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/InstructionSimplify.h" 17 using namespace llvm; 18 using namespace PatternMatch; 19 20 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms, 21 /// returning the kind and providing the out parameter results if we 22 /// successfully match. 23 static SelectPatternFlavor 24 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) { 25 SelectInst *SI = dyn_cast<SelectInst>(V); 26 if (SI == 0) return SPF_UNKNOWN; 27 28 ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition()); 29 if (ICI == 0) return SPF_UNKNOWN; 30 31 LHS = ICI->getOperand(0); 32 RHS = ICI->getOperand(1); 33 34 // (icmp X, Y) ? X : Y 35 if (SI->getTrueValue() == ICI->getOperand(0) && 36 SI->getFalseValue() == ICI->getOperand(1)) { 37 switch (ICI->getPredicate()) { 38 default: return SPF_UNKNOWN; // Equality. 39 case ICmpInst::ICMP_UGT: 40 case ICmpInst::ICMP_UGE: return SPF_UMAX; 41 case ICmpInst::ICMP_SGT: 42 case ICmpInst::ICMP_SGE: return SPF_SMAX; 43 case ICmpInst::ICMP_ULT: 44 case ICmpInst::ICMP_ULE: return SPF_UMIN; 45 case ICmpInst::ICMP_SLT: 46 case ICmpInst::ICMP_SLE: return SPF_SMIN; 47 } 48 } 49 50 // (icmp X, Y) ? Y : X 51 if (SI->getTrueValue() == ICI->getOperand(1) && 52 SI->getFalseValue() == ICI->getOperand(0)) { 53 switch (ICI->getPredicate()) { 54 default: return SPF_UNKNOWN; // Equality. 55 case ICmpInst::ICMP_UGT: 56 case ICmpInst::ICMP_UGE: return SPF_UMIN; 57 case ICmpInst::ICMP_SGT: 58 case ICmpInst::ICMP_SGE: return SPF_SMIN; 59 case ICmpInst::ICMP_ULT: 60 case ICmpInst::ICMP_ULE: return SPF_UMAX; 61 case ICmpInst::ICMP_SLT: 62 case ICmpInst::ICMP_SLE: return SPF_SMAX; 63 } 64 } 65 66 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5) 67 68 return SPF_UNKNOWN; 69 } 70 71 72 /// GetSelectFoldableOperands - We want to turn code that looks like this: 73 /// %C = or %A, %B 74 /// %D = select %cond, %C, %A 75 /// into: 76 /// %C = select %cond, %B, 0 77 /// %D = or %A, %C 78 /// 79 /// Assuming that the specified instruction is an operand to the select, return 80 /// a bitmask indicating which operands of this instruction are foldable if they 81 /// equal the other incoming value of the select. 82 /// 83 static unsigned GetSelectFoldableOperands(Instruction *I) { 84 switch (I->getOpcode()) { 85 case Instruction::Add: 86 case Instruction::Mul: 87 case Instruction::And: 88 case Instruction::Or: 89 case Instruction::Xor: 90 return 3; // Can fold through either operand. 91 case Instruction::Sub: // Can only fold on the amount subtracted. 92 case Instruction::Shl: // Can only fold on the shift amount. 93 case Instruction::LShr: 94 case Instruction::AShr: 95 return 1; 96 default: 97 return 0; // Cannot fold 98 } 99 } 100 101 /// GetSelectFoldableConstant - For the same transformation as the previous 102 /// function, return the identity constant that goes into the select. 103 static Constant *GetSelectFoldableConstant(Instruction *I) { 104 switch (I->getOpcode()) { 105 default: llvm_unreachable("This cannot happen!"); 106 case Instruction::Add: 107 case Instruction::Sub: 108 case Instruction::Or: 109 case Instruction::Xor: 110 case Instruction::Shl: 111 case Instruction::LShr: 112 case Instruction::AShr: 113 return Constant::getNullValue(I->getType()); 114 case Instruction::And: 115 return Constant::getAllOnesValue(I->getType()); 116 case Instruction::Mul: 117 return ConstantInt::get(I->getType(), 1); 118 } 119 } 120 121 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI 122 /// have the same opcode and only one use each. Try to simplify this. 123 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI, 124 Instruction *FI) { 125 if (TI->getNumOperands() == 1) { 126 // If this is a non-volatile load or a cast from the same type, 127 // merge. 128 if (TI->isCast()) { 129 if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType()) 130 return 0; 131 } else { 132 return 0; // unknown unary op. 133 } 134 135 // Fold this by inserting a select from the input values. 136 Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0), 137 FI->getOperand(0), SI.getName()+".v"); 138 return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI, 139 TI->getType()); 140 } 141 142 // Only handle binary operators here. 143 if (!isa<BinaryOperator>(TI)) 144 return 0; 145 146 // Figure out if the operations have any operands in common. 