if (SimpleLoopNests.count(DomLoop))
        break;
      // If we have not already checked this loop nest, remember the loop
      // header nearest to BB. The nearest loop may not contain BB.
      if (!NearestLoop)
        NearestLoop = DomLoop;
    }
  }
  if (NearestLoop)
    SimpleLoopNests.insert(NearestLoop);
  return true;
}

/// AddUsersImpl - Inspect the specified instruction.  If it is a
/// reducible SCEV, recursively add its users to the IVUsesByStride set and
/// return true.  Otherwise, return false.
bool IVUsers::AddUsersImpl(Instruction *I,
                           SmallPtrSet<Loop*,16> &SimpleLoopNests) {
  // Add this IV user to the Processed set before returning false to ensure that
  // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
  if (!Processed.insert(I))
    return true;    // Instruction already handled.

  if (!SE->isSCEVable(I->getType()))
    return false;   // Void and FP expressions cannot be reduced.

  // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
  // pass to SCEVExpander. Expressions are not safe to expand if they represent
  // operations that are not safe to speculate, namely integer division.
  if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I, TD))
    return false;

  // LSR is not APInt clean, do not touch integers bigger than 64-bits.
  // Also avoid creating IVs of non-native types. For example, we don't want a
  // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
  uint64_t Width = SE->getTypeSizeInBits(I->getType());
  if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
    return false;

  // Get the symbolic expression for this instruction.
  const SCEV *ISE = SE->getSCEV(I);

  // If we've come to an uninteresting expression, stop the traversal and
  // call this a user.
  if (!isInteresting(ISE, I, L, SE, LI))
    return false;

  SmallPtrSet<Instruction *, 4> UniqueUsers;
  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
       UI != E; ++UI) {
    Instruction *User = cast<Instruction>(*UI);
    if (!UniqueUsers.insert(User))
      continue;

    // Do not infinitely recurse on PHI nodes.
    if (isa<PHINode>(User) && Processed.count(User))
      continue;

    // Only consider IVUsers that are dominated by simplified loop
    // headers. Otherwise, SCEVExpander will crash.
    BasicBlock *UseBB = User->getParent();
    // A phi's use is live out of its predecessor block.
    if (PHINode *PHI = dyn_cast<PHINode>(User)) {
      unsigned OperandNo = UI.getOperandNo();
      unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
      UseBB = PHI->getIncomingBlock(ValNo);
    }
    if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
      return false;

    // Descend recursively, but not into PHI nodes outside the current loop.
    // It's important to see the entire expression outside the loop to get
    // choices that depend on addressing mode use right, although we won't
    // consider references outside the loop in all cases.
    // If User is already in Processed, we don't want to recurse into it again,
    // but do want to record a second reference in the same instruction.
    bool AddUserToIVUsers = false;
    if (LI->getLoopFor(User->getParent()) != L) {
      if (isa<PHINode>(User) || Processed.count(User) ||
          !AddUsersImpl(User, SimpleLoopNests)) {
        DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
                     << "   OF SCEV: " << *ISE << '\n');
        AddUserToIVUsers = true;
      }
    } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
      DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
                   << "   OF SCEV: " << *ISE << '\n');
      AddUserToIVUsers = true;
    }

    if (AddUserToIVUsers) {
      // Okay, we found a user that we cannot reduce.
      IVUses.push_back(new IVStrideUse(this, User, I));
      IVStrideUse &NewUse = IVUses.back();
      // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
      // The regular return value here is discarded; instead of recording
      // it, we just recompute it when we need it.
      ISE = TransformForPostIncUse(NormalizeAutodetect,
                                   ISE, User, I,
                                   NewUse.PostIncLoops,
                                   *SE, *DT);
      DEBUG(if (SE->getSCEV(I) != ISE)
              dbgs() << "   NORMALIZED TO: " << *ISE << '\n');
    }
  }
  return true;
}

bool IVUsers::AddUsersIfInteresting(Instruction *I) {
  // SCEVExpander can only handle users that are dominated by simplified loop
  // entries. Keep track of all loops that are only dominated by other simple
  // loops so we don't traverse the domtree for each user.
  SmallPtrSet<Loop*,16> SimpleLoopNests;

  return AddUsersImpl(I, SimpleLoopNests);
}

IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
  IVUses.push_back(new IVStrideUse(this, User, Operand));
  return IVUses.back();
}

IVUsers::IVUsers()
    : LoopPass(ID) {
  initializeIVUsersPass(*PassRegistry::getPassRegistry());
}

void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequired<LoopInfo>();
  AU.addRequired<DominatorTree>();
  AU.addRequired<ScalarEvolution>();
  AU.setPreservesAll();
}

bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {

  L = l;
  LI = &getAnalysis<LoopInfo>();
  DT = &getAnalysis<DominatorTree>();
  SE = &getAnalysis<ScalarEvolution>();
  TD = getAnalysisIfAvailable<DataLayout>();

  // Find all uses of induction variables in this loop, and categorize
  // them by stride.  Start by finding all of the PHI nodes in the header for
  // this loop.  If they are induction variables, inspect their uses.
  for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
    (void)AddUsersIfInteresting(I);

  return false;
}

void IVUsers::print(raw_ostream &OS, const Module *M) const {
  OS << "IV Users for loop ";
  WriteAsOperand(OS, L->getHeader(), false);
  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
    OS << " with backedge-taken count "
       << *SE->getBackedgeTakenCount(L);
  }
  OS << ":\n";

  for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
       E = IVUses.end(); UI != E; ++UI) {
    OS << "  ";
    WriteAsOperand(OS, UI->getOperandValToReplace(), false);
    OS << " = " << *getReplacementExpr(*UI);
    for (PostIncLoopSet::const_iterator
         I = UI->PostIncLoops.begin(),
         E = UI->PostIncLoops.end(); I != E; ++I) {
      OS << " (post-inc with loop ";
      WriteAsOperand(OS, (*I)->getHeader(), false);
      OS << ")";
    }
    OS << " in  ";
    UI->getUser()->print(OS);
    OS << '\n';
  }
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void IVUsers::dump() const {
  print(dbgs());
}
#endif

void IVUsers::releaseMemory() {
  Processed.clear();
  IVUses.clear();
}

/// getReplacementExpr - Return a SCEV expression which computes the
/// value of the OperandValToReplace.
const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
  return SE->getSCEV(IU.getOperandValToReplace());
}

/// getExpr - Return the expression for the use.
const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
  return
    TransformForPostIncUse(Normalize, getReplacementExpr(IU),
                           IU.getUser(), IU.getOperandValToReplace(),
                           const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
                           *SE, *DT);
}

static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
    if (AR->getLoop() == L)
      return AR;
    return findAddRecForLoop(AR->getStart(), L);
  }

  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
    for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
         I != E; ++I)
      if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
        return AR;
    return 0;
  }

  return 0;
}

const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
  if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
    return AR->getStepRecurrence(*SE);
  return 0;
}

void IVStrideUse::transformToPostInc(const Loop *L) {
  PostIncLoops.insert(L);
}

void IVStrideUse::deleted() {
  // Remove this user from the list.
  Parent->Processed.erase(this->getUser());
  Parent->IVUses.erase(this);
  // this now dangles!
}