InstCombineSelect.cpp revision 46431d7a931ecc54d563a7674977a9a566b1d4fb
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 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TVI)) 231 return BinaryOperator::Create(BO->getOpcode(), FalseVal, NewSel); 232 llvm_unreachable("Unknown instruction!!"); 233 } 234 } 235 } 236 } 237 } 238 239 if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) { 240 if (FVI->hasOneUse() && FVI->getNumOperands() == 2 && 241 !isa<Constant>(TrueVal)) { 242 if (unsigned SFO = GetSelectFoldableOperands(FVI)) { 243 unsigned OpToFold = 0; 244 if ((SFO & 1) && TrueVal == FVI->getOperand(0)) { 245 OpToFold = 1; 246 } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) { 247 OpToFold = 2; 248 } 249 250 if (OpToFold) { 251 Constant *C = GetSelectFoldableConstant(FVI); 252 Value *OOp = FVI->getOperand(2-OpToFold); 253 // Avoid creating select between 2 constants unless it's selecting 254 // between 0, 1 and -1. 255 if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { 256 Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp); 257 InsertNewInstBefore(NewSel, SI); 258 NewSel->takeName(FVI); 259 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FVI)) 260 return BinaryOperator::Create(BO->getOpcode(), TrueVal, NewSel); 261 llvm_unreachable("Unknown instruction!!"); 262 } 263 } 264 } 265 } 266 } 267 268 return 0; 269} 270 271/// visitSelectInstWithICmp - Visit a SelectInst that has an 272/// ICmpInst as its first operand. 273/// 274Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, 275 ICmpInst *ICI) { 276 bool Changed = false; 277 ICmpInst::Predicate Pred = ICI->getPredicate(); 278 Value *CmpLHS = ICI->getOperand(0); 279 Value *CmpRHS = ICI->getOperand(1); 280 Value *TrueVal = SI.getTrueValue(); 281 Value *FalseVal = SI.getFalseValue(); 282 283 // Check cases where the comparison is with a constant that 284 // can be adjusted to fit the min/max idiom. We may edit ICI in 285 // place here, so make sure the select is the only user. 286 if (ICI->hasOneUse()) 287 if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { 288 // X < MIN ? T : F --> F 289 if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) 290 && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 291 return ReplaceInstUsesWith(SI, FalseVal); 292 // X > MAX ? T : F --> F 293 else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) 294 && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 295 return ReplaceInstUsesWith(SI, FalseVal); 296 switch (Pred) { 297 default: break; 298 case ICmpInst::ICMP_ULT: 299 case ICmpInst::ICMP_SLT: 300 case ICmpInst::ICMP_UGT: 301 case ICmpInst::ICMP_SGT: { 302 Constant *AdjustedRHS; 303 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) 304 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); 305 else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) 306 AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); 307 308 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 309 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 310 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 311 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) 312 ; // Nothing to do here. Values match without any sign/zero extension. 313 314 // Types do not match. Instead of calculating this with mixed types 315 // promote all to the larger type. This enables scalar evolution to 316 // analyze this expression. 317 else if (CmpRHS->getType()->getScalarSizeInBits() 318 < SI.getType()->getScalarSizeInBits()) { 319 Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, 320 SI.getType()); 321 322 // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X 323 // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X 324 // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X 325 // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X 326 if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && 327 sextRHS == FalseVal) { 328 CmpLHS = TrueVal; 329 AdjustedRHS = sextRHS; 330 } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && 331 sextRHS == TrueVal) { 332 CmpLHS = FalseVal; 333 AdjustedRHS = sextRHS; 334 } else if (ICI->isUnsigned()) { 