147 Value *MatchOp, *OtherOpT, *OtherOpF; 148 bool MatchIsOpZero; 149 if (TI->getOperand(0) == FI->getOperand(0)) { 150 MatchOp = TI->getOperand(0); 151 OtherOpT = TI->getOperand(1); 152 OtherOpF = FI->getOperand(1); 153 MatchIsOpZero = true; 154 } else if (TI->getOperand(1) == FI->getOperand(1)) { 155 MatchOp = TI->getOperand(1); 156 OtherOpT = TI->getOperand(0); 157 OtherOpF = FI->getOperand(0); 158 MatchIsOpZero = false; 159 } else if (!TI->isCommutative()) { 160 return 0; 161 } else if (TI->getOperand(0) == FI->getOperand(1)) { 162 MatchOp = TI->getOperand(0); 163 OtherOpT = TI->getOperand(1); 164 OtherOpF = FI->getOperand(0); 165 MatchIsOpZero = true; 166 } else if (TI->getOperand(1) == FI->getOperand(0)) { 167 MatchOp = TI->getOperand(1); 168 OtherOpT = TI->getOperand(0); 169 OtherOpF = FI->getOperand(1); 170 MatchIsOpZero = true; 171 } else { 172 return 0; 173 } 174 175 // If we reach here, they do have operations in common. 176 Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT, 177 OtherOpF, SI.getName()+".v"); 178 179 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) { 180 if (MatchIsOpZero) 181 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI); 182 else 183 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp); 184 } 185 llvm_unreachable("Shouldn't get here"); 186 return 0; 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 // Trivial replacement. 286 if (V == Op) 287 return RepOp; 288 289 Instruction *I = dyn_cast<Instruction>(V); 290 if (!I) 291 return 0; 292 293 // If this is a binary operator, try to simplify it with the replaced op. 294 if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) { 295 if (B->getOperand(0) == Op) 296 return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD); 297 if (B->getOperand(1) == Op) 298 return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD); 299 } 300 301 // Same for CmpInsts. 302 if (CmpInst *C = dyn_cast<CmpInst>(I)) { 303 if (C->getOperand(0) == Op) 304 return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD); 305 if (C->getOperand(1) == Op) 306 return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD); 307 } 308 309 // TODO: We could hand off more cases to instsimplify here. 310 311 // If all operands are constant after substituting Op for RepOp then we can 312 // constant fold the instruction. 313 if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) { 314 // Build a list of all constant operands. 315 SmallVector<Constant*, 8> ConstOps; 316 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 317 if (I->getOperand(i) == Op) 318 ConstOps.push_back(CRepOp); 319 else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i))) 320 ConstOps.push_back(COp); 321 else 322 break; 323 } 324 325 // All operands were constants, fold it. 326 if (ConstOps.size() == I->getNumOperands()) 327 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), 328 ConstOps, TD); 329 } 330 331 return 0; 332 } 333 334 /// visitSelectInstWithICmp - Visit a SelectInst that has an 335 /// ICmpInst as its first operand. 336 /// 337 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 338 ICmpInst *ICI) { 339 bool Changed = false; 340 ICmpInst::Predicate Pred = ICI->getPredicate(); 341 Value *CmpLHS = ICI->getOperand(0); 342 Value *CmpRHS = ICI->getOperand(1); 343 Value *TrueVal = SI.getTrueValue(); 344 Value *FalseVal = SI.getFalseValue(); 345 346 // Check cases where the comparison is with a constant that 347 // can be adjusted to fit the min/max idiom. We may move or edit ICI 348 // here, so make sure the select is the only user. 349 if (ICI->hasOneUse()) 350 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 351 // X < MIN ? T : F --> F 352 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) 353 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 354 return ReplaceInstUsesWith(SI, FalseVal); 355 // X > MAX ? T : F --> F 356 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) 357 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 358 return ReplaceInstUsesWith(SI, FalseVal); 359 switch (Pred) { 360 default: break; 361 case ICmpInst::ICMP_ULT: 362 case ICmpInst::ICMP_SLT: 363 case ICmpInst::ICMP_UGT: 364 case ICmpInst::ICMP_SGT: { 365 // These transformations only work for selects over integers. 