InstCombineSelect.cpp revision e87ca454ba39e57a34acab42e4391045d4c8c6cf
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" 17using namespace llvm; 18using 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. 23static SelectPatternFlavor 24MatchSelectPattern(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/// 83static 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. 103static 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. 123Instruction *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 SelectInst *NewSI = SelectInst::Create(SI.getCondition(), TI->getOperand(0), 137 FI->getOperand(0), SI.getName()+".v"); 138 InsertNewInstBefore(NewSI, SI); 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 SelectInst *NewSI = SelectInst::Create(SI.getCondition(), OtherOpT, 178 OtherOpF, SI.getName()+".v"); 179 InsertNewInstBefore(NewSI, SI); 180 181 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) { 182 if (MatchIsOpZero) 183 return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI); 184 else 185 return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp); 186 } 187 llvm_unreachable("Shouldn't get here"); 188 return 0; 189} 190 191static bool isSelect01(Constant *C1, Constant *C2) { 192 ConstantInt *C1I = dyn_cast<ConstantInt>(C1); 193 if (!C1I) 194 return false; 195 ConstantInt *C2I = dyn_cast<ConstantInt>(C2); 196 if (!C2I) 197 return false; 198 if (!C1I->isZero() && !C2I->isZero()) // One side must be zero. 199 return false; 200 return C1I->isOne() || C1I->isAllOnesValue() || 201 C2I->isOne() || C2I->isAllOnesValue(); 202} 203 204/// FoldSelectIntoOp - Try fold the select into one of the operands to 205/// facilitate further optimization. 206Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal, 207 Value *FalseVal) { 208 // See the comment above GetSelectFoldableOperands for a description of the 209 // transformation we are doing here. 210 if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) { 211 if (TVI->hasOneUse() && TVI->getNumOperands() == 2 && 212 !isa<Constant>(FalseVal)) { 213 if (unsigned SFO = GetSelectFoldableOperands(TVI)) { 214 unsigned OpToFold = 0; 215 if ((SFO & 1) && FalseVal == TVI->getOperand(0)) { 216 OpToFold = 1; 217 } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) { 218 OpToFold = 2; 219 } 220 221 if (OpToFold) { 222 Constant *C = GetSelectFoldableConstant(TVI); 223 Value *OOp = TVI->getOperand(2-OpToFold); 224 // Avoid creating select between 2 constants unless it's selecting 225 // between 0, 1 and -1. 226 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 227 Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C); 228 InsertNewInstBefore(NewSel, SI); 229 NewSel->takeName(TVI); 230 BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI); 231 BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(), 232 FalseVal, NewSel); 233 if (isa<PossiblyExactOperator>(BO)) 234 BO->setIsExact(TVI_BO->isExact()); 235 if (isa<OverflowingBinaryOperator>(BO)) { 236 BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap()); 237 BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap()); 238 } 239 return BO; 240 } 241 } 242 } 243 } 244 } 245 246 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) { 247 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 && 248 !isa<Constant>(TrueVal)) { 249 if (unsigned SFO = GetSelectFoldableOperands(FVI)) { 250 unsigned OpToFold = 0; 251 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) { 252 OpToFold = 1; 253 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) { 254 OpToFold = 2; 255 } 256 257 if (OpToFold) { 258 Constant *C = GetSelectFoldableConstant(FVI); 259 Value *OOp = FVI->getOperand(2-OpToFold); 260 // Avoid creating select between 2 constants unless it's selecting 261 // between 0, 1 and -1. 262 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 263 Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp); 264 InsertNewInstBefore(NewSel, SI); 265 NewSel->takeName(FVI); 266 BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI); 267 BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(), 268 TrueVal, NewSel); 269 if (isa<PossiblyExactOperator>(BO)) 270 BO->setIsExact(FVI_BO->isExact()); 271 if (isa<OverflowingBinaryOperator>(BO)) { 272 BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap()); 273 BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap()); 274 } 275 return BO; 276 } 277 } 278 } 279 } 280 } 281 282 return 0; 283} 284 285/// visitSelectInstWithICmp - Visit a SelectInst that has an 286/// ICmpInst as its first operand. 