InstCombineSelect.cpp revision 747032522f9f3b2d9bae71aa303c1a0fd953eee9
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" 18using namespace llvm; 19using 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. 24static SelectPatternFlavor 25MatchSelectPattern(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/// 84static 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. 104static 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. 124Instruction *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 190static bool isSelect01(Constant *C1, Constant *C2) { 191 ConstantInt *C1I = dyn_cast<ConstantInt>(C1); 192 if (!C1I) 193 return false; 194 ConstantInt *C2I = dyn_cast<ConstantInt>(C2); 195 if (!C2I) 196 return false; 197 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. 205Instruction *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. 284static 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 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), 329 ConstOps, TD); 330 } 331 332 return 0; 333} 334 335/// visitSelectInstWithICmp - Visit a SelectInst that has an 336/// ICmpInst as its first operand. 337/// 338Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 339 ICmpInst *ICI) { 340 bool Changed = false; 341 ICmpInst::Predicate Pred = ICI->getPredicate(); 342 Value *CmpLHS = ICI->getOperand(0); 343 Value *CmpRHS = ICI->getOperand(1); 344 Value *TrueVal = SI.getTrueValue(); 345 Value *FalseVal = SI.getFalseValue(); 346 347 // Check cases where the comparison is with a constant that 348 // can be adjusted to fit the min/max idiom. We may move or edit ICI 349 // here, so make sure the select is the only user. 350 if (ICI->hasOneUse()) 351 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 352 // X < MIN ? T : F --> F 353 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) 354 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 355 return ReplaceInstUsesWith(SI, FalseVal); 356 // X > MAX ? T : F --> F 357 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) 358 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 359 return ReplaceInstUsesWith(SI, FalseVal); 360 switch (Pred) { 361 default: break; 362 case ICmpInst::ICMP_ULT: 363 case ICmpInst::ICMP_SLT: 364 case ICmpInst::ICMP_UGT: 365 case ICmpInst::ICMP_SGT: { 366 // These transformations only work for selects over integers. 367 IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType()); 368 if (!SelectTy) 369 break; 370 371 Constant *AdjustedRHS; 372 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) 373 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); 374 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) 375 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); 376 377 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 378 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 379 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 380 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) 381 ; // Nothing to do here. Values match without any sign/zero extension. 382 383 // Types do not match. Instead of calculating this with mixed types 384 // promote all to the larger type. This enables scalar evolution to 385 // analyze this expression. 386 else if (CmpRHS->getType()->getScalarSizeInBits() 387 < SelectTy->getBitWidth()) { 388 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy); 389 390 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X 391 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s 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 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X 394 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && 395 sextRHS == FalseVal) { 396 CmpLHS = TrueVal; 397 AdjustedRHS = sextRHS; 398 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && 399 sextRHS == TrueVal) { 400 CmpLHS = FalseVal; 401 AdjustedRHS = sextRHS; 402 } else if (ICI->isUnsigned()) { 403 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy); 404 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X 405 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X 406 // zext + signed compare cannot be changed: 407 // 0xff <s 0x00, but 0x00ff >s 0x0000 408 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && 409 zextRHS == FalseVal) { 410 CmpLHS = TrueVal; 411 AdjustedRHS = zextRHS; 412 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && 413 zextRHS == TrueVal) { 414 CmpLHS = FalseVal; 415 AdjustedRHS = zextRHS; 416 } else 417 break; 418 } else 419 break; 420 } else 421 break; 422 423 Pred = ICmpInst::getSwappedPredicate(Pred); 424 CmpRHS = AdjustedRHS; 425 std::swap(FalseVal, TrueVal); 426 ICI->setPredicate(Pred); 427 ICI->setOperand(0, CmpLHS); 428 ICI->setOperand(1, CmpRHS); 429 SI.setOperand(1, TrueVal); 430 SI.setOperand(2, FalseVal); 431 432 // Move ICI instruction right before the select instruction. Otherwise 433 // the sext/zext value may be defined after the ICI instruction uses it. 434 ICI->moveBefore(&SI); 435 436 Changed = true; 437 break; 438 } 439 } 440 } 441 442 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 443 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 444 // FIXME: Type and constness constraints could be lifted, but we have to 445 // watch code size carefully. We should consider xor instead of 446 // sub/add when we decide to do that. 447 if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 448 if (TrueVal->getType() == Ty) { 449 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 450 ConstantInt *C1 = NULL, *C2 = NULL; 451 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 452 C1 = dyn_cast<ConstantInt>(TrueVal); 453 C2 = dyn_cast<ConstantInt>(FalseVal); 454 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 455 C1 = dyn_cast<ConstantInt>(FalseVal); 456 C2 = dyn_cast<ConstantInt>(TrueVal); 457 } 458 if (C1 && C2) { 459 // This shift results in either -1 or 0. 