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 // The select condition may be a vector. We may only change the operand 133 // type if the vector width remains the same (and matches the condition). 134 Type *CondTy = SI.getCondition()->getType(); 135 if (CondTy->isVectorTy() && CondTy->getVectorNumElements() != 136 FI->getOperand(0)->getType()->getVectorNumElements()) 137 return 0; 138 } else { 139 return 0; // unknown unary op. 140 } 141 142 // Fold this by inserting a select from the input values. 143 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0), 144 FI->getOperand(0), SI.getName()+".v"); 145 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI, 146 TI->getType()); 147 } 148 149 // Only handle binary operators here. 150 if (!isa<BinaryOperator>(TI)) 151 return 0; 152 153 // Figure out if the operations have any operands in common. 154 Value *MatchOp, *OtherOpT, *OtherOpF; 155 bool MatchIsOpZero; 156 if (TI->getOperand(0) == FI->getOperand(0)) { 157 MatchOp = TI->getOperand(0); 158 OtherOpT = TI->getOperand(1); 159 OtherOpF = FI->getOperand(1); 160 MatchIsOpZero = true; 161 } else if (TI->getOperand(1) == FI->getOperand(1)) { 162 MatchOp = TI->getOperand(1); 163 OtherOpT = TI->getOperand(0); 164 OtherOpF = FI->getOperand(0); 165 MatchIsOpZero = false; 166 } else if (!TI->isCommutative()) { 167 return 0; 168 } else if (TI->getOperand(0) == FI->getOperand(1)) { 169 MatchOp = TI->getOperand(0); 170 OtherOpT = TI->getOperand(1); 171 OtherOpF = FI->getOperand(0); 172 MatchIsOpZero = true; 173 } else if (TI->getOperand(1) == FI->getOperand(0)) { 174 MatchOp = TI->getOperand(1); 175 OtherOpT = TI->getOperand(0); 176 OtherOpF = FI->getOperand(1); 177 MatchIsOpZero = true; 178 } else { 179 return 0; 180 } 181 182 // If we reach here, they do have operations in common. 183 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT, 184 OtherOpF, SI.getName()+".v"); 185 186 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) { 187 if (MatchIsOpZero) 188 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI); 189 else 190 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp); 191 } 192 llvm_unreachable("Shouldn't get here"); 193 } 194 195 static bool isSelect01(Constant *C1, Constant *C2) { 196 ConstantInt *C1I = dyn_cast<ConstantInt>(C1); 197 if (!C1I) 198 return false; 199 ConstantInt *C2I = dyn_cast<ConstantInt>(C2); 200 if (!C2I) 201 return false; 202 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero. 203 return false; 204 return C1I->isOne() || C1I->isAllOnesValue() || 205 C2I->isOne() || C2I->isAllOnesValue(); 206 } 207 208 /// FoldSelectIntoOp - Try fold the select into one of the operands to 209 /// facilitate further optimization. 210 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal, 211 Value *FalseVal) { 212 // See the comment above GetSelectFoldableOperands for a description of the 213 // transformation we are doing here. 214 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) { 215 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 && 216 !isa<Constant>(FalseVal)) { 217 if (unsigned SFO = GetSelectFoldableOperands(TVI)) { 218 unsigned OpToFold = 0; 219 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) { 220 OpToFold = 1; 221 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) { 222 OpToFold = 2; 223 } 224 225 if (OpToFold) { 226 Constant *C = GetSelectFoldableConstant(TVI); 227 Value *OOp = TVI->getOperand(2-OpToFold); 228 // Avoid creating select between 2 constants unless it's selecting 229 // between 0, 1 and -1. 230 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 231 Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C); 232 NewSel->takeName(TVI); 233 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI); 234 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(), 235 FalseVal, NewSel); 236 if (isa<PossiblyExactOperator>(BO)) 237 BO->setIsExact(TVI_BO->isExact()); 238 if (isa<OverflowingBinaryOperator>(BO)) { 239 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap()); 240 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap()); 241 } 242 return BO; 243 } 244 } 245 } 246 } 247 } 248 249 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) { 250 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 && 251 !isa<Constant>(TrueVal)) { 252 if (unsigned SFO = GetSelectFoldableOperands(FVI)) { 253 unsigned OpToFold = 0; 254 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) { 255 OpToFold = 1; 256 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) { 257 OpToFold = 2; 258 } 259 260 if (OpToFold) { 261 Constant *C = GetSelectFoldableConstant(FVI); 262 Value *OOp = FVI->getOperand(2-OpToFold); 263 // Avoid creating select between 2 constants unless it's selecting 264 // between 0, 1 and -1. 