335 Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, 336 SI.getType()); 337 // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X 338 // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X 339 // zext + signed compare cannot be changed: 340 // 0xff <s 0x00, but 0x00ff >s 0x0000 341 if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && 342 zextRHS == FalseVal) { 343 CmpLHS = TrueVal; 344 AdjustedRHS = zextRHS; 345 } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && 346 zextRHS == TrueVal) { 347 CmpLHS = FalseVal; 348 AdjustedRHS = zextRHS; 349 } else 350 break; 351 } else 352 break; 353 } else 354 break; 355 356 Pred = ICmpInst::getSwappedPredicate(Pred); 357 CmpRHS = AdjustedRHS; 358 std::swap(FalseVal, TrueVal); 359 ICI->setPredicate(Pred); 360 ICI->setOperand(0, CmpLHS); 361 ICI->setOperand(1, CmpRHS); 362 SI.setOperand(1, TrueVal); 363 SI.setOperand(2, FalseVal); 364 Changed = true; 365 break; 366 } 367 } 368 } 369 370 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 371 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 372 // FIXME: Type and constness constraints could be lifted, but we have to 373 // watch code size carefully. We should consider xor instead of 374 // sub/add when we decide to do that. 375 if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 376 if (TrueVal->getType() == Ty) { 377 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 378 ConstantInt *C1 = NULL, *C2 = NULL; 379 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 380 C1 = dyn_cast<ConstantInt>(TrueVal); 381 C2 = dyn_cast<ConstantInt>(FalseVal); 382 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 383 C1 = dyn_cast<ConstantInt>(FalseVal); 384 C2 = dyn_cast<ConstantInt>(TrueVal); 385 } 386 if (C1 && C2) { 387 // This shift results in either -1 or 0. 388 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 389 390 // Check if we can express the operation with a single or. 391 if (C2->isAllOnesValue()) 392 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 393 394 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 395 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 396 } 397 } 398 } 399 } 400 401 if (CmpLHS == TrueVal && CmpRHS == FalseVal) { 402 // Transform (X == Y) ? X : Y -> Y 403 if (Pred == ICmpInst::ICMP_EQ) 404 return ReplaceInstUsesWith(SI, FalseVal); 405 // Transform (X != Y) ? X : Y -> X 406 if (Pred == ICmpInst::ICMP_NE) 407 return ReplaceInstUsesWith(SI, TrueVal); 408 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 409 410 } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) { 411 // Transform (X == Y) ? Y : X -> X 412 if (Pred == ICmpInst::ICMP_EQ) 413 return ReplaceInstUsesWith(SI, FalseVal); 414 // Transform (X != Y) ? Y : X -> Y 415 if (Pred == ICmpInst::ICMP_NE) 416 return ReplaceInstUsesWith(SI, TrueVal); 417 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 418 } 419 return Changed ? &SI : 0; 420} 421 422 423/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 424/// PHI node (but the two may be in different blocks). See if the true/false 425/// values (V) are live in all of the predecessor blocks of the PHI. For 426/// example, cases like this cannot be mapped: 427/// 428/// X = phi [ C1, BB1], [C2, BB2] 429/// Y = add 430/// Z = select X, Y, 0 431/// 432/// because Y is not live in BB1/BB2. 433/// 434static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 435 const SelectInst &SI) { 436 // If the value is a non-instruction value like a constant or argument, it 437 // can always be mapped. 438 const Instruction *I = dyn_cast<Instruction>(V); 439 if (I == 0) return true; 440 441 // If V is a PHI node defined in the same block as the condition PHI, we can 442 // map the arguments. 