Reassociate.cpp revision 280031
1//===- Reassociate.cpp - Reassociate binary expressions -------------------===// 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 pass reassociates commutative expressions in an order that is designed 11// to promote better constant propagation, GCSE, LICM, PRE, etc. 12// 13// For example: 4 + (x + 5) -> x + (4 + 5) 14// 15// In the implementation of this algorithm, constants are assigned rank = 0, 16// function arguments are rank = 1, and other values are assigned ranks 17// corresponding to the reverse post order traversal of current function 18// (starting at 2), which effectively gives values in deep loops higher rank 19// than values not in loops. 20// 21//===----------------------------------------------------------------------===// 22 23#include "llvm/Transforms/Scalar.h" 24#include "llvm/ADT/DenseMap.h" 25#include "llvm/ADT/PostOrderIterator.h" 26#include "llvm/ADT/STLExtras.h" 27#include "llvm/ADT/SetVector.h" 28#include "llvm/ADT/Statistic.h" 29#include "llvm/IR/CFG.h" 30#include "llvm/IR/Constants.h" 31#include "llvm/IR/DerivedTypes.h" 32#include "llvm/IR/Function.h" 33#include "llvm/IR/IRBuilder.h" 34#include "llvm/IR/Instructions.h" 35#include "llvm/IR/IntrinsicInst.h" 36#include "llvm/IR/ValueHandle.h" 37#include "llvm/Pass.h" 38#include "llvm/Support/Debug.h" 39#include "llvm/Support/raw_ostream.h" 40#include "llvm/Transforms/Utils/Local.h" 41#include <algorithm> 42using namespace llvm; 43 44#define DEBUG_TYPE "reassociate" 45 46STATISTIC(NumChanged, "Number of insts reassociated"); 47STATISTIC(NumAnnihil, "Number of expr tree annihilated"); 48STATISTIC(NumFactor , "Number of multiplies factored"); 49 50namespace { 51 struct ValueEntry { 52 unsigned Rank; 53 Value *Op; 54 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {} 55 }; 56 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) { 57 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start. 58 } 59} 60 61#ifndef NDEBUG 62/// PrintOps - Print out the expression identified in the Ops list. 63/// 64static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) { 65 Module *M = I->getParent()->getParent()->getParent(); 66 dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " " 67 << *Ops[0].Op->getType() << '\t'; 68 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 69 dbgs() << "[ "; 70 Ops[i].Op->printAsOperand(dbgs(), false, M); 71 dbgs() << ", #" << Ops[i].Rank << "] "; 72 } 73} 74#endif 75 76namespace { 77 /// \brief Utility class representing a base and exponent pair which form one 78 /// factor of some product. 79 struct Factor { 80 Value *Base; 81 unsigned Power; 82 83 Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {} 84 85 /// \brief Sort factors by their Base. 86 struct BaseSorter { 87 bool operator()(const Factor &LHS, const Factor &RHS) { 88 return LHS.Base < RHS.Base; 89 } 90 }; 91 92 /// \brief Compare factors for equal bases. 93 struct BaseEqual { 94 bool operator()(const Factor &LHS, const Factor &RHS) { 95 return LHS.Base == RHS.Base; 96 } 97 }; 98 99 /// \brief Sort factors in descending order by their power. 100 struct PowerDescendingSorter { 101 bool operator()(const Factor &LHS, const Factor &RHS) { 102 return LHS.Power > RHS.Power; 103 } 104 }; 105 106 /// \brief Compare factors for equal powers. 107 struct PowerEqual { 108 bool operator()(const Factor &LHS, const Factor &RHS) { 109 return LHS.Power == RHS.Power; 110 } 111 }; 112 }; 113 114 /// Utility class representing a non-constant Xor-operand. We classify 115 /// non-constant Xor-Operands into two categories: 116 /// C1) The operand is in the form "X & C", where C is a constant and C != ~0 117 /// C2) 118 /// C2.1) The operand is in the form of "X | C", where C is a non-zero 119 /// constant. 120 /// C2.2) Any operand E which doesn't fall into C1 and C2.1, we view this 121 /// operand as "E | 0" 122 class XorOpnd { 123 public: 124 XorOpnd(Value *V); 125 126 bool isInvalid() const { return SymbolicPart == nullptr; } 127 bool isOrExpr() const { return isOr; } 128 Value *getValue() const { return OrigVal; } 129 Value *getSymbolicPart() const { return SymbolicPart; } 130 unsigned getSymbolicRank() const { return SymbolicRank; } 131 const APInt &getConstPart() const { return ConstPart; } 132 133 void Invalidate() { SymbolicPart = OrigVal = nullptr; } 134 void setSymbolicRank(unsigned R) { SymbolicRank = R; } 135 136 // Sort the XorOpnd-Pointer in ascending order of symbolic-value-rank. 137 // The purpose is twofold: 138 // 1) Cluster together the operands sharing the same symbolic-value. 139 // 2) Operand having smaller symbolic-value-rank is permuted earlier, which 140 // could potentially shorten crital path, and expose more loop-invariants. 141 // Note that values' rank are basically defined in RPO order (FIXME). 142 // So, if Rank(X) < Rank(Y) < Rank(Z), it means X is defined earlier 143 // than Y which is defined earlier than Z. Permute "x | 1", "Y & 2", 144 // "z" in the order of X-Y-Z is better than any other orders. 145 struct PtrSortFunctor { 146 bool operator()(XorOpnd * const &LHS, XorOpnd * const &RHS) { 147 return LHS->getSymbolicRank() < RHS->getSymbolicRank(); 148 } 149 }; 150 private: 151 Value *OrigVal; 152 Value *SymbolicPart; 153 APInt ConstPart; 154 unsigned SymbolicRank; 155 bool isOr; 156 }; 157} 158 159namespace { 160 class Reassociate : public FunctionPass { 161 DenseMap<BasicBlock*, unsigned> RankMap; 162 DenseMap<AssertingVH<Value>, unsigned> ValueRankMap; 163 SetVector<AssertingVH<Instruction> > RedoInsts; 164 bool MadeChange; 165 public: 166 static char ID; // Pass identification, replacement for typeid 167 Reassociate() : FunctionPass(ID) { 168 initializeReassociatePass(*PassRegistry::getPassRegistry()); 169 } 170 171 bool runOnFunction(Function &F) override; 172 173 void getAnalysisUsage(AnalysisUsage &AU) const override { 174 AU.setPreservesCFG(); 175 } 176 private: 177 void BuildRankMap(Function &F); 178 unsigned getRank(Value *V); 179 void canonicalizeOperands(Instruction *I); 180 void ReassociateExpression(BinaryOperator *I); 181 void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops); 182 Value *OptimizeExpression(BinaryOperator *I, 183 SmallVectorImpl<ValueEntry> &Ops); 184 Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops); 185 Value *OptimizeXor(Instruction *I, SmallVectorImpl<ValueEntry> &Ops); 186 bool CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, APInt &ConstOpnd, 187 Value *&Res); 188 bool CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2, 189 APInt &ConstOpnd, Value *&Res); 190 bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops, 191 SmallVectorImpl<Factor> &Factors); 192 Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder, 193 SmallVectorImpl<Factor> &Factors); 194 Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops); 195 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 196 void EraseInst(Instruction *I); 197 void OptimizeInst(Instruction *I); 198 Instruction *canonicalizeNegConstExpr(Instruction *I); 199 }; 200} 201 202XorOpnd::XorOpnd(Value *V) { 203 assert(!isa<ConstantInt>(V) && "No ConstantInt"); 204 OrigVal = V; 205 Instruction *I = dyn_cast<Instruction>(V); 206 SymbolicRank = 0; 207 208 if (I && (I->getOpcode() == Instruction::Or || 209 I->getOpcode() == Instruction::And)) { 210 Value *V0 = I->getOperand(0); 211 Value *V1 = I->getOperand(1); 212 if (isa<ConstantInt>(V0)) 213 std::swap(V0, V1); 214 215 if (ConstantInt *C = dyn_cast<ConstantInt>(V1)) { 216 ConstPart = C->getValue(); 217 SymbolicPart = V0; 218 isOr = (I->getOpcode() == Instruction::Or); 219 return; 220 } 221 } 222 223 // view the operand as "V | 0" 224 SymbolicPart = V; 225 ConstPart = APInt::getNullValue(V->getType()->getIntegerBitWidth()); 226 isOr = true; 227} 228 229char Reassociate::ID = 0; 230INITIALIZE_PASS(Reassociate, "reassociate", 231 "Reassociate expressions", false, false) 232 233// Public interface to the Reassociate pass 234FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 235 236/// isReassociableOp - Return true if V is an instruction of the specified 237/// opcode and if it only has one use. 238static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) { 239 if (V->hasOneUse() && isa<Instruction>(V) && 240 cast<Instruction>(V)->getOpcode() == Opcode && 241 (!isa<FPMathOperator>(V) || 242 cast<Instruction>(V)->hasUnsafeAlgebra())) 243 return cast<BinaryOperator>(V); 244 return nullptr; 245} 246 247static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode1, 248 unsigned Opcode2) { 249 if (V->hasOneUse() && isa<Instruction>(V) && 250 (cast<Instruction>(V)->getOpcode() == Opcode1 || 251 cast<Instruction>(V)->getOpcode() == Opcode2) && 252 (!isa<FPMathOperator>(V) || 253 cast<Instruction>(V)->hasUnsafeAlgebra())) 254 return cast<BinaryOperator>(V); 255 return nullptr; 256} 257 258static bool isUnmovableInstruction(Instruction *I) { 259 switch (I->getOpcode()) { 260 case Instruction::PHI: 261 case Instruction::LandingPad: 262 case Instruction::Alloca: 263 case Instruction::Load: 264 case Instruction::Invoke: 265 case Instruction::UDiv: 266 case Instruction::SDiv: 267 case Instruction::FDiv: 268 case Instruction::URem: 269 case Instruction::SRem: 270 case Instruction::FRem: 271 return true; 272 case Instruction::Call: 273 return !isa<DbgInfoIntrinsic>(I); 274 default: 275 return false; 276 } 277} 278 279void Reassociate::BuildRankMap(Function &F) { 280 unsigned i = 2; 281 282 // Assign distinct ranks to function arguments. 283 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) { 284 ValueRankMap[&*I] = ++i; 285 DEBUG(dbgs() << "Calculated Rank[" << I->getName() << "] = " << i << "\n"); 286 } 287 288 ReversePostOrderTraversal<Function*> RPOT(&F); 289 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), 290 E = RPOT.end(); I != E; ++I) { 291 BasicBlock *BB = *I; 292 unsigned BBRank = RankMap[BB] = ++i << 16; 293 294 // Walk the basic block, adding precomputed ranks for any instructions that 295 // we cannot move. This ensures that the ranks for these instructions are 296 // all different in the block. 297 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 298 if (isUnmovableInstruction(I)) 299 ValueRankMap[&*I] = ++BBRank; 300 } 301} 302 303unsigned Reassociate::getRank(Value *V) { 304 Instruction *I = dyn_cast<Instruction>(V); 305 if (!I) { 306 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument. 307 return 0; // Otherwise it's a global or constant, rank 0. 308 } 309 310 if (unsigned Rank = ValueRankMap[I]) 311 return Rank; // Rank already known? 312 313 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that 314 // we can reassociate expressions for code motion! Since we do not recurse 315 // for PHI nodes, we cannot have infinite recursion here, because there 316 // cannot be loops in the value graph that do not go through PHI nodes. 