287/// 288Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 289 ICmpInst *ICI) { 290 bool Changed = false; 291 ICmpInst::Predicate Pred = ICI->getPredicate(); 292 Value *CmpLHS = ICI->getOperand(0); 293 Value *CmpRHS = ICI->getOperand(1); 294 Value *TrueVal = SI.getTrueValue(); 295 Value *FalseVal = SI.getFalseValue(); 296 297 // Check cases where the comparison is with a constant that 298 // can be adjusted to fit the min/max idiom. We may move or edit ICI 299 // here, so make sure the select is the only user. 300 if (ICI->hasOneUse()) 301 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 302 // X < MIN ? T : F --> F 303 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) 304 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 305 return ReplaceInstUsesWith(SI, FalseVal); 306 // X > MAX ? T : F --> F 307 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) 308 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 309 return ReplaceInstUsesWith(SI, FalseVal); 310 switch (Pred) { 311 default: break; 312 case ICmpInst::ICMP_ULT: 313 case ICmpInst::ICMP_SLT: 314 case ICmpInst::ICMP_UGT: 315 case ICmpInst::ICMP_SGT: { 316 // These transformations only work for selects over integers. 317 const IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType()); 318 if (!SelectTy) 319 break; 320 321 Constant *AdjustedRHS; 322 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) 323 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); 324 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) 325 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); 326 327 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 328 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 329 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 330 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) 331 ; // Nothing to do here. Values match without any sign/zero extension. 332 333 // Types do not match. Instead of calculating this with mixed types 334 // promote all to the larger type. This enables scalar evolution to 335 // analyze this expression. 336 else if (CmpRHS->getType()->getScalarSizeInBits() 337 < SelectTy->getBitWidth()) { 338 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy); 339 340 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X 341 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X 342 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X 343 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X 344 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && 345 sextRHS == FalseVal) { 346 CmpLHS = TrueVal; 347 AdjustedRHS = sextRHS; 348 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && 349 sextRHS == TrueVal) { 350 CmpLHS = FalseVal; 351 AdjustedRHS = sextRHS; 352 } else if (ICI->isUnsigned()) { 353 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy); 354 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X 355 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X 356 // zext + signed compare cannot be changed: 357 // 0xff <s 0x00, but 0x00ff >s 0x0000 358 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && 359 zextRHS == FalseVal) { 360 CmpLHS = TrueVal; 361 AdjustedRHS = zextRHS; 362 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && 363 zextRHS == TrueVal) { 364 CmpLHS = FalseVal; 365 AdjustedRHS = zextRHS; 366 } else 367 break; 368 } else 369 break; 370 } else 371 break; 372 373 Pred = ICmpInst::getSwappedPredicate(Pred); 374 CmpRHS = AdjustedRHS; 375 std::swap(FalseVal, TrueVal); 376 ICI->setPredicate(Pred); 377 ICI->setOperand(0, CmpLHS); 378 ICI->setOperand(1, CmpRHS); 379 SI.setOperand(1, TrueVal); 380 SI.setOperand(2, FalseVal); 381 382 // Move ICI instruction right before the select instruction. Otherwise 383 // the sext/zext value may be defined after the ICI instruction uses it. 384 ICI->moveBefore(&SI); 385 386 Changed = true; 387 break; 388 } 389 } 390 } 391 392 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 393 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 394 // FIXME: Type and constness constraints could be lifted, but we have to 395 // watch code size carefully. We should consider xor instead of 396 // sub/add when we decide to do that. 397 if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 398 if (TrueVal->getType() == Ty) { 399 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 400 ConstantInt *C1 = NULL, *C2 = NULL; 401 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 402 C1 = dyn_cast<ConstantInt>(TrueVal); 403 C2 = dyn_cast<ConstantInt>(FalseVal); 404 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 405 C1 = dyn_cast<ConstantInt>(FalseVal); 406 C2 = dyn_cast<ConstantInt>(TrueVal); 407 } 408 if (C1 && C2) { 409 // This shift results in either -1 or 0. 