InstCombineCompares.cpp revision 40f8f6264d5af2c38e797e0dc59827cd231e8ff7
1//===- InstCombineCompares.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 visitICmp and visitFCmp functions. 11// 12//===----------------------------------------------------------------------===// 13 14#include "InstCombine.h" 15#include "llvm/IntrinsicInst.h" 16#include "llvm/Analysis/InstructionSimplify.h" 17#include "llvm/Analysis/MemoryBuiltins.h" 18#include "llvm/Target/TargetData.h" 19#include "llvm/Support/ConstantRange.h" 20#include "llvm/Support/GetElementPtrTypeIterator.h" 21#include "llvm/Support/PatternMatch.h" 22using namespace llvm; 23using namespace PatternMatch; 24 25/// AddOne - Add one to a ConstantInt 26static Constant *AddOne(Constant *C) { 27 return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1)); 28} 29/// SubOne - Subtract one from a ConstantInt 30static Constant *SubOne(ConstantInt *C) { 31 return ConstantExpr::getSub(C, ConstantInt::get(C->getType(), 1)); 32} 33 34static ConstantInt *ExtractElement(Constant *V, Constant *Idx) { 35 return cast<ConstantInt>(ConstantExpr::getExtractElement(V, Idx)); 36} 37 38static bool HasAddOverflow(ConstantInt *Result, 39 ConstantInt *In1, ConstantInt *In2, 40 bool IsSigned) { 41 if (IsSigned) 42 if (In2->getValue().isNegative()) 43 return Result->getValue().sgt(In1->getValue()); 44 else 45 return Result->getValue().slt(In1->getValue()); 46 else 47 return Result->getValue().ult(In1->getValue()); 48} 49 50/// AddWithOverflow - Compute Result = In1+In2, returning true if the result 51/// overflowed for this type. 52static bool AddWithOverflow(Constant *&Result, Constant *In1, 53 Constant *In2, bool IsSigned = false) { 54 Result = ConstantExpr::getAdd(In1, In2); 55 56 if (const VectorType *VTy = dyn_cast<VectorType>(In1->getType())) { 57 for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) { 58 Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i); 59 if (HasAddOverflow(ExtractElement(Result, Idx), 60 ExtractElement(In1, Idx), 61 ExtractElement(In2, Idx), 62 IsSigned)) 63 return true; 64 } 65 return false; 66 } 67 68 return HasAddOverflow(cast<ConstantInt>(Result), 69 cast<ConstantInt>(In1), cast<ConstantInt>(In2), 70 IsSigned); 71} 72 73static bool HasSubOverflow(ConstantInt *Result, 74 ConstantInt *In1, ConstantInt *In2, 75 bool IsSigned) { 76 if (IsSigned) 77 if (In2->getValue().isNegative()) 78 return Result->getValue().slt(In1->getValue()); 79 else 80 return Result->getValue().sgt(In1->getValue()); 81 else 82 return Result->getValue().ugt(In1->getValue()); 83} 84 85/// SubWithOverflow - Compute Result = In1-In2, returning true if the result 86/// overflowed for this type. 87static bool SubWithOverflow(Constant *&Result, Constant *In1, 88 Constant *In2, bool IsSigned = false) { 89 Result = ConstantExpr::getSub(In1, In2); 90 91 if (const VectorType *VTy = dyn_cast<VectorType>(In1->getType())) { 92 for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) { 93 Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i); 94 if (HasSubOverflow(ExtractElement(Result, Idx), 95 ExtractElement(In1, Idx), 96 ExtractElement(In2, Idx), 97 IsSigned)) 98 return true; 99 } 100 return false; 101 } 102 103 return HasSubOverflow(cast<ConstantInt>(Result), 104 cast<ConstantInt>(In1), cast<ConstantInt>(In2), 105 IsSigned); 106} 107 108/// isSignBitCheck - Given an exploded icmp instruction, return true if the 109/// comparison only checks the sign bit. If it only checks the sign bit, set 110/// TrueIfSigned if the result of the comparison is true when the input value is 111/// signed. 