InstCombineSelect.cpp revision 11acaa374cdcebb161bf0de5f244265d78a749c1
1//===- InstCombineSelect.cpp ----------------------------------------------===// 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 the visitSelect function. 11// 12//===----------------------------------------------------------------------===// 13 14#include "InstCombine.h" 15#include "llvm/Support/PatternMatch.h" 16using namespace llvm; 17using namespace PatternMatch; 18 19/// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms, 20/// returning the kind and providing the out parameter results if we 21/// successfully match. 22static SelectPatternFlavor 23MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) { 24 SelectInst *SI = dyn_cast<SelectInst>(V); 25 if (SI == 0) return SPF_UNKNOWN; 26 27 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition()); 28 if (ICI == 0) return SPF_UNKNOWN; 29 30 LHS = ICI->getOperand(0); 31 RHS = ICI->getOperand(1); 32 33 // (icmp X, Y) ? X : Y 34 if (SI->getTrueValue() == ICI->getOperand(0) && 35 SI->getFalseValue() == ICI->getOperand(1)) { 36 switch (ICI->getPredicate()) { 37 default: return SPF_UNKNOWN; // Equality. 38 case ICmpInst::ICMP_UGT: 39 case ICmpInst::ICMP_UGE: return SPF_UMAX; 40 case ICmpInst::ICMP_SGT: 41 case ICmpInst::ICMP_SGE: return SPF_SMAX; 42 case ICmpInst::ICMP_ULT: 43 case ICmpInst::ICMP_ULE: return SPF_UMIN; 44 case ICmpInst::ICMP_SLT: 45 case ICmpInst::ICMP_SLE: return SPF_SMIN; 46 } 47 } 48 49 // (icmp X, Y) ? Y : X 50 if (SI->getTrueValue() == ICI->getOperand(1) && 51 SI->getFalseValue() == ICI->getOperand(0)) { 52 switch (ICI->getPredicate()) { 53 default: return SPF_UNKNOWN; // Equality. 54 case ICmpInst::ICMP_UGT: 55 case ICmpInst::ICMP_UGE: return SPF_UMIN; 56 case ICmpInst::ICMP_SGT: 57 case ICmpInst::ICMP_SGE: return SPF_SMIN; 58 case ICmpInst::ICMP_ULT: 59 case ICmpInst::ICMP_ULE: return SPF_UMAX; 60 case ICmpInst::ICMP_SLT: 61 case ICmpInst::ICMP_SLE: return SPF_SMAX; 62 } 63 } 64 65 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5) 66 67 return SPF_UNKNOWN; 68} 69 70 71/// GetSelectFoldableOperands - We want to turn code that looks like this: 72/// %C = or %A, %B 73/// %D = select %cond, %C, %A 74/// into: 75/// %C = select %cond, %B, 0 76/// %D = or %A, %C 77/// 78/// Assuming that the specified instruction is an operand to the select, return 79/// a bitmask indicating which operands of this instruction are foldable if they 80/// equal the other incoming value of the select. 81/// 82static unsigned GetSelectFoldableOperands(Instruction *I) { 83 switch (I->getOpcode()) { 84 case Instruction::Add: 85 case Instruction::Mul: 86 case Instruction::And: 87 case Instruction::Or: 88 case Instruction::Xor: 89 return 3; // Can fold through either operand. 90 case Instruction::Sub: // Can only fold on the amount subtracted. 91 case Instruction::Shl: // Can only fold on the shift amount. 92 case Instruction::LShr: 93 case Instruction::AShr: 94 return 1; 95 default: 96 return 0; // Cannot fold 97 } 98} 99 100/// GetSelectFoldableConstant - For the same transformation as the previous 101/// function, return the identity constant that goes into the select. 102static Constant *GetSelectFoldableConstant(Instruction *I) { 103 switch (I->getOpcode()) { 104 default: llvm_unreachable("This cannot happen!"); 105 case Instruction::Add: 106 case Instruction::Sub: 107 case Instruction::Or: 108 case Instruction::Xor: 109 case Instruction::Shl: 110 case Instruction::LShr: 111 case Instruction::AShr: 112 return Constant::getNullValue(I->getType()); 113 case Instruction::And: 114 return Constant::getAllOnesValue(I->getType()); 115 case Instruction::Mul: 116 return ConstantInt::get(I->getType(), 1); 117 } 118} 119 120/// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI 121/// have the same opcode and only one use each. Try to simplify this. 122Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI, 123 Instruction *FI) { 124 if (TI->getNumOperands() == 1) { 125 // If this is a non-volatile load or a cast from the same type, 126 // merge. 