265 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 266 Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp); 267 NewSel->takeName(FVI); 268 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI); 269 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(), 270 TrueVal, NewSel); 271 if (isa<PossiblyExactOperator>(BO)) 272 BO->setIsExact(FVI_BO->isExact()); 273 if (isa<OverflowingBinaryOperator>(BO)) { 274 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap()); 275 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap()); 276 } 277 return BO; 278 } 279 } 280 } 281 } 282 } 283 284 return 0; 285 } 286 287 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is 288 /// replaced with RepOp. 289 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp, 290 const TargetData *TD, 291 const TargetLibraryInfo *TLI) { 292 // Trivial replacement. 293 if (V == Op) 294 return RepOp; 295 296 Instruction *I = dyn_cast<Instruction>(V); 297 if (!I) 298 return 0; 299 300 // If this is a binary operator, try to simplify it with the replaced op. 301 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) { 302 if (B->getOperand(0) == Op) 303 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI); 304 if (B->getOperand(1) == Op) 305 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI); 306 } 307 308 // Same for CmpInsts. 309 if (CmpInst *C = dyn_cast<CmpInst>(I)) { 310 if (C->getOperand(0) == Op) 311 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD, 312 TLI); 313 if (C->getOperand(1) == Op) 314 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD, 315 TLI); 316 } 317 318 // TODO: We could hand off more cases to instsimplify here. 319 320 // If all operands are constant after substituting Op for RepOp then we can 321 // constant fold the instruction. 322 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) { 323 // Build a list of all constant operands. 324 SmallVector<Constant*, 8> ConstOps; 325 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 326 if (I->getOperand(i) == Op) 327 ConstOps.push_back(CRepOp); 328 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i))) 329 ConstOps.push_back(COp); 330 else 331 break; 332 } 333 334 // All operands were constants, fold it. 335 if (ConstOps.size() == I->getNumOperands()) { 336 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 337 if (!LI->isVolatile()) 338 return ConstantFoldLoadFromConstPtr(ConstOps[0], TD); 339 340 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), 341 ConstOps, TD, TLI); 342 } 343 } 344 345 return 0; 346 } 347 348 /// visitSelectInstWithICmp - Visit a SelectInst that has an 349 /// ICmpInst as its first operand. 350 /// 351 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 352 ICmpInst *ICI) { 353 bool Changed = false; 354 ICmpInst::Predicate Pred = ICI->getPredicate(); 355 Value *CmpLHS = ICI->getOperand(0); 356 Value *CmpRHS = ICI->getOperand(1); 357 Value *TrueVal = SI.getTrueValue(); 358 Value *FalseVal = SI.getFalseValue(); 359 360 // Check cases where the comparison is with a constant that 361 // can be adjusted to fit the min/max idiom. We may move or edit ICI 362 // here, so make sure the select is the only user. 363 if (ICI->hasOneUse()) 364 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 365 // X < MIN ? T : F --> F 366 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) 367 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 368 return ReplaceInstUsesWith(SI, FalseVal); 369 // X > MAX ? T : F --> F 370 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) 371 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 372 return ReplaceInstUsesWith(SI, FalseVal); 373 switch (Pred) { 374 default: break; 375 case ICmpInst::ICMP_ULT: 376 case ICmpInst::ICMP_SLT: 377 case ICmpInst::ICMP_UGT: 378 case ICmpInst::ICMP_SGT: { 379 // These transformations only work for selects over integers. 380 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType()); 381 if (!SelectTy) 382 break; 383 384 Constant *AdjustedRHS; 385 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) 386 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); 387 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) 388 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); 389 390 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 391 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 392 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 393 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) 394 ; // Nothing to do here. Values match without any sign/zero extension. 395 396 // Types do not match. Instead of calculating this with mixed types 397 // promote all to the larger type. This enables scalar evolution to 398 // analyze this expression. 