IVUsers.cpp revision 207618 
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/Assembly/AsmAnnotationWriter.h"
25#include "llvm/ADT/STLExtras.h"
26#include "llvm/Support/Debug.h"
27#include "llvm/Support/raw_ostream.h"
28#include <algorithm>
29using namespace llvm;
30
31char IVUsers::ID = 0;
32static RegisterPass<IVUsers>
33X("iv-users", "Induction Variable Users", false, true);
34
35Pass *llvm::createIVUsersPass() {
36  return new IVUsers();
37}
38
39/// isInteresting - Test whether the given expression is "interesting" when
40/// used by the given expression, within the context of analyzing the
41/// given loop.
42static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
43  // Anything loop-invariant is interesting.
44  if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
45    return true;
46
47  // An addrec is interesting if it's affine or if it has an interesting start.
48  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
49    // Keep things simple. Don't touch loop-variant strides.
50    if (AR->getLoop() == L)
51      return AR->isAffine() || !L->contains(I);
52    // Otherwise recurse to see if the start value is interesting.
53    return isInteresting(AR->getStart(), I, L);
54  }
55
56  // An add is interesting if any of its operands is.
57  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
58    for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
59         OI != OE; ++OI)
60      if (isInteresting(*OI, I, L))
61        return true;
62    return false;
63  }
64
65  // Nothing else is interesting here.
66  return false;
67}
68
69/// AddUsersIfInteresting - Inspect the specified instruction.  If it is a
70/// reducible SCEV, recursively add its users to the IVUsesByStride set and
71/// return true.  Otherwise, return false.
72bool IVUsers::AddUsersIfInteresting(Instruction *I) {
73  if (!SE->isSCEVable(I->getType()))
74    return false;   // Void and FP expressions cannot be reduced.
75
76  // LSR is not APInt clean, do not touch integers bigger than 64-bits.
77  if (SE->getTypeSizeInBits(I->getType()) > 64)
78    return false;
79
80  if (!Processed.insert(I))
81    return true;    // Instruction already handled.
82
83  // Get the symbolic expression for this instruction.
84  const SCEV *ISE = SE->getSCEV(I);
85
86  // If we've come to an uninteresting expression, stop the traversal and
87  // call this a user.
88  if (!isInteresting(ISE, I, L))
89    return false;
90
91  SmallPtrSet<Instruction *, 4> UniqueUsers;
92  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
93       UI != E; ++UI) {
94    Instruction *User = cast<Instruction>(*UI);
95    if (!UniqueUsers.insert(User))
96      continue;
97
98    // Do not infinitely recurse on PHI nodes.
99    if (isa<PHINode>(User) && Processed.count(User))
100      continue;
101
102    // Descend recursively, but not into PHI nodes outside the current loop.
103    // It's important to see the entire expression outside the loop to get
104    // choices that depend on addressing mode use right, although we won't
105    // consider references outside the loop in all cases.
106    // If User is already in Processed, we don't want to recurse into it again,
107    // but do want to record a second reference in the same instruction.
108    bool AddUserToIVUsers = false;
109    if (LI->getLoopFor(User->getParent()) != L) {
110      if (isa<PHINode>(User) || Processed.count(User) ||
111          !AddUsersIfInteresting(User)) {
112        DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
113                     << "   OF SCEV: " << *ISE << '\n');
114        AddUserToIVUsers = true;
115      }
116    } else if (Processed.count(User) ||
117               !AddUsersIfInteresting(User)) {
118      DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
119                   << "   OF SCEV: " << *ISE << '\n');
120      AddUserToIVUsers = true;
121    }
122
123    if (AddUserToIVUsers) {
124      // Okay, we found a user that we cannot reduce.
125      IVUses.push_back(new IVStrideUse(this, User, I));
126      IVStrideUse &NewUse = IVUses.back();
127      // Transform the expression into a normalized form.
128      ISE = TransformForPostIncUse(NormalizeAutodetect,
129                                   ISE, User, I,
130                                   NewUse.PostIncLoops,
131                                   *SE, *DT);
132      DEBUG(dbgs() << "   NORMALIZED TO: " << *ISE << '\n');
133    }
134  }
135  return true;
136}
137
138IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
139  IVUses.push_back(new IVStrideUse(this, User, Operand));
140  return IVUses.back();
141}
142
143IVUsers::IVUsers()
144 : LoopPass(&ID) {
145}
146
147void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
148  AU.addRequired<LoopInfo>();
149  AU.addRequired<DominatorTree>();
150  AU.addRequired<ScalarEvolution>();
151  AU.setPreservesAll();
152}
153
154bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
155
156  L = l;
157  LI = &getAnalysis<LoopInfo>();
158  DT = &getAnalysis<DominatorTree>();
159  SE = &getAnalysis<ScalarEvolution>();
160
161  // Find all uses of induction variables in this loop, and categorize
162  // them by stride.  Start by finding all of the PHI nodes in the header for
163  // this loop.  If they are induction variables, inspect their uses.
164  for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
165    (void)AddUsersIfInteresting(I);
166
167  return false;
168}
169
170void IVUsers::print(raw_ostream &OS, const Module *M) const {
171  OS << "IV Users for loop ";
172  WriteAsOperand(OS, L->getHeader(), false);
173  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
174    OS << " with backedge-taken count "
175       << *SE->getBackedgeTakenCount(L);
176  }
177  OS << ":\n";
178
179  // Use a default AssemblyAnnotationWriter to suppress the default info
180  // comments, which aren't relevant here.
181  AssemblyAnnotationWriter Annotator;
182  for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
183       E = IVUses.end(); UI != E; ++UI) {
184    OS << "  ";
185    WriteAsOperand(OS, UI->getOperandValToReplace(), false);
186    OS << " = " << *getReplacementExpr(*UI);
187    for (PostIncLoopSet::const_iterator
188         I = UI->PostIncLoops.begin(),
189         E = UI->PostIncLoops.end(); I != E; ++I) {
190      OS << " (post-inc with loop ";
191      WriteAsOperand(OS, (*I)->getHeader(), false);
192      OS << ")";
193    }
194    OS << " in  ";
195    UI->getUser()->print(OS, &Annotator);
196    OS << '\n';
197  }
198}
199
200void IVUsers::dump() const {
201  print(dbgs());
202}
203
204void IVUsers::releaseMemory() {
205  Processed.clear();
206  IVUses.clear();
207}
208
209/// getReplacementExpr - Return a SCEV expression which computes the
210/// value of the OperandValToReplace.
211const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
212  return SE->getSCEV(IU.getOperandValToReplace());
213}
214
215/// getExpr - Return the expression for the use.
216const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
217  return
218    TransformForPostIncUse(Normalize, getReplacementExpr(IU),
219                           IU.getUser(), IU.getOperandValToReplace(),
220                           const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
221                           *SE, *DT);
222}
223
224static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
225  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
226    if (AR->getLoop() == L)
227      return AR;
228    return findAddRecForLoop(AR->getStart(), L);
229  }
230
231  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
232    for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
233         I != E; ++I)
234      if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
235        return AR;
236    return 0;
237  }
238
239  return 0;
240}
241
242const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
243  if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
244    return AR->getStepRecurrence(*SE);
245  return 0;
246}
247
248void IVStrideUse::transformToPostInc(const Loop *L) {
249  PostIncLoops.insert(L);
250}
251
252void IVStrideUse::deleted() {
253  // Remove this user from the list.
254  Parent->IVUses.erase(this);
255  // this now dangles!
256}
257