InstCombineSelect.cpp revision 4ac19470dc26decba85f5bf4dd7e6edb54d77152
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 switch (Pred) { 289 default: break; 290 case ICmpInst::ICMP_ULT: 291 case ICmpInst::ICMP_SLT: { 292 // X < MIN ? T : F --> F 293 if (CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) 294 return ReplaceInstUsesWith(SI, FalseVal); 295 // X < C ? X : C-1 --> X > C-1 ? C-1 : X 296 Constant *AdjustedRHS = 297 ConstantInt::get(CI->getContext(), CI->getValue()-1); 298 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 299 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) { 300 Pred = ICmpInst::getSwappedPredicate(Pred); 301 CmpRHS = AdjustedRHS; 302 std::swap(FalseVal, TrueVal); 303 ICI->setPredicate(Pred); 304 ICI->setOperand(1, CmpRHS); 305 SI.setOperand(1, TrueVal); 306 SI.setOperand(2, FalseVal); 307 Changed = true; 308 } 309 break; 310 } 311 case ICmpInst::ICMP_UGT: 312 case ICmpInst::ICMP_SGT: { 313 // X > MAX ? T : F --> F 314 if (CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) 315 return ReplaceInstUsesWith(SI, FalseVal); 316 // X > C ? X : C+1 --> X < C+1 ? C+1 : X 317 Constant *AdjustedRHS = 318 ConstantInt::get(CI->getContext(), CI->getValue()+1); 319 if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || 320 (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) { 321 Pred = ICmpInst::getSwappedPredicate(Pred); 322 CmpRHS = AdjustedRHS; 323 std::swap(FalseVal, TrueVal); 324 ICI->setPredicate(Pred); 325 ICI->setOperand(1, CmpRHS); 326 SI.setOperand(1, TrueVal); 327 SI.setOperand(2, FalseVal); 328 Changed = true; 329 } 330 break; 331 } 332 } 333 } 334 335 // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 336 // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 337 // FIXME: Type and constness constraints could be lifted, but we have to 338 // watch code size carefully. We should consider xor instead of 339 // sub/add when we decide to do that. 340 if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { 341 if (TrueVal->getType() == Ty) { 342 if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { 343 ConstantInt *C1 = NULL, *C2 = NULL; 344 if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { 345 C1 = dyn_cast<ConstantInt>(TrueVal); 346 C2 = dyn_cast<ConstantInt>(FalseVal); 347 } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { 348 C1 = dyn_cast<ConstantInt>(FalseVal); 349 C2 = dyn_cast<ConstantInt>(TrueVal); 350 } 351 if (C1 && C2) { 352 // This shift results in either -1 or 0. 353 Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); 354 355 // Check if we can express the operation with a single or. 356 if (C2->isAllOnesValue()) 357 return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); 358 359 Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); 360 return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); 361 } 362 } 363 } 364 } 365 366 if (CmpLHS == TrueVal && CmpRHS == FalseVal) { 367 // Transform (X == Y) ? X : Y -> Y 368 if (Pred == ICmpInst::ICMP_EQ) 369 return ReplaceInstUsesWith(SI, FalseVal); 370 // Transform (X != Y) ? X : Y -> X 371 if (Pred == ICmpInst::ICMP_NE) 372 return ReplaceInstUsesWith(SI, TrueVal); 373 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 374 375 } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) { 376 // Transform (X == Y) ? Y : X -> X 377 if (Pred == ICmpInst::ICMP_EQ) 378 return ReplaceInstUsesWith(SI, FalseVal); 379 // Transform (X != Y) ? Y : X -> Y 380 if (Pred == ICmpInst::ICMP_NE) 381 return ReplaceInstUsesWith(SI, TrueVal); 382 /// NOTE: if we wanted to, this is where to detect integer MIN/MAX 383 } 384 return Changed ? &SI : 0; 385} 386 387 388/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a 389/// PHI node (but the two may be in different blocks). See if the true/false 390/// values (V) are live in all of the predecessor blocks of the PHI. For 391/// example, cases like this cannot be mapped: 392/// 393/// X = phi [ C1, BB1], [C2, BB2] 394/// Y = add 395/// Z = select X, Y, 0 396/// 397/// because Y is not live in BB1/BB2. 398/// 399static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, 400 const SelectInst &SI) { 401 // If the value is a non-instruction value like a constant or argument, it 402 // can always be mapped. 403 const Instruction *I = dyn_cast<Instruction>(V); 404 if (I == 0) return true; 405 406 // If V is a PHI node defined in the same block as the condition PHI, we can 407 // map the arguments. 