317 unsigned Rank = 0, MaxRank = RankMap[I->getParent()]; 318 for (unsigned i = 0, e = I->getNumOperands(); 319 i != e && Rank != MaxRank; ++i) 320 Rank = std::max(Rank, getRank(I->getOperand(i))); 321 322 // If this is a not or neg instruction, do not count it for rank. This 323 // assures us that X and ~X will have the same rank. 324 Type *Ty = V->getType(); 325 if ((!Ty->isIntegerTy() && !Ty->isFloatingPointTy()) || 326 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I) && 327 !BinaryOperator::isFNeg(I))) 328 ++Rank; 329 330 DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = " << Rank << "\n"); 331 332 return ValueRankMap[I] = Rank; 333} 334 335// Canonicalize constants to RHS. Otherwise, sort the operands by rank. 336void Reassociate::canonicalizeOperands(Instruction *I) { 337 assert(isa<BinaryOperator>(I) && "Expected binary operator."); 338 assert(I->isCommutative() && "Expected commutative operator."); 339 340 Value *LHS = I->getOperand(0); 341 Value *RHS = I->getOperand(1); 342 unsigned LHSRank = getRank(LHS); 343 unsigned RHSRank = getRank(RHS); 344 345 if (isa<Constant>(RHS)) 346 return; 347 348 if (isa<Constant>(LHS) || RHSRank < LHSRank) 349 cast<BinaryOperator>(I)->swapOperands(); 350} 351 352static BinaryOperator *CreateAdd(Value *S1, Value *S2, const Twine &Name, 353 Instruction *InsertBefore, Value *FlagsOp) { 354 if (S1->getType()->isIntegerTy()) 355 return BinaryOperator::CreateAdd(S1, S2, Name, InsertBefore); 356 else { 357 BinaryOperator *Res = 358 BinaryOperator::CreateFAdd(S1, S2, Name, InsertBefore); 359 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags()); 360 return Res; 361 } 362} 363 364static BinaryOperator *CreateMul(Value *S1, Value *S2, const Twine &Name, 365 Instruction *InsertBefore, Value *FlagsOp) { 366 if (S1->getType()->isIntegerTy()) 367 return BinaryOperator::CreateMul(S1, S2, Name, InsertBefore); 368 else { 369 BinaryOperator *Res = 370 BinaryOperator::CreateFMul(S1, S2, Name, InsertBefore); 371 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags()); 372 return Res; 373 } 374} 375 376static BinaryOperator *CreateNeg(Value *S1, const Twine &Name, 377 Instruction *InsertBefore, Value *FlagsOp) { 378 if (S1->getType()->isIntegerTy()) 379 return BinaryOperator::CreateNeg(S1, Name, InsertBefore); 380 else { 381 BinaryOperator *Res = BinaryOperator::CreateFNeg(S1, Name, InsertBefore); 382 Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags()); 383 return Res; 384 } 385} 386 387/// LowerNegateToMultiply - Replace 0-X with X*-1. 388/// 389static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) { 390 Type *Ty = Neg->getType(); 391 Constant *NegOne = Ty->isIntegerTy() ? ConstantInt::getAllOnesValue(Ty) 392 : ConstantFP::get(Ty, -1.0); 393 394 BinaryOperator *Res = CreateMul(Neg->getOperand(1), NegOne, "", Neg, Neg); 395 Neg->setOperand(1, Constant::getNullValue(Ty)); // Drop use of op. 396 Res->takeName(Neg); 397 Neg->replaceAllUsesWith(Res); 398 Res->setDebugLoc(Neg->getDebugLoc()); 399 return Res; 400} 401 402/// CarmichaelShift - Returns k such that lambda(2^Bitwidth) = 2^k, where lambda 403/// is the Carmichael function. This means that x^(2^k) === 1 mod 2^Bitwidth for 404/// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic. 405/// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every 406/// even x in Bitwidth-bit arithmetic. 407static unsigned CarmichaelShift(unsigned Bitwidth) { 408 if (Bitwidth < 3) 409 return Bitwidth - 1; 410 return Bitwidth - 2; 411} 412 413/// IncorporateWeight - Add the extra weight 'RHS' to the existing weight 'LHS', 414/// reducing the combined weight using any special properties of the operation. 415/// The existing weight LHS represents the computation X op X op ... op X where 416/// X occurs LHS times. The combined weight represents X op X op ... op X with 417/// X occurring LHS + RHS times. If op is "Xor" for example then the combined 418/// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even; 419/// the routine returns 1 in LHS in the first case, and 0 in LHS in the second. 420static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) { 421 // If we were working with infinite precision arithmetic then the combined 422 // weight would be LHS + RHS. But we are using finite precision arithmetic, 423 // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct 424 // for nilpotent operations and addition, but not for idempotent operations 425 // and multiplication), so it is important to correctly reduce the combined 426 // weight back into range if wrapping would be wrong. 427 428 // If RHS is zero then the weight didn't change. 429 if (RHS.isMinValue()) 430 return; 431 // If LHS is zero then the combined weight is RHS. 432 if (LHS.isMinValue()) { 433 LHS = RHS; 434 return; 435 } 436 // From this point on we know that neither LHS nor RHS is zero. 437 438 if (Instruction::isIdempotent(Opcode)) { 439 // Idempotent means X op X === X, so any non-zero weight is equivalent to a 440 // weight of 1. Keeping weights at zero or one also means that wrapping is 441 // not a problem. 442 assert(LHS == 1 && RHS == 1 && "Weights not reduced!"); 443 return; // Return a weight of 1. 444 } 445 if (Instruction::isNilpotent(Opcode)) { 446 // Nilpotent means X op X === 0, so reduce weights modulo 2. 447 assert(LHS == 1 && RHS == 1 && "Weights not reduced!"); 448 LHS = 0; // 1 + 1 === 0 modulo 2. 449 return; 450 } 451 if (Opcode == Instruction::Add || Opcode == Instruction::FAdd) { 452 // TODO: Reduce the weight by exploiting nsw/nuw? 453 LHS += RHS; 454 return; 455 } 456 457 assert((Opcode == Instruction::Mul || Opcode == Instruction::FMul) && 458 "Unknown associative operation!"); 459 unsigned Bitwidth = LHS.getBitWidth(); 460 // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth 461 // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth 462 // bit number x, since either x is odd in which case x^CM = 1, or x is even in 463 // which case both x^W and x^(W - CM) are zero. By subtracting off multiples 464 // of CM like this weights can always be reduced to the range [0, CM+Bitwidth) 465 // which by a happy accident means that they can always be represented using 466 // Bitwidth bits. 467 // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than 468 // the Carmichael number). 469 if (Bitwidth > 3) { 470 /// CM - The value of Carmichael's lambda function. 471 APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth)); 472 // Any weight W >= Threshold can be replaced with W - CM. 473 APInt Threshold = CM + Bitwidth; 474 assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!"); 475 // For Bitwidth 4 or more the following sum does not overflow. 476 LHS += RHS; 477 while (LHS.uge(Threshold)) 478 LHS -= CM; 479 } else { 480 // To avoid problems with overflow do everything the same as above but using 481 // a larger type. 482 unsigned CM = 1U << CarmichaelShift(Bitwidth); 483 unsigned Threshold = CM + Bitwidth; 484 assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold && 485 "Weights not reduced!"); 486 unsigned Total = LHS.getZExtValue() + RHS.getZExtValue(); 487 while (Total >= Threshold) 488 Total -= CM; 489 LHS = Total; 490 } 491} 492 493typedef std::pair<Value*, APInt> RepeatedValue; 494 495/// LinearizeExprTree - Given an associative binary expression, return the leaf 496/// nodes in Ops along with their weights (how many times the leaf occurs). The 497/// original expression is the same as 498/// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times 499/// op 500/// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times 501/// op 502/// ... 503/// op 504/// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times 505/// 506/// Note that the values Ops[0].first, ..., Ops[N].first are all distinct. 507/// 508/// This routine may modify the function, in which case it returns 'true'. The 509/// changes it makes may well be destructive, changing the value computed by 'I' 510/// to something completely different. Thus if the routine returns 'true' then 511/// you MUST either replace I with a new expression computed from the Ops array, 512/// or use RewriteExprTree to put the values back in. 513/// 514/// A leaf node is either not a binary operation of the same kind as the root 515/// node 'I' (i.e. is not a binary operator at all, or is, but with a different 516/// opcode), or is the same kind of binary operator but has a use which either 517/// does not belong to the expression, or does belong to the expression but is 518/// a leaf node. Every leaf node has at least one use that is a non-leaf node 519/// of the expression, while for non-leaf nodes (except for the root 'I') every 520/// use is a non-leaf node of the expression. 521/// 522/// For example: 523/// expression graph node names 524/// 525/// + | I 526/// / \ | 527/// + + | A, B 528/// / \ / \ | 529/// * + * | C, D, E 530/// / \ / \ / \ | 531/// + * | F, G 532/// 533/// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in 534/// that order) (C, 1), (E, 1), (F, 2), (G, 2). 535/// 536/// The expression is maximal: if some instruction is a binary operator of the 537/// same kind as 'I', and all of its uses are non-leaf nodes of the expression, 538/// then the instruction also belongs to the expression, is not a leaf node of 539/// it, and its operands also belong to the expression (but may be leaf nodes). 540/// 541/// NOTE: This routine will set operands of non-leaf non-root nodes to undef in 542/// order to ensure that every non-root node in the expression has *exactly one* 543/// use by a non-leaf node of the expression. This destruction means that the 544/// caller MUST either replace 'I' with a new expression or use something like 545/// RewriteExprTree to put the values back in if the routine indicates that it 546/// made a change by returning 'true'. 547/// 548/// In the above example either the right operand of A or the left operand of B 549/// will be replaced by undef. If it is B's operand then this gives: 550/// 551/// + | I 552/// / \ | 553/// + + | A, B - operand of B replaced with undef 554/// / \ \ | 555/// * + * | C, D, E 556/// / \ / \ / \ | 557/// + * | F, G 558/// 559/// Note that such undef operands can only be reached by passing through 'I'. 560/// For example, if you visit operands recursively starting from a leaf node 561/// then you will never see such an undef operand unless you get back to 'I', 562/// which requires passing through a phi node. 563/// 564/// Note that this routine may also mutate binary operators of the wrong type 565/// that have all uses inside the expression (i.e. only used by non-leaf nodes 566/// of the expression) if it can turn them into binary operators of the right 567/// type and thus make the expression bigger. 