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" 16 #include "llvm/Analysis/ConstantFolding.h" 17 #include "llvm/Analysis/InstructionSimplify.h" 18 using namespace llvm; 19 using namespace PatternMatch; 20 21 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms, 22 /// returning the kind and providing the out parameter results if we 23 /// successfully match. 24 static SelectPatternFlavor 25 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) { 26 SelectInst *SI = dyn_cast<SelectInst>(V); 27 if (SI == 0) return SPF_UNKNOWN; 28 29 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition()); 30 if (ICI == 0) return SPF_UNKNOWN; 31 32 LHS = ICI->getOperand(0); 33 RHS = ICI->getOperand(1); 34 35 // (icmp X, Y) ? X : Y 36 if (SI->getTrueValue() == ICI->getOperand(0) && 37 SI->getFalseValue() == ICI->getOperand(1)) { 38 switch (ICI->getPredicate()) { 39 default: return SPF_UNKNOWN; // Equality. 40 case ICmpInst::ICMP_UGT: 41 case ICmpInst::ICMP_UGE: return SPF_UMAX; 42 case ICmpInst::ICMP_SGT: 43 case ICmpInst::ICMP_SGE: return SPF_SMAX; 44 case ICmpInst::ICMP_ULT: 45 case ICmpInst::ICMP_ULE: return SPF_UMIN; 46 case ICmpInst::ICMP_SLT: 47 case ICmpInst::ICMP_SLE: return SPF_SMIN; 48 } 49 } 50 51 // (icmp X, Y) ? Y : X 52 if (SI->getTrueValue() == ICI->getOperand(1) && 53 SI->getFalseValue() == ICI->getOperand(0)) { 54 switch (ICI->getPredicate()) { 55 default: return SPF_UNKNOWN; // Equality. 56 case ICmpInst::ICMP_UGT: 57 case ICmpInst::ICMP_UGE: return SPF_UMIN; 58 case ICmpInst::ICMP_SGT: 59 case ICmpInst::ICMP_SGE: return SPF_SMIN; 60 case ICmpInst::ICMP_ULT: 61 case ICmpInst::ICMP_ULE: return SPF_UMAX; 62 case ICmpInst::ICMP_SLT: 63 case ICmpInst::ICMP_SLE: return SPF_SMAX; 64 } 65 } 66 67 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5) 68 69 return SPF_UNKNOWN; 70 } 71 72 73 /// GetSelectFoldableOperands - We want to turn code that looks like this: 74 /// %C = or %A, %B 75 /// %D = select %cond, %C, %A 76 /// into: 77 /// %C = select %cond, %B, 0 78 /// %D = or %A, %C 79 /// 80 /// Assuming that the specified instruction is an operand to the select, return 81 /// a bitmask indicating which operands of this instruction are foldable if they 82 /// equal the other incoming value of the select. 83 /// 84 static unsigned GetSelectFoldableOperands(Instruction *I) { 85 switch (I->getOpcode()) { 86 case Instruction::Add: 87 case Instruction::Mul: 88 case Instruction::And: 89 case Instruction::Or: 90 case Instruction::Xor: 91 return 3; // Can fold through either operand. 92 case Instruction::Sub: // Can only fold on the amount subtracted. 93 case Instruction::Shl: // Can only fold on the shift amount. 94 case Instruction::LShr: 95 case Instruction::AShr: 96 return 1; 97 default: 98 return 0; // Cannot fold 99 } 100 } 101 102 /// GetSelectFoldableConstant - For the same transformation as the previous 103 /// function, return the identity constant that goes into the select. 104 static Constant *GetSelectFoldableConstant(Instruction *I) { 105 switch (I->getOpcode()) { 106 default: llvm_unreachable("This cannot happen!"); 107 case Instruction::Add: 108 case Instruction::Sub: 109 case Instruction::Or: 110 case Instruction::Xor: 111 case Instruction::Shl: 112 case Instruction::LShr: 113 case Instruction::AShr: 114 return Constant::getNullValue(I->getType()); 115 case Instruction::And: 116 return Constant::getAllOnesValue(I->getType()); 117 case Instruction::Mul: 118 return ConstantInt::get(I->getType(), 1); 119 } 120 } 121 122 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI 123 /// have the same opcode and only one use each. Try to simplify this. 124 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI, 125 Instruction *FI) { 126 if (TI->getNumOperands() == 1) { 127 // If this is a non-volatile load or a cast from the same type, 128 // merge. 129 if (TI->isCast()) { 130 if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType()) 131 return 0; 132 } else { 133 return 0; // unknown unary op. 134 } 135 136 // Fold this by inserting a select from the input values. 137 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0), 138 FI->getOperand(0), SI.getName()+".v"); 139 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI, 140 TI->getType()); 141 } 142 143 // Only handle binary operators here. 144 if (!isa<BinaryOperator>(TI)) 145 return 0; 146 147 // Figure out if the operations have any operands in common. 