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> 30using namespace llvm; 31 32char IVUsers::ID = 0; 33INITIALIZE_PASS_BEGIN(IVUsers, "iv-users", 34 "Induction Variable Users", false, true) 35INITIALIZE_PASS_DEPENDENCY(LoopInfo) 36INITIALIZE_PASS_DEPENDENCY(DominatorTree) 37INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) 38INITIALIZE_PASS_END(IVUsers, "iv-users", 39 "Induction Variable Users", false, true) 40 41Pass *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. 48static 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. 85bool 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 156IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) { 157 IVUses.push_back(new IVStrideUse(this, User, Operand)); 158 return IVUses.back(); 159} 160 161IVUsers::IVUsers() 162 : LoopPass(ID) { 163 initializeIVUsersPass(*PassRegistry::getPassRegistry()); 164} 165 166void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const { 167 AU.addRequired<LoopInfo>(); 168 AU.addRequired<DominatorTree>(); 169 AU.addRequired<ScalarEvolution>(); 170 AU.setPreservesAll(); 171} 172 173bool 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 190void 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 217void IVUsers::dump() const { 218 print(dbgs()); 219} 220 221void IVUsers::releaseMemory() { 222 Processed.clear(); 223 IVUses.clear(); 224} 225 226/// getReplacementExpr - Return a SCEV expression which computes the 227/// value of the OperandValToReplace. 228const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const { 229 return SE->getSCEV(IU.getOperandValToReplace()); 230} 231 232/// getExpr - Return the expression for the use. 233const 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 241static 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 259const 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 265void IVStrideUse::transformToPostInc(const Loop *L) { 266 PostIncLoops.insert(L); 267} 268 269void IVStrideUse::deleted() { 270 // Remove this user from the list. 271 Parent->IVUses.erase(this); 272 // this now dangles! 273} 274