lib/Analysis/IVUsers.cpp

   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/ADT/STLExtras.h"
  25 #include "llvm/Support/Debug.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 #include <algorithm>
  28 using namespace llvm;
  29
  30 char IVUsers::ID = 0;
  31 INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
  32                       "Induction Variable Users", false, true)
  33 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
  34 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
  35 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
  36 INITIALIZE_PASS_END(IVUsers, "iv-users",
  37                       "Induction Variable Users", false, true)
  38
  39 Pass *llvm::createIVUsersPass() {
  40   return new IVUsers();
  41 }
  42
  43 /// isInteresting - Test whether the given expression is "interesting" when
  44 /// used by the given expression, within the context of analyzing the
  45 /// given loop.
  46 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
  47                           ScalarEvolution *SE) {
  48   // An addrec is interesting if it's affine or if it has an interesting start.
  49   if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
  50     // Keep things simple. Don't touch loop-variant strides.
  51     if (AR->getLoop() == L)
  52       return AR->isAffine() || !L->contains(I);
  53     // Otherwise recurse to see if the start value is interesting, and that
  54     // the step value is not interesting, since we don't yet know how to
  55     // do effective SCEV expansions for addrecs with interesting steps.
  56     return isInteresting(AR->getStart(), I, L, SE) &&
  57           !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
  58   }
  59
  60   // An add is interesting if exactly one of its operands is interesting.
  61   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
  62     bool AnyInterestingYet = false;
  63     for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
  64          OI != OE; ++OI)
  65       if (isInteresting(*OI, I, L, SE)) {
  66         if (AnyInterestingYet)
  67           return false;
  68         AnyInterestingYet = true;
  69       }
  70     return AnyInterestingYet;
  71   }
  72
  73   // Nothing else is interesting here.
  74   return false;
  75 }
  76
  77 /// AddUsersIfInteresting - Inspect the specified instruction.  If it is a
  78 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
  79 /// return true.  Otherwise, return false.
  80 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
  81   if (!SE->isSCEVable(I->getType()))
  82     return false;   // Void and FP expressions cannot be reduced.
  83
  84   // LSR is not APInt clean, do not touch integers bigger than 64-bits.
  85   if (SE->getTypeSizeInBits(I->getType()) > 64)
  86     return false;
  87
  88   if (!Processed.insert(I))
  89     return true;    // Instruction already handled.
  90
  91   // Get the symbolic expression for this instruction.
  92   const SCEV *ISE = SE->getSCEV(I);
  93
  94   // If we've come to an uninteresting expression, stop the traversal and
  95   // call this a user.
  96   if (!isInteresting(ISE, I, L, SE))
  97     return false;
  98
  99   SmallPtrSet<Instruction *, 4> UniqueUsers;
 100   for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
 101        UI != E; ++UI) {
 102     Instruction *User = cast<Instruction>(*UI);
 103     if (!UniqueUsers.insert(User))
 104       continue;
 105
 106     // Do not infinitely recurse on PHI nodes.
 107     if (isa<PHINode>(User) && Processed.count(User))
 108       continue;
 109
 110     // Descend recursively, but not into PHI nodes outside the current loop.
 111     // It's important to see the entire expression outside the loop to get
 112     // choices that depend on addressing mode use right, although we won't
 113     // consider references outside the loop in all cases.
 114     // If User is already in Processed, we don't want to recurse into it again,
 115     // but do want to record a second reference in the same instruction.
 116     bool AddUserToIVUsers = false;
 117     if (LI->getLoopFor(User->getParent()) != L) {
 118       if (isa<PHINode>(User) || Processed.count(User) ||
 119           !AddUsersIfInteresting(User)) {
 120         DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
 121                      << "   OF SCEV: " << *ISE << '\n');
 122         AddUserToIVUsers = true;
 123       }
 124     } else if (Processed.count(User) ||
 125                !AddUsersIfInteresting(User)) {
 126       DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
 127                    << "   OF SCEV: " << *ISE << '\n');
 128       AddUserToIVUsers = true;
 129     }
 130
 131     if (AddUserToIVUsers) {
 132       // Okay, we found a user that we cannot reduce.