148 Value *MatchOp, *OtherOpT, *OtherOpF; 149 bool MatchIsOpZero; 150 if (TI->getOperand(0) == FI->getOperand(0)) { 151 MatchOp = TI->getOperand(0); 152 OtherOpT = TI->getOperand(1); 153 OtherOpF = FI->getOperand(1); 154 MatchIsOpZero = true; 155 } else if (TI->getOperand(1) == FI->getOperand(1)) { 156 MatchOp = TI->getOperand(1); 157 OtherOpT = TI->getOperand(0); 158 OtherOpF = FI->getOperand(0); 159 MatchIsOpZero = false; 160 } else if (!TI->isCommutative()) { 161 return 0; 162 } else if (TI->getOperand(0) == FI->getOperand(1)) { 163 MatchOp = TI->getOperand(0); 164 OtherOpT = TI->getOperand(1); 165 OtherOpF = FI->getOperand(0); 166 MatchIsOpZero = true; 167 } else if (TI->getOperand(1) == FI->getOperand(0)) { 168 MatchOp = TI->getOperand(1); 169 OtherOpT = TI->getOperand(0); 170 OtherOpF = FI->getOperand(1); 171 MatchIsOpZero = true; 172 } else { 173 return 0; 174 } 175 176 // If we reach here, they do have operations in common. 177 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT, 178 OtherOpF, SI.getName()+".v"); 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 } 188 189 static bool isSelect01(Constant *C1, Constant *C2) { 190 ConstantInt *C1I = dyn_cast<ConstantInt>(C1); 191 if (!C1I) 192 return false; 193 ConstantInt *C2I = dyn_cast<ConstantInt>(C2); 194 if (!C2I) 195 return false; 196 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero. 197 return false; 198 return C1I->isOne() || C1I->isAllOnesValue() || 199 C2I->isOne() || C2I->isAllOnesValue(); 200 } 201 202 /// FoldSelectIntoOp - Try fold the select into one of the operands to 203 /// facilitate further optimization. 204 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal, 205 Value *FalseVal) { 206 // See the comment above GetSelectFoldableOperands for a description of the 207 // transformation we are doing here. 208 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) { 209 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 && 210 !isa<Constant>(FalseVal)) { 211 if (unsigned SFO = GetSelectFoldableOperands(TVI)) { 212 unsigned OpToFold = 0; 213 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) { 214 OpToFold = 1; 215 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) { 216 OpToFold = 2; 217 } 218 219 if (OpToFold) { 220 Constant *C = GetSelectFoldableConstant(TVI); 221 Value *OOp = TVI->getOperand(2-OpToFold); 222 // Avoid creating select between 2 constants unless it's selecting 223 // between 0, 1 and -1. 224 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 225 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C); 226 NewSel->takeName(TVI); 227 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI); 228 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(), 229 FalseVal, NewSel); 230 if (isa<PossiblyExactOperator>(BO)) 231 BO->setIsExact(TVI_BO->isExact()); 232 if (isa<OverflowingBinaryOperator>(BO)) { 233 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap()); 234 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap()); 235 } 236 return BO; 237 } 238 } 239 } 240 } 241 } 242 243 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) { 244 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 && 245 !isa<Constant>(TrueVal)) { 246 if (unsigned SFO = GetSelectFoldableOperands(FVI)) { 247 unsigned OpToFold = 0; 248 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) { 249 OpToFold = 1; 250 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) { 251 OpToFold = 2; 252 } 253 254 if (OpToFold) { 255 Constant *C = GetSelectFoldableConstant(FVI); 256 Value *OOp = FVI->getOperand(2-OpToFold); 257 // Avoid creating select between 2 constants unless it's selecting 258 // between 0, 1 and -1. 259 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 260 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp); 261 NewSel->takeName(FVI); 262 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI); 263 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(), 264 TrueVal, NewSel); 265 if (isa<PossiblyExactOperator>(BO)) 266 BO->setIsExact(FVI_BO->isExact()); 267 if (isa<OverflowingBinaryOperator>(BO)) { 268 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap()); 269 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap()); 270 } 271 return BO; 272 } 273 } 274 } 275 } 276 } 277 278 return 0; 279 } 280 281 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is 282 /// replaced with RepOp. 283 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp, 284 const TargetData *TD, 285 const TargetLibraryInfo *TLI) { 286 // Trivial replacement. 