568 569static bool LinearizeExprTree(BinaryOperator *I, 570 SmallVectorImpl<RepeatedValue> &Ops) { 571 DEBUG(dbgs() << "LINEARIZE: " << *I << '\n'); 572 unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits(); 573 unsigned Opcode = I->getOpcode(); 574 assert(I->isAssociative() && I->isCommutative() && 575 "Expected an associative and commutative operation!"); 576 577 // Visit all operands of the expression, keeping track of their weight (the 578 // number of paths from the expression root to the operand, or if you like 579 // the number of times that operand occurs in the linearized expression). 580 // For example, if I = X + A, where X = A + B, then I, X and B have weight 1 581 // while A has weight two. 582 583 // Worklist of non-leaf nodes (their operands are in the expression too) along 584 // with their weights, representing a certain number of paths to the operator. 585 // If an operator occurs in the worklist multiple times then we found multiple 586 // ways to get to it. 587 SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight) 588 Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1))); 589 bool Changed = false; 590 591 // Leaves of the expression are values that either aren't the right kind of 592 // operation (eg: a constant, or a multiply in an add tree), or are, but have 593 // some uses that are not inside the expression. For example, in I = X + X, 594 // X = A + B, the value X has two uses (by I) that are in the expression. If 595 // X has any other uses, for example in a return instruction, then we consider 596 // X to be a leaf, and won't analyze it further. When we first visit a value, 597 // if it has more than one use then at first we conservatively consider it to 598 // be a leaf. Later, as the expression is explored, we may discover some more 599 // uses of the value from inside the expression. If all uses turn out to be 600 // from within the expression (and the value is a binary operator of the right 601 // kind) then the value is no longer considered to be a leaf, and its operands 602 // are explored. 603 604 // Leaves - Keeps track of the set of putative leaves as well as the number of 605 // paths to each leaf seen so far. 606 typedef DenseMap<Value*, APInt> LeafMap; 607 LeafMap Leaves; // Leaf -> Total weight so far. 608 SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order. 609 610#ifndef NDEBUG 611 SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme. 612#endif 613 while (!Worklist.empty()) { 614 std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val(); 615 I = P.first; // We examine the operands of this binary operator. 616 617 for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands. 618 Value *Op = I->getOperand(OpIdx); 619 APInt Weight = P.second; // Number of paths to this operand. 620 DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n"); 621 assert(!Op->use_empty() && "No uses, so how did we get to it?!"); 622 623 // If this is a binary operation of the right kind with only one use then 624 // add its operands to the expression. 625 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) { 626 assert(Visited.insert(Op).second && "Not first visit!"); 627 DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n"); 628 Worklist.push_back(std::make_pair(BO, Weight)); 629 continue; 630 } 631 632 // Appears to be a leaf. Is the operand already in the set of leaves? 633 LeafMap::iterator It = Leaves.find(Op); 634 if (It == Leaves.end()) { 635 // Not in the leaf map. Must be the first time we saw this operand. 636 assert(Visited.insert(Op).second && "Not first visit!"); 637 if (!Op->hasOneUse()) { 638 // This value has uses not accounted for by the expression, so it is 639 // not safe to modify. Mark it as being a leaf. 640 DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n"); 641 LeafOrder.push_back(Op); 642 Leaves[Op] = Weight; 643 continue; 644 } 645 // No uses outside the expression, try morphing it. 646 } else if (It != Leaves.end()) { 647 // Already in the leaf map. 648 assert(Visited.count(Op) && "In leaf map but not visited!"); 649 650 // Update the number of paths to the leaf. 651 IncorporateWeight(It->second, Weight, Opcode); 652 653#if 0 // TODO: Re-enable once PR13021 is fixed. 654 // The leaf already has one use from inside the expression. As we want 655 // exactly one such use, drop this new use of the leaf. 656 assert(!Op->hasOneUse() && "Only one use, but we got here twice!"); 657 I->setOperand(OpIdx, UndefValue::get(I->getType())); 658 Changed = true; 659 660 // If the leaf is a binary operation of the right kind and we now see 661 // that its multiple original uses were in fact all by nodes belonging 662 // to the expression, then no longer consider it to be a leaf and add 663 // its operands to the expression. 664 if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) { 665 DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n"); 666 Worklist.push_back(std::make_pair(BO, It->second)); 667 Leaves.erase(It); 668 continue; 669 } 670#endif 671 672 // If we still have uses that are not accounted for by the expression 673 // then it is not safe to modify the value. 674 if (!Op->hasOneUse()) 675 continue; 676 677 // No uses outside the expression, try morphing it. 678 Weight = It->second; 679 Leaves.erase(It); // Since the value may be morphed below. 680 } 681 682 // At this point we have a value which, first of all, is not a binary 683 // expression of the right kind, and secondly, is only used inside the 684 // expression. This means that it can safely be modified. See if we 685 // can usefully morph it into an expression of the right kind. 686 assert((!isa<Instruction>(Op) || 687 cast<Instruction>(Op)->getOpcode() != Opcode 688 || (isa<FPMathOperator>(Op) && 689 !cast<Instruction>(Op)->hasUnsafeAlgebra())) && 690 "Should have been handled above!"); 691 assert(Op->hasOneUse() && "Has uses outside the expression tree!"); 692 693 // If this is a multiply expression, turn any internal negations into 694 // multiplies by -1 so they can be reassociated. 695 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op)) 696 if ((Opcode == Instruction::Mul && BinaryOperator::isNeg(BO)) || 697 (Opcode == Instruction::FMul && BinaryOperator::isFNeg(BO))) { 698 DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO "); 699 BO = LowerNegateToMultiply(BO); 700 DEBUG(dbgs() << *BO << '\n'); 701 Worklist.push_back(std::make_pair(BO, Weight)); 702 Changed = true; 703 continue; 704 } 705 706 // Failed to morph into an expression of the right type. This really is 707 // a leaf. 708 DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n"); 709 assert(!isReassociableOp(Op, Opcode) && "Value was morphed?"); 710 LeafOrder.push_back(Op); 711 Leaves[Op] = Weight; 712 } 713 } 714 715 // The leaves, repeated according to their weights, represent the linearized 716 // form of the expression. 717 for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) { 718 Value *V = LeafOrder[i]; 719 LeafMap::iterator It = Leaves.find(V); 720 if (It == Leaves.end()) 721 // Node initially thought to be a leaf wasn't. 722 continue; 723 assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!"); 724 APInt Weight = It->second; 725 if (Weight.isMinValue()) 726 // Leaf already output or weight reduction eliminated it. 727 continue; 728 // Ensure the leaf is only output once. 729 It->second = 0; 730 Ops.push_back(std::make_pair(V, Weight)); 731 } 732 733 // For nilpotent operations or addition there may be no operands, for example 734 // because the expression was "X xor X" or consisted of 2^Bitwidth additions: 735 // in both cases the weight reduces to 0 causing the value to be skipped. 736 if (Ops.empty()) { 737 Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType()); 738 assert(Identity && "Associative operation without identity!"); 739 Ops.push_back(std::make_pair(Identity, APInt(Bitwidth, 1))); 740 } 741 742 return Changed; 743} 744 745// RewriteExprTree - Now that the operands for this expression tree are 746// linearized and optimized, emit them in-order. 747void Reassociate::RewriteExprTree(BinaryOperator *I, 748 SmallVectorImpl<ValueEntry> &Ops) { 749 assert(Ops.size() > 1 && "Single values should be used directly!"); 750 751 // Since our optimizations should never increase the number of operations, the 752 // new expression can usually be written reusing the existing binary operators 753 // from the original expression tree, without creating any new instructions, 754 // though the rewritten expression may have a completely different topology. 755 // We take care to not change anything if the new expression will be the same 756 // as the original. If more than trivial changes (like commuting operands) 757 // were made then we are obliged to clear out any optional subclass data like 758 // nsw flags. 759 760 /// NodesToRewrite - Nodes from the original expression available for writing 761 /// the new expression into. 762 SmallVector<BinaryOperator*, 8> NodesToRewrite; 763 unsigned Opcode = I->getOpcode(); 764 BinaryOperator *Op = I; 765 766 /// NotRewritable - The operands being written will be the leaves of the new 767 /// expression and must not be used as inner nodes (via NodesToRewrite) by 768 /// mistake. Inner nodes are always reassociable, and usually leaves are not 769 /// (if they were they would have been incorporated into the expression and so 770 /// would not be leaves), so most of the time there is no danger of this. But 771 /// in rare cases a leaf may become reassociable if an optimization kills uses 772 /// of it, or it may momentarily become reassociable during rewriting (below) 773 /// due it being removed as an operand of one of its uses. Ensure that misuse 774 /// of leaf nodes as inner nodes cannot occur by remembering all of the future 775 /// leaves and refusing to reuse any of them as inner nodes. 776 SmallPtrSet<Value*, 8> NotRewritable; 777 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 778 NotRewritable.insert(Ops[i].Op); 779 780 // ExpressionChanged - Non-null if the rewritten expression differs from the 781 // original in some non-trivial way, requiring the clearing of optional flags. 782 // Flags are cleared from the operator in ExpressionChanged up to I inclusive. 783 BinaryOperator *ExpressionChanged = nullptr; 784 for (unsigned i = 0; ; ++i) { 785 // The last operation (which comes earliest in the IR) is special as both 786 // operands will come from Ops, rather than just one with the other being 787 // a subexpression. 788 if (i+2 == Ops.size()) { 789 Value *NewLHS = Ops[i].Op; 790 Value *NewRHS = Ops[i+1].Op; 791 Value *OldLHS = Op->getOperand(0); 792 Value *OldRHS = Op->getOperand(1); 793 794 if (NewLHS == OldLHS && NewRHS == OldRHS) 795 // Nothing changed, leave it alone. 