399 else if (CmpRHS->getType()->getScalarSizeInBits() 400 < SelectTy->getBitWidth()) { 401 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy); 402 403 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X 404 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X 405 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X 406 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X 407 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && 408 sextRHS == FalseVal) { 409 CmpLHS = TrueVal; 410 AdjustedRHS = sextRHS; 411 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && 412 sextRHS == TrueVal) { 413 CmpLHS = FalseVal; 414 AdjustedRHS = sextRHS; 415 } else if (ICI->isUnsigned()) { 416 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy); 417 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X 418 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X 419 // zext + signed compare cannot be changed: 420 // 0xff <s 0x00, but 0x00ff >s 0x0000 421 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && 422 zextRHS == FalseVal) { 423 CmpLHS = TrueVal; 424 AdjustedRHS = zextRHS; 425 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && 426 zextRHS == TrueVal) { 427 CmpLHS = FalseVal; 428 AdjustedRHS = zextRHS; 429 } else 430 break; 431 } else 432 break; 433 } else 434 break; 435 436 Pred = ICmpInst::getSwappedPredicate(Pred); 437 CmpRHS = AdjustedRHS; 438 std::swap(FalseVal, TrueVal); 439 ICI->setPredicate(Pred); 440 ICI->setOperand(0, CmpLHS); 441 ICI->setOperand(1, CmpRHS); 442 SI.setOperand(1, TrueVal); 443 SI.setOperand(2, FalseVal); 444 445 // Move ICI instruction right before the select instruction. Otherwise 446 // the sext/zext value may be defined after the ICI instruction uses it. 447 ICI->moveBefore(&SI); 448 449 Changed = true; 450 break; 451 } 452 } 453 } 454 455 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 456 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 457 // FIXME: Type and constness constraints could be lifted, but we have to 458 // watch code size carefully. We should consider xor instead of 459 // sub/add when we decide to do that. 460 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 461 if (TrueVal->getType() == Ty) { 462 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 463 ConstantInt *C1 = NULL, *C2 = NULL; 464 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 465 C1 = dyn_cast<ConstantInt>(TrueVal); 466 C2 = dyn_cast<ConstantInt>(FalseVal); 467 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 468 C1 = dyn_cast<ConstantInt>(FalseVal); 469 C2 = dyn_cast<ConstantInt>(TrueVal); 470 } 471 if (C1 && C2) { 472 // This shift results in either -1 or 0. 473 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 474 475 // Check if we can express the operation with a single or. 476 if (C2->isAllOnesValue()) 477 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 478 479 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 480 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 481 } 482 } 483 } 484 } 485 486 // If we have an equality comparison then we know the value in one of the 487 // arms of the select. See if substituting this value into the arm and 488 // simplifying the result yields the same value as the other arm. 489 if (Pred == ICmpInst::ICMP_EQ) { 490 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal || 491 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal) 492 return ReplaceInstUsesWith(SI, FalseVal); 493 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal || 494 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal) 495 return ReplaceInstUsesWith(SI, FalseVal); 496 } else if (Pred == ICmpInst::ICMP_NE) { 497 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal || 498 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal) 499 return ReplaceInstUsesWith(SI, TrueVal); 500 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal || 501 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal) 502 return ReplaceInstUsesWith(SI, TrueVal); 503 } 504 505 // NOTE: if we wanted to, this is where to detect integer MIN/MAX 506 507 if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) { 508 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) { 509 // Transform (X == C) ? X : Y -> (X == C) ? C : Y 510 SI.setOperand(1, CmpRHS); 511 Changed = true; 512 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) { 513 // Transform (X != C) ? Y : X -> (X != C) ? Y : C 514 SI.setOperand(2, CmpRHS); 515 Changed = true; 516 } 517 } 518 519 return Changed ? &SI : 0; 520 } 521 522 523 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 524 /// PHI node (but the two may be in different blocks). See if the true/false 525 /// values (V) are live in all of the predecessor blocks of the PHI. For 526 /// example, cases like this cannot be mapped: 527 /// 528 /// X = phi [ C1, BB1], [C2, BB2] 529 /// Y = add 530 /// Z = select X, Y, 0 531 /// 532 /// because Y is not live in BB1/BB2. 