287 if (V == Op) 288 return RepOp; 289 290 Instruction *I = dyn_cast<Instruction>(V); 291 if (!I) 292 return 0; 293 294 // If this is a binary operator, try to simplify it with the replaced op. 295 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) { 296 if (B->getOperand(0) == Op) 297 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI); 298 if (B->getOperand(1) == Op) 299 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI); 300 } 301 302 // Same for CmpInsts. 303 if (CmpInst *C = dyn_cast<CmpInst>(I)) { 304 if (C->getOperand(0) == Op) 305 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD, 306 TLI); 307 if (C->getOperand(1) == Op) 308 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD, 309 TLI); 310 } 311 312 // TODO: We could hand off more cases to instsimplify here. 313 314 // If all operands are constant after substituting Op for RepOp then we can 315 // constant fold the instruction. 316 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) { 317 // Build a list of all constant operands. 318 SmallVector<Constant*, 8> ConstOps; 319 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 320 if (I->getOperand(i) == Op) 321 ConstOps.push_back(CRepOp); 322 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i))) 323 ConstOps.push_back(COp); 324 else 325 break; 326 } 327 328 // All operands were constants, fold it. 329 if (ConstOps.size() == I->getNumOperands()) { 330 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 331 if (!LI->isVolatile()) 332 return ConstantFoldLoadFromConstPtr(ConstOps[0], TD); 333 334 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), 335 ConstOps, TD, TLI); 336 } 337 } 338 339 return 0; 340 } 341 342 /// visitSelectInstWithICmp - Visit a SelectInst that has an 343 /// ICmpInst as its first operand. 344 /// 345 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 346 ICmpInst *ICI) { 347 bool Changed = false; 348 ICmpInst::Predicate Pred = ICI->getPredicate(); 349 Value *CmpLHS = ICI->getOperand(0); 350 Value *CmpRHS = ICI->getOperand(1); 351 Value *TrueVal = SI.getTrueValue(); 352 Value *FalseVal = SI.getFalseValue(); 353 354 // Check cases where the comparison is with a constant that 355 // can be adjusted to fit the min/max idiom. We may move or edit ICI 356 // here, so make sure the select is the only user. 357 if (ICI->hasOneUse()) 358 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 359 // X < MIN ? T : F --> F 360 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) 361 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 362 return ReplaceInstUsesWith(SI, FalseVal); 363 // X > MAX ? T : F --> F 364 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) 365 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 366 return ReplaceInstUsesWith(SI, FalseVal); 367 switch (Pred) { 368 default: break; 369 case ICmpInst::ICMP_ULT: 370 case ICmpInst::ICMP_SLT: 371 case ICmpInst::ICMP_UGT: 372 case ICmpInst::ICMP_SGT: { 373 // These transformations only work for selects over integers. 374 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType()); 375 if (!SelectTy) 376 break; 377 378 Constant *AdjustedRHS; 379 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) 380 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); 381 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) 382 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); 383 384 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 385 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 386 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 387 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) 388 ; // Nothing to do here. Values match without any sign/zero extension. 389 390 // Types do not match. Instead of calculating this with mixed types 391 // promote all to the larger type. This enables scalar evolution to 392 // analyze this expression. 