460 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 461 462 // Check if we can express the operation with a single or. 463 if (C2->isAllOnesValue()) 464 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 465 466 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 467 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 468 } 469 } 470 } 471 } 472 473 // If we have an equality comparison then we know the value in one of the 474 // arms of the select. See if substituting this value into the arm and 475 // simplifying the result yields the same value as the other arm. 476 if (Pred == ICmpInst::ICMP_EQ) { 477 if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal || 478 SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal) 479 return ReplaceInstUsesWith(SI, FalseVal); 480 } else if (Pred == ICmpInst::ICMP_NE) { 481 if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal || 482 SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal) 483 return ReplaceInstUsesWith(SI, TrueVal); 484 } 485 486 // NOTE: if we wanted to, this is where to detect integer MIN/MAX 487 488 if (isa<Constant>(CmpRHS)) { 489 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) { 490 // Transform (X == C) ? X : Y -> (X == C) ? C : Y 491 SI.setOperand(1, CmpRHS); 492 Changed = true; 493 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) { 494 // Transform (X != C) ? Y : X -> (X != C) ? Y : C 495 SI.setOperand(2, CmpRHS); 496 Changed = true; 497 } 498 } 499 500 return Changed ? &SI : 0; 501} 502 503 504/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 505/// PHI node (but the two may be in different blocks). See if the true/false 506/// values (V) are live in all of the predecessor blocks of the PHI. For 507/// example, cases like this cannot be mapped: 508/// 509/// X = phi [ C1, BB1], [C2, BB2] 510/// Y = add 511/// Z = select X, Y, 0 512/// 513/// because Y is not live in BB1/BB2. 514/// 515static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 516 const SelectInst &SI) { 517 // If the value is a non-instruction value like a constant or argument, it 518 // can always be mapped. 519 const Instruction *I = dyn_cast<Instruction>(V); 520 if (I == 0) return true; 521 522 // If V is a PHI node defined in the same block as the condition PHI, we can 523 // map the arguments. 524 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 525 526 if (const PHINode *VP = dyn_cast<PHINode>(I)) 527 if (VP->getParent() == CondPHI->getParent()) 528 return true; 529 530 // Otherwise, if the PHI and select are defined in the same block and if V is 531 // defined in a different block, then we can transform it. 532 if (SI.getParent() == CondPHI->getParent() && 533 I->getParent() != CondPHI->getParent()) 534 return true; 535 536 // Otherwise we have a 'hard' case and we can't tell without doing more 537 // detailed dominator based analysis, punt. 538 return false; 539} 540 541/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 542/// SPF2(SPF1(A, B), C) 543Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 544 SelectPatternFlavor SPF1, 545 Value *A, Value *B, 546 Instruction &Outer, 547 SelectPatternFlavor SPF2, Value *C) { 548 if (C == A || C == B) { 549 // MAX(MAX(A, B), B) -> MAX(A, B) 550 // MIN(MIN(a, b), a) -> MIN(a, b) 551 if (SPF1 == SPF2) 552 return ReplaceInstUsesWith(Outer, Inner); 553 554 // MAX(MIN(a, b), a) -> a 555 // MIN(MAX(a, b), a) -> a 556 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 557 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 558 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 559 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 560 return ReplaceInstUsesWith(Outer, C); 561 } 562 563 // TODO: MIN(MIN(A, 23), 97) 564 return 0; 565} 566 567 568/// foldSelectICmpAnd - If one of the constants is zero (we know they can't 569/// both be) and we have an icmp instruction with zero, and we have an 'and' 570/// with the non-constant value and a power of two we can turn the select 571/// into a shift on the result of the 'and'. 572static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 573 ConstantInt *FalseVal, 574 InstCombiner::BuilderTy *Builder) { 575 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 576 if (!IC || !IC->isEquality()) 577 return 0; 578 579 if (!match(IC->getOperand(1), m_Zero())) 580 return 0; 581 582 ConstantInt *AndRHS; 583 Value *LHS = IC->getOperand(0); 584 if (LHS->getType() != SI.getType() || 585 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 586 return 0; 587 588 // If both select arms are non-zero see if we have a select of the form 589 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 590 // for 'x ? 