112static bool isSignBitCheck(ICmpInst::Predicate pred, ConstantInt *RHS, 113 bool &TrueIfSigned) { 114 switch (pred) { 115 case ICmpInst::ICMP_SLT: // True if LHS s< 0 116 TrueIfSigned = true; 117 return RHS->isZero(); 118 case ICmpInst::ICMP_SLE: // True if LHS s<= RHS and RHS == -1 119 TrueIfSigned = true; 120 return RHS->isAllOnesValue(); 121 case ICmpInst::ICMP_SGT: // True if LHS s> -1 122 TrueIfSigned = false; 123 return RHS->isAllOnesValue(); 124 case ICmpInst::ICMP_UGT: 125 // True if LHS u> RHS and RHS == high-bit-mask - 1 126 TrueIfSigned = true; 127 return RHS->getValue() == 128 APInt::getSignedMaxValue(RHS->getType()->getPrimitiveSizeInBits()); 129 case ICmpInst::ICMP_UGE: 130 // True if LHS u>= RHS and RHS == high-bit-mask (2^7, 2^15, 2^31, etc) 131 TrueIfSigned = true; 132 return RHS->getValue().isSignBit(); 133 default: 134 return false; 135 } 136} 137 138// isHighOnes - Return true if the constant is of the form 1+0+. 139// This is the same as lowones(~X). 140static bool isHighOnes(const ConstantInt *CI) { 141 return (~CI->getValue() + 1).isPowerOf2(); 142} 143 144/// ComputeSignedMinMaxValuesFromKnownBits - Given a signed integer type and a 145/// set of known zero and one bits, compute the maximum and minimum values that 146/// could have the specified known zero and known one bits, returning them in 147/// min/max. 148static void ComputeSignedMinMaxValuesFromKnownBits(const APInt& KnownZero, 149 const APInt& KnownOne, 150 APInt& Min, APInt& Max) { 151 assert(KnownZero.getBitWidth() == KnownOne.getBitWidth() && 152 KnownZero.getBitWidth() == Min.getBitWidth() && 153 KnownZero.getBitWidth() == Max.getBitWidth() && 154 "KnownZero, KnownOne and Min, Max must have equal bitwidth."); 155 APInt UnknownBits = ~(KnownZero|KnownOne); 156 157 // The minimum value is when all unknown bits are zeros, EXCEPT for the sign 158 // bit if it is unknown. 159 Min = KnownOne; 160 Max = KnownOne|UnknownBits; 161 162 if (UnknownBits.isNegative()) { // Sign bit is unknown 163 Min.setBit(Min.getBitWidth()-1); 164 Max.clearBit(Max.getBitWidth()-1); 165 } 166} 167 168// ComputeUnsignedMinMaxValuesFromKnownBits - Given an unsigned integer type and 169// a set of known zero and one bits, compute the maximum and minimum values that 170// could have the specified known zero and known one bits, returning them in 171// min/max. 172static void ComputeUnsignedMinMaxValuesFromKnownBits(const APInt &KnownZero, 173 const APInt &KnownOne, 174 APInt &Min, APInt &Max) { 175 assert(KnownZero.getBitWidth() == KnownOne.getBitWidth() && 176 KnownZero.getBitWidth() == Min.getBitWidth() && 177 KnownZero.getBitWidth() == Max.getBitWidth() && 178 "Ty, KnownZero, KnownOne and Min, Max must have equal bitwidth."); 179 APInt UnknownBits = ~(KnownZero|KnownOne); 180 181 // The minimum value is when the unknown bits are all zeros. 182 Min = KnownOne; 183 // The maximum value is when the unknown bits are all ones. 184 Max = KnownOne|UnknownBits; 185} 186 187 188 189/// FoldCmpLoadFromIndexedGlobal - Called we see this pattern: 190/// cmp pred (load (gep GV, ...)), cmpcst 191/// where GV is a global variable with a constant initializer. Try to simplify 192/// this into some simple computation that does not need the load. For example 193/// we can optimize "icmp eq (load (gep "foo", 0, i)), 0" into "icmp eq i, 3". 194/// 195/// If AndCst is non-null, then the loaded value is masked with that constant 196/// before doing the comparison. This handles cases like "A[i]&4 == 0". 197Instruction *InstCombiner:: 198FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV, 199 CmpInst &ICI, ConstantInt *AndCst) { 200 // We need TD information to know the pointer size unless this is inbounds. 201 if (!GEP->isInBounds() && TD == 0) return 0; 202 203 ConstantArray *Init = dyn_cast<ConstantArray>(GV->getInitializer()); 204 if (Init == 0 || Init->getNumOperands() > 1024) return 0; 205 206 // There are many forms of this optimization we can handle, for now, just do 207 // the simple index into a single-dimensional array. 