393 else if (CmpRHS->getType()->getScalarSizeInBits() 394 < SelectTy->getBitWidth()) { 395 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy); 396 397 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X 398 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X 399 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X 400 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X 401 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && 402 sextRHS == FalseVal) { 403 CmpLHS = TrueVal; 404 AdjustedRHS = sextRHS; 405 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && 406 sextRHS == TrueVal) { 407 CmpLHS = FalseVal; 408 AdjustedRHS = sextRHS; 409 } else if (ICI->isUnsigned()) { 410 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy); 411 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X 412 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X 413 // zext + signed compare cannot be changed: 414 // 0xff <s 0x00, but 0x00ff >s 0x0000 415 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && 416 zextRHS == FalseVal) { 417 CmpLHS = TrueVal; 418 AdjustedRHS = zextRHS; 419 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && 420 zextRHS == TrueVal) { 421 CmpLHS = FalseVal; 422 AdjustedRHS = zextRHS; 423 } else 424 break; 425 } else 426 break; 427 } else 428 break; 429 430 Pred = ICmpInst::getSwappedPredicate(Pred); 431 CmpRHS = AdjustedRHS; 432 std::swap(FalseVal, TrueVal); 433 ICI->setPredicate(Pred); 434 ICI->setOperand(0, CmpLHS); 435 ICI->setOperand(1, CmpRHS); 436 SI.setOperand(1, TrueVal); 437 SI.setOperand(2, FalseVal); 438 439 // Move ICI instruction right before the select instruction. Otherwise 440 // the sext/zext value may be defined after the ICI instruction uses it. 441 ICI->moveBefore(&SI); 442 443 Changed = true; 444 break; 445 } 446 } 447 } 448 449 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 450 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 451 // FIXME: Type and constness constraints could be lifted, but we have to 452 // watch code size carefully. We should consider xor instead of 453 // sub/add when we decide to do that. 454 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 455 if (TrueVal->getType() == Ty) { 456 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 457 ConstantInt *C1 = NULL, *C2 = NULL; 458 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 459 C1 = dyn_cast<ConstantInt>(TrueVal); 460 C2 = dyn_cast<ConstantInt>(FalseVal); 461 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 462 C1 = dyn_cast<ConstantInt>(FalseVal); 463 C2 = dyn_cast<ConstantInt>(TrueVal); 464 } 465 if (C1 && C2) { 466 // This shift results in either -1 or 0. 467 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 468 469 // Check if we can express the operation with a single or. 470 if (C2->isAllOnesValue()) 471 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 472 473 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 474 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 475 } 476 } 477 } 478 } 479 480 // If we have an equality comparison then we know the value in one of the 481 // arms of the select. See if substituting this value into the arm and 482 // simplifying the result yields the same value as the other arm. 483 if (Pred == ICmpInst::ICMP_EQ) { 484 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal || 485 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal) 486 return ReplaceInstUsesWith(SI, FalseVal); 487 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal || 488 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal) 489 return ReplaceInstUsesWith(SI, FalseVal); 490 } else if (Pred == ICmpInst::ICMP_NE) { 491 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal || 492 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal) 493 return ReplaceInstUsesWith(SI, TrueVal); 494 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal || 495 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal) 496 return ReplaceInstUsesWith(SI, TrueVal); 497 } 498 499 // NOTE: if we wanted to, this is where to detect integer MIN/MAX 500 501 if (isa<Constant>(CmpRHS)) { 502 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) { 503 // Transform (X == C) ? X : Y -> (X == C) ? C : Y 504 SI.setOperand(1, CmpRHS); 505 Changed = true; 506 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) { 507 // Transform (X != C) ? Y : X -> (X != C) ? Y : C 508 SI.setOperand(2, CmpRHS); 509 Changed = true; 510 } 511 } 512 513 return Changed ? &SI : 0; 514 } 515 516 517 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 518 /// PHI node (but the two may be in different blocks). See if the true/false 519 /// values (V) are live in all of the predecessor blocks of the PHI. For 520 /// example, cases like this cannot be mapped: 521 /// 522 /// X = phi [ C1, BB1], [C2, BB2] 523 /// Y = add 524 /// Z = select X, Y, 0 525 /// 526 /// because Y is not live in BB1/BB2. 