410 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 411 412 // Check if we can express the operation with a single or. 413 if (C2->isAllOnesValue()) 414 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 415 416 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 417 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 418 } 419 } 420 } 421 } 422 423 if (CmpLHS == TrueVal && CmpRHS == FalseVal) { 424 // Transform (X == Y) ? X : Y -> Y 425 if (Pred == ICmpInst::ICMP_EQ) 426 return ReplaceInstUsesWith(SI, FalseVal); 427 // Transform (X != Y) ? X : Y -> X 428 if (Pred == ICmpInst::ICMP_NE) 429 return ReplaceInstUsesWith(SI, TrueVal); 430 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 431 432 } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) { 433 // Transform (X == Y) ? Y : X -> X 434 if (Pred == ICmpInst::ICMP_EQ) 435 return ReplaceInstUsesWith(SI, FalseVal); 436 // Transform (X != Y) ? Y : X -> Y 437 if (Pred == ICmpInst::ICMP_NE) 438 return ReplaceInstUsesWith(SI, TrueVal); 439 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 440 } 441 442 if (isa<Constant>(CmpRHS)) { 443 if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) { 444 // Transform (X == C) ? X : Y -> (X == C) ? C : Y 445 SI.setOperand(1, CmpRHS); 446 Changed = true; 447 } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) { 448 // Transform (X != C) ? Y : X -> (X != C) ? Y : C 449 SI.setOperand(2, CmpRHS); 450 Changed = true; 451 } 452 } 453 454 return Changed ? &SI : 0; 455} 456 457 458/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 459/// PHI node (but the two may be in different blocks). See if the true/false 460/// values (V) are live in all of the predecessor blocks of the PHI. For 461/// example, cases like this cannot be mapped: 462/// 463/// X = phi [ C1, BB1], [C2, BB2] 464/// Y = add 465/// Z = select X, Y, 0 466/// 467/// because Y is not live in BB1/BB2. 468/// 469static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 470 const SelectInst &SI) { 471 // If the value is a non-instruction value like a constant or argument, it 472 // can always be mapped. 473 const Instruction *I = dyn_cast<Instruction>(V); 474 if (I == 0) return true; 475 476 // If V is a PHI node defined in the same block as the condition PHI, we can 477 // map the arguments. 478 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 479 480 if (const PHINode *VP = dyn_cast<PHINode>(I)) 481 if (VP->getParent() == CondPHI->getParent()) 482 return true; 483 484 // Otherwise, if the PHI and select are defined in the same block and if V is 485 // defined in a different block, then we can transform it. 486 if (SI.getParent() == CondPHI->getParent() && 487 I->getParent() != CondPHI->getParent()) 488 return true; 489 490 // Otherwise we have a 'hard' case and we can't tell without doing more 491 // detailed dominator based analysis, punt. 492 return false; 493} 494 495/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 496/// SPF2(SPF1(A, B), C) 497Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 498 SelectPatternFlavor SPF1, 499 Value *A, Value *B, 500 Instruction &Outer, 501 SelectPatternFlavor SPF2, Value *C) { 502 if (C == A || C == B) { 503 // MAX(MAX(A, B), B) -> MAX(A, B) 504 // MIN(MIN(a, b), a) -> MIN(a, b) 505 if (SPF1 == SPF2) 506 return ReplaceInstUsesWith(Outer, Inner); 507 508 // MAX(MIN(a, b), a) -> a 509 // MIN(MAX(a, b), a) -> a 510 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 511 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 512 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 513 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 514 return ReplaceInstUsesWith(Outer, C); 515 } 516 517 // TODO: MIN(MIN(A, 23), 97) 518 return 0; 519} 520 521 522/// foldSelectICmpAnd - If one of the constants is zero (we know they can't 523/// both be) and we have an icmp instruction with zero, and we have an 'and' 524/// with the non-constant value and a power of two we can turn the select 525/// into a shift on the result of the 'and'. 526static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 527 ConstantInt *FalseVal, 528 InstCombiner::BuilderTy *Builder) { 529 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 530 if (!IC || !IC->isEquality()) 531 return 0; 532 533 if (!match(IC->getOperand(1), m_Zero())) 534 return 0; 535 536 ConstantInt *AndRHS; 537 Value *LHS = IC->getOperand(0); 538 if (LHS->getType() != SI.getType() || 539 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 540 return 0; 541 542 // If both select arms are non-zero see if we have a select of the form 543 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 544 // for 'x ? 2^n : 0' and fix the thing up at the end. 545 ConstantInt *Offset = 0; 546 if (!TrueVal->isZero() && !FalseVal->isZero()) { 547 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 548 Offset = FalseVal; 549 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 550 Offset = TrueVal; 551 else 552 return 0; 553 554 // Adjust TrueVal and FalseVal to the offset. 555 TrueVal = ConstantInt::get(Builder->getContext(), 556 TrueVal->getValue() - Offset->getValue()); 557 FalseVal = ConstantInt::get(Builder->getContext(), 558 FalseVal->getValue() - Offset->getValue()); 559 } 560 561 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 562 if (!AndRHS->getValue().isPowerOf2() || 563 (!TrueVal->getValue().isPowerOf2() && 564 !FalseVal->getValue().isPowerOf2())) 565 return 0; 566 567 // Determine which shift is needed to transform result of the 'and' into the 568 // desired result. 