408 const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); 409 410 if (const PHINode *VP = dyn_cast<PHINode>(I)) 411 if (VP->getParent() == CondPHI->getParent()) 412 return true; 413 414 // Otherwise, if the PHI and select are defined in the same block and if V is 415 // defined in a different block, then we can transform it. 416 if (SI.getParent() == CondPHI->getParent() && 417 I->getParent() != CondPHI->getParent()) 418 return true; 419 420 // Otherwise we have a 'hard' case and we can't tell without doing more 421 // detailed dominator based analysis, punt. 422 return false; 423} 424 425/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: 426/// SPF2(SPF1(A, B), C) 427Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, 428 SelectPatternFlavor SPF1, 429 Value *A, Value *B, 430 Instruction &Outer, 431 SelectPatternFlavor SPF2, Value *C) { 432 if (C == A || C == B) { 433 // MAX(MAX(A, B), B) -> MAX(A, B) 434 // MIN(MIN(a, b), a) -> MIN(a, b) 435 if (SPF1 == SPF2) 436 return ReplaceInstUsesWith(Outer, Inner); 437 438 // MAX(MIN(a, b), a) -> a 439 // MIN(MAX(a, b), a) -> a 440 if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || 441 (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || 442 (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || 443 (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) 444 return ReplaceInstUsesWith(Outer, C); 445 } 446 447 // TODO: MIN(MIN(A, 23), 97) 448 return 0; 449} 450 451 452/// foldSelectICmpAnd - If one of the constants is zero (we know they can't 453/// both be) and we have an icmp instruction with zero, and we have an 'and' 454/// with the non-constant value and a power of two we can turn the select 455/// into a shift on the result of the 'and'. 456static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, 457 ConstantInt *FalseVal, 458 InstCombiner::BuilderTy *Builder) { 459 const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); 460 if (!IC || !IC->isEquality()) 461 return 0; 462 463 if (ConstantInt *C = dyn_cast<ConstantInt>(IC->getOperand(1))) 464 if (!C->isZero()) 465 return 0; 466 467 ConstantInt *AndRHS; 468 Value *LHS = IC->getOperand(0); 469 if (LHS->getType() != SI.getType() || 470 !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) 471 return 0; 472 473 // If both select arms are non-zero see if we have a select of the form 474 // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic 475 // for 'x ? 2^n : 0' and fix the thing up at the end. 476 ConstantInt *Offset = 0; 477 if (!TrueVal->isZero() && !FalseVal->isZero()) { 478 if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) 479 Offset = FalseVal; 480 else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) 481 Offset = TrueVal; 482 else 483 return 0; 484 485 // Adjust TrueVal and FalseVal to the offset. 486 TrueVal = ConstantInt::get(Builder->getContext(), 487 TrueVal->getValue() - Offset->getValue()); 488 FalseVal = ConstantInt::get(Builder->getContext(), 489 FalseVal->getValue() - Offset->getValue()); 490 } 491 492 // Make sure the mask in the 'and' and one of the select arms is a power of 2. 493 if (!AndRHS->getValue().isPowerOf2() || 494 (!TrueVal->getValue().isPowerOf2() && 495 !FalseVal->getValue().isPowerOf2())) 496 return 0; 497 498 // Determine which shift is needed to transform result of the 'and' into the 499 // desired result. 500 ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; 501 unsigned ValZeros = ValC->getValue().logBase2(); 502 unsigned AndZeros = AndRHS->getValue().logBase2(); 503 504 Value *V = LHS; 505 if (ValZeros > AndZeros) 506 V = Builder->CreateShl(V, ValZeros - AndZeros); 507 else if (ValZeros < AndZeros) 508 V = Builder->CreateLShr(V, AndZeros - ValZeros); 509 510 // Okay, now we know that everything is set up, we just don't know whether we 511 // have a icmp_ne or icmp_eq and whether the true or false val is the zero. 512 bool ShouldNotVal = !TrueVal->isZero(); 513 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; 514 if (ShouldNotVal) 515 V = Builder->CreateXor(V, ValC); 516 517 // Apply an offset if needed. 