796 break; 797 798 if (NewLHS == OldRHS && NewRHS == OldLHS) { 799 // The order of the operands was reversed. Swap them. 800 DEBUG(dbgs() << "RA: " << *Op << '\n'); 801 Op->swapOperands(); 802 DEBUG(dbgs() << "TO: " << *Op << '\n'); 803 MadeChange = true; 804 ++NumChanged; 805 break; 806 } 807 808 // The new operation differs non-trivially from the original. Overwrite 809 // the old operands with the new ones. 810 DEBUG(dbgs() << "RA: " << *Op << '\n'); 811 if (NewLHS != OldLHS) { 812 BinaryOperator *BO = isReassociableOp(OldLHS, Opcode); 813 if (BO && !NotRewritable.count(BO)) 814 NodesToRewrite.push_back(BO); 815 Op->setOperand(0, NewLHS); 816 } 817 if (NewRHS != OldRHS) { 818 BinaryOperator *BO = isReassociableOp(OldRHS, Opcode); 819 if (BO && !NotRewritable.count(BO)) 820 NodesToRewrite.push_back(BO); 821 Op->setOperand(1, NewRHS); 822 } 823 DEBUG(dbgs() << "TO: " << *Op << '\n'); 824 825 ExpressionChanged = Op; 826 MadeChange = true; 827 ++NumChanged; 828 829 break; 830 } 831 832 // Not the last operation. The left-hand side will be a sub-expression 833 // while the right-hand side will be the current element of Ops. 834 Value *NewRHS = Ops[i].Op; 835 if (NewRHS != Op->getOperand(1)) { 836 DEBUG(dbgs() << "RA: " << *Op << '\n'); 837 if (NewRHS == Op->getOperand(0)) { 838 // The new right-hand side was already present as the left operand. If 839 // we are lucky then swapping the operands will sort out both of them. 840 Op->swapOperands(); 841 } else { 842 // Overwrite with the new right-hand side. 843 BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode); 844 if (BO && !NotRewritable.count(BO)) 845 NodesToRewrite.push_back(BO); 846 Op->setOperand(1, NewRHS); 847 ExpressionChanged = Op; 848 } 849 DEBUG(dbgs() << "TO: " << *Op << '\n'); 850 MadeChange = true; 851 ++NumChanged; 852 } 853 854 // Now deal with the left-hand side. If this is already an operation node 855 // from the original expression then just rewrite the rest of the expression 856 // into it. 857 BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode); 858 if (BO && !NotRewritable.count(BO)) { 859 Op = BO; 860 continue; 861 } 862 863 // Otherwise, grab a spare node from the original expression and use that as 864 // the left-hand side. If there are no nodes left then the optimizers made 865 // an expression with more nodes than the original! This usually means that 866 // they did something stupid but it might mean that the problem was just too 867 // hard (finding the mimimal number of multiplications needed to realize a 868 // multiplication expression is NP-complete). Whatever the reason, smart or 869 // stupid, create a new node if there are none left. 870 BinaryOperator *NewOp; 871 if (NodesToRewrite.empty()) { 872 Constant *Undef = UndefValue::get(I->getType()); 873 NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode), 874 Undef, Undef, "", I); 875 if (NewOp->getType()->isFloatingPointTy()) 876 NewOp->setFastMathFlags(I->getFastMathFlags()); 877 } else { 878 NewOp = NodesToRewrite.pop_back_val(); 879 } 880 881 DEBUG(dbgs() << "RA: " << *Op << '\n'); 882 Op->setOperand(0, NewOp); 883 DEBUG(dbgs() << "TO: " << *Op << '\n'); 884 ExpressionChanged = Op; 885 MadeChange = true; 886 ++NumChanged; 887 Op = NewOp; 888 } 889 890 // If the expression changed non-trivially then clear out all subclass data 891 // starting from the operator specified in ExpressionChanged, and compactify 892 // the operators to just before the expression root to guarantee that the 893 // expression tree is dominated by all of Ops. 894 if (ExpressionChanged) 895 do { 896 // Preserve FastMathFlags. 897 if (isa<FPMathOperator>(I)) { 898 FastMathFlags Flags = I->getFastMathFlags(); 899 ExpressionChanged->clearSubclassOptionalData(); 900 ExpressionChanged->setFastMathFlags(Flags); 901 } else 902 ExpressionChanged->clearSubclassOptionalData(); 903 904 if (ExpressionChanged == I) 905 break; 906 ExpressionChanged->moveBefore(I); 907 ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->user_begin()); 908 } while (1); 909 910 // Throw away any left over nodes from the original expression. 911 for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i) 912 RedoInsts.insert(NodesToRewrite[i]); 913} 914 915/// NegateValue - Insert instructions before the instruction pointed to by BI, 916/// that computes the negative version of the value specified. The negative 917/// version of the value is returned, and BI is left pointing at the instruction 918/// that should be processed next by the reassociation pass. 919static Value *NegateValue(Value *V, Instruction *BI) { 920 if (ConstantFP *C = dyn_cast<ConstantFP>(V)) 921 return ConstantExpr::getFNeg(C); 922 if (Constant *C = dyn_cast<Constant>(V)) 923 return ConstantExpr::getNeg(C); 924 925 // We are trying to expose opportunity for reassociation. One of the things 926 // that we want to do to achieve this is to push a negation as deep into an 927 // expression chain as possible, to expose the add instructions. In practice, 928 // this means that we turn this: 929 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D 930 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate 931 // the constants. We assume that instcombine will clean up the mess later if 932 // we introduce tons of unnecessary negation instructions. 933 // 934 if (BinaryOperator *I = 935 isReassociableOp(V, Instruction::Add, Instruction::FAdd)) { 936 // Push the negates through the add. 937 I->setOperand(0, NegateValue(I->getOperand(0), BI)); 938 I->setOperand(1, NegateValue(I->getOperand(1), BI)); 939 940 // We must move the add instruction here, because the neg instructions do 941 // not dominate the old add instruction in general. By moving it, we are 942 // assured that the neg instructions we just inserted dominate the 943 // instruction we are about to insert after them. 944 // 945 I->moveBefore(BI); 946 I->setName(I->getName()+".neg"); 947 return I; 948 } 949 950 // Okay, we need to materialize a negated version of V with an instruction. 951 // Scan the use lists of V to see if we have one already. 952 for (User *U : V->users()) { 953 if (!BinaryOperator::isNeg(U) && !BinaryOperator::isFNeg(U)) 954 continue; 955 956 // We found one! Now we have to make sure that the definition dominates 957 // this use. We do this by moving it to the entry block (if it is a 958 // non-instruction value) or right after the definition. These negates will 959 // be zapped by reassociate later, so we don't need much finesse here. 960 BinaryOperator *TheNeg = cast<BinaryOperator>(U); 961 962 // Verify that the negate is in this function, V might be a constant expr. 963 if (TheNeg->getParent()->getParent() != BI->getParent()->getParent()) 964 continue; 965 966 BasicBlock::iterator InsertPt; 967 if (Instruction *InstInput = dyn_cast<Instruction>(V)) { 968 if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) { 969 InsertPt = II->getNormalDest()->begin(); 970 } else { 971 InsertPt = InstInput; 972 ++InsertPt; 973 } 974 while (isa<PHINode>(InsertPt)) ++InsertPt; 975 } else { 976 InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin(); 977 } 978 TheNeg->moveBefore(InsertPt); 979 return TheNeg; 980 } 981 982 // Insert a 'neg' instruction that subtracts the value from zero to get the 983 // negation. 984 return CreateNeg(V, V->getName() + ".neg", BI, BI); 985} 986 987/// ShouldBreakUpSubtract - Return true if we should break up this subtract of 988/// X-Y into (X + -Y). 989static bool ShouldBreakUpSubtract(Instruction *Sub) { 990 // If this is a negation, we can't split it up! 991 if (BinaryOperator::isNeg(Sub) || BinaryOperator::isFNeg(Sub)) 992 return false; 993 994 // Don't breakup X - undef. 995 if (isa<UndefValue>(Sub->getOperand(1))) 996 return false; 997 998 // Don't bother to break this up unless either the LHS is an associable add or 999 // subtract or if this is only used by one. 1000 Value *V0 = Sub->getOperand(0); 1001 if (isReassociableOp(V0, Instruction::Add, Instruction::FAdd) || 1002 isReassociableOp(V0, Instruction::Sub, Instruction::FSub)) 1003 return true; 1004 Value *V1 = Sub->getOperand(1); 1005 if (isReassociableOp(V1, Instruction::Add, Instruction::FAdd) || 1006 isReassociableOp(V1, Instruction::Sub, Instruction::FSub)) 1007 return true; 1008 Value *VB = Sub->user_back(); 1009 if (Sub->hasOneUse() && 1010 (isReassociableOp(VB, Instruction::Add, Instruction::FAdd) || 1011 isReassociableOp(VB, Instruction::Sub, Instruction::FSub))) 1012 return true; 1013 1014 return false; 1015} 1016 1017/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 1018/// only used by an add, transform this into (X+(0-Y)) to promote better 1019/// reassociation. 1020static BinaryOperator *BreakUpSubtract(Instruction *Sub) { 1021 // Convert a subtract into an add and a neg instruction. This allows sub 1022 // instructions to be commuted with other add instructions. 1023 // 1024 // Calculate the negative value of Operand 1 of the sub instruction, 1025 // and set it as the RHS of the add instruction we just made. 1026 // 1027 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 1028 BinaryOperator *New = CreateAdd(Sub->getOperand(0), NegVal, "", Sub, Sub); 1029 Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op. 1030 Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op. 1031 New->takeName(Sub); 1032 1033 // Everyone now refers to the add instruction. 1034 Sub->replaceAllUsesWith(New); 1035 New->setDebugLoc(Sub->getDebugLoc()); 1036 1037 DEBUG(dbgs() << "Negated: " << *New << '\n'); 1038 return New; 1039} 1040 1041/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 1042/// by one, change this into a multiply by a constant to assist with further 1043/// reassociation. 1044static BinaryOperator *ConvertShiftToMul(Instruction *Shl) { 1045 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 1046 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 1047 1048 BinaryOperator *Mul = 1049 BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl); 1050 Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op. 1051 Mul->takeName(Shl); 1052 1053 // Everyone now refers to the mul instruction. 1054 Shl->replaceAllUsesWith(Mul); 1055 Mul->setDebugLoc(Shl->getDebugLoc()); 1056 1057 // We can safely preserve the nuw flag in all cases. It's also safe to turn a 1058 // nuw nsw shl into a nuw nsw mul. However, nsw in isolation requires special 1059 // handling. 1060 bool NSW = cast<BinaryOperator>(Shl)->hasNoSignedWrap(); 1061 bool NUW = cast<BinaryOperator>(Shl)->hasNoUnsignedWrap(); 1062 if (NSW && NUW) 1063 Mul->setHasNoSignedWrap(true); 1064 Mul->setHasNoUnsignedWrap(NUW); 1065 return Mul; 1066} 1067 1068/// FindInOperandList - Scan backwards and forwards among values with the same 1069/// rank as element i to see if X exists. If X does not exist, return i. This 1070/// is useful when scanning for 'x' when we see '-x' because they both get the 1071/// same rank. 1072static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i, 1073 Value *X) { 1074 unsigned XRank = Ops[i].Rank; 1075 unsigned e = Ops.size(); 1076 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) { 1077 if (Ops[j].Op == X) 1078 return j; 1079 if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op)) 1080 if (Instruction *I2 = dyn_cast<Instruction>(X)) 1081 if (I1->isIdenticalTo(I2)) 1082 return j; 1083 } 1084 // Scan backwards. 