127 if (TI->isCast()) { 128 if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType()) 129 return 0; 130 } else { 131 return 0; // unknown unary op. 132 } 133 134 // Fold this by inserting a select from the input values. 135 SelectInst *NewSI = SelectInst::Create(SI.getCondition(), TI->getOperand(0), 136 FI->getOperand(0), SI.getName()+".v"); 137 InsertNewInstBefore(NewSI, SI); 138 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI, 139 TI->getType()); 140 } 141 142 // Only handle binary operators here. 143 if (!isa<BinaryOperator>(TI)) 144 return 0; 145 146 // Figure out if the operations have any operands in common. 147 Value *MatchOp, *OtherOpT, *OtherOpF; 148 bool MatchIsOpZero; 149 if (TI->getOperand(0) == FI->getOperand(0)) { 150 MatchOp = TI->getOperand(0); 151 OtherOpT = TI->getOperand(1); 152 OtherOpF = FI->getOperand(1); 153 MatchIsOpZero = true; 154 } else if (TI->getOperand(1) == FI->getOperand(1)) { 155 MatchOp = TI->getOperand(1); 156 OtherOpT = TI->getOperand(0); 157 OtherOpF = FI->getOperand(0); 158 MatchIsOpZero = false; 159 } else if (!TI->isCommutative()) { 160 return 0; 161 } else if (TI->getOperand(0) == FI->getOperand(1)) { 162 MatchOp = TI->getOperand(0); 163 OtherOpT = TI->getOperand(1); 164 OtherOpF = FI->getOperand(0); 165 MatchIsOpZero = true; 166 } else if (TI->getOperand(1) == FI->getOperand(0)) { 167 MatchOp = TI->getOperand(1); 168 OtherOpT = TI->getOperand(0); 169 OtherOpF = FI->getOperand(1); 170 MatchIsOpZero = true; 171 } else { 172 return 0; 173 } 174 175 // If we reach here, they do have operations in common. 176 SelectInst *NewSI = SelectInst::Create(SI.getCondition(), OtherOpT, 177 OtherOpF, SI.getName()+".v"); 178 InsertNewInstBefore(NewSI, SI); 179 180 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) { 181 if (MatchIsOpZero) 182 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI); 183 else 184 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp); 185 } 186 llvm_unreachable("Shouldn't get here"); 187 return 0; 188} 189 190static bool isSelect01(Constant *C1, Constant *C2) { 191 ConstantInt *C1I = dyn_cast<ConstantInt>(C1); 192 if (!C1I) 193 return false; 194 ConstantInt *C2I = dyn_cast<ConstantInt>(C2); 195 if (!C2I) 196 return false; 197 return (C1I->isZero() || C1I->isOne()) && (C2I->isZero() || C2I->isOne()); 198} 199 200/// FoldSelectIntoOp - Try fold the select into one of the operands to 201/// facilitate further optimization. 202Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal, 203 Value *FalseVal) { 204 // See the comment above GetSelectFoldableOperands for a description of the 205 // transformation we are doing here. 206 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) { 207 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 && 208 !isa<Constant>(FalseVal)) { 209 if (unsigned SFO = GetSelectFoldableOperands(TVI)) { 210 unsigned OpToFold = 0; 211 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) { 212 OpToFold = 1; 213 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) { 214 OpToFold = 2; 215 } 216 217 if (OpToFold) { 218 Constant *C = GetSelectFoldableConstant(TVI); 219 Value *OOp = TVI->getOperand(2-OpToFold); 220 // Avoid creating select between 2 constants unless it's selecting 221 // between 0 and 1. 222 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 223 Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C); 224 InsertNewInstBefore(NewSel, SI); 225 NewSel->takeName(TVI); 226 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TVI)) 227 return BinaryOperator::Create(BO->getOpcode(), FalseVal, NewSel); 228 llvm_unreachable("Unknown instruction!!"); 229 } 230 } 231 } 232 } 233 } 234 235 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) { 236 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 && 237 !isa<Constant>(TrueVal)) { 238 if (unsigned SFO = GetSelectFoldableOperands(FVI)) { 239 unsigned OpToFold = 0; 240 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) { 241 OpToFold = 1; 242 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) { 243 OpToFold = 2; 244 } 245 246 if (OpToFold) { 247 Constant *C = GetSelectFoldableConstant(FVI); 248 Value *OOp = FVI->getOperand(2-OpToFold); 249 // Avoid creating select between 2 constants unless it's selecting 250 // between 0 and 1. 