443 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 444 445 if (const PHINode *VP = dyn_cast<PHINode>(I)) 446 if (VP->getParent() == CondPHI->getParent()) 447 return true; 448 449 // Otherwise, if the PHI and select are defined in the same block and if V is 450 // defined in a different block, then we can transform it. 451 if (SI.getParent() == CondPHI->getParent() && 452 I->getParent() != CondPHI->getParent()) 453 return true; 454 455 // Otherwise we have a 'hard' case and we can't tell without doing more 456 // detailed dominator based analysis, punt. 457 return false; 458} 459 460/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 461/// SPF2(SPF1(A, B), C) 462Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 463 SelectPatternFlavor SPF1, 464 Value *A, Value *B, 465 Instruction &Outer, 466 SelectPatternFlavor SPF2, Value *C) { 467 if (C == A || C == B) { 468 // MAX(MAX(A, B), B) -> MAX(A, B) 469 // MIN(MIN(a, b), a) -> MIN(a, b) 470 if (SPF1 == SPF2) 471 return ReplaceInstUsesWith(Outer, Inner); 472 473 // MAX(MIN(a, b), a) -> a 474 // MIN(MAX(a, b), a) -> a 475 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 476 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 477 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 478 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 479 return ReplaceInstUsesWith(Outer, C); 480 } 481 482 // TODO: MIN(MIN(A, 23), 97) 483 return 0; 484} 485 486 487/// foldSelectICmpAnd - If one of the constants is zero (we know they can't 488/// both be) and we have an icmp instruction with zero, and we have an 'and' 489/// with the non-constant value and a power of two we can turn the select 490/// into a shift on the result of the 'and'. 491static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 492 ConstantInt *FalseVal, 493 InstCombiner::BuilderTy *Builder) { 494 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 495 if (!IC || !IC->isEquality()) 496 return 0; 497 498 if (ConstantInt *C = dyn_cast<ConstantInt>(IC->getOperand(1))) 499 if (!C->isZero()) 500 return 0; 501 502 ConstantInt *AndRHS; 503 Value *LHS = IC->getOperand(0); 504 if (LHS->getType() != SI.getType() || 505 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 506 return 0; 507 508 // If both select arms are non-zero see if we have a select of the form 509 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 510 // for 'x ? 2^n : 0' and fix the thing up at the end. 511 ConstantInt *Offset = 0; 512 if (!TrueVal->isZero() && !FalseVal->isZero()) { 513 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 514 Offset = FalseVal; 515 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 516 Offset = TrueVal; 517 else 518 return 0; 519 520 // Adjust TrueVal and FalseVal to the offset. 521 TrueVal = ConstantInt::get(Builder->getContext(), 522 TrueVal->getValue() - Offset->getValue()); 523 FalseVal = ConstantInt::get(Builder->getContext(), 524 FalseVal->getValue() - Offset->getValue()); 525 } 526 527 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 528 if (!AndRHS->getValue().isPowerOf2() || 529 (!TrueVal->getValue().isPowerOf2() && 530 !FalseVal->getValue().isPowerOf2())) 531 return 0; 532 533 // Determine which shift is needed to transform result of the 'and' into the 534 // desired result. 535 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 536 unsigned ValZeros = ValC->getValue().logBase2(); 537 unsigned AndZeros = AndRHS->getValue().logBase2(); 538 539 Value *V = LHS; 540 if (ValZeros > AndZeros) 541 V = Builder->CreateShl(V, ValZeros - AndZeros); 542 else if (ValZeros < AndZeros) 543 V = Builder->CreateLShr(V, AndZeros - ValZeros); 544 545 // Okay, now we know that everything is set up, we just don't know whether we 546 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 547 bool ShouldNotVal = !TrueVal->isZero(); 548 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 549 if (ShouldNotVal) 550 V = Builder->CreateXor(V, ValC); 551 552 // Apply an offset if needed. 553 if (Offset) 554 V = Builder->CreateAdd(V, Offset); 555 return V; 556} 557 558Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 559 Value *CondVal = SI.getCondition(); 560 Value *TrueVal = SI.getTrueValue(); 561 Value *FalseVal = SI.getFalseValue(); 562 563 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 564 return ReplaceInstUsesWith(SI, V); 565 566 if (SI.getType()->isIntegerTy(1)) { 567 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 568 if (C->getZExtValue()) { 569 // Change: A = select B, true, C --> A = or B, C 570 return BinaryOperator::CreateOr(CondVal, FalseVal); 571 } 572 // Change: A = select B, false, C --> A = and !B, C 573 Value *NotCond = 574 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 575 "not."