1085 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) { 1086 if (Ops[j].Op == X) 1087 return j; 1088 if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op)) 1089 if (Instruction *I2 = dyn_cast<Instruction>(X)) 1090 if (I1->isIdenticalTo(I2)) 1091 return j; 1092 } 1093 return i; 1094} 1095 1096/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 1097/// and returning the result. Insert the tree before I. 1098static Value *EmitAddTreeOfValues(Instruction *I, 1099 SmallVectorImpl<WeakVH> &Ops){ 1100 if (Ops.size() == 1) return Ops.back(); 1101 1102 Value *V1 = Ops.back(); 1103 Ops.pop_back(); 1104 Value *V2 = EmitAddTreeOfValues(I, Ops); 1105 return CreateAdd(V2, V1, "tmp", I, I); 1106} 1107 1108/// RemoveFactorFromExpression - If V is an expression tree that is a 1109/// multiplication sequence, and if this sequence contains a multiply by Factor, 1110/// remove Factor from the tree and return the new tree. 1111Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 1112 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul); 1113 if (!BO) 1114 return nullptr; 1115 1116 SmallVector<RepeatedValue, 8> Tree; 1117 MadeChange |= LinearizeExprTree(BO, Tree); 1118 SmallVector<ValueEntry, 8> Factors; 1119 Factors.reserve(Tree.size()); 1120 for (unsigned i = 0, e = Tree.size(); i != e; ++i) { 1121 RepeatedValue E = Tree[i]; 1122 Factors.append(E.second.getZExtValue(), 1123 ValueEntry(getRank(E.first), E.first)); 1124 } 1125 1126 bool FoundFactor = false; 1127 bool NeedsNegate = false; 1128 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 1129 if (Factors[i].Op == Factor) { 1130 FoundFactor = true; 1131 Factors.erase(Factors.begin()+i); 1132 break; 1133 } 1134 1135 // If this is a negative version of this factor, remove it. 1136 if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor)) { 1137 if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op)) 1138 if (FC1->getValue() == -FC2->getValue()) { 1139 FoundFactor = NeedsNegate = true; 1140 Factors.erase(Factors.begin()+i); 1141 break; 1142 } 1143 } else if (ConstantFP *FC1 = dyn_cast<ConstantFP>(Factor)) { 1144 if (ConstantFP *FC2 = dyn_cast<ConstantFP>(Factors[i].Op)) { 1145 APFloat F1(FC1->getValueAPF()); 1146 APFloat F2(FC2->getValueAPF()); 1147 F2.changeSign(); 1148 if (F1.compare(F2) == APFloat::cmpEqual) { 1149 FoundFactor = NeedsNegate = true; 1150 Factors.erase(Factors.begin() + i); 1151 break; 1152 } 1153 } 1154 } 1155 } 1156 1157 if (!FoundFactor) { 1158 // Make sure to restore the operands to the expression tree. 1159 RewriteExprTree(BO, Factors); 1160 return nullptr; 1161 } 1162 1163 BasicBlock::iterator InsertPt = BO; ++InsertPt; 1164 1165 // If this was just a single multiply, remove the multiply and return the only 1166 // remaining operand. 1167 if (Factors.size() == 1) { 1168 RedoInsts.insert(BO); 1169 V = Factors[0].Op; 1170 } else { 1171 RewriteExprTree(BO, Factors); 1172 V = BO; 1173 } 1174 1175 if (NeedsNegate) 1176 V = CreateNeg(V, "neg", InsertPt, BO); 1177 1178 return V; 1179} 1180 1181/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 1182/// add its operands as factors, otherwise add V to the list of factors. 1183/// 1184/// Ops is the top-level list of add operands we're trying to factor. 1185static void FindSingleUseMultiplyFactors(Value *V, 1186 SmallVectorImpl<Value*> &Factors, 1187 const SmallVectorImpl<ValueEntry> &Ops) { 1188 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul); 1189 if (!BO) { 1190 Factors.push_back(V); 1191 return; 1192 } 1193 1194 // Otherwise, add the LHS and RHS to the list of factors. 1195 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops); 1196 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops); 1197} 1198 1199/// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor' 1200/// instruction. This optimizes based on identities. If it can be reduced to 1201/// a single Value, it is returned, otherwise the Ops list is mutated as 1202/// necessary. 1203static Value *OptimizeAndOrXor(unsigned Opcode, 1204 SmallVectorImpl<ValueEntry> &Ops) { 1205 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 1206 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 1207 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 1208 // First, check for X and ~X in the operand list. 1209 assert(i < Ops.size()); 1210 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 1211 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 1212 unsigned FoundX = FindInOperandList(Ops, i, X); 1213 if (FoundX != i) { 1214 if (Opcode == Instruction::And) // ...&X&~X = 0 1215 return Constant::getNullValue(X->getType()); 1216 1217 if (Opcode == Instruction::Or) // ...|X|~X = -1 1218 return Constant::getAllOnesValue(X->getType()); 1219 } 1220 } 1221 1222 // Next, check for duplicate pairs of values, which we assume are next to 1223 // each other, due to our sorting criteria. 1224 assert(i < Ops.size()); 1225 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 1226 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 1227 // Drop duplicate values for And and Or. 1228 Ops.erase(Ops.begin()+i); 1229 --i; --e; 1230 ++NumAnnihil; 1231 continue; 1232 } 1233 1234 // Drop pairs of values for Xor. 1235 assert(Opcode == Instruction::Xor); 1236 if (e == 2) 1237 return Constant::getNullValue(Ops[0].Op->getType()); 1238 1239 // Y ^ X^X -> Y 1240 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 1241 i -= 1; e -= 2; 1242 ++NumAnnihil; 1243 } 1244 } 1245 return nullptr; 1246} 1247 1248/// Helper funciton of CombineXorOpnd(). It creates a bitwise-and 1249/// instruction with the given two operands, and return the resulting 1250/// instruction. There are two special cases: 1) if the constant operand is 0, 1251/// it will return NULL. 2) if the constant is ~0, the symbolic operand will 1252/// be returned. 1253static Value *createAndInstr(Instruction *InsertBefore, Value *Opnd, 1254 const APInt &ConstOpnd) { 1255 if (ConstOpnd != 0) { 1256 if (!ConstOpnd.isAllOnesValue()) { 1257 LLVMContext &Ctx = Opnd->getType()->getContext(); 1258 Instruction *I; 1259 I = BinaryOperator::CreateAnd(Opnd, ConstantInt::get(Ctx, ConstOpnd), 1260 "and.ra", InsertBefore); 1261 I->setDebugLoc(InsertBefore->getDebugLoc()); 1262 return I; 1263 } 1264 return Opnd; 1265 } 1266 return nullptr; 1267} 1268 1269// Helper function of OptimizeXor(). It tries to simplify "Opnd1 ^ ConstOpnd" 1270// into "R ^ C", where C would be 0, and R is a symbolic value. 1271// 1272// If it was successful, true is returned, and the "R" and "C" is returned 1273// via "Res" and "ConstOpnd", respectively; otherwise, false is returned, 1274// and both "Res" and "ConstOpnd" remain unchanged. 1275// 1276bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, 1277 APInt &ConstOpnd, Value *&Res) { 1278 // Xor-Rule 1: (x | c1) ^ c2 = (x | c1) ^ (c1 ^ c1) ^ c2 1279 // = ((x | c1) ^ c1) ^ (c1 ^ c2) 1280 // = (x & ~c1) ^ (c1 ^ c2) 1281 // It is useful only when c1 == c2. 1282 if (Opnd1->isOrExpr() && Opnd1->getConstPart() != 0) { 1283 if (!Opnd1->getValue()->hasOneUse()) 1284 return false; 1285 1286 const APInt &C1 = Opnd1->getConstPart(); 1287 if (C1 != ConstOpnd) 1288 return false; 1289 1290 Value *X = Opnd1->getSymbolicPart(); 1291 Res = createAndInstr(I, X, ~C1); 1292 // ConstOpnd was C2, now C1 ^ C2. 1293 ConstOpnd ^= C1; 1294 1295 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue())) 1296 RedoInsts.insert(T); 1297 return true; 1298 } 1299 return false; 1300} 1301 1302 1303// Helper function of OptimizeXor(). It tries to simplify 1304// "Opnd1 ^ Opnd2 ^ ConstOpnd" into "R ^ C", where C would be 0, and R is a 1305// symbolic value. 1306// 1307// If it was successful, true is returned, and the "R" and "C" is returned 1308// via "Res" and "ConstOpnd", respectively (If the entire expression is 1309// evaluated to a constant, the Res is set to NULL); otherwise, false is 1310// returned, and both "Res" and "ConstOpnd" remain unchanged. 1311bool Reassociate::CombineXorOpnd(Instruction *I, XorOpnd *Opnd1, XorOpnd *Opnd2, 1312 APInt &ConstOpnd, Value *&Res) { 1313 Value *X = Opnd1->getSymbolicPart(); 1314 if (X != Opnd2->getSymbolicPart()) 1315 return false; 1316 1317 // This many instruction become dead.(At least "Opnd1 ^ Opnd2" will die.) 1318 int DeadInstNum = 1; 1319 if (Opnd1->getValue()->hasOneUse()) 1320 DeadInstNum++; 1321 if (Opnd2->getValue()->hasOneUse()) 1322 DeadInstNum++; 1323 1324 // Xor-Rule 2: 1325 // (x | c1) ^ (x & c2) 1326 // = (x|c1) ^ (x&c2) ^ (c1 ^ c1) = ((x|c1) ^ c1) ^ (x & c2) ^ c1 1327 // = (x & ~c1) ^ (x & c2) ^ c1 // Xor-Rule 1 1328 // = (x & c3) ^ c1, where c3 = ~c1 ^ c2 // Xor-rule 3 1329 // 1330 if (Opnd1->isOrExpr() != Opnd2->isOrExpr()) { 1331 if (Opnd2->isOrExpr()) 1332 std::swap(Opnd1, Opnd2); 1333 1334 const APInt &C1 = Opnd1->getConstPart(); 1335 const APInt &C2 = Opnd2->getConstPart(); 1336 APInt C3((~C1) ^ C2); 1337 1338 // Do not increase code size! 1339 if (C3 != 0 && !C3.isAllOnesValue()) { 1340 int NewInstNum = ConstOpnd != 0 ? 1 : 2; 1341 if (NewInstNum > DeadInstNum) 1342 return false; 1343 } 1344 1345 Res = createAndInstr(I, X, C3); 1346 ConstOpnd ^= C1; 1347 1348 } else if (Opnd1->isOrExpr()) { 1349 // Xor-Rule 3: (x | c1) ^ (x | c2) = (x & c3) ^ c3 where c3 = c1 ^ c2 1350 // 1351 const APInt &C1 = Opnd1->getConstPart(); 1352 const APInt &C2 = Opnd2->getConstPart(); 1353 APInt C3 = C1 ^ C2; 1354 1355 // Do not increase code size 1356 if (C3 != 0 && !C3.isAllOnesValue()) { 1357 int NewInstNum = ConstOpnd != 0 ? 1 : 2; 1358 if (NewInstNum > DeadInstNum) 1359 return false; 1360 } 1361 1362 Res = createAndInstr(I, X, C3); 1363 ConstOpnd ^= C3; 1364 } else { 1365 // Xor-Rule 4: (x & c1) ^ (x & c2) = (x & (c1^c2)) 1366 // 1367 const APInt &C1 = Opnd1->getConstPart(); 1368 const APInt &C2 = Opnd2->getConstPart(); 1369 APInt C3 = C1 ^ C2; 1370 Res = createAndInstr(I, X, C3); 1371 } 1372 1373 // Put the original operands in the Redo list; hope they will be deleted 1374 // as dead code. 1375 if (Instruction *T = dyn_cast<Instruction>(Opnd1->getValue())) 1376 RedoInsts.insert(T); 1377 if (Instruction *T = dyn_cast<Instruction>(Opnd2->getValue())) 1378 RedoInsts.insert(T); 1379 1380 return true; 1381} 1382 1383/// Optimize a series of operands to an 'xor' instruction. If it can be reduced 1384/// to a single Value, it is returned, otherwise the Ops list is mutated as 1385/// necessary. 1386Value *Reassociate::OptimizeXor(Instruction *I, 1387 SmallVectorImpl<ValueEntry> &Ops) { 1388 if (Value *V = OptimizeAndOrXor(Instruction::Xor, Ops)) 1389 return V; 1390 1391 if (Ops.size() == 1) 1392 return nullptr; 1393 1394 SmallVector<XorOpnd, 8> Opnds; 1395 SmallVector<XorOpnd*, 8> OpndPtrs; 1396 Type *Ty = Ops[0].Op->getType(); 1397 APInt ConstOpnd(Ty->getIntegerBitWidth(), 0); 1398 1399 // Step 1: Convert ValueEntry to XorOpnd 1400 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 1401 Value *V = Ops[i].Op; 1402 if (!isa<ConstantInt>(V)) { 1403 XorOpnd O(V); 1404 O.setSymbolicRank(getRank(O.getSymbolicPart())); 1405 Opnds.push_back(O); 1406 } else 1407 ConstOpnd ^= cast<ConstantInt>(V)->getValue(); 1408 } 1409 1410 // NOTE: From this point on, do *NOT* add/delete element to/from "Opnds". 