251 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 252 Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp); 253 InsertNewInstBefore(NewSel, SI); 254 NewSel->takeName(FVI); 255 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FVI)) 256 return BinaryOperator::Create(BO->getOpcode(), TrueVal, NewSel); 257 llvm_unreachable("Unknown instruction!!"); 258 } 259 } 260 } 261 } 262 } 263 264 return 0; 265} 266 267/// visitSelectInstWithICmp - Visit a SelectInst that has an 268/// ICmpInst as its first operand. 269/// 270Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 271 ICmpInst *ICI) { 272 bool Changed = false; 273 ICmpInst::Predicate Pred = ICI->getPredicate(); 274 Value *CmpLHS = ICI->getOperand(0); 275 Value *CmpRHS = ICI->getOperand(1); 276 Value *TrueVal = SI.getTrueValue(); 277 Value *FalseVal = SI.getFalseValue(); 278 279 // Check cases where the comparison is with a constant that 280 // can be adjusted to fit the min/max idiom. We may edit ICI in 281 // place here, so make sure the select is the only user. 282 if (ICI->hasOneUse()) 283 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 284 switch (Pred) { 285 default: break; 286 case ICmpInst::ICMP_ULT: 287 case ICmpInst::ICMP_SLT: { 288 // X < MIN ? T : F --> F 289 if (CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 290 return ReplaceInstUsesWith(SI, FalseVal); 291 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 292 Constant *AdjustedRHS = 293 ConstantInt::get(CI->getContext(), CI->getValue()-1); 294 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 295 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) { 296 Pred = ICmpInst::getSwappedPredicate(Pred); 297 CmpRHS = AdjustedRHS; 298 std::swap(FalseVal, TrueVal); 299 ICI->setPredicate(Pred); 300 ICI->setOperand(1, CmpRHS); 301 SI.setOperand(1, TrueVal); 302 SI.setOperand(2, FalseVal); 303 Changed = true; 304 } 305 break; 306 } 307 case ICmpInst::ICMP_UGT: 308 case ICmpInst::ICMP_SGT: { 309 // X > MAX ? T : F --> F 310 if (CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 311 return ReplaceInstUsesWith(SI, FalseVal); 312 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 313 Constant *AdjustedRHS = 314 ConstantInt::get(CI->getContext(), CI->getValue()+1); 315 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 316 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) { 317 Pred = ICmpInst::getSwappedPredicate(Pred); 318 CmpRHS = AdjustedRHS; 319 std::swap(FalseVal, TrueVal); 320 ICI->setPredicate(Pred); 321 ICI->setOperand(1, CmpRHS); 322 SI.setOperand(1, TrueVal); 323 SI.setOperand(2, FalseVal); 324 Changed = true; 325 } 326 break; 327 } 328 } 329 330 // (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed 331 // (x >s -1) ? -1 : 0 -> ashr x, 31 -> all ones if not signed 332 CmpInst::Predicate Pred = CmpInst::BAD_ICMP_PREDICATE; 333 if (match(TrueVal, m_ConstantInt<-1>()) && 334 match(FalseVal, m_ConstantInt<0>())) 335 Pred = ICI->getPredicate(); 336 else if (match(TrueVal, m_ConstantInt<0>()) && 337 match(FalseVal, m_ConstantInt<-1>())) 338 Pred = CmpInst::getInversePredicate(ICI->getPredicate()); 339 340 if (Pred != CmpInst::BAD_ICMP_PREDICATE) { 341 // If we are just checking for a icmp eq of a single bit and zext'ing it 342 // to an integer, then shift the bit to the appropriate place and then 343 // cast to integer to avoid the comparison. 344 const APInt &Op1CV = CI->getValue(); 345 346 // sext (x <s 0) to i32 --> x>>s31 true if signbit set. 347 // sext (x >s -1) to i32 --> (x>>s31)^-1 true if signbit clear. 