366 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType()); 367 if (!SelectTy) 368 break; 369 370 Constant *AdjustedRHS; 371 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) 372 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); 373 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) 374 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); 375 376 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 377 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 378 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 379 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) 380 ; // Nothing to do here. Values match without any sign/zero extension. 381 382 // Types do not match. Instead of calculating this with mixed types 383 // promote all to the larger type. This enables scalar evolution to 384 // analyze this expression. 385 else if (CmpRHS->getType()->getScalarSizeInBits() 386 < SelectTy->getBitWidth()) { 387 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy); 388 389 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X 390 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X 391 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X 392 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X 393 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && 394 sextRHS == FalseVal) { 395 CmpLHS = TrueVal; 396 AdjustedRHS = sextRHS; 397 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && 398 sextRHS == TrueVal) { 399 CmpLHS = FalseVal; 400 AdjustedRHS = sextRHS; 401 } else if (ICI->isUnsigned()) { 402 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy); 403 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X 404 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X 405 // zext + signed compare cannot be changed: 406 // 0xff <s 0x00, but 0x00ff >s 0x0000 407 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && 408 zextRHS == FalseVal) { 409 CmpLHS = TrueVal; 410 AdjustedRHS = zextRHS; 411 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && 412 zextRHS == TrueVal) { 413 CmpLHS = FalseVal; 414 AdjustedRHS = zextRHS; 415 } else 416 break; 417 } else 418 break; 419 } else 420 break; 421 422 Pred = ICmpInst::getSwappedPredicate(Pred); 423 CmpRHS = AdjustedRHS; 424 std::swap(FalseVal, TrueVal); 425 ICI->setPredicate(Pred); 426 ICI->setOperand(0, CmpLHS); 427 ICI->setOperand(1, CmpRHS); 428 SI.setOperand(1, TrueVal); 429 SI.setOperand(2, FalseVal); 430 431 // Move ICI instruction right before the select instruction. Otherwise 432 // the sext/zext value may be defined after the ICI instruction uses it. 433 ICI->moveBefore(&SI); 434 435 Changed = true; 436 break; 437 } 438 } 439 } 440 441 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 442 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 443 // FIXME: Type and constness constraints could be lifted, but we have to 444 // watch code size carefully. We should consider xor instead of 445 // sub/add when we decide to do that. 446 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 447 if (TrueVal->getType() == Ty) { 448 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 449 ConstantInt *C1 = NULL, *C2 = NULL; 450 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 451 C1 = dyn_cast<ConstantInt>(TrueVal); 452 C2 = dyn_cast<ConstantInt>(FalseVal); 453 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 454 C1 = dyn_cast<ConstantInt>(FalseVal); 455 C2 = dyn_cast<ConstantInt>(TrueVal); 456 } 457 if (C1 && C2) { 458 // This shift results in either -1 or 0. 459 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 460 461 // Check if we can express the operation with a single or. 462 if (C2->isAllOnesValue()) 463 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 464 465 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 466 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 467 } 468 } 469 } 470 } 471 472 // If we have an equality comparison then we know the value in one of the 473 // arms of the select. See if substituting this value into the arm and 474 // simplifying the result yields the same value as the other arm. 475 if (Pred == ICmpInst::ICMP_EQ) { 476 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal || 477 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal) 478 return ReplaceInstUsesWith(SI, FalseVal); 479 } else if (Pred == ICmpInst::ICMP_NE) { 