1411 // It would otherwise invalidate the "Opnds"'s iterator, and hence invalidate 1412 // the "OpndPtrs" as well. For the similar reason, do not fuse this loop 1413 // with the previous loop --- the iterator of the "Opnds" may be invalidated 1414 // when new elements are added to the vector. 1415 for (unsigned i = 0, e = Opnds.size(); i != e; ++i) 1416 OpndPtrs.push_back(&Opnds[i]); 1417 1418 // Step 2: Sort the Xor-Operands in a way such that the operands containing 1419 // the same symbolic value cluster together. For instance, the input operand 1420 // sequence ("x | 123", "y & 456", "x & 789") will be sorted into: 1421 // ("x | 123", "x & 789", "y & 456"). 1422 std::stable_sort(OpndPtrs.begin(), OpndPtrs.end(), XorOpnd::PtrSortFunctor()); 1423 1424 // Step 3: Combine adjacent operands 1425 XorOpnd *PrevOpnd = nullptr; 1426 bool Changed = false; 1427 for (unsigned i = 0, e = Opnds.size(); i < e; i++) { 1428 XorOpnd *CurrOpnd = OpndPtrs[i]; 1429 // The combined value 1430 Value *CV; 1431 1432 // Step 3.1: Try simplifying "CurrOpnd ^ ConstOpnd" 1433 if (ConstOpnd != 0 && CombineXorOpnd(I, CurrOpnd, ConstOpnd, CV)) { 1434 Changed = true; 1435 if (CV) 1436 *CurrOpnd = XorOpnd(CV); 1437 else { 1438 CurrOpnd->Invalidate(); 1439 continue; 1440 } 1441 } 1442 1443 if (!PrevOpnd || CurrOpnd->getSymbolicPart() != PrevOpnd->getSymbolicPart()) { 1444 PrevOpnd = CurrOpnd; 1445 continue; 1446 } 1447 1448 // step 3.2: When previous and current operands share the same symbolic 1449 // value, try to simplify "PrevOpnd ^ CurrOpnd ^ ConstOpnd" 1450 // 1451 if (CombineXorOpnd(I, CurrOpnd, PrevOpnd, ConstOpnd, CV)) { 1452 // Remove previous operand 1453 PrevOpnd->Invalidate(); 1454 if (CV) { 1455 *CurrOpnd = XorOpnd(CV); 1456 PrevOpnd = CurrOpnd; 1457 } else { 1458 CurrOpnd->Invalidate(); 1459 PrevOpnd = nullptr; 1460 } 1461 Changed = true; 1462 } 1463 } 1464 1465 // Step 4: Reassemble the Ops 1466 if (Changed) { 1467 Ops.clear(); 1468 for (unsigned int i = 0, e = Opnds.size(); i < e; i++) { 1469 XorOpnd &O = Opnds[i]; 1470 if (O.isInvalid()) 1471 continue; 1472 ValueEntry VE(getRank(O.getValue()), O.getValue()); 1473 Ops.push_back(VE); 1474 } 1475 if (ConstOpnd != 0) { 1476 Value *C = ConstantInt::get(Ty->getContext(), ConstOpnd); 1477 ValueEntry VE(getRank(C), C); 1478 Ops.push_back(VE); 1479 } 1480 int Sz = Ops.size(); 1481 if (Sz == 1) 1482 return Ops.back().Op; 1483 else if (Sz == 0) { 1484 assert(ConstOpnd == 0); 1485 return ConstantInt::get(Ty->getContext(), ConstOpnd); 1486 } 1487 } 1488 1489 return nullptr; 1490} 1491 1492/// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This 1493/// optimizes based on identities. If it can be reduced to a single Value, it 1494/// is returned, otherwise the Ops list is mutated as necessary. 1495Value *Reassociate::OptimizeAdd(Instruction *I, 1496 SmallVectorImpl<ValueEntry> &Ops) { 1497 // Scan the operand lists looking for X and -X pairs. If we find any, we 1498 // can simplify expressions like X+-X == 0 and X+~X ==-1. While we're at it, 1499 // scan for any 1500 // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z. 1501 1502 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 1503 Value *TheOp = Ops[i].Op; 1504 // Check to see if we've seen this operand before. If so, we factor all 1505 // instances of the operand together. Due to our sorting criteria, we know 1506 // that these need to be next to each other in the vector. 1507 if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) { 1508 // Rescan the list, remove all instances of this operand from the expr. 1509 unsigned NumFound = 0; 1510 do { 1511 Ops.erase(Ops.begin()+i); 1512 ++NumFound; 1513 } while (i != Ops.size() && Ops[i].Op == TheOp); 1514 1515 DEBUG(dbgs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n'); 1516 ++NumFactor; 1517 1518 // Insert a new multiply. 1519 Type *Ty = TheOp->getType(); 1520 Constant *C = Ty->isIntegerTy() ? ConstantInt::get(Ty, NumFound) 1521 : ConstantFP::get(Ty, NumFound); 1522 Instruction *Mul = CreateMul(TheOp, C, "factor", I, I); 1523 1524 // Now that we have inserted a multiply, optimize it. This allows us to 1525 // handle cases that require multiple factoring steps, such as this: 1526 // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6 1527 RedoInsts.insert(Mul); 1528 1529 // If every add operand was a duplicate, return the multiply. 1530 if (Ops.empty()) 1531 return Mul; 1532 1533 // Otherwise, we had some input that didn't have the dupe, such as 1534 // "A + A + B" -> "A*2 + B". Add the new multiply to the list of 1535 // things being added by this operation. 1536 Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul)); 1537 1538 --i; 1539 e = Ops.size(); 1540 continue; 1541 } 1542 1543 // Check for X and -X or X and ~X in the operand list. 1544 if (!BinaryOperator::isNeg(TheOp) && !BinaryOperator::isFNeg(TheOp) && 1545 !BinaryOperator::isNot(TheOp)) 1546 continue; 1547 1548 Value *X = nullptr; 1549 if (BinaryOperator::isNeg(TheOp) || BinaryOperator::isFNeg(TheOp)) 1550 X = BinaryOperator::getNegArgument(TheOp); 1551 else if (BinaryOperator::isNot(TheOp)) 1552 X = BinaryOperator::getNotArgument(TheOp); 1553 1554 unsigned FoundX = FindInOperandList(Ops, i, X); 1555 if (FoundX == i) 1556 continue; 1557 1558 // Remove X and -X from the operand list. 1559 if (Ops.size() == 2 && 1560 (BinaryOperator::isNeg(TheOp) || BinaryOperator::isFNeg(TheOp))) 1561 return Constant::getNullValue(X->getType()); 1562 1563 // Remove X and ~X from the operand list. 1564 if (Ops.size() == 2 && BinaryOperator::isNot(TheOp)) 1565 return Constant::getAllOnesValue(X->getType()); 1566 1567 Ops.erase(Ops.begin()+i); 1568 if (i < FoundX) 1569 --FoundX; 1570 else 1571 --i; // Need to back up an extra one. 1572 Ops.erase(Ops.begin()+FoundX); 1573 ++NumAnnihil; 1574 --i; // Revisit element. 1575 e -= 2; // Removed two elements. 1576 1577 // if X and ~X we append -1 to the operand list. 1578 if (BinaryOperator::isNot(TheOp)) { 1579 Value *V = Constant::getAllOnesValue(X->getType()); 1580 Ops.insert(Ops.end(), ValueEntry(getRank(V), V)); 1581 e += 1; 1582 } 1583 } 1584 1585 // Scan the operand list, checking to see if there are any common factors 1586 // between operands. Consider something like A*A+A*B*C+D. We would like to 1587 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 1588 // To efficiently find this, we count the number of times a factor occurs 1589 // for any ADD operands that are MULs. 1590 DenseMap<Value*, unsigned> FactorOccurrences; 1591 1592 // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4) 1593 // where they are actually the same multiply. 1594 unsigned MaxOcc = 0; 1595 Value *MaxOccVal = nullptr; 1596 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 1597 BinaryOperator *BOp = 1598 isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul); 1599 if (!BOp) 1600 continue; 1601 1602 // Compute all of the factors of this added value. 1603 SmallVector<Value*, 8> Factors; 1604 FindSingleUseMultiplyFactors(BOp, Factors, Ops); 1605 assert(Factors.size() > 1 && "Bad linearize!"); 1606 1607 // Add one to FactorOccurrences for each unique factor in this op. 1608 SmallPtrSet<Value*, 8> Duplicates; 1609 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 1610 Value *Factor = Factors[i]; 1611 if (!Duplicates.insert(Factor).second) 1612 continue; 1613 1614 unsigned Occ = ++FactorOccurrences[Factor]; 1615 if (Occ > MaxOcc) { 1616 MaxOcc = Occ; 1617 MaxOccVal = Factor; 1618 } 1619 1620 // If Factor is a negative constant, add the negated value as a factor 1621 // because we can percolate the negate out. Watch for minint, which 1622 // cannot be positivified. 1623 if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor)) { 1624 if (CI->isNegative() && !CI->isMinValue(true)) { 1625 Factor = ConstantInt::get(CI->getContext(), -CI->getValue()); 1626 assert(!Duplicates.count(Factor) && 1627 "Shouldn't have two constant factors, missed a canonicalize"); 1628 unsigned Occ = ++FactorOccurrences[Factor]; 1629 if (Occ > MaxOcc) { 1630 MaxOcc = Occ; 1631 MaxOccVal = Factor; 1632 } 1633 } 1634 } else if (ConstantFP *CF = dyn_cast<ConstantFP>(Factor)) { 1635 if (CF->isNegative()) { 1636 APFloat F(CF->getValueAPF()); 1637 F.changeSign(); 1638 Factor = ConstantFP::get(CF->getContext(), F); 1639 assert(!Duplicates.count(Factor) && 1640 "Shouldn't have two constant factors, missed a canonicalize"); 1641 unsigned Occ = ++FactorOccurrences[Factor]; 1642 if (Occ > MaxOcc) { 1643 MaxOcc = Occ; 1644 MaxOccVal = Factor; 1645 } 1646 } 1647 } 1648 } 1649 } 1650 1651 // If any factor occurred more than one time, we can pull it out. 1652 if (MaxOcc > 1) { 1653 DEBUG(dbgs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n'); 1654 ++NumFactor; 1655 1656 // Create a new instruction that uses the MaxOccVal twice. If we don't do 1657 // this, we could otherwise run into situations where removing a factor 1658 // from an expression will drop a use of maxocc, and this can cause 1659 // RemoveFactorFromExpression on successive values to behave differently. 1660 Instruction *DummyInst = 1661 I->getType()->isIntegerTy() 1662 ? BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal) 1663 : BinaryOperator::CreateFAdd(MaxOccVal, MaxOccVal); 1664 1665 SmallVector<WeakVH, 4> NewMulOps; 1666 for (unsigned i = 0; i != Ops.size(); ++i) { 1667 // Only try to remove factors from expressions we're allowed to. 1668 BinaryOperator *BOp = 1669 isReassociableOp(Ops[i].Op, Instruction::Mul, Instruction::FMul); 1670 if (!BOp) 1671 continue; 1672 1673 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 1674 // The factorized operand may occur several times. Convert them all in 1675 // one fell swoop. 1676 for (unsigned j = Ops.size(); j != i;) { 1677 --j; 1678 if (Ops[j].Op == Ops[i].Op) { 1679 NewMulOps.push_back(V); 1680 Ops.erase(Ops.begin()+j); 1681 } 1682 } 1683 --i; 1684 } 1685 } 1686 1687 // No need for extra uses anymore. 1688 delete DummyInst; 1689 1690 unsigned NumAddedValues = NewMulOps.size(); 1691 Value *V = EmitAddTreeOfValues(I, NewMulOps); 1692 1693 // Now that we have inserted the add tree, optimize it. This allows us to 1694 // handle cases that require multiple factoring steps, such as this: 1695 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 1696 assert(NumAddedValues > 1 && "Each occurrence should contribute a value"); 1697 (void)NumAddedValues; 1698 if (Instruction *VI = dyn_cast<Instruction>(V)) 1699 RedoInsts.insert(VI); 1700 1701 // Create the multiply. 