 133       IVUses.push_back(new IVStrideUse(this, User, I));
 134       IVStrideUse &NewUse = IVUses.back();
 135       // Transform the expression into a normalized form.
 136       ISE = TransformForPostIncUse(NormalizeAutodetect,
 137                                    ISE, User, I,
 138                                    NewUse.PostIncLoops,
 139                                    *SE, *DT);
 140       DEBUG(dbgs() << "   NORMALIZED TO: " << *ISE << '\n');
 141     }
 142   }
 143   return true;
 144 }
 145
 146 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
 147   IVUses.push_back(new IVStrideUse(this, User, Operand));
 148   return IVUses.back();
 149 }
 150
 151 IVUsers::IVUsers()
 152     : LoopPass(ID) {
 153   initializeIVUsersPass(*PassRegistry::getPassRegistry());
 154 }
 155
 156 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
 157   AU.addRequired<LoopInfo>();
 158   AU.addRequired<DominatorTree>();
 159   AU.addRequired<ScalarEvolution>();
 160   AU.setPreservesAll();
 161 }
 162
 163 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
 164
 165   L = l;
 166   LI = &getAnalysis<LoopInfo>();
 167   DT = &getAnalysis<DominatorTree>();
 168   SE = &getAnalysis<ScalarEvolution>();
 169
 170   // Find all uses of induction variables in this loop, and categorize
 171   // them by stride.  Start by finding all of the PHI nodes in the header for
 172   // this loop.  If they are induction variables, inspect their uses.
 173   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
 174     (void)AddUsersIfInteresting(I);
 175
 176   return false;
 177 }
 178
 179 void IVUsers::print(raw_ostream &OS, const Module *M) const {
 180   OS << "IV Users for loop ";
 181   WriteAsOperand(OS, L->getHeader(), false);
 182   if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
 183     OS << " with backedge-taken count "
 184        << *SE->getBackedgeTakenCount(L);
 185   }
 186   OS << ":\n";
 187
 188   for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
 189        E = IVUses.end(); UI != E; ++UI) {
 190     OS << "  ";
 191     WriteAsOperand(OS, UI->getOperandValToReplace(), false);
 192     OS << " = " << *getReplacementExpr(*UI);
 193     for (PostIncLoopSet::const_iterator
 194          I = UI->PostIncLoops.begin(),
 195          E = UI->PostIncLoops.end(); I != E; ++I) {
 196       OS << " (post-inc with loop ";
 197       WriteAsOperand(OS, (*I)->getHeader(), false);
 198       OS << ")";
 199     }
 200     OS << " in  ";
 201     UI->getUser()->print(OS);
 202     OS << '\n';
 203   }
 204 }
 205
 206 void IVUsers::dump() const {
 207   print(dbgs());
 208 }
 209
 210 void IVUsers::releaseMemory() {
 211   Processed.clear();
 212   IVUses.clear();
 213 }
 214
 215 /// getReplacementExpr - Return a SCEV expression which computes the
 216 /// value of the OperandValToReplace.
 217 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
 218   return SE->getSCEV(IU.getOperandValToReplace());
 219 }
 220
 221 /// getExpr - Return the expression for the use.
 222 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
 223   return
 224     TransformForPostIncUse(Normalize, getReplacementExpr(IU),
 225                            IU.getUser(), IU.getOperandValToReplace(),
 226                            const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
 227                            *SE, *DT);
 228 }
 229
 230 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
 231   if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
 232     if (AR->getLoop() == L)
 233       return AR;
 234     return findAddRecForLoop(AR->getStart(), L);
 235   }
 236
 237   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
 238     for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
 239          I != E; ++I)
 240       if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
 241         return AR;
 242     return 0;
 243   }
 244
 245   return 0;
 246 }
 247
 248 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
 249   if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
 250     return AR->getStepRecurrence(*SE);
 251   return 0;
 252 }
 253
 254 void IVStrideUse::transformToPostInc(const Loop *L) {
 255   PostIncLoops.insert(L);
 256 }
 257
 258 void IVStrideUse::deleted() {
 259   // Remove this user from the list.
 260   Parent->IVUses.erase(this);
 261   // this now dangles!
 262 }