+CondVal->getName()), SI); 576 return BinaryOperator::CreateAnd(NotCond, FalseVal); 577 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 578 if (C->getZExtValue() == false) { 579 // Change: A = select B, C, false --> A = and B, C 580 return BinaryOperator::CreateAnd(CondVal, TrueVal); 581 } 582 // Change: A = select B, C, true --> A = or !B, C 583 Value *NotCond = 584 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 585 "not."+CondVal->getName()), SI); 586 return BinaryOperator::CreateOr(NotCond, TrueVal); 587 } 588 589 // select a, b, a -> a&b 590 // select a, a, b -> a|b 591 if (CondVal == TrueVal) 592 return BinaryOperator::CreateOr(CondVal, FalseVal); 593 else if (CondVal == FalseVal) 594 return BinaryOperator::CreateAnd(CondVal, TrueVal); 595 } 596 597 // Selecting between two integer constants? 598 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 599 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 600 // select C, 1, 0 -> zext C to int 601 if (FalseValC->isZero() && TrueValC->getValue() == 1) 602 return new ZExtInst(CondVal, SI.getType()); 603 604 // select C, -1, 0 -> sext C to int 605 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 606 return new SExtInst(CondVal, SI.getType()); 607 608 // select C, 0, 1 -> zext !C to int 609 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 610 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 611 return new ZExtInst(NotCond, SI.getType()); 612 } 613 614 // select C, 0, -1 -> sext !C to int 615 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 616 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 617 return new SExtInst(NotCond, SI.getType()); 618 } 619 620 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 621 return ReplaceInstUsesWith(SI, V); 622 } 623 624 // See if we are selecting two values based on a comparison of the two values. 625 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 626 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 627 // Transform (X == Y) ? X : Y -> Y 628 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 629 // This is not safe in general for floating point: 630 // consider X== -0, Y== +0. 631 // It becomes safe if either operand is a nonzero constant. 632 ConstantFP *CFPt, *CFPf; 633 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 634 !CFPt->getValueAPF().isZero()) || 635 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 636 !CFPf->getValueAPF().isZero())) 637 return ReplaceInstUsesWith(SI, FalseVal); 638 } 639 // Transform (X une Y) ? X : Y -> X 640 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 641 // This is not safe in general for floating point: 642 // consider X== -0, Y== +0. 643 // It becomes safe if either operand is a nonzero constant. 644 ConstantFP *CFPt, *CFPf; 645 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 646 !CFPt->getValueAPF().isZero()) || 647 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 648 !CFPf->getValueAPF().isZero())) 649 return ReplaceInstUsesWith(SI, TrueVal); 650 } 651 // NOTE: if we wanted to, this is where to detect MIN/MAX 652 653 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 654 // Transform (X == Y) ? Y : X -> X 655 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 656 // This is not safe in general for floating point: 657 // consider X== -0, Y== +0. 658 // It becomes safe if either operand is a nonzero constant. 659 ConstantFP *CFPt, *CFPf; 660 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 661 !CFPt->getValueAPF().isZero()) || 662 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 663 !CFPf->getValueAPF().isZero())) 664 return ReplaceInstUsesWith(SI, FalseVal); 665 } 666 // Transform (X une Y) ? Y : X -> Y 667 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 668 // This is not safe in general for floating point: 669 // consider X== -0, Y== +0. 670 // It becomes safe if either operand is a nonzero constant. 