348 if ((Pred == ICmpInst::ICMP_SLT && Op1CV == 0) || 349 (Pred == ICmpInst::ICMP_SGT && Op1CV.isAllOnesValue())) { 350 Value *In = ICI->getOperand(0); 351 Value *Sh = ConstantInt::get(In->getType(), 352 In->getType()->getScalarSizeInBits()-1); 353 In = InsertNewInstBefore(BinaryOperator::CreateAShr(In, Sh, 354 In->getName()+".lobit"), 355 *ICI); 356 if (In->getType() != SI.getType()) 357 In = CastInst::CreateIntegerCast(In, SI.getType(), 358 true/*SExt*/, "tmp", ICI); 359 360 if (Pred == ICmpInst::ICMP_SGT) 361 In = InsertNewInstBefore(BinaryOperator::CreateNot(In, 362 In->getName()+".not"), *ICI); 363 364 return ReplaceInstUsesWith(SI, In); 365 } 366 } 367 } 368 369 if (CmpLHS == TrueVal && CmpRHS == FalseVal) { 370 // Transform (X == Y) ? X : Y -> Y 371 if (Pred == ICmpInst::ICMP_EQ) 372 return ReplaceInstUsesWith(SI, FalseVal); 373 // Transform (X != Y) ? X : Y -> X 374 if (Pred == ICmpInst::ICMP_NE) 375 return ReplaceInstUsesWith(SI, TrueVal); 376 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 377 378 } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) { 379 // Transform (X == Y) ? Y : X -> X 380 if (Pred == ICmpInst::ICMP_EQ) 381 return ReplaceInstUsesWith(SI, FalseVal); 382 // Transform (X != Y) ? Y : X -> Y 383 if (Pred == ICmpInst::ICMP_NE) 384 return ReplaceInstUsesWith(SI, TrueVal); 385 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 386 } 387 return Changed ? &SI : 0; 388} 389 390 391/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 392/// PHI node (but the two may be in different blocks). See if the true/false 393/// values (V) are live in all of the predecessor blocks of the PHI. For 394/// example, cases like this cannot be mapped: 395/// 396/// X = phi [ C1, BB1], [C2, BB2] 397/// Y = add 398/// Z = select X, Y, 0 399/// 400/// because Y is not live in BB1/BB2. 401/// 402static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 403 const SelectInst &SI) { 404 // If the value is a non-instruction value like a constant or argument, it 405 // can always be mapped. 406 const Instruction *I = dyn_cast<Instruction>(V); 407 if (I == 0) return true; 408 409 // If V is a PHI node defined in the same block as the condition PHI, we can 410 // map the arguments. 411 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 412 413 if (const PHINode *VP = dyn_cast<PHINode>(I)) 414 if (VP->getParent() == CondPHI->getParent()) 415 return true; 416 417 // Otherwise, if the PHI and select are defined in the same block and if V is 418 // defined in a different block, then we can transform it. 419 if (SI.getParent() == CondPHI->getParent() && 420 I->getParent() != CondPHI->getParent()) 421 return true; 422 423 // Otherwise we have a 'hard' case and we can't tell without doing more 424 // detailed dominator based analysis, punt. 425 return false; 426} 427 428/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 429/// SPF2(SPF1(A, B), C) 430Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 431 SelectPatternFlavor SPF1, 432 Value *A, Value *B, 433 Instruction &Outer, 434 SelectPatternFlavor SPF2, Value *C) { 435 if (C == A || C == B) { 436 // MAX(MAX(A, B), B) -> MAX(A, B) 437 // MIN(MIN(a, b), a) -> MIN(a, b) 438 if (SPF1 == SPF2) 439 return ReplaceInstUsesWith(Outer, Inner); 440 441 // MAX(MIN(a, b), a) -> a 442 // MIN(MAX(a, b), a) -> a 443 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 444 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 445 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 446 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 447 return ReplaceInstUsesWith(Outer, C); 448 } 449 450 // TODO: MIN(MIN(A, 23), 97) 451 return 0; 452} 453 454 455 456 457Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 458 Value *CondVal = SI.getCondition(); 459 Value *TrueVal = SI.getTrueValue(); 460 Value *FalseVal = SI.getFalseValue(); 461 462 // select true, X, Y -> X 463 // select false, X, Y -> Y 464 if (ConstantInt *C = dyn_cast<ConstantInt>(CondVal)) 465 return ReplaceInstUsesWith(SI, C->getZExtValue() ? TrueVal : FalseVal); 466 467 // select C, X, X -> X 468 if (TrueVal == FalseVal) 469 return ReplaceInstUsesWith(SI, TrueVal); 470 471 if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X 472 return ReplaceInstUsesWith(SI, FalseVal); 473 if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X 474 return ReplaceInstUsesWith(SI, TrueVal); 475 if (isa<UndefValue>(CondVal)) { // select undef, X, Y -> X or Y 476 if (isa<Constant>(TrueVal)) 477 return ReplaceInstUsesWith(SI, TrueVal); 478 else 479 return ReplaceInstUsesWith(SI, FalseVal); 480 } 481 482 if (SI.getType()->isInteger(1)) { 483 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 484 if (C->getZExtValue()) { 485 // Change: A = select B, true, C --> A = or B, C 486 return BinaryOperator::CreateOr(CondVal, FalseVal); 487 } else { 488 // Change: A = select B, false, C --> A = and !B, C 489 Value *NotCond = 490 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 491 "not."