480 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal || 481 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal) 482 return ReplaceInstUsesWith(SI, TrueVal); 483 } 484 485 // NOTE: if we wanted to, this is where to detect integer MIN/MAX 486 487 if (isa<Constant>(CmpRHS)) { 488 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) { 489 // Transform (X == C) ? X : Y -> (X == C) ? C : Y 490 SI.setOperand(1, CmpRHS); 491 Changed = true; 492 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) { 493 // Transform (X != C) ? Y : X -> (X != C) ? Y : C 494 SI.setOperand(2, CmpRHS); 495 Changed = true; 496 } 497 } 498 499 return Changed ? &SI : 0; 500 } 501 502 503 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 504 /// PHI node (but the two may be in different blocks). See if the true/false 505 /// values (V) are live in all of the predecessor blocks of the PHI. For 506 /// example, cases like this cannot be mapped: 507 /// 508 /// X = phi [ C1, BB1], [C2, BB2] 509 /// Y = add 510 /// Z = select X, Y, 0 511 /// 512 /// because Y is not live in BB1/BB2. 513 /// 514 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 515 const SelectInst &SI) { 516 // If the value is a non-instruction value like a constant or argument, it 517 // can always be mapped. 518 const Instruction *I = dyn_cast<Instruction>(V); 519 if (I == 0) return true; 520 521 // If V is a PHI node defined in the same block as the condition PHI, we can 522 // map the arguments. 523 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 524 525 if (const PHINode *VP = dyn_cast<PHINode>(I)) 526 if (VP->getParent() == CondPHI->getParent()) 527 return true; 528 529 // Otherwise, if the PHI and select are defined in the same block and if V is 530 // defined in a different block, then we can transform it. 531 if (SI.getParent() == CondPHI->getParent() && 532 I->getParent() != CondPHI->getParent()) 533 return true; 534 535 // Otherwise we have a 'hard' case and we can't tell without doing more 536 // detailed dominator based analysis, punt. 537 return false; 538 } 539 540 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 541 /// SPF2(SPF1(A, B), C) 542 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 543 SelectPatternFlavor SPF1, 544 Value *A, Value *B, 545 Instruction &Outer, 546 SelectPatternFlavor SPF2, Value *C) { 547 if (C == A || C == B) { 548 // MAX(MAX(A, B), B) -> MAX(A, B) 549 // MIN(MIN(a, b), a) -> MIN(a, b) 550 if (SPF1 == SPF2) 551 return ReplaceInstUsesWith(Outer, Inner); 552 553 // MAX(MIN(a, b), a) -> a 554 // MIN(MAX(a, b), a) -> a 555 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 556 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 557 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 558 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 559 return ReplaceInstUsesWith(Outer, C); 560 } 561 562 // TODO: MIN(MIN(A, 23), 97) 563 return 0; 564 } 565 566 567 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't 568 /// both be) and we have an icmp instruction with zero, and we have an 'and' 569 /// with the non-constant value and a power of two we can turn the select 570 /// into a shift on the result of the 'and'. 571 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 572 ConstantInt *FalseVal, 573 InstCombiner::BuilderTy *Builder) { 574 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 575 if (!IC || !IC->isEquality()) 576 return 0; 577 578 if (!match(IC->getOperand(1), m_Zero())) 579 return 0; 580 581 ConstantInt *AndRHS; 582 Value *LHS = IC->getOperand(0); 583 if (LHS->getType() != SI.getType() || 584 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 585 return 0; 586 587 // If both select arms are non-zero see if we have a select of the form 588 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 589 // for 'x ? 2^n : 0' and fix the thing up at the end. 590 ConstantInt *Offset = 0; 591 if (!TrueVal->isZero() && !FalseVal->isZero()) { 592 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 593 Offset = FalseVal; 594 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 595 Offset = TrueVal; 596 else 597 return 0; 598 599 // Adjust TrueVal and FalseVal to the offset. 