671 ConstantFP *CFPt, *CFPf; 672 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 673 !CFPt->getValueAPF().isZero()) || 674 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 675 !CFPf->getValueAPF().isZero())) 676 return ReplaceInstUsesWith(SI, TrueVal); 677 } 678 // NOTE: if we wanted to, this is where to detect MIN/MAX 679 } 680 // NOTE: if we wanted to, this is where to detect ABS 681 } 682 683 // See if we are selecting two values based on a comparison of the two values. 684 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 685 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 686 return Result; 687 688 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 689 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 690 if (TI->hasOneUse() && FI->hasOneUse()) { 691 Instruction *AddOp = 0, *SubOp = 0; 692 693 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 694 if (TI->getOpcode() == FI->getOpcode()) 695 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 696 return IV; 697 698 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 699 // even legal for FP. 700 if ((TI->getOpcode() == Instruction::Sub && 701 FI->getOpcode() == Instruction::Add) || 702 (TI->getOpcode() == Instruction::FSub && 703 FI->getOpcode() == Instruction::FAdd)) { 704 AddOp = FI; SubOp = TI; 705 } else if ((FI->getOpcode() == Instruction::Sub && 706 TI->getOpcode() == Instruction::Add) || 707 (FI->getOpcode() == Instruction::FSub && 708 TI->getOpcode() == Instruction::FAdd)) { 709 AddOp = TI; SubOp = FI; 710 } 711 712 if (AddOp) { 713 Value *OtherAddOp = 0; 714 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 715 OtherAddOp = AddOp->getOperand(1); 716 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 717 OtherAddOp = AddOp->getOperand(0); 718 } 719 720 if (OtherAddOp) { 721 // So at this point we know we have (Y -> OtherAddOp): 722 // select C, (add X, Y), (sub X, Z) 723 Value *NegVal; // Compute -Z 724 if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) { 725 NegVal = ConstantExpr::getNeg(C); 726 } else if (SI.getType()->isFloatingPointTy()) { 727 NegVal = InsertNewInstBefore( 728 BinaryOperator::CreateFNeg(SubOp->getOperand(1), 729 "tmp"), SI); 730 } else { 731 NegVal = InsertNewInstBefore( 732 BinaryOperator::CreateNeg(SubOp->getOperand(1), 733 "tmp"), SI); 734 } 735 736 Value *NewTrueOp = OtherAddOp; 737 Value *NewFalseOp = NegVal; 738 if (AddOp != TI) 739 std::swap(NewTrueOp, NewFalseOp); 740 Instruction *NewSel = 741 SelectInst::Create(CondVal, NewTrueOp, 742 NewFalseOp, SI.getName() + ".p"); 743 744 NewSel = InsertNewInstBefore(NewSel, SI); 745 if (SI.getType()->isFloatingPointTy()) 746 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 747 else 748 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 749 } 750 } 751 } 752 753 // See if we can fold the select into one of our operands. 754 if (SI.getType()->isIntegerTy()) { 755 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 756 return FoldI; 757 758 // MAX(MAX(a, b), a) -> MAX(a, b) 759 // MIN(MIN(a, b), a) -> MIN(a, b) 760 // MAX(MIN(a, b), a) -> a 761 // MIN(MAX(a, b), a) -> a 762 Value *LHS, *RHS, *LHS2, *RHS2; 763 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 764 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 765 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 766 SI, SPF, RHS)) 767 return R; 768 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 769 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 770 SI, SPF, LHS)) 771 return R; 772 } 773 774 // TODO. 775 // ABS(-X) -> ABS(X) 776 // ABS(ABS(X)) -> ABS(X) 777 } 778 779 // See if we can fold the select into a phi node if the condition is a select. 780 if (isa<PHINode>(SI.getCondition())) 781 // The true/false values have to be live in the PHI predecessor's blocks. 782 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 783 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 784 if (Instruction *NV = FoldOpIntoPhi(SI)) 785 return NV; 786 787 if (BinaryOperator::isNot(CondVal)) { 788 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 789 SI.setOperand(1, FalseVal); 790 SI.setOperand(2, TrueVal); 791 return &SI; 792 } 793 794 return 0; 795} 796