208 // 209 // Require: GEP GV, 0, i {{, constant indices}} 210 if (GEP->getNumOperands() < 3 || 211 !isa<ConstantInt>(GEP->getOperand(1)) || 212 !cast<ConstantInt>(GEP->getOperand(1))->isZero() || 213 isa<Constant>(GEP->getOperand(2))) 214 return 0; 215 216 // Check that indices after the variable are constants and in-range for the 217 // type they index. Collect the indices. This is typically for arrays of 218 // structs. 219 SmallVector<unsigned, 4> LaterIndices; 220 221 const Type *EltTy = cast<ArrayType>(Init->getType())->getElementType(); 222 for (unsigned i = 3, e = GEP->getNumOperands(); i != e; ++i) { 223 ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i)); 224 if (Idx == 0) return 0; // Variable index. 225 226 uint64_t IdxVal = Idx->getZExtValue(); 227 if ((unsigned)IdxVal != IdxVal) return 0; // Too large array index. 228 229 if (const StructType *STy = dyn_cast<StructType>(EltTy)) 230 EltTy = STy->getElementType(IdxVal); 231 else if (const ArrayType *ATy = dyn_cast<ArrayType>(EltTy)) { 232 if (IdxVal >= ATy->getNumElements()) return 0; 233 EltTy = ATy->getElementType(); 234 } else { 235 return 0; // Unknown type. 236 } 237 238 LaterIndices.push_back(IdxVal); 239 } 240 241 enum { Overdefined = -3, Undefined = -2 }; 242 243 // Variables for our state machines. 244 245 // FirstTrueElement/SecondTrueElement - Used to emit a comparison of the form 246 // "i == 47 | i == 87", where 47 is the first index the condition is true for, 247 // and 87 is the second (and last) index. FirstTrueElement is -2 when 248 // undefined, otherwise set to the first true element. SecondTrueElement is 249 // -2 when undefined, -3 when overdefined and >= 0 when that index is true. 250 int FirstTrueElement = Undefined, SecondTrueElement = Undefined; 251 252 // FirstFalseElement/SecondFalseElement - Used to emit a comparison of the 253 // form "i != 47 & i != 87". Same state transitions as for true elements. 254 int FirstFalseElement = Undefined, SecondFalseElement = Undefined; 255 256 /// TrueRangeEnd/FalseRangeEnd - In conjunction with First*Element, these 257 /// define a state machine that triggers for ranges of values that the index 258 /// is true or false for. This triggers on things like "abbbbc"[i] == 'b'. 259 /// This is -2 when undefined, -3 when overdefined, and otherwise the last 260 /// index in the range (inclusive). We use -2 for undefined here because we 261 /// use relative comparisons and don't want 0-1 to match -1. 262 int TrueRangeEnd = Undefined, FalseRangeEnd = Undefined; 263 264 // MagicBitvector - This is a magic bitvector where we set a bit if the 265 // comparison is true for element 'i'. If there are 64 elements or less in 266 // the array, this will fully represent all the comparison results. 267 uint64_t MagicBitvector = 0; 268 269 270 // Scan the array and see if one of our patterns matches. 271 Constant *CompareRHS = cast<Constant>(ICI.getOperand(1)); 272 for (unsigned i = 0, e = Init->getNumOperands(); i != e; ++i) { 273 Constant *Elt = Init->getOperand(i); 274 275 // If this is indexing an array of structures, get the structure element. 276 if (!LaterIndices.empty()) 277 Elt = ConstantExpr::getExtractValue(Elt, LaterIndices.data(), 278 LaterIndices.size()); 279 280 // If the element is masked, handle it. 281 if (AndCst) Elt = ConstantExpr::getAnd(Elt, AndCst); 282 283 // Find out if the comparison would be true or false for the i'th element. 284 Constant *C = ConstantFoldCompareInstOperands(ICI.getPredicate(), Elt, 285 CompareRHS, TD); 286 // If the result is undef for this element, ignore it. 287 if (isa<UndefValue>(C)) { 288 // Extend range state machines to cover this element in case there is an 289 // undef in the middle of the range. 290 if (TrueRangeEnd == (int)i-1) 291 TrueRangeEnd = i; 292 if (FalseRangeEnd == (int)i-1) 293 FalseRangeEnd = i; 294 continue; 295 } 296 297 // If we can't compute the result for any of the elements, we have to give 298 // up evaluating the entire conditional. 