518 if (Offset) 519 V = Builder->CreateAdd(V, Offset); 520 return V; 521} 522 523Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { 524 Value *CondVal = SI.getCondition(); 525 Value *TrueVal = SI.getTrueValue(); 526 Value *FalseVal = SI.getFalseValue(); 527 528 if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) 529 return ReplaceInstUsesWith(SI, V); 530 531 if (SI.getType()->isIntegerTy(1)) { 532 if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { 533 if (C->getZExtValue()) { 534 // Change: A = select B, true, C --> A = or B, C 535 return BinaryOperator::CreateOr(CondVal, FalseVal); 536 } 537 // Change: A = select B, false, C --> A = and !B, C 538 Value *NotCond = 539 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 540 "not."+CondVal->getName()), SI); 541 return BinaryOperator::CreateAnd(NotCond, FalseVal); 542 } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { 543 if (C->getZExtValue() == false) { 544 // Change: A = select B, C, false --> A = and B, C 545 return BinaryOperator::CreateAnd(CondVal, TrueVal); 546 } 547 // Change: A = select B, C, true --> A = or !B, C 548 Value *NotCond = 549 InsertNewInstBefore(BinaryOperator::CreateNot(CondVal, 550 "not."+CondVal->getName()), SI); 551 return BinaryOperator::CreateOr(NotCond, TrueVal); 552 } 553 554 // select a, b, a -> a&b 555 // select a, a, b -> a|b 556 if (CondVal == TrueVal) 557 return BinaryOperator::CreateOr(CondVal, FalseVal); 558 else if (CondVal == FalseVal) 559 return BinaryOperator::CreateAnd(CondVal, TrueVal); 560 } 561 562 // Selecting between two integer constants? 563 if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) 564 if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { 565 // select C, 1, 0 -> zext C to int 566 if (FalseValC->isZero() && TrueValC->getValue() == 1) 567 return new ZExtInst(CondVal, SI.getType()); 568 569 // select C, -1, 0 -> sext C to int 570 if (FalseValC->isZero() && TrueValC->isAllOnesValue()) 571 return new SExtInst(CondVal, SI.getType()); 572 573 // select C, 0, 1 -> zext !C to int 574 if (TrueValC->isZero() && FalseValC->getValue() == 1) { 575 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 576 return new ZExtInst(NotCond, SI.getType()); 577 } 578 579 // select C, 0, -1 -> sext !C to int 580 if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { 581 Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); 582 return new SExtInst(NotCond, SI.getType()); 583 } 584 585 if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) 586 return ReplaceInstUsesWith(SI, V); 587 } 588 589 // See if we are selecting two values based on a comparison of the two values. 590 if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { 591 if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { 592 // Transform (X == Y) ? X : Y -> Y 593 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 594 // This is not safe in general for floating point: 595 // consider X== -0, Y== +0. 596 // It becomes safe if either operand is a nonzero constant. 597 ConstantFP *CFPt, *CFPf; 598 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 599 !CFPt->getValueAPF().isZero()) || 600 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 601 !CFPf->getValueAPF().isZero())) 602 return ReplaceInstUsesWith(SI, FalseVal); 603 } 604 // Transform (X une Y) ? X : Y -> X 605 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 606 // This is not safe in general for floating point: 607 // consider X== -0, Y== +0. 608 // It becomes safe if either operand is a nonzero constant. 609 ConstantFP *CFPt, *CFPf; 610 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 611 !CFPt->getValueAPF().isZero()) || 612 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 613 !CFPf->getValueAPF().isZero())) 614 return ReplaceInstUsesWith(SI, TrueVal); 615 } 616 // NOTE: if we wanted to, this is where to detect MIN/MAX 617 618 } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ 619 // Transform (X == Y) ? Y : X -> X 620 if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { 621 // This is not safe in general for floating point: 622 // consider X== -0, Y== +0. 623 // It becomes safe if either operand is a nonzero constant. 624 ConstantFP *CFPt, *CFPf; 625 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 626 !CFPt->getValueAPF().isZero()) || 627 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 628 !CFPf->getValueAPF().isZero())) 629 return ReplaceInstUsesWith(SI, FalseVal); 630 } 631 // Transform (X une Y) ? Y : X -> Y 632 if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { 633 // This is not safe in general for floating point: 634 // consider X== -0, Y== +0. 