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