+CondVal->getName()), SI); 492 return BinaryOperator::CreateAnd(NotCond, FalseVal); 493 } 494 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 495 if (C->getZExtValue() == false) { 496 // Change: A = select B, C, false --> A = and B, C 497 return BinaryOperator::CreateAnd(CondVal, TrueVal); 498 } else { 499 // Change: A = select B, C, true --> A = or !B, C 500 Value *NotCond = 501 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 502 "not."+CondVal->getName()), SI); 503 return BinaryOperator::CreateOr(NotCond, TrueVal); 504 } 505 } 506 507 // select a, b, a -> a&b 508 // select a, a, b -> a|b 509 if (CondVal == TrueVal) 510 return BinaryOperator::CreateOr(CondVal, FalseVal); 511 else if (CondVal == FalseVal) 512 return BinaryOperator::CreateAnd(CondVal, TrueVal); 513 } 514 515 // Selecting between two integer constants? 516 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 517 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 518 // select C, 1, 0 -> zext C to int 519 if (FalseValC->isZero() && TrueValC->getValue() == 1) { 520 return CastInst::Create(Instruction::ZExt, CondVal, SI.getType()); 521 } else if (TrueValC->isZero() && FalseValC->getValue() == 1) { 522 // select C, 0, 1 -> zext !C to int 523 Value *NotCond = 524 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 525 "not."+CondVal->getName()), SI); 526 return CastInst::Create(Instruction::ZExt, NotCond, SI.getType()); 527 } 528 529 if (ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition())) { 530 // If one of the constants is zero (we know they can't both be) and we 531 // have an icmp instruction with zero, and we have an 'and' with the 532 // non-constant value, eliminate this whole mess. This corresponds to 533 // cases like this: ((X & 27) ? 27 : 0) 534 if (TrueValC->isZero() || FalseValC->isZero()) 535 if (IC->isEquality() && isa<ConstantInt>(IC->getOperand(1)) && 536 cast<Constant>(IC->getOperand(1))->isNullValue()) 537 if (Instruction *ICA = dyn_cast<Instruction>(IC->getOperand(0))) 538 if (ICA->getOpcode() == Instruction::And && 539 isa<ConstantInt>(ICA->getOperand(1)) && 540 (ICA->getOperand(1) == TrueValC || 541 ICA->getOperand(1) == FalseValC) && 542 cast<ConstantInt>(ICA->getOperand(1))->getValue().isPowerOf2()) { 543 // Okay, now we know that everything is set up, we just don't 544 // know whether we have a icmp_ne or icmp_eq and whether the 545 // true or false val is the zero. 546 bool ShouldNotVal = !TrueValC->isZero(); 547 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 548 Value *V = ICA; 549 if (ShouldNotVal) 550 V = InsertNewInstBefore(BinaryOperator::Create( 551 Instruction::Xor, V, ICA->getOperand(1)), SI); 552 return ReplaceInstUsesWith(SI, V); 553 } 554 } 555 } 556 557 // See if we are selecting two values based on a comparison of the two values. 558 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 559 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 560 // Transform (X == Y) ? X : Y -> Y 561 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 562 // This is not safe in general for floating point: 563 // consider X== -0, Y== +0. 564 // It becomes safe if either operand is a nonzero constant. 565 ConstantFP *CFPt, *CFPf; 566 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 567 !CFPt->getValueAPF().isZero()) || 568 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 569 !CFPf->getValueAPF().isZero())) 570 return ReplaceInstUsesWith(SI, FalseVal); 571 } 572 // Transform (X != Y) ? X : Y -> X 573 if (FCI->getPredicate() == FCmpInst::FCMP_ONE) 574 return ReplaceInstUsesWith(SI, TrueVal); 575 // NOTE: if we wanted to, this is where to detect MIN/MAX 576 577 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 578 // Transform (X == Y) ? Y : X -> X 579 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 580 // This is not safe in general for floating point: 581 // consider X== -0, Y== +0. 