533 /// 534 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 535 const SelectInst &SI) { 536 // If the value is a non-instruction value like a constant or argument, it 537 // can always be mapped. 538 const Instruction *I = dyn_cast<Instruction>(V); 539 if (I == 0) return true; 540 541 // If V is a PHI node defined in the same block as the condition PHI, we can 542 // map the arguments. 543 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 544 545 if (const PHINode *VP = dyn_cast<PHINode>(I)) 546 if (VP->getParent() == CondPHI->getParent()) 547 return true; 548 549 // Otherwise, if the PHI and select are defined in the same block and if V is 550 // defined in a different block, then we can transform it. 551 if (SI.getParent() == CondPHI->getParent() && 552 I->getParent() != CondPHI->getParent()) 553 return true; 554 555 // Otherwise we have a 'hard' case and we can't tell without doing more 556 // detailed dominator based analysis, punt. 557 return false; 558 } 559 560 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 561 /// SPF2(SPF1(A, B), C) 562 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 563 SelectPatternFlavor SPF1, 564 Value *A, Value *B, 565 Instruction &Outer, 566 SelectPatternFlavor SPF2, Value *C) { 567 if (C == A || C == B) { 568 // MAX(MAX(A, B), B) -> MAX(A, B) 569 // MIN(MIN(a, b), a) -> MIN(a, b) 570 if (SPF1 == SPF2) 571 return ReplaceInstUsesWith(Outer, Inner); 572 573 // MAX(MIN(a, b), a) -> a 574 // MIN(MAX(a, b), a) -> a 575 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 576 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 577 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 578 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 579 return ReplaceInstUsesWith(Outer, C); 580 } 581 582 // TODO: MIN(MIN(A, 23), 97) 583 return 0; 584 } 585 586 587 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't 588 /// both be) and we have an icmp instruction with zero, and we have an 'and' 589 /// with the non-constant value and a power of two we can turn the select 590 /// into a shift on the result of the 'and'. 591 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 592 ConstantInt *FalseVal, 593 InstCombiner::BuilderTy *Builder) { 594 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 595 if (!IC || !IC->isEquality()) 596 return 0; 597 598 if (!match(IC->getOperand(1), m_Zero())) 599 return 0; 600 601 ConstantInt *AndRHS; 602 Value *LHS = IC->getOperand(0); 603 if (LHS->getType() != SI.getType() || 604 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 605 return 0; 606 607 // If both select arms are non-zero see if we have a select of the form 608 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 609 // for 'x ? 2^n : 0' and fix the thing up at the end. 610 ConstantInt *Offset = 0; 611 if (!TrueVal->isZero() && !FalseVal->isZero()) { 612 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 613 Offset = FalseVal; 614 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 615 Offset = TrueVal; 616 else 617 return 0; 618 619 // Adjust TrueVal and FalseVal to the offset. 620 TrueVal = ConstantInt::get(Builder->getContext(), 621 TrueVal->getValue() - Offset->getValue()); 622 FalseVal = ConstantInt::get(Builder->getContext(), 623 FalseVal->getValue() - Offset->getValue()); 624 } 625 626 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 627 if (!AndRHS->getValue().isPowerOf2() || 628 (!TrueVal->getValue().isPowerOf2() && 629 !FalseVal->getValue().isPowerOf2())) 630 return 0; 631 632 // Determine which shift is needed to transform result of the 'and' into the 633 // desired result. 634 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 635 unsigned ValZeros = ValC->getValue().logBase2(); 636 unsigned AndZeros = AndRHS->getValue().logBase2(); 637 638 Value *V = LHS; 639 if (ValZeros > AndZeros) 640 V = Builder->CreateShl(V, ValZeros - AndZeros); 641 else if (ValZeros < AndZeros) 642 V = Builder->CreateLShr(V, AndZeros - ValZeros); 643 644 // Okay, now we know that everything is set up, we just don't know whether we 645 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 646 bool ShouldNotVal = !TrueVal->isZero(); 647 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 648 if (ShouldNotVal) 649 V = Builder->CreateXor(V, ValC); 650 651 // Apply an offset if needed. 