569 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 570 unsigned ValZeros = ValC->getValue().logBase2(); 571 unsigned AndZeros = AndRHS->getValue().logBase2(); 572 573 Value *V = LHS; 574 if (ValZeros > AndZeros) 575 V = Builder->CreateShl(V, ValZeros - AndZeros); 576 else if (ValZeros < AndZeros) 577 V = Builder->CreateLShr(V, AndZeros - ValZeros); 578 579 // Okay, now we know that everything is set up, we just don't know whether we 580 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 581 bool ShouldNotVal = !TrueVal->isZero(); 582 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 583 if (ShouldNotVal) 584 V = Builder->CreateXor(V, ValC); 585 586 // Apply an offset if needed. 587 if (Offset) 588 V = Builder->CreateAdd(V, Offset); 589 return V; 590} 591 592Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 593 Value *CondVal = SI.getCondition(); 594 Value *TrueVal = SI.getTrueValue(); 595 Value *FalseVal = SI.getFalseValue(); 596 597 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 598 return ReplaceInstUsesWith(SI, V); 599 600 if (SI.getType()->isIntegerTy(1)) { 601 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 602 if (C->getZExtValue()) { 603 // Change: A = select B, true, C --> A = or B, C 604 return BinaryOperator::CreateOr(CondVal, FalseVal); 605 } 606 // Change: A = select B, false, C --> A = and !B, C 607 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 608 return BinaryOperator::CreateAnd(NotCond, FalseVal); 609 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 610 if (C->getZExtValue() == false) { 611 // Change: A = select B, C, false --> A = and B, C 612 return BinaryOperator::CreateAnd(CondVal, TrueVal); 613 } 614 // Change: A = select B, C, true --> A = or !B, C 615 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 616 return BinaryOperator::CreateOr(NotCond, TrueVal); 617 } 618 619 // select a, b, a -> a&b 620 // select a, a, b -> a|b 621 if (CondVal == TrueVal) 622 return BinaryOperator::CreateOr(CondVal, FalseVal); 623 else if (CondVal == FalseVal) 624 return BinaryOperator::CreateAnd(CondVal, TrueVal); 625 } 626 627 // Selecting between two integer constants? 628 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 629 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 630 // select C, 1, 0 -> zext C to int 631 if (FalseValC->isZero() && TrueValC->getValue() == 1) 632 return new ZExtInst(CondVal, SI.getType()); 633 634 // select C, -1, 0 -> sext C to int 635 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 636 return new SExtInst(CondVal, SI.getType()); 637 638 // select C, 0, 1 -> zext !C to int 639 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 640 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 641 return new ZExtInst(NotCond, SI.getType()); 642 } 643 644 // select C, 0, -1 -> sext !C to int 645 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 646 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 647 return new SExtInst(NotCond, SI.getType()); 648 } 649 650 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 651 return ReplaceInstUsesWith(SI, V); 652 } 653 654 // See if we are selecting two values based on a comparison of the two values. 655 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 656 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 657 // Transform (X == Y) ? X : Y -> Y 658 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 659 // This is not safe in general for floating point: 660 // consider X== -0, Y== +0. 661 // It becomes safe if either operand is a nonzero constant. 662 ConstantFP *CFPt, *CFPf; 663 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 664 !CFPt->getValueAPF().isZero()) || 665 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 666 !CFPf->getValueAPF().isZero())) 667 return ReplaceInstUsesWith(SI, FalseVal); 668 } 669 // Transform (X une Y) ? X : Y -> X 670 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 671 // This is not safe in general for floating point: 672 // consider X== -0, Y== +0. 673 // It becomes safe if either operand is a nonzero constant. 674 ConstantFP *CFPt, *CFPf; 675 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 676 !CFPt->getValueAPF().isZero()) || 677 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 678 !CFPf->getValueAPF().isZero())) 679 return ReplaceInstUsesWith(SI, TrueVal); 680 } 681 // NOTE: if we wanted to, this is where to detect MIN/MAX 682 683 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 684 // Transform (X == Y) ? Y : X -> X 685 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 686 // This is not safe in general for floating point: 687 // consider X== -0, Y== +0. 688 // It becomes safe if either operand is a nonzero constant. 