2^n : 0' and fix the thing up at the end. 591 ConstantInt *Offset = 0; 592 if (!TrueVal->isZero() && !FalseVal->isZero()) { 593 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 594 Offset = FalseVal; 595 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 596 Offset = TrueVal; 597 else 598 return 0; 599 600 // Adjust TrueVal and FalseVal to the offset. 601 TrueVal = ConstantInt::get(Builder->getContext(), 602 TrueVal->getValue() - Offset->getValue()); 603 FalseVal = ConstantInt::get(Builder->getContext(), 604 FalseVal->getValue() - Offset->getValue()); 605 } 606 607 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 608 if (!AndRHS->getValue().isPowerOf2() || 609 (!TrueVal->getValue().isPowerOf2() && 610 !FalseVal->getValue().isPowerOf2())) 611 return 0; 612 613 // Determine which shift is needed to transform result of the 'and' into the 614 // desired result. 615 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 616 unsigned ValZeros = ValC->getValue().logBase2(); 617 unsigned AndZeros = AndRHS->getValue().logBase2(); 618 619 Value *V = LHS; 620 if (ValZeros > AndZeros) 621 V = Builder->CreateShl(V, ValZeros - AndZeros); 622 else if (ValZeros < AndZeros) 623 V = Builder->CreateLShr(V, AndZeros - ValZeros); 624 625 // Okay, now we know that everything is set up, we just don't know whether we 626 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 627 bool ShouldNotVal = !TrueVal->isZero(); 628 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 629 if (ShouldNotVal) 630 V = Builder->CreateXor(V, ValC); 631 632 // Apply an offset if needed. 633 if (Offset) 634 V = Builder->CreateAdd(V, Offset); 635 return V; 636} 637 638Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 639 Value *CondVal = SI.getCondition(); 640 Value *TrueVal = SI.getTrueValue(); 641 Value *FalseVal = SI.getFalseValue(); 642 643 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 644 return ReplaceInstUsesWith(SI, V); 645 646 if (SI.getType()->isIntegerTy(1)) { 647 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 648 if (C->getZExtValue()) { 649 // Change: A = select B, true, C --> A = or B, C 650 return BinaryOperator::CreateOr(CondVal, FalseVal); 651 } 652 // Change: A = select B, false, C --> A = and !B, C 653 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 654 return BinaryOperator::CreateAnd(NotCond, FalseVal); 655 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 656 if (C->getZExtValue() == false) { 657 // Change: A = select B, C, false --> A = and B, C 658 return BinaryOperator::CreateAnd(CondVal, TrueVal); 659 } 660 // Change: A = select B, C, true --> A = or !B, C 661 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 662 return BinaryOperator::CreateOr(NotCond, TrueVal); 663 } 664 665 // select a, b, a -> a&b 666 // select a, a, b -> a|b 667 if (CondVal == TrueVal) 668 return BinaryOperator::CreateOr(CondVal, FalseVal); 669 else if (CondVal == FalseVal) 670 return BinaryOperator::CreateAnd(CondVal, TrueVal); 671 } 672 673 // Selecting between two integer constants? 674 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 675 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 676 // select C, 1, 0 -> zext C to int 677 if (FalseValC->isZero() && TrueValC->getValue() == 1) 678 return new ZExtInst(CondVal, SI.getType()); 679 680 // select C, -1, 0 -> sext C to int 681 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 682 return new SExtInst(CondVal, SI.getType()); 683 684 // select C, 0, 1 -> zext !C to int 685 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 686 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 687 return new ZExtInst(NotCond, SI.getType()); 688 } 689 690 // select C, 0, -1 -> sext !C to int 691 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 692 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 693 return new SExtInst(NotCond, SI.getType()); 694 } 695 696 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 697 return ReplaceInstUsesWith(SI, V); 698 } 699 700 // See if we are selecting two values based on a comparison of the two values. 701 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 702 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 703 // Transform (X == Y) ? X : Y -> Y 704 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 705 // This is not safe in general for floating point: 706 // consider X== -0, Y== +0. 707 // It becomes safe if either operand is a nonzero constant. 708 ConstantFP *CFPt, *CFPf; 709 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 710 !CFPt->getValueAPF().isZero()) || 711 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 712 !CFPf->getValueAPF().isZero())) 713 return ReplaceInstUsesWith(SI, FalseVal); 714 } 715 // Transform (X une Y) ? X : Y -> X 716 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 717 // This is not safe in general for floating point: 718 // consider X== -0, Y== +0. 719 // It becomes safe if either operand is a nonzero constant. 