652 if (Offset) 653 V = Builder->CreateAdd(V, Offset); 654 return V; 655 } 656 657 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 658 Value *CondVal = SI.getCondition(); 659 Value *TrueVal = SI.getTrueValue(); 660 Value *FalseVal = SI.getFalseValue(); 661 662 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 663 return ReplaceInstUsesWith(SI, V); 664 665 if (SI.getType()->isIntegerTy(1)) { 666 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 667 if (C->getZExtValue()) { 668 // Change: A = select B, true, C --> A = or B, C 669 return BinaryOperator::CreateOr(CondVal, FalseVal); 670 } 671 // Change: A = select B, false, C --> A = and !B, C 672 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 673 return BinaryOperator::CreateAnd(NotCond, FalseVal); 674 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 675 if (C->getZExtValue() == false) { 676 // Change: A = select B, C, false --> A = and B, C 677 return BinaryOperator::CreateAnd(CondVal, TrueVal); 678 } 679 // Change: A = select B, C, true --> A = or !B, C 680 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 681 return BinaryOperator::CreateOr(NotCond, TrueVal); 682 } 683 684 // select a, b, a -> a&b 685 // select a, a, b -> a|b 686 if (CondVal == TrueVal) 687 return BinaryOperator::CreateOr(CondVal, FalseVal); 688 else if (CondVal == FalseVal) 689 return BinaryOperator::CreateAnd(CondVal, TrueVal); 690 691 // select a, ~a, b -> (~a)&b 692 // select a, b, ~a -> (~a)|b 693 if (match(TrueVal, m_Not(m_Specific(CondVal)))) 694 return BinaryOperator::CreateAnd(TrueVal, FalseVal); 695 else if (match(FalseVal, m_Not(m_Specific(CondVal)))) 696 return BinaryOperator::CreateOr(TrueVal, FalseVal); 697 } 698 699 // Selecting between two integer constants? 700 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 701 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 702 // select C, 1, 0 -> zext C to int 703 if (FalseValC->isZero() && TrueValC->getValue() == 1) 704 return new ZExtInst(CondVal, SI.getType()); 705 706 // select C, -1, 0 -> sext C to int 707 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 708 return new SExtInst(CondVal, SI.getType()); 709 710 // select C, 0, 1 -> zext !C to int 711 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 712 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 713 return new ZExtInst(NotCond, SI.getType()); 714 } 715 716 // select C, 0, -1 -> sext !C to int 717 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 718 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 719 return new SExtInst(NotCond, SI.getType()); 720 } 721 722 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 723 return ReplaceInstUsesWith(SI, V); 724 } 725 726 // See if we are selecting two values based on a comparison of the two values. 727 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 728 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 729 // Transform (X == Y) ? X : Y -> Y 730 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 731 // This is not safe in general for floating point: 732 // consider X== -0, Y== +0. 733 // It becomes safe if either operand is a nonzero constant. 734 ConstantFP *CFPt, *CFPf; 735 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 736 !CFPt->getValueAPF().isZero()) || 737 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 738 !CFPf->getValueAPF().isZero())) 739 return ReplaceInstUsesWith(SI, FalseVal); 740 } 741 // Transform (X une Y) ? X : Y -> X 742 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 743 // This is not safe in general for floating point: 744 // consider X== -0, Y== +0. 745 // It becomes safe if either operand is a nonzero constant. 746 ConstantFP *CFPt, *CFPf; 747 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 748 !CFPt->getValueAPF().isZero()) || 749 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 750 !CFPf->getValueAPF().isZero())) 751 return ReplaceInstUsesWith(SI, TrueVal); 752 } 753 // NOTE: if we wanted to, this is where to detect MIN/MAX 754 755 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 756 // Transform (X == Y) ? Y : X -> X 757 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 758 // This is not safe in general for floating point: 759 // consider X== -0, Y== +0. 760 // It becomes safe if either operand is a nonzero constant. 761 ConstantFP *CFPt, *CFPf; 762 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 763 !CFPt->getValueAPF().isZero()) || 764 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 765 !CFPf->getValueAPF().isZero())) 766 return ReplaceInstUsesWith(SI, FalseVal); 767 } 768 // Transform (X une Y) ? Y : X -> Y 769 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 770 // This is not safe in general for floating point: 771 // consider X== -0, Y== +0. 772 // It becomes safe if either operand is a nonzero constant. 