299 if (!isa<ConstantInt>(C)) return 0; 300 301 // Otherwise, we know if the comparison is true or false for this element, 302 // update our state machines. 303 bool IsTrueForElt = !cast<ConstantInt>(C)->isZero(); 304 305 // State machine for single/double/range index comparison. 306 if (IsTrueForElt) { 307 // Update the TrueElement state machine. 308 if (FirstTrueElement == Undefined) 309 FirstTrueElement = TrueRangeEnd = i; // First true element. 310 else { 311 // Update double-compare state machine. 312 if (SecondTrueElement == Undefined) 313 SecondTrueElement = i; 314 else 315 SecondTrueElement = Overdefined; 316 317 // Update range state machine. 318 if (TrueRangeEnd == (int)i-1) 319 TrueRangeEnd = i; 320 else 321 TrueRangeEnd = Overdefined; 322 } 323 } else { 324 // Update the FalseElement state machine. 325 if (FirstFalseElement == Undefined) 326 FirstFalseElement = FalseRangeEnd = i; // First false element. 327 else { 328 // Update double-compare state machine. 329 if (SecondFalseElement == Undefined) 330 SecondFalseElement = i; 331 else 332 SecondFalseElement = Overdefined; 333 334 // Update range state machine. 335 if (FalseRangeEnd == (int)i-1) 336 FalseRangeEnd = i; 337 else 338 FalseRangeEnd = Overdefined; 339 } 340 } 341 342 343 // If this element is in range, update our magic bitvector. 344 if (i < 64 && IsTrueForElt) 345 MagicBitvector |= 1ULL << i; 346 347 // If all of our states become overdefined, bail out early. Since the 348 // predicate is expensive, only check it every 8 elements. This is only 349 // really useful for really huge arrays. 350 if ((i & 8) == 0 && i >= 64 && SecondTrueElement == Overdefined && 351 SecondFalseElement == Overdefined && TrueRangeEnd == Overdefined && 352 FalseRangeEnd == Overdefined) 353 return 0; 354 } 355 356 // Now that we've scanned the entire array, emit our new comparison(s). We 357 // order the state machines in complexity of the generated code. 358 Value *Idx = GEP->getOperand(2); 359 360 // If the index is larger than the pointer size of the target, truncate the 361 // index down like the GEP would do implicitly. We don't have to do this for 362 // an inbounds GEP because the index can't be out of range. 363 if (!GEP->isInBounds() && 364 Idx->getType()->getPrimitiveSizeInBits() > TD->getPointerSizeInBits()) 365 Idx = Builder->CreateTrunc(Idx, TD->getIntPtrType(Idx->getContext())); 366 367 // If the comparison is only true for one or two elements, emit direct 368 // comparisons. 369 if (SecondTrueElement != Overdefined) { 370 // None true -> false. 371 if (FirstTrueElement == Undefined) 372 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(GEP->getContext())); 373 374 Value *FirstTrueIdx = ConstantInt::get(Idx->getType(), FirstTrueElement); 375 376 // True for one element -> 'i == 47'. 377 if (SecondTrueElement == Undefined) 378 return new ICmpInst(ICmpInst::ICMP_EQ, Idx, FirstTrueIdx); 379 380 // True for two elements -> 'i == 47 | i == 72'. 381 Value *C1 = Builder->CreateICmpEQ(Idx, FirstTrueIdx); 382 Value *SecondTrueIdx = ConstantInt::get(Idx->getType(), SecondTrueElement); 383 Value *C2 = Builder->CreateICmpEQ(Idx, SecondTrueIdx); 384 return BinaryOperator::CreateOr(C1, C2); 385 } 386 387 // If the comparison is only false for one or two elements, emit direct 388 // comparisons. 389 if (SecondFalseElement != Overdefined) { 390 // None false -> true. 391 if (FirstFalseElement == Undefined) 392 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(GEP->getContext())); 393 394 Value *FirstFalseIdx = ConstantInt::get(Idx->getType(), FirstFalseElement); 395 396 // False for one element -> 'i != 47'. 397 if (SecondFalseElement == Undefined) 398 return new ICmpInst(ICmpInst::ICMP_NE, Idx, FirstFalseIdx); 399 400 // False for two elements -> 'i != 47 & i != 72'. 