720 ConstantFP *CFPt, *CFPf; 721 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 722 !CFPt->getValueAPF().isZero()) || 723 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 724 !CFPf->getValueAPF().isZero())) 725 return ReplaceInstUsesWith(SI, TrueVal); 726 } 727 // NOTE: if we wanted to, this is where to detect MIN/MAX 728 729 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 730 // Transform (X == Y) ? Y : X -> X 731 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 732 // This is not safe in general for floating point: 733 // consider X== -0, Y== +0. 734 // It becomes safe if either operand is a nonzero constant. 735 ConstantFP *CFPt, *CFPf; 736 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 737 !CFPt->getValueAPF().isZero()) || 738 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 739 !CFPf->getValueAPF().isZero())) 740 return ReplaceInstUsesWith(SI, FalseVal); 741 } 742 // Transform (X une Y) ? Y : X -> Y 743 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 744 // This is not safe in general for floating point: 745 // consider X== -0, Y== +0. 746 // It becomes safe if either operand is a nonzero constant. 747 ConstantFP *CFPt, *CFPf; 748 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 749 !CFPt->getValueAPF().isZero()) || 750 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 751 !CFPf->getValueAPF().isZero())) 752 return ReplaceInstUsesWith(SI, TrueVal); 753 } 754 // NOTE: if we wanted to, this is where to detect MIN/MAX 755 } 756 // NOTE: if we wanted to, this is where to detect ABS 757 } 758 759 // See if we are selecting two values based on a comparison of the two values. 760 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 761 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 762 return Result; 763 764 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 765 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 766 if (TI->hasOneUse() && FI->hasOneUse()) { 767 Instruction *AddOp = 0, *SubOp = 0; 768 769 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 770 if (TI->getOpcode() == FI->getOpcode()) 771 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 772 return IV; 773 774 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 775 // even legal for FP. 776 if ((TI->getOpcode() == Instruction::Sub && 777 FI->getOpcode() == Instruction::Add) || 778 (TI->getOpcode() == Instruction::FSub && 779 FI->getOpcode() == Instruction::FAdd)) { 780 AddOp = FI; SubOp = TI; 781 } else if ((FI->getOpcode() == Instruction::Sub && 782 TI->getOpcode() == Instruction::Add) || 783 (FI->getOpcode() == Instruction::FSub && 784 TI->getOpcode() == Instruction::FAdd)) { 785 AddOp = TI; SubOp = FI; 786 } 787 788 if (AddOp) { 789 Value *OtherAddOp = 0; 790 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 791 OtherAddOp = AddOp->getOperand(1); 792 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 793 OtherAddOp = AddOp->getOperand(0); 794 } 795 796 if (OtherAddOp) { 797 // So at this point we know we have (Y -> OtherAddOp): 798 // select C, (add X, Y), (sub X, Z) 799 Value *NegVal; // Compute -Z 800 if (SI.getType()->isFPOrFPVectorTy()) { 801 NegVal = Builder->CreateFNeg(SubOp->getOperand(1)); 802 } else { 803 NegVal = Builder->CreateNeg(SubOp->getOperand(1)); 804 } 805 806 Value *NewTrueOp = OtherAddOp; 807 Value *NewFalseOp = NegVal; 808 if (AddOp != TI) 809 std::swap(NewTrueOp, NewFalseOp); 810 Value *NewSel = 811 Builder->CreateSelect(CondVal, NewTrueOp, 812 NewFalseOp, SI.getName() + ".p"); 813 814 if (SI.getType()->isFPOrFPVectorTy()) 815 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 816 else 817 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 818 } 819 } 820 } 821 822 // See if we can fold the select into one of our operands. 823 if (SI.getType()->isIntegerTy()) { 824 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 825 return FoldI; 826 827 // MAX(MAX(a, b), a) -> MAX(a, b) 828 // MIN(MIN(a, b), a) -> MIN(a, b) 829 // MAX(MIN(a, b), a) -> a 830 // MIN(MAX(a, b), a) -> a 831 Value *LHS, *RHS, *LHS2, *RHS2; 832 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 833 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 834 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 835 SI, SPF, RHS)) 836 return R; 837 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 838 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 839 SI, SPF, LHS)) 840 return R; 841 } 842 843 // TODO. 844 // ABS(-X) -> ABS(X) 845 // ABS(ABS(X)) -> ABS(X) 846 } 847 848 // See if we can fold the select into a phi node if the condition is a select. 849 if (isa<PHINode>(SI.getCondition())) 850 // The true/false values have to be live in the PHI predecessor's blocks. 851 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 852 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 853 if (Instruction *NV = FoldOpIntoPhi(SI)) 854 return NV; 855 856 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) { 857 if (TrueSI->getCondition() == CondVal) { 858 SI.setOperand(1, TrueSI->getTrueValue()); 859 return &SI; 860 } 861 } 862 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) { 863 if (FalseSI->getCondition() == CondVal) { 864 SI.setOperand(2, FalseSI->getFalseValue()); 865 return &SI; 866 } 867 } 868 869 if (BinaryOperator::isNot(CondVal)) { 870 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 871 SI.setOperand(1, FalseVal); 872 SI.setOperand(2, TrueVal); 873 return &SI; 874 } 875 876 return 0; 877} 878