600 TrueVal = ConstantInt::get(Builder->getContext(), 601 TrueVal->getValue() - Offset->getValue()); 602 FalseVal = ConstantInt::get(Builder->getContext(), 603 FalseVal->getValue() - Offset->getValue()); 604 } 605 606 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 607 if (!AndRHS->getValue().isPowerOf2() || 608 (!TrueVal->getValue().isPowerOf2() && 609 !FalseVal->getValue().isPowerOf2())) 610 return 0; 611 612 // Determine which shift is needed to transform result of the 'and' into the 613 // desired result. 614 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 615 unsigned ValZeros = ValC->getValue().logBase2(); 616 unsigned AndZeros = AndRHS->getValue().logBase2(); 617 618 Value *V = LHS; 619 if (ValZeros > AndZeros) 620 V = Builder->CreateShl(V, ValZeros - AndZeros); 621 else if (ValZeros < AndZeros) 622 V = Builder->CreateLShr(V, AndZeros - ValZeros); 623 624 // Okay, now we know that everything is set up, we just don't know whether we 625 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 626 bool ShouldNotVal = !TrueVal->isZero(); 627 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 628 if (ShouldNotVal) 629 V = Builder->CreateXor(V, ValC); 630 631 // Apply an offset if needed. 632 if (Offset) 633 V = Builder->CreateAdd(V, Offset); 634 return V; 635 } 636 637 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 638 Value *CondVal = SI.getCondition(); 639 Value *TrueVal = SI.getTrueValue(); 640 Value *FalseVal = SI.getFalseValue(); 641 642 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 643 return ReplaceInstUsesWith(SI, V); 644 645 if (SI.getType()->isIntegerTy(1)) { 646 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 647 if (C->getZExtValue()) { 648 // Change: A = select B, true, C --> A = or B, C 649 return BinaryOperator::CreateOr(CondVal, FalseVal); 650 } 651 // Change: A = select B, false, C --> A = and !B, C 652 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 653 return BinaryOperator::CreateAnd(NotCond, FalseVal); 654 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 655 if (C->getZExtValue() == false) { 656 // Change: A = select B, C, false --> A = and B, C 657 return BinaryOperator::CreateAnd(CondVal, TrueVal); 658 } 659 // Change: A = select B, C, true --> A = or !B, C 660 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 661 return BinaryOperator::CreateOr(NotCond, TrueVal); 662 } 663 664 // select a, b, a -> a&b 665 // select a, a, b -> a|b 666 if (CondVal == TrueVal) 667 return BinaryOperator::CreateOr(CondVal, FalseVal); 668 else if (CondVal == FalseVal) 669 return BinaryOperator::CreateAnd(CondVal, TrueVal); 670 } 671 672 // Selecting between two integer constants? 673 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 674 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 675 // select C, 1, 0 -> zext C to int 676 if (FalseValC->isZero() && TrueValC->getValue() == 1) 677 return new ZExtInst(CondVal, SI.getType()); 678 679 // select C, -1, 0 -> sext C to int 680 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 681 return new SExtInst(CondVal, SI.getType()); 682 683 // select C, 0, 1 -> zext !C to int 684 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 685 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 686 return new ZExtInst(NotCond, SI.getType()); 687 } 688 689 // select C, 0, -1 -> sext !C to int 690 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 691 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 692 return new SExtInst(NotCond, SI.getType()); 693 } 694 695 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 696 return ReplaceInstUsesWith(SI, V); 697 } 698 699 // See if we are selecting two values based on a comparison of the two values. 700 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 701 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 702 // Transform (X == Y) ? X : Y -> Y 703 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 704 // This is not safe in general for floating point: 705 // consider X== -0, Y== +0. 706 // It becomes safe if either operand is a nonzero constant. 