635 // It becomes safe if either operand is a nonzero constant. 636 ConstantFP *CFPt, *CFPf; 637 if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && 638 !CFPt->getValueAPF().isZero()) || 639 ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && 640 !CFPf->getValueAPF().isZero())) 641 return ReplaceInstUsesWith(SI, TrueVal); 642 } 643 // NOTE: if we wanted to, this is where to detect MIN/MAX 644 } 645 // NOTE: if we wanted to, this is where to detect ABS 646 } 647 648 // See if we are selecting two values based on a comparison of the two values. 649 if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) 650 if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) 651 return Result; 652 653 if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) 654 if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) 655 if (TI->hasOneUse() && FI->hasOneUse()) { 656 Instruction *AddOp = 0, *SubOp = 0; 657 658 // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) 659 if (TI->getOpcode() == FI->getOpcode()) 660 if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) 661 return IV; 662 663 // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is 664 // even legal for FP. 665 if ((TI->getOpcode() == Instruction::Sub && 666 FI->getOpcode() == Instruction::Add) || 667 (TI->getOpcode() == Instruction::FSub && 668 FI->getOpcode() == Instruction::FAdd)) { 669 AddOp = FI; SubOp = TI; 670 } else if ((FI->getOpcode() == Instruction::Sub && 671 TI->getOpcode() == Instruction::Add) || 672 (FI->getOpcode() == Instruction::FSub && 673 TI->getOpcode() == Instruction::FAdd)) { 674 AddOp = TI; SubOp = FI; 675 } 676 677 if (AddOp) { 678 Value *OtherAddOp = 0; 679 if (SubOp->getOperand(0) == AddOp->getOperand(0)) { 680 OtherAddOp = AddOp->getOperand(1); 681 } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { 682 OtherAddOp = AddOp->getOperand(0); 683 } 684 685 if (OtherAddOp) { 686 // So at this point we know we have (Y -> OtherAddOp): 687 // select C, (add X, Y), (sub X, Z) 688 Value *NegVal; // Compute -Z 689 if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) { 690 NegVal = ConstantExpr::getNeg(C); 691 } else if (SI.getType()->isFloatingPointTy()) { 692 NegVal = InsertNewInstBefore( 693 BinaryOperator::CreateFNeg(SubOp->getOperand(1), 694 "tmp"), SI); 695 } else { 696 NegVal = InsertNewInstBefore( 697 BinaryOperator::CreateNeg(SubOp->getOperand(1), 698 "tmp"), SI); 699 } 700 701 Value *NewTrueOp = OtherAddOp; 702 Value *NewFalseOp = NegVal; 703 if (AddOp != TI) 704 std::swap(NewTrueOp, NewFalseOp); 705 Instruction *NewSel = 706 SelectInst::Create(CondVal, NewTrueOp, 707 NewFalseOp, SI.getName() + ".p"); 708 709 NewSel = InsertNewInstBefore(NewSel, SI); 710 if (SI.getType()->isFloatingPointTy()) 711 return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); 712 else 713 return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); 714 } 715 } 716 } 717 718 // See if we can fold the select into one of our operands. 719 if (SI.getType()->isIntegerTy()) { 720 if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) 721 return FoldI; 722 723 // MAX(MAX(a, b), a) -> MAX(a, b) 724 // MIN(MIN(a, b), a) -> MIN(a, b) 725 // MAX(MIN(a, b), a) -> a 726 // MIN(MAX(a, b), a) -> a 727 Value *LHS, *RHS, *LHS2, *RHS2; 728 if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { 729 if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) 730 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, 731 SI, SPF, RHS)) 732 return R; 733 if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) 734 if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, 735 SI, SPF, LHS)) 736 return R; 737 } 738 739 // TODO. 740 // ABS(-X) -> ABS(X) 741 // ABS(ABS(X)) -> ABS(X) 742 } 743 744 // See if we can fold the select into a phi node if the condition is a select. 745 if (isa<PHINode>(SI.getCondition())) 746 // The true/false values have to be live in the PHI predecessor's blocks. 747 if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && 748 CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) 749 if (Instruction *NV = FoldOpIntoPhi(SI)) 750 return NV; 751 752 if (BinaryOperator::isNot(CondVal)) { 753 SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); 754 SI.setOperand(1, FalseVal); 755 SI.setOperand(2, TrueVal); 756 return &SI; 757 } 758 759 return 0; 760} 761