1702 Instruction *V2 = CreateMul(V, MaxOccVal, "tmp", I, I); 1703 1704 // Rerun associate on the multiply in case the inner expression turned into 1705 // a multiply. We want to make sure that we keep things in canonical form. 1706 RedoInsts.insert(V2); 1707 1708 // If every add operand included the factor (e.g. "A*B + A*C"), then the 1709 // entire result expression is just the multiply "A*(B+C)". 1710 if (Ops.empty()) 1711 return V2; 1712 1713 // Otherwise, we had some input that didn't have the factor, such as 1714 // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of 1715 // things being added by this operation. 1716 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 1717 } 1718 1719 return nullptr; 1720} 1721 1722/// \brief Build up a vector of value/power pairs factoring a product. 1723/// 1724/// Given a series of multiplication operands, build a vector of factors and 1725/// the powers each is raised to when forming the final product. Sort them in 1726/// the order of descending power. 1727/// 1728/// (x*x) -> [(x, 2)] 1729/// ((x*x)*x) -> [(x, 3)] 1730/// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)] 1731/// 1732/// \returns Whether any factors have a power greater than one. 1733bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops, 1734 SmallVectorImpl<Factor> &Factors) { 1735 // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this. 1736 // Compute the sum of powers of simplifiable factors. 1737 unsigned FactorPowerSum = 0; 1738 for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) { 1739 Value *Op = Ops[Idx-1].Op; 1740 1741 // Count the number of occurrences of this value. 1742 unsigned Count = 1; 1743 for (; Idx < Size && Ops[Idx].Op == Op; ++Idx) 1744 ++Count; 1745 // Track for simplification all factors which occur 2 or more times. 1746 if (Count > 1) 1747 FactorPowerSum += Count; 1748 } 1749 1750 // We can only simplify factors if the sum of the powers of our simplifiable 1751 // factors is 4 or higher. When that is the case, we will *always* have 1752 // a simplification. This is an important invariant to prevent cyclicly 1753 // trying to simplify already minimal formations. 1754 if (FactorPowerSum < 4) 1755 return false; 1756 1757 // Now gather the simplifiable factors, removing them from Ops. 1758 FactorPowerSum = 0; 1759 for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) { 1760 Value *Op = Ops[Idx-1].Op; 1761 1762 // Count the number of occurrences of this value. 1763 unsigned Count = 1; 1764 for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx) 1765 ++Count; 1766 if (Count == 1) 1767 continue; 1768 // Move an even number of occurrences to Factors. 1769 Count &= ~1U; 1770 Idx -= Count; 1771 FactorPowerSum += Count; 1772 Factors.push_back(Factor(Op, Count)); 1773 Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count); 1774 } 1775 1776 // None of the adjustments above should have reduced the sum of factor powers 1777 // below our mininum of '4'. 1778 assert(FactorPowerSum >= 4); 1779 1780 std::stable_sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter()); 1781 return true; 1782} 1783 1784/// \brief Build a tree of multiplies, computing the product of Ops. 1785static Value *buildMultiplyTree(IRBuilder<> &Builder, 1786 SmallVectorImpl<Value*> &Ops) { 1787 if (Ops.size() == 1) 1788 return Ops.back(); 1789 1790 Value *LHS = Ops.pop_back_val(); 1791 do { 1792 if (LHS->getType()->isIntegerTy()) 1793 LHS = Builder.CreateMul(LHS, Ops.pop_back_val()); 1794 else 1795 LHS = Builder.CreateFMul(LHS, Ops.pop_back_val()); 1796 } while (!Ops.empty()); 1797 1798 return LHS; 1799} 1800 1801/// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*... 1802/// 1803/// Given a vector of values raised to various powers, where no two values are 1804/// equal and the powers are sorted in decreasing order, compute the minimal 1805/// DAG of multiplies to compute the final product, and return that product 1806/// value. 1807Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder, 1808 SmallVectorImpl<Factor> &Factors) { 1809 assert(Factors[0].Power); 1810 SmallVector<Value *, 4> OuterProduct; 1811 for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size(); 1812 Idx < Size && Factors[Idx].Power > 0; ++Idx) { 1813 if (Factors[Idx].Power != Factors[LastIdx].Power) { 1814 LastIdx = Idx; 1815 continue; 1816 } 1817 1818 // We want to multiply across all the factors with the same power so that 1819 // we can raise them to that power as a single entity. Build a mini tree 1820 // for that. 1821 SmallVector<Value *, 4> InnerProduct; 1822 InnerProduct.push_back(Factors[LastIdx].Base); 1823 do { 1824 InnerProduct.push_back(Factors[Idx].Base); 1825 ++Idx; 1826 } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power); 1827 1828 // Reset the base value of the first factor to the new expression tree. 1829 // We'll remove all the factors with the same power in a second pass. 1830 Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct); 1831 if (Instruction *MI = dyn_cast<Instruction>(M)) 1832 RedoInsts.insert(MI); 1833 1834 LastIdx = Idx; 1835 } 1836 // Unique factors with equal powers -- we've folded them into the first one's 1837 // base. 1838 Factors.erase(std::unique(Factors.begin(), Factors.end(), 1839 Factor::PowerEqual()), 1840 Factors.end()); 1841 1842 // Iteratively collect the base of each factor with an add power into the 1843 // outer product, and halve each power in preparation for squaring the 1844 // expression. 1845 for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) { 1846 if (Factors[Idx].Power & 1) 1847 OuterProduct.push_back(Factors[Idx].Base); 1848 Factors[Idx].Power >>= 1; 1849 } 1850 if (Factors[0].Power) { 1851 Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors); 1852 OuterProduct.push_back(SquareRoot); 1853 OuterProduct.push_back(SquareRoot); 1854 } 1855 if (OuterProduct.size() == 1) 1856 return OuterProduct.front(); 1857 1858 Value *V = buildMultiplyTree(Builder, OuterProduct); 1859 return V; 1860} 1861 1862Value *Reassociate::OptimizeMul(BinaryOperator *I, 1863 SmallVectorImpl<ValueEntry> &Ops) { 1864 // We can only optimize the multiplies when there is a chain of more than 1865 // three, such that a balanced tree might require fewer total multiplies. 1866 if (Ops.size() < 4) 1867 return nullptr; 1868 1869 // Try to turn linear trees of multiplies without other uses of the 1870 // intermediate stages into minimal multiply DAGs with perfect sub-expression 1871 // re-use. 1872 SmallVector<Factor, 4> Factors; 1873 if (!collectMultiplyFactors(Ops, Factors)) 1874 return nullptr; // All distinct factors, so nothing left for us to do. 1875 1876 IRBuilder<> Builder(I); 1877 Value *V = buildMinimalMultiplyDAG(Builder, Factors); 1878 if (Ops.empty()) 1879 return V; 1880 1881 ValueEntry NewEntry = ValueEntry(getRank(V), V); 1882 Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry); 1883 return nullptr; 1884} 1885 1886Value *Reassociate::OptimizeExpression(BinaryOperator *I, 1887 SmallVectorImpl<ValueEntry> &Ops) { 1888 // Now that we have the linearized expression tree, try to optimize it. 1889 // Start by folding any constants that we found. 1890 Constant *Cst = nullptr; 1891 unsigned Opcode = I->getOpcode(); 1892 while (!Ops.empty() && isa<Constant>(Ops.back().Op)) { 1893 Constant *C = cast<Constant>(Ops.pop_back_val().Op); 1894 Cst = Cst ? ConstantExpr::get(Opcode, C, Cst) : C; 1895 } 1896 // If there was nothing but constants then we are done. 1897 if (Ops.empty()) 1898 return Cst; 1899 1900 // Put the combined constant back at the end of the operand list, except if 1901 // there is no point. For example, an add of 0 gets dropped here, while a 1902 // multiplication by zero turns the whole expression into zero. 1903 if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) { 1904 if (Cst == ConstantExpr::getBinOpAbsorber(Opcode, I->getType())) 1905 return Cst; 1906 Ops.push_back(ValueEntry(0, Cst)); 1907 } 1908 1909 if (Ops.size() == 1) return Ops[0].Op; 1910 1911 // Handle destructive annihilation due to identities between elements in the 1912 // argument list here. 1913 unsigned NumOps = Ops.size(); 1914 switch (Opcode) { 1915 default: break; 1916 case Instruction::And: 1917 case Instruction::Or: 1918 if (Value *Result = OptimizeAndOrXor(Opcode, Ops)) 1919 return Result; 1920 break; 1921 1922 case Instruction::Xor: 1923 if (Value *Result = OptimizeXor(I, Ops)) 1924 return Result; 1925 break; 1926 1927 case Instruction::Add: 1928 case Instruction::FAdd: 1929 if (Value *Result = OptimizeAdd(I, Ops)) 1930 return Result; 1931 break; 1932 1933 case Instruction::Mul: 1934 case Instruction::FMul: 1935 if (Value *Result = OptimizeMul(I, Ops)) 1936 return Result; 1937 break; 1938 } 1939 1940 if (Ops.size() != NumOps) 1941 return OptimizeExpression(I, Ops); 1942 return nullptr; 1943} 1944 1945/// EraseInst - Zap the given instruction, adding interesting operands to the 1946/// work list. 1947void Reassociate::EraseInst(Instruction *I) { 1948 assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!"); 1949 SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end()); 1950 // Erase the dead instruction. 1951 ValueRankMap.erase(I); 1952 RedoInsts.remove(I); 1953 I->eraseFromParent(); 1954 // Optimize its operands. 1955 SmallPtrSet<Instruction *, 8> Visited; // Detect self-referential nodes. 1956 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 1957 if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) { 1958 // If this is a node in an expression tree, climb to the expression root 1959 // and add that since that's where optimization actually happens. 1960 unsigned Opcode = Op->getOpcode(); 1961 while (Op->hasOneUse() && Op->user_back()->getOpcode() == Opcode && 1962 Visited.insert(Op).second) 1963 Op = Op->user_back(); 1964 RedoInsts.insert(Op); 1965 } 1966} 1967 1968// Canonicalize expressions of the following form: 1969// x + (-Constant * y) -> x - (Constant * y) 1970// x - (-Constant * y) -> x + (Constant * y) 1971Instruction *Reassociate::canonicalizeNegConstExpr(Instruction *I) { 1972 if (!I->hasOneUse() || I->getType()->isVectorTy()) 1973 return nullptr; 1974 1975 // Must be a mul, fmul, or fdiv instruction. 1976 unsigned Opcode = I->getOpcode(); 1977 if (Opcode != Instruction::Mul && Opcode != Instruction::FMul && 1978 Opcode != Instruction::FDiv) 1979 return nullptr; 1980 1981 // Must have at least one constant operand. 1982 Constant *C0 = dyn_cast<Constant>(I->getOperand(0)); 1983 Constant *C1 = dyn_cast<Constant>(I->getOperand(1)); 1984 if (!C0 && !C1) 1985 return nullptr; 1986 1987 // Must be a negative ConstantInt or ConstantFP. 1988 Constant *C = C0 ? C0 : C1; 1989 unsigned ConstIdx = C0 ? 