773 ConstantFP *CFPt, *CFPf; 774 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 775 !CFPt->getValueAPF().isZero()) || 776 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 777 !CFPf->getValueAPF().isZero())) 778 return ReplaceInstUsesWith(SI, TrueVal); 779 } 780 // NOTE: if we wanted to, this is where to detect MIN/MAX 781 } 782 // NOTE: if we wanted to, this is where to detect ABS 783 } 784 785 // See if we are selecting two values based on a comparison of the two values. 786 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 787 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 788 return Result; 789 790 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 791 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 792 if (TI->hasOneUse() && FI->hasOneUse()) { 793 Instruction *AddOp = 0, *SubOp = 0; 794 795 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 796 if (TI->getOpcode() == FI->getOpcode()) 797 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 798 return IV; 799 800 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 801 // even legal for FP. 802 if ((TI->getOpcode() == Instruction::Sub && 803 FI->getOpcode() == Instruction::Add) || 804 (TI->getOpcode() == Instruction::FSub && 805 FI->getOpcode() == Instruction::FAdd)) { 806 AddOp = FI; SubOp = TI; 807 } else if ((FI->getOpcode() == Instruction::Sub && 808 TI->getOpcode() == Instruction::Add) || 809 (FI->getOpcode() == Instruction::FSub && 810 TI->getOpcode() == Instruction::FAdd)) { 811 AddOp = TI; SubOp = FI; 812 } 813 814 if (AddOp) { 815 Value *OtherAddOp = 0; 816 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 817 OtherAddOp = AddOp->getOperand(1); 818 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 819 OtherAddOp = AddOp->getOperand(0); 820 } 821 822 if (OtherAddOp) { 823 // So at this point we know we have (Y -> OtherAddOp): 824 // select C, (add X, Y), (sub X, Z) 825 Value *NegVal; // Compute -Z 826 if (SI.getType()->isFPOrFPVectorTy()) { 827 NegVal = Builder->CreateFNeg(SubOp->getOperand(1)); 828 } else { 829 NegVal = Builder->CreateNeg(SubOp->getOperand(1)); 830 } 831 832 Value *NewTrueOp = OtherAddOp; 833 Value *NewFalseOp = NegVal; 834 if (AddOp != TI) 835 std::swap(NewTrueOp, NewFalseOp); 836 Value *NewSel = 837 Builder->CreateSelect(CondVal, NewTrueOp, 838 NewFalseOp, SI.getName() + ".p"); 839 840 if (SI.getType()->isFPOrFPVectorTy()) 841 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 842 else 843 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 844 } 845 } 846 } 847 848 // See if we can fold the select into one of our operands. 849 if (SI.getType()->isIntegerTy()) { 850 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 851 return FoldI; 852 853 // MAX(MAX(a, b), a) -> MAX(a, b) 854 // MIN(MIN(a, b), a) -> MIN(a, b) 855 // MAX(MIN(a, b), a) -> a 856 // MIN(MAX(a, b), a) -> a 857 Value *LHS, *RHS, *LHS2, *RHS2; 858 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 859 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 860 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 861 SI, SPF, RHS)) 862 return R; 863 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 864 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 865 SI, SPF, LHS)) 866 return R; 867 } 868 869 // TODO. 870 // ABS(-X) -> ABS(X) 871 // ABS(ABS(X)) -> ABS(X) 872 } 873 874 // See if we can fold the select into a phi node if the condition is a select. 875 if (isa<PHINode>(SI.getCondition())) 876 // The true/false values have to be live in the PHI predecessor's blocks. 877 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 878 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 879 if (Instruction *NV = FoldOpIntoPhi(SI)) 880 return NV; 881 882 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) { 883 if (TrueSI->getCondition() == CondVal) { 884 if (SI.getTrueValue() == TrueSI->getTrueValue()) 885 return 0; 886 SI.setOperand(1, TrueSI->getTrueValue()); 887 return &SI; 888 } 889 } 890 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) { 891 if (FalseSI->getCondition() == CondVal) { 892 if (SI.getFalseValue() == FalseSI->getFalseValue()) 893 return 0; 894 SI.setOperand(2, FalseSI->getFalseValue()); 895 return &SI; 896 } 897 } 898 899 if (BinaryOperator::isNot(CondVal)) { 900 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 901 SI.setOperand(1, FalseVal); 902 SI.setOperand(2, TrueVal); 903 return &SI; 904 } 905 906 if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) { 907 unsigned VWidth = VecTy->getNumElements(); 908 APInt UndefElts(VWidth, 0); 909 APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth)); 910 if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) { 911 if (V != &SI) 912 return ReplaceInstUsesWith(SI, V); 913 return &SI; 914 } 915 } 916 917 return 0; 918 } 919