527 /// 528 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 529 const SelectInst &SI) { 530 // If the value is a non-instruction value like a constant or argument, it 531 // can always be mapped. 532 const Instruction *I = dyn_cast<Instruction>(V); 533 if (I == 0) return true; 534 535 // If V is a PHI node defined in the same block as the condition PHI, we can 536 // map the arguments. 537 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 538 539 if (const PHINode *VP = dyn_cast<PHINode>(I)) 540 if (VP->getParent() == CondPHI->getParent()) 541 return true; 542 543 // Otherwise, if the PHI and select are defined in the same block and if V is 544 // defined in a different block, then we can transform it. 545 if (SI.getParent() == CondPHI->getParent() && 546 I->getParent() != CondPHI->getParent()) 547 return true; 548 549 // Otherwise we have a 'hard' case and we can't tell without doing more 550 // detailed dominator based analysis, punt. 551 return false; 552 } 553 554 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 555 /// SPF2(SPF1(A, B), C) 556 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 557 SelectPatternFlavor SPF1, 558 Value *A, Value *B, 559 Instruction &Outer, 560 SelectPatternFlavor SPF2, Value *C) { 561 if (C == A || C == B) { 562 // MAX(MAX(A, B), B) -> MAX(A, B) 563 // MIN(MIN(a, b), a) -> MIN(a, b) 564 if (SPF1 == SPF2) 565 return ReplaceInstUsesWith(Outer, Inner); 566 567 // MAX(MIN(a, b), a) -> a 568 // MIN(MAX(a, b), a) -> a 569 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 570 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 571 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 572 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 573 return ReplaceInstUsesWith(Outer, C); 574 } 575 576 // TODO: MIN(MIN(A, 23), 97) 577 return 0; 578 } 579 580 581 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't 582 /// both be) and we have an icmp instruction with zero, and we have an 'and' 583 /// with the non-constant value and a power of two we can turn the select 584 /// into a shift on the result of the 'and'. 585 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 586 ConstantInt *FalseVal, 587 InstCombiner::BuilderTy *Builder) { 588 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 589 if (!IC || !IC->isEquality()) 590 return 0; 591 592 if (!match(IC->getOperand(1), m_Zero())) 593 return 0; 594 595 ConstantInt *AndRHS; 596 Value *LHS = IC->getOperand(0); 597 if (LHS->getType() != SI.getType() || 598 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 599 return 0; 600 601 // If both select arms are non-zero see if we have a select of the form 602 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 603 // for 'x ? 2^n : 0' and fix the thing up at the end. 604 ConstantInt *Offset = 0; 605 if (!TrueVal->isZero() && !FalseVal->isZero()) { 606 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 607 Offset = FalseVal; 608 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 609 Offset = TrueVal; 610 else 611 return 0; 612 613 // Adjust TrueVal and FalseVal to the offset. 614 TrueVal = ConstantInt::get(Builder->getContext(), 615 TrueVal->getValue() - Offset->getValue()); 616 FalseVal = ConstantInt::get(Builder->getContext(), 617 FalseVal->getValue() - Offset->getValue()); 618 } 619 620 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 621 if (!AndRHS->getValue().isPowerOf2() || 622 (!TrueVal->getValue().isPowerOf2() && 623 !FalseVal->getValue().isPowerOf2())) 624 return 0; 625 626 // Determine which shift is needed to transform result of the 'and' into the 627 // desired result. 628 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 629 unsigned ValZeros = ValC->getValue().logBase2(); 630 unsigned AndZeros = AndRHS->getValue().logBase2(); 631 632 Value *V = LHS; 633 if (ValZeros > AndZeros) 634 V = Builder->CreateShl(V, ValZeros - AndZeros); 635 else if (ValZeros < AndZeros) 636 V = Builder->CreateLShr(V, AndZeros - ValZeros); 637 638 // Okay, now we know that everything is set up, we just don't know whether we 639 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 640 bool ShouldNotVal = !TrueVal->isZero(); 641 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 642 if (ShouldNotVal) 643 V = Builder->CreateXor(V, ValC); 644 645 // Apply an offset if needed. 