401 Value *C1 = Builder->CreateICmpNE(Idx, FirstFalseIdx); 402 Value *SecondFalseIdx = ConstantInt::get(Idx->getType(),SecondFalseElement); 403 Value *C2 = Builder->CreateICmpNE(Idx, SecondFalseIdx); 404 return BinaryOperator::CreateAnd(C1, C2); 405 } 406 407 // If the comparison can be replaced with a range comparison for the elements 408 // where it is true, emit the range check. 409 if (TrueRangeEnd != Overdefined) { 410 assert(TrueRangeEnd != FirstTrueElement && "Should emit single compare"); 411 412 // Generate (i-FirstTrue) <u (TrueRangeEnd-FirstTrue+1). 413 if (FirstTrueElement) { 414 Value *Offs = ConstantInt::get(Idx->getType(), -FirstTrueElement); 415 Idx = Builder->CreateAdd(Idx, Offs); 416 } 417 418 Value *End = ConstantInt::get(Idx->getType(), 419 TrueRangeEnd-FirstTrueElement+1); 420 return new ICmpInst(ICmpInst::ICMP_ULT, Idx, End); 421 } 422 423 // False range check. 424 if (FalseRangeEnd != Overdefined) { 425 assert(FalseRangeEnd != FirstFalseElement && "Should emit single compare"); 426 // Generate (i-FirstFalse) >u (FalseRangeEnd-FirstFalse). 427 if (FirstFalseElement) { 428 Value *Offs = ConstantInt::get(Idx->getType(), -FirstFalseElement); 429 Idx = Builder->CreateAdd(Idx, Offs); 430 } 431 432 Value *End = ConstantInt::get(Idx->getType(), 433 FalseRangeEnd-FirstFalseElement); 434 return new ICmpInst(ICmpInst::ICMP_UGT, Idx, End); 435 } 436 437 438 // If a 32-bit or 64-bit magic bitvector captures the entire comparison state 439 // of this load, replace it with computation that does: 440 // ((magic_cst >> i) & 1) != 0 441 if (Init->getNumOperands() <= 32 || 442 (TD && Init->getNumOperands() <= 64 && TD->isLegalInteger(64))) { 443 const Type *Ty; 444 if (Init->getNumOperands() <= 32) 445 Ty = Type::getInt32Ty(Init->getContext()); 446 else 447 Ty = Type::getInt64Ty(Init->getContext()); 448 Value *V = Builder->CreateIntCast(Idx, Ty, false); 449 V = Builder->CreateLShr(ConstantInt::get(Ty, MagicBitvector), V); 450 V = Builder->CreateAnd(ConstantInt::get(Ty, 1), V); 451 return new ICmpInst(ICmpInst::ICMP_NE, V, ConstantInt::get(Ty, 0)); 452 } 453 454 return 0; 455} 456 457 458/// EvaluateGEPOffsetExpression - Return a value that can be used to compare 459/// the *offset* implied by a GEP to zero. For example, if we have &A[i], we 460/// want to return 'i' for "icmp ne i, 0". Note that, in general, indices can 461/// be complex, and scales are involved. The above expression would also be 462/// legal to codegen as "icmp ne (i*4), 0" (assuming A is a pointer to i32). 463/// This later form is less amenable to optimization though, and we are allowed 464/// to generate the first by knowing that pointer arithmetic doesn't overflow. 465/// 466/// If we can't emit an optimized form for this expression, this returns null. 467/// 468static Value *EvaluateGEPOffsetExpression(User *GEP, Instruction &I, 469 InstCombiner &IC) { 470 TargetData &TD = *IC.getTargetData(); 471 gep_type_iterator GTI = gep_type_begin(GEP); 472 473 // Check to see if this gep only has a single variable index. If so, and if 474 // any constant indices are a multiple of its scale, then we can compute this 475 // in terms of the scale of the variable index. For example, if the GEP 476 // implies an offset of "12 + i*4", then we can codegen this as "3 + i", 477 // because the expression will cross zero at the same point. 478 unsigned i, e = GEP->getNumOperands(); 479 int64_t Offset = 0; 480 for (i = 1; i != e; ++i, ++GTI) { 481 if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i))) { 482 // Compute the aggregate offset of constant indices. 483 if (CI->isZero()) continue; 484 485 // Handle a struct index, which adds its field offset to the pointer. 486 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 487 Offset += TD.getStructLayout(STy)->getElementOffset(CI->getZExtValue()); 488 } else { 489 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 490 Offset += Size*CI->getSExtValue(); 491 } 492 } else { 493 // Found our variable index. 