0 : 1; 1990 if (auto *CI = dyn_cast<ConstantInt>(C)) { 1991 if (!CI->isNegative()) 1992 return nullptr; 1993 } else if (auto *CF = dyn_cast<ConstantFP>(C)) { 1994 if (!CF->isNegative()) 1995 return nullptr; 1996 } else 1997 return nullptr; 1998 1999 // User must be a binary operator with one or more uses. 2000 Instruction *User = I->user_back(); 2001 if (!isa<BinaryOperator>(User) || !User->getNumUses()) 2002 return nullptr; 2003 2004 unsigned UserOpcode = User->getOpcode(); 2005 if (UserOpcode != Instruction::Add && UserOpcode != Instruction::FAdd && 2006 UserOpcode != Instruction::Sub && UserOpcode != Instruction::FSub) 2007 return nullptr; 2008 2009 // Subtraction is not commutative. Explicitly, the following transform is 2010 // not valid: (-Constant * y) - x -> x + (Constant * y) 2011 if (!User->isCommutative() && User->getOperand(1) != I) 2012 return nullptr; 2013 2014 // Change the sign of the constant. 2015 if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) 2016 I->setOperand(ConstIdx, ConstantInt::get(CI->getContext(), -CI->getValue())); 2017 else { 2018 ConstantFP *CF = cast<ConstantFP>(C); 2019 APFloat Val = CF->getValueAPF(); 2020 Val.changeSign(); 2021 I->setOperand(ConstIdx, ConstantFP::get(CF->getContext(), Val)); 2022 } 2023 2024 // Canonicalize I to RHS to simplify the next bit of logic. E.g., 2025 // ((-Const*y) + x) -> (x + (-Const*y)). 2026 if (User->getOperand(0) == I && User->isCommutative()) 2027 cast<BinaryOperator>(User)->swapOperands(); 2028 2029 Value *Op0 = User->getOperand(0); 2030 Value *Op1 = User->getOperand(1); 2031 BinaryOperator *NI; 2032 switch(UserOpcode) { 2033 default: 2034 llvm_unreachable("Unexpected Opcode!"); 2035 case Instruction::Add: 2036 NI = BinaryOperator::CreateSub(Op0, Op1); 2037 break; 2038 case Instruction::Sub: 2039 NI = BinaryOperator::CreateAdd(Op0, Op1); 2040 break; 2041 case Instruction::FAdd: 2042 NI = BinaryOperator::CreateFSub(Op0, Op1); 2043 NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags()); 2044 break; 2045 case Instruction::FSub: 2046 NI = BinaryOperator::CreateFAdd(Op0, Op1); 2047 NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags()); 2048 break; 2049 } 2050 2051 NI->insertBefore(User); 2052 NI->setName(User->getName()); 2053 User->replaceAllUsesWith(NI); 2054 NI->setDebugLoc(I->getDebugLoc()); 2055 RedoInsts.insert(I); 2056 MadeChange = true; 2057 return NI; 2058} 2059 2060/// OptimizeInst - Inspect and optimize the given instruction. Note that erasing 2061/// instructions is not allowed. 2062void Reassociate::OptimizeInst(Instruction *I) { 2063 // Only consider operations that we understand. 2064 if (!isa<BinaryOperator>(I)) 2065 return; 2066 2067 if (I->getOpcode() == Instruction::Shl && isa<ConstantInt>(I->getOperand(1))) 2068 // If an operand of this shift is a reassociable multiply, or if the shift 2069 // is used by a reassociable multiply or add, turn into a multiply. 2070 if (isReassociableOp(I->getOperand(0), Instruction::Mul) || 2071 (I->hasOneUse() && 2072 (isReassociableOp(I->user_back(), Instruction::Mul) || 2073 isReassociableOp(I->user_back(), Instruction::Add)))) { 2074 Instruction *NI = ConvertShiftToMul(I); 2075 RedoInsts.insert(I); 2076 MadeChange = true; 2077 I = NI; 2078 } 2079 2080 // Canonicalize negative constants out of expressions. 2081 if (Instruction *Res = canonicalizeNegConstExpr(I)) 2082 I = Res; 2083 2084 // Commute binary operators, to canonicalize the order of their operands. 2085 // This can potentially expose more CSE opportunities, and makes writing other 2086 // transformations simpler. 2087 if (I->isCommutative()) 2088 canonicalizeOperands(I); 2089 2090 // Don't optimize vector instructions. 2091 if (I->getType()->isVectorTy()) 2092 return; 2093 2094 // Don't optimize floating point instructions that don't have unsafe algebra. 2095 if (I->getType()->isFloatingPointTy() && !I->hasUnsafeAlgebra()) 2096 return; 2097 2098 // Do not reassociate boolean (i1) expressions. We want to preserve the 2099 // original order of evaluation for short-circuited comparisons that 2100 // SimplifyCFG has folded to AND/OR expressions. If the expression 2101 // is not further optimized, it is likely to be transformed back to a 2102 // short-circuited form for code gen, and the source order may have been 2103 // optimized for the most likely conditions. 2104 if (I->getType()->isIntegerTy(1)) 2105 return; 2106 2107 // If this is a subtract instruction which is not already in negate form, 2108 // see if we can convert it to X+-Y. 2109 if (I->getOpcode() == Instruction::Sub) { 2110 if (ShouldBreakUpSubtract(I)) { 2111 Instruction *NI = BreakUpSubtract(I); 2112 RedoInsts.insert(I); 2113 MadeChange = true; 2114 I = NI; 2115 } else if (BinaryOperator::isNeg(I)) { 2116 // Otherwise, this is a negation. See if the operand is a multiply tree 2117 // and if this is not an inner node of a multiply tree. 2118 if (isReassociableOp(I->getOperand(1), Instruction::Mul) && 2119 (!I->hasOneUse() || 2120 !isReassociableOp(I->user_back(), Instruction::Mul))) { 2121 Instruction *NI = LowerNegateToMultiply(I); 2122 RedoInsts.insert(I); 2123 MadeChange = true; 2124 I = NI; 2125 } 2126 } 2127 } else if (I->getOpcode() == Instruction::FSub) { 2128 if (ShouldBreakUpSubtract(I)) { 2129 Instruction *NI = BreakUpSubtract(I); 2130 RedoInsts.insert(I); 2131 MadeChange = true; 2132 I = NI; 2133 } else if (BinaryOperator::isFNeg(I)) { 2134 // Otherwise, this is a negation. See if the operand is a multiply tree 2135 // and if this is not an inner node of a multiply tree. 2136 if (isReassociableOp(I->getOperand(1), Instruction::FMul) && 2137 (!I->hasOneUse() || 2138 !isReassociableOp(I->user_back(), Instruction::FMul))) { 2139 Instruction *NI = LowerNegateToMultiply(I); 2140 RedoInsts.insert(I); 2141 MadeChange = true; 2142 I = NI; 2143 } 2144 } 2145 } 2146 2147 // If this instruction is an associative binary operator, process it. 2148 if (!I->isAssociative()) return; 2149 BinaryOperator *BO = cast<BinaryOperator>(I); 2150 2151 // If this is an interior node of a reassociable tree, ignore it until we 2152 // get to the root of the tree, to avoid N^2 analysis. 2153 unsigned Opcode = BO->getOpcode(); 2154 if (BO->hasOneUse() && BO->user_back()->getOpcode() == Opcode) 2155 return; 2156 2157 // If this is an add tree that is used by a sub instruction, ignore it 2158 // until we process the subtract. 2159 if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add && 2160 cast<Instruction>(BO->user_back())->getOpcode() == Instruction::Sub) 2161 return; 2162 if (BO->hasOneUse() && BO->getOpcode() == Instruction::FAdd && 2163 cast<Instruction>(BO->user_back())->getOpcode() == Instruction::FSub) 2164 return; 2165 2166 ReassociateExpression(BO); 2167} 2168 2169void Reassociate::ReassociateExpression(BinaryOperator *I) { 2170 assert(!I->getType()->isVectorTy() && 2171 "Reassociation of vector instructions is not supported."); 2172 2173 // First, walk the expression tree, linearizing the tree, collecting the 2174 // operand information. 2175 SmallVector<RepeatedValue, 8> Tree; 2176 MadeChange |= LinearizeExprTree(I, Tree); 2177 SmallVector<ValueEntry, 8> Ops; 2178 Ops.reserve(Tree.size()); 2179 for (unsigned i = 0, e = Tree.size(); i != e; ++i) { 2180 RepeatedValue E = Tree[i]; 2181 Ops.append(E.second.getZExtValue(), 2182 ValueEntry(getRank(E.first), E.first)); 2183 } 2184 2185 DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n'); 2186 2187 // Now that we have linearized the tree to a list and have gathered all of 2188 // the operands and their ranks, sort the operands by their rank. Use a 2189 // stable_sort so that values with equal ranks will have their relative 2190 // positions maintained (and so the compiler is deterministic). Note that 2191 // this sorts so that the highest ranking values end up at the beginning of 2192 // the vector. 2193 std::stable_sort(Ops.begin(), Ops.end()); 2194 2195 // OptimizeExpression - Now that we have the expression tree in a convenient 2196 // sorted form, optimize it globally if possible. 2197 if (Value *V = OptimizeExpression(I, Ops)) { 2198 if (V == I) 2199 // Self-referential expression in unreachable code. 2200 return; 2201 // This expression tree simplified to something that isn't a tree, 2202 // eliminate it. 2203 DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n'); 2204 I->replaceAllUsesWith(V); 2205 if (Instruction *VI = dyn_cast<Instruction>(V)) 2206 VI->setDebugLoc(I->getDebugLoc()); 2207 RedoInsts.insert(I); 2208 ++NumAnnihil; 2209 return; 2210 } 2211 2212 // We want to sink immediates as deeply as possible except in the case where 2213 // this is a multiply tree used only by an add, and the immediate is a -1. 2214 // In this case we reassociate to put the negation on the outside so that we 2215 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 2216 if (I->hasOneUse()) { 2217 if (I->getOpcode() == Instruction::Mul && 2218 cast<Instruction>(I->user_back())->getOpcode() == Instruction::Add && 2219 isa<ConstantInt>(Ops.back().Op) && 2220 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 2221 ValueEntry Tmp = Ops.pop_back_val(); 2222 Ops.insert(Ops.begin(), Tmp); 2223 } else if (I->getOpcode() == Instruction::FMul && 2224 cast<Instruction>(I->user_back())->getOpcode() == 2225 Instruction::FAdd && 2226 isa<ConstantFP>(Ops.back().Op) && 2227 cast<ConstantFP>(Ops.back().Op)->isExactlyValue(-1.0)) { 2228 ValueEntry Tmp = Ops.pop_back_val(); 2229 Ops.insert(Ops.begin(), Tmp); 2230 } 2231 } 2232 2233 DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n'); 2234 2235 if (Ops.size() == 1) { 2236 if (Ops[0].Op == I) 2237 // Self-referential expression in unreachable code. 2238 return; 2239 2240 // This expression tree simplified to something that isn't a tree, 2241 // eliminate it. 2242 I->replaceAllUsesWith(Ops[0].Op); 2243 if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op)) 2244 OI->setDebugLoc(I->getDebugLoc()); 2245 RedoInsts.insert(I); 2246 return; 2247 } 2248 2249 // Now that we ordered and optimized the expressions, splat them back into 2250 // the expression tree, removing any unneeded nodes. 2251 RewriteExprTree(I, Ops); 2252} 2253 2254bool Reassociate::runOnFunction(Function &F) { 2255 if (skipOptnoneFunction(F)) 2256 return false; 2257 2258 // Calculate the rank map for F 2259 BuildRankMap(F); 2260 2261 MadeChange = false; 2262 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) { 2263 // Optimize every instruction in the basic block. 2264 for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; ) 2265 if (isInstructionTriviallyDead(II)) { 2266 EraseInst(II++); 2267 } else { 2268 OptimizeInst(II); 2269 assert(II->getParent() == BI && "Moved to a different block!"); 2270 ++II; 2271 } 2272 2273 // If this produced extra instructions to optimize, handle them now. 2274 while (!RedoInsts.empty()) { 2275 Instruction *I = RedoInsts.pop_back_val(); 2276 if (isInstructionTriviallyDead(I)) 2277 EraseInst(I); 2278 else 2279 OptimizeInst(I); 2280 } 2281 } 2282 2283 // We are done with the rank map. 2284 RankMap.clear(); 2285 ValueRankMap.clear(); 2286 2287 return MadeChange; 2288} 2289