646 if (Offset) 647 V = Builder->CreateAdd(V, Offset); 648 return V; 649 } 650 651 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 652 Value *CondVal = SI.getCondition(); 653 Value *TrueVal = SI.getTrueValue(); 654 Value *FalseVal = SI.getFalseValue(); 655 656 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 657 return ReplaceInstUsesWith(SI, V); 658 659 if (SI.getType()->isIntegerTy(1)) { 660 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 661 if (C->getZExtValue()) { 662 // Change: A = select B, true, C --> A = or B, C 663 return BinaryOperator::CreateOr(CondVal, FalseVal); 664 } 665 // Change: A = select B, false, C --> A = and !B, C 666 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 667 return BinaryOperator::CreateAnd(NotCond, FalseVal); 668 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 669 if (C->getZExtValue() == false) { 670 // Change: A = select B, C, false --> A = and B, C 671 return BinaryOperator::CreateAnd(CondVal, TrueVal); 672 } 673 // Change: A = select B, C, true --> A = or !B, C 674 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 675 return BinaryOperator::CreateOr(NotCond, TrueVal); 676 } 677 678 // select a, b, a -> a&b 679 // select a, a, b -> a|b 680 if (CondVal == TrueVal) 681 return BinaryOperator::CreateOr(CondVal, FalseVal); 682 else if (CondVal == FalseVal) 683 return BinaryOperator::CreateAnd(CondVal, TrueVal); 684 685 // select a, ~a, b -> (~a)&b 686 // select a, b, ~a -> (~a)|b 687 if (match(TrueVal, m_Not(m_Specific(CondVal)))) 688 return BinaryOperator::CreateAnd(TrueVal, FalseVal); 689 else if (match(FalseVal, m_Not(m_Specific(CondVal)))) 690 return BinaryOperator::CreateOr(TrueVal, FalseVal); 691 } 692 693 // Selecting between two integer constants? 694 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 695 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 696 // select C, 1, 0 -> zext C to int 697 if (FalseValC->isZero() && TrueValC->getValue() == 1) 698 return new ZExtInst(CondVal, SI.getType()); 699 700 // select C, -1, 0 -> sext C to int 701 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 702 return new SExtInst(CondVal, SI.getType()); 703 704 // select C, 0, 1 -> zext !C to int 705 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 706 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 707 return new ZExtInst(NotCond, SI.getType()); 708 } 709 710 // select C, 0, -1 -> sext !C to int 711 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 712 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 713 return new SExtInst(NotCond, SI.getType()); 714 } 715 716 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 717 return ReplaceInstUsesWith(SI, V); 718 } 719 720 // See if we are selecting two values based on a comparison of the two values. 721 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 722 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 723 // Transform (X == Y) ? X : Y -> Y 724 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 725 // This is not safe in general for floating point: 726 // consider X== -0, Y== +0. 727 // It becomes safe if either operand is a nonzero constant. 728 ConstantFP *CFPt, *CFPf; 729 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 730 !CFPt->getValueAPF().isZero()) || 731 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 732 !CFPf->getValueAPF().isZero())) 733 return ReplaceInstUsesWith(SI, FalseVal); 734 } 735 // Transform (X une Y) ? X : Y -> X 736 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 737 // This is not safe in general for floating point: 738 // consider X== -0, Y== +0. 739 // It becomes safe if either operand is a nonzero constant. 740 ConstantFP *CFPt, *CFPf; 741 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 742 !CFPt->getValueAPF().isZero()) || 743 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 744 !CFPf->getValueAPF().isZero())) 745 return ReplaceInstUsesWith(SI, TrueVal); 746 } 747 // NOTE: if we wanted to, this is where to detect MIN/MAX 748 749 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 750 // Transform (X == Y) ? Y : X -> X 751 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 752 // This is not safe in general for floating point: 753 // consider X== -0, Y== +0. 754 // It becomes safe if either operand is a nonzero constant. 755 ConstantFP *CFPt, *CFPf; 756 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 757 !CFPt->getValueAPF().isZero()) || 758 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 759 !CFPf->getValueAPF().isZero())) 760 return ReplaceInstUsesWith(SI, FalseVal); 761 } 762 // Transform (X une Y) ? Y : X -> Y 763 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 764 // This is not safe in general for floating point: 765 // consider X== -0, Y== +0. 