689 ConstantFP *CFPt, *CFPf; 690 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 691 !CFPt->getValueAPF().isZero()) || 692 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 693 !CFPf->getValueAPF().isZero())) 694 return ReplaceInstUsesWith(SI, FalseVal); 695 } 696 // Transform (X une Y) ? Y : X -> Y 697 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 698 // This is not safe in general for floating point: 699 // consider X== -0, Y== +0. 700 // It becomes safe if either operand is a nonzero constant. 701 ConstantFP *CFPt, *CFPf; 702 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 703 !CFPt->getValueAPF().isZero()) || 704 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 705 !CFPf->getValueAPF().isZero())) 706 return ReplaceInstUsesWith(SI, TrueVal); 707 } 708 // NOTE: if we wanted to, this is where to detect MIN/MAX 709 } 710 // NOTE: if we wanted to, this is where to detect ABS 711 } 712 713 // See if we are selecting two values based on a comparison of the two values. 714 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 715 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 716 return Result; 717 718 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 719 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 720 if (TI->hasOneUse() && FI->hasOneUse()) { 721 Instruction *AddOp = 0, *SubOp = 0; 722 723 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 724 if (TI->getOpcode() == FI->getOpcode()) 725 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 726 return IV; 727 728 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 729 // even legal for FP. 730 if ((TI->getOpcode() == Instruction::Sub && 731 FI->getOpcode() == Instruction::Add) || 732 (TI->getOpcode() == Instruction::FSub && 733 FI->getOpcode() == Instruction::FAdd)) { 734 AddOp = FI; SubOp = TI; 735 } else if ((FI->getOpcode() == Instruction::Sub && 736 TI->getOpcode() == Instruction::Add) || 737 (FI->getOpcode() == Instruction::FSub && 738 TI->getOpcode() == Instruction::FAdd)) { 739 AddOp = TI; SubOp = FI; 740 } 741 742 if (AddOp) { 743 Value *OtherAddOp = 0; 744 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 745 OtherAddOp = AddOp->getOperand(1); 746 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 747 OtherAddOp = AddOp->getOperand(0); 748 } 749 750 if (OtherAddOp) { 751 // So at this point we know we have (Y -> OtherAddOp): 752 // select C, (add X, Y), (sub X, Z) 753 Value *NegVal; // Compute -Z 754 if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) { 755 NegVal = ConstantExpr::getNeg(C); 756 } else if (SI.getType()->isFloatingPointTy()) { 757 NegVal = InsertNewInstBefore( 758 BinaryOperator::CreateFNeg(SubOp->getOperand(1), 759 "tmp"), SI); 760 } else { 761 NegVal = InsertNewInstBefore( 762 BinaryOperator::CreateNeg(SubOp->getOperand(1), 763 "tmp"), SI); 764 } 765 766 Value *NewTrueOp = OtherAddOp; 767 Value *NewFalseOp = NegVal; 768 if (AddOp != TI) 769 std::swap(NewTrueOp, NewFalseOp); 770 Instruction *NewSel = 771 SelectInst::Create(CondVal, NewTrueOp, 772 NewFalseOp, SI.getName() + ".p"); 773 774 NewSel = InsertNewInstBefore(NewSel, SI); 775 if (SI.getType()->isFloatingPointTy()) 776 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 777 else 778 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 779 } 780 } 781 } 782 783 // See if we can fold the select into one of our operands. 784 if (SI.getType()->isIntegerTy()) { 785 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 786 return FoldI; 787 788 // MAX(MAX(a, b), a) -> MAX(a, b) 789 // MIN(MIN(a, b), a) -> MIN(a, b) 790 // MAX(MIN(a, b), a) -> a 791 // MIN(MAX(a, b), a) -> a 792 Value *LHS, *RHS, *LHS2, *RHS2; 793 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 794 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 795 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 796 SI, SPF, RHS)) 797 return R; 798 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 799 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 800 SI, SPF, LHS)) 801 return R; 802 } 803 804 // TODO. 805 // ABS(-X) -> ABS(X) 806 // ABS(ABS(X)) -> ABS(X) 807 } 808 809 // See if we can fold the select into a phi node if the condition is a select. 810 if (isa<PHINode>(SI.getCondition())) 811 // The true/false values have to be live in the PHI predecessor's blocks. 812 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 813 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 814 if (Instruction *NV = FoldOpIntoPhi(SI)) 815 return NV; 816 817 if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) { 818 if (TrueSI->getCondition() == CondVal) { 819 SI.setOperand(1, TrueSI->getTrueValue()); 820 return &SI; 821 } 822 } 823 if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) { 824 if (FalseSI->getCondition() == CondVal) { 825 SI.setOperand(2, FalseSI->getFalseValue()); 826 return &SI; 827 } 828 } 829 830 if (BinaryOperator::isNot(CondVal)) { 831 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 832 SI.setOperand(1, FalseVal); 833 SI.setOperand(2, TrueVal); 834 return &SI; 835 } 836 837 return 0; 838} 839