494 break; 495 } 496 } 497 498 // If there are no variable indices, we must have a constant offset, just 499 // evaluate it the general way. 500 if (i == e) return 0; 501 502 Value *VariableIdx = GEP->getOperand(i); 503 // Determine the scale factor of the variable element. For example, this is 504 // 4 if the variable index is into an array of i32. 505 uint64_t VariableScale = TD.getTypeAllocSize(GTI.getIndexedType()); 506 507 // Verify that there are no other variable indices. If so, emit the hard way. 508 for (++i, ++GTI; i != e; ++i, ++GTI) { 509 ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i)); 510 if (!CI) return 0; 511 512 // Compute the aggregate offset of constant indices. 513 if (CI->isZero()) continue; 514 515 // Handle a struct index, which adds its field offset to the pointer. 516 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 517 Offset += TD.getStructLayout(STy)->getElementOffset(CI->getZExtValue()); 518 } else { 519 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 520 Offset += Size*CI->getSExtValue(); 521 } 522 } 523 524 // Okay, we know we have a single variable index, which must be a 525 // pointer/array/vector index. If there is no offset, life is simple, return 526 // the index. 527 unsigned IntPtrWidth = TD.getPointerSizeInBits(); 528 if (Offset == 0) { 529 // Cast to intptrty in case a truncation occurs. If an extension is needed, 530 // we don't need to bother extending: the extension won't affect where the 531 // computation crosses zero. 532 if (VariableIdx->getType()->getPrimitiveSizeInBits() > IntPtrWidth) 533 VariableIdx = new TruncInst(VariableIdx, 534 TD.getIntPtrType(VariableIdx->getContext()), 535 VariableIdx->getName(), &I); 536 return VariableIdx; 537 } 538 539 // Otherwise, there is an index. The computation we will do will be modulo 540 // the pointer size, so get it. 541 uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth); 542 543 Offset &= PtrSizeMask; 544 VariableScale &= PtrSizeMask; 545 546 // To do this transformation, any constant index must be a multiple of the 547 // variable scale factor. For example, we can evaluate "12 + 4*i" as "3 + i", 548 // but we can't evaluate "10 + 3*i" in terms of i. Check that the offset is a 549 // multiple of the variable scale. 550 int64_t NewOffs = Offset / (int64_t)VariableScale; 551 if (Offset != NewOffs*(int64_t)VariableScale) 552 return 0; 553 554 // Okay, we can do this evaluation. Start by converting the index to intptr. 555 const Type *IntPtrTy = TD.getIntPtrType(VariableIdx->getContext()); 556 if (VariableIdx->getType() != IntPtrTy) 557 VariableIdx = CastInst::CreateIntegerCast(VariableIdx, IntPtrTy, 558 true /*SExt*/, 559 VariableIdx->getName(), &I); 560 Constant *OffsetVal = ConstantInt::get(IntPtrTy, NewOffs); 561 return BinaryOperator::CreateAdd(VariableIdx, OffsetVal, "offset", &I); 562} 563 564/// FoldGEPICmp - Fold comparisons between a GEP instruction and something 565/// else. At this point we know that the GEP is on the LHS of the comparison. 566Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS, 567 ICmpInst::Predicate Cond, 568 Instruction &I) { 569 // Look through bitcasts. 570 if (BitCastInst *BCI = dyn_cast<BitCastInst>(RHS)) 571 RHS = BCI->getOperand(0); 572 573 Value *PtrBase = GEPLHS->getOperand(0); 574 if (TD && PtrBase == RHS && GEPLHS->isInBounds()) { 575 // ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0). 576 // This transformation (ignoring the base and scales) is valid because we 577 // know pointers can't overflow since the gep is inbounds. See if we can 578 // output an optimized form. 579 Value *Offset = EvaluateGEPOffsetExpression(GEPLHS, I, *this); 580 581 // If not, synthesize the offset the hard