582 // It becomes safe if either operand is a nonzero constant. 583 ConstantFP *CFPt, *CFPf; 584 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 585 !CFPt->getValueAPF().isZero()) || 586 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 587 !CFPf->getValueAPF().isZero())) 588 return ReplaceInstUsesWith(SI, FalseVal); 589 } 590 // Transform (X != Y) ? Y : X -> Y 591 if (FCI->getPredicate() == FCmpInst::FCMP_ONE) 592 return ReplaceInstUsesWith(SI, TrueVal); 593 // NOTE: if we wanted to, this is where to detect MIN/MAX 594 } 595 // NOTE: if we wanted to, this is where to detect ABS 596 } 597 598 // See if we are selecting two values based on a comparison of the two values. 599 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 600 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 601 return Result; 602 603 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 604 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 605 if (TI->hasOneUse() && FI->hasOneUse()) { 606 Instruction *AddOp = 0, *SubOp = 0; 607 608 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 609 if (TI->getOpcode() == FI->getOpcode()) 610 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 611 return IV; 612 613 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 614 // even legal for FP. 615 if ((TI->getOpcode() == Instruction::Sub && 616 FI->getOpcode() == Instruction::Add) || 617 (TI->getOpcode() == Instruction::FSub && 618 FI->getOpcode() == Instruction::FAdd)) { 619 AddOp = FI; SubOp = TI; 620 } else if ((FI->getOpcode() == Instruction::Sub && 621 TI->getOpcode() == Instruction::Add) || 622 (FI->getOpcode() == Instruction::FSub && 623 TI->getOpcode() == Instruction::FAdd)) { 624 AddOp = TI; SubOp = FI; 625 } 626 627 if (AddOp) { 628 Value *OtherAddOp = 0; 629 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 630 OtherAddOp = AddOp->getOperand(1); 631 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 632 OtherAddOp = AddOp->getOperand(0); 633 } 634 635 if (OtherAddOp) { 636 // So at this point we know we have (Y -> OtherAddOp): 637 // select C, (add X, Y), (sub X, Z) 638 Value *NegVal; // Compute -Z 639 if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) { 640 NegVal = ConstantExpr::getNeg(C); 641 } else { 642 NegVal = InsertNewInstBefore( 643 BinaryOperator::CreateNeg(SubOp->getOperand(1), 644 "tmp"), SI); 645 } 646 647 Value *NewTrueOp = OtherAddOp; 648 Value *NewFalseOp = NegVal; 649 if (AddOp != TI) 650 std::swap(NewTrueOp, NewFalseOp); 651 Instruction *NewSel = 652 SelectInst::Create(CondVal, NewTrueOp, 653 NewFalseOp, SI.getName() + ".p"); 654 655 NewSel = InsertNewInstBefore(NewSel, SI); 656 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 657 } 658 } 659 } 660 661 // See if we can fold the select into one of our operands. 662 if (SI.getType()->isInteger()) { 663 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 664 return FoldI; 665 666 // MAX(MAX(a, b), a) -> MAX(a, b) 667 // MIN(MIN(a, b), a) -> MIN(a, b) 668 // MAX(MIN(a, b), a) -> a 669 // MIN(MAX(a, b), a) -> a 670 Value *LHS, *RHS, *LHS2, *RHS2; 671 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 672 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 673 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 674 SI, SPF, RHS)) 675 return R; 676 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 677 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 678 SI, SPF, LHS)) 679 return R; 680 } 681 682 // TODO. 683 // ABS(-X) -> ABS(X) 684 // ABS(ABS(X)) -> ABS(X) 685 } 686 687 // See if we can fold the select into a phi node if the condition is a select. 688 if (isa<PHINode>(SI.getCondition())) 689 // The true/false values have to be live in the PHI predecessor's blocks. 690 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 691 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 692 if (Instruction *NV = FoldOpIntoPhi(SI)) 693 return NV; 694 695 if (BinaryOperator::isNot(CondVal)) { 696 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 697 SI.setOperand(1, FalseVal); 698 SI.setOperand(2, TrueVal); 699 return &SI; 700 } 701 702 return 0; 703} 704