766 // It becomes safe if either operand is a nonzero constant. 767 ConstantFP *CFPt, *CFPf; 768 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 769 !CFPt->getValueAPF().isZero()) || 770 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 771 !CFPf->getValueAPF().isZero())) 772 return ReplaceInstUsesWith(SI, TrueVal); 773 } 774 // NOTE: if we wanted to, this is where to detect MIN/MAX 775 } 776 // NOTE: if we wanted to, this is where to detect ABS 777 } 778 779 // See if we are selecting two values based on a comparison of the two values. 780 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 781 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 782 return Result; 783 784 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 785 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 786 if (TI->hasOneUse() && FI->hasOneUse()) { 787 Instruction *AddOp = 0, *SubOp = 0; 788 789 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 790 if (TI->getOpcode() == FI->getOpcode()) 791 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 792 return IV; 793 794 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 795 // even legal for FP. 796 if ((TI->getOpcode() == Instruction::Sub && 797 FI->getOpcode() == Instruction::Add) || 798 (TI->getOpcode() == Instruction::FSub && 799 FI->getOpcode() == Instruction::FAdd)) { 800 AddOp = FI; SubOp = TI; 801 } else if ((FI->getOpcode() == Instruction::Sub && 802 TI->getOpcode() == Instruction::Add) || 803 (FI->getOpcode() == Instruction::FSub && 804 TI->getOpcode() == Instruction::FAdd)) { 805 AddOp = TI; SubOp = FI; 806 } 807 808 if (AddOp) { 809 Value *OtherAddOp = 0; 810 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 811 OtherAddOp = AddOp->getOperand(1); 812 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 813 OtherAddOp = AddOp->getOperand(0); 814 } 815 816 if (OtherAddOp) { 817 // So at this point we know we have (Y -> OtherAddOp): 818 // select C, (add X, Y), (sub X, Z) 819 Value *NegVal; // Compute -Z 820 if (SI.getType()->isFPOrFPVectorTy()) { 821 NegVal = Builder->CreateFNeg(SubOp->getOperand(1)); 822 } else { 823 NegVal = Builder->CreateNeg(SubOp->getOperand(1)); 824 } 825 826 Value *NewTrueOp = OtherAddOp; 827 Value *NewFalseOp = NegVal; 828 if (AddOp != TI) 829 std::swap(NewTrueOp, NewFalseOp); 830 Value *NewSel = 831 Builder->CreateSelect(CondVal, NewTrueOp, 832 NewFalseOp, SI.getName() + ".p"); 833 834 if (SI.getType()->isFPOrFPVectorTy()) 835 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 836 else 837 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 838 } 839 } 840 } 841 842 // See if we can fold the select into one of our operands. 843 if (SI.getType()->isIntegerTy()) { 844 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 845 return FoldI; 846 847 // MAX(MAX(a, b), a) -> MAX(a, b) 848 // MIN(MIN(a, b), a) -> MIN(a, b) 849 // MAX(MIN(a, b), a) -> a 850 // MIN(MAX(a, b), a) -> a 851 Value *LHS, *RHS, *LHS2, *RHS2; 852 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 853 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 854 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 855 SI, SPF, RHS)) 856 return R; 857 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 858 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 859 SI, SPF, LHS)) 860 return R; 861 } 862 863 // TODO. 864 // ABS(-X) -> ABS(X) 865 // ABS(ABS(X)) -> ABS(X) 866 } 867 868 // See if we can fold the select into a phi node if the condition is a select. 869 if (isa<PHINode>(SI.getCondition())) 870 // The true/false values have to be live in the PHI predecessor's blocks. 871 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 872 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 873 if (Instruction *NV = FoldOpIntoPhi(SI)) 874 return NV; 875 876 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) { 877 if (TrueSI->getCondition() == CondVal) { 878 SI.setOperand(1, TrueSI->getTrueValue()); 879 return &SI; 880 } 881 } 882 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) { 883 if (FalseSI->getCondition() == CondVal) { 884 SI.setOperand(2, FalseSI->getFalseValue()); 885 return &SI; 886 } 887 } 888 889 if (BinaryOperator::isNot(CondVal)) { 890 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 891 SI.setOperand(1, FalseVal); 892 SI.setOperand(2, TrueVal); 893 return &SI; 894 } 895 896 return 0; 897 } 898