707 ConstantFP *CFPt, *CFPf; 708 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 709 !CFPt->getValueAPF().isZero()) || 710 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 711 !CFPf->getValueAPF().isZero())) 712 return ReplaceInstUsesWith(SI, FalseVal); 713 } 714 // Transform (X une Y) ? X : Y -> X 715 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 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, TrueVal); 725 } 726 // NOTE: if we wanted to, this is where to detect MIN/MAX 727 728 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 729 // Transform (X == Y) ? Y : X -> X 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) ? Y : X -> Y 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 // NOTE: if we wanted to, this is where to detect ABS 756 } 757 758 // See if we are selecting two values based on a comparison of the two values. 759 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 760 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 761 return Result; 762 763 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 764 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 765 if (TI->hasOneUse() && FI->hasOneUse()) { 766 Instruction *AddOp = 0, *SubOp = 0; 767 768 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 769 if (TI->getOpcode() == FI->getOpcode()) 770 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 771 return IV; 772 773 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 774 // even legal for FP. 775 if ((TI->getOpcode() == Instruction::Sub && 776 FI->getOpcode() == Instruction::Add) || 777 (TI->getOpcode() == Instruction::FSub && 778 FI->getOpcode() == Instruction::FAdd)) { 779 AddOp = FI; SubOp = TI; 780 } else if ((FI->getOpcode() == Instruction::Sub && 781 TI->getOpcode() == Instruction::Add) || 782 (FI->getOpcode() == Instruction::FSub && 783 TI->getOpcode() == Instruction::FAdd)) { 784 AddOp = TI; SubOp = FI; 785 } 786 787 if (AddOp) { 788 Value *OtherAddOp = 0; 789 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 790 OtherAddOp = AddOp->getOperand(1); 791 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 792 OtherAddOp = AddOp->getOperand(0); 793 } 794 795 if (OtherAddOp) { 796 // So at this point we know we have (Y -> OtherAddOp): 797 // select C, (add X, Y), (sub X, Z) 798 Value *NegVal; // Compute -Z 799 if (SI.getType()->isFPOrFPVectorTy()) { 800 NegVal = Builder->CreateFNeg(SubOp->getOperand(1)); 801 } else { 802 NegVal = Builder->CreateNeg(SubOp->getOperand(1)); 803 } 804 805 Value *NewTrueOp = OtherAddOp; 806 Value *NewFalseOp = NegVal; 807 if (AddOp != TI) 808 std::swap(NewTrueOp, NewFalseOp); 809 Value *NewSel = 810 Builder->CreateSelect(CondVal, NewTrueOp, 811 NewFalseOp, SI.getName() + ".p"); 812 813 if (SI.getType()->isFPOrFPVectorTy()) 814 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 815 else 816 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 817 } 818 } 819 } 820 821 // See if we can fold the select into one of our operands. 822 if (SI.getType()->isIntegerTy()) { 823 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 824 return FoldI; 825 826 // MAX(MAX(a, b), a) -> MAX(a, b) 827 // MIN(MIN(a, b), a) -> MIN(a, b) 828 // MAX(MIN(a, b), a) -> a 829 // MIN(MAX(a, b), a) -> a 830 Value *LHS, *RHS, *LHS2, *RHS2; 831 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 832 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 833 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 834 SI, SPF, RHS)) 835 return R; 836 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 837 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 838 SI, SPF, LHS)) 839 return R; 840 } 841 842 // TODO. 843 // ABS(-X) -> ABS(X) 844 // ABS(ABS(X)) -> ABS(X) 845 } 846 847 // See if we can fold the select into a phi node if the condition is a select. 848 if (isa<PHINode>(SI.getCondition())) 849 // The true/false values have to be live in the PHI predecessor's blocks. 850 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 851 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 852 if (Instruction *NV = FoldOpIntoPhi(SI)) 853 return NV; 854 855 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) { 856 if (TrueSI->getCondition() == CondVal) { 857 SI.setOperand(1, TrueSI->getTrueValue()); 858 return &SI; 859 } 860 } 861 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) { 862 if (FalseSI->getCondition() == CondVal) { 863 SI.setOperand(2, FalseSI->getFalseValue()); 864 return &SI; 865 } 866 } 867 868 if (BinaryOperator::isNot(CondVal)) { 869 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 870 SI.setOperand(1, FalseVal); 871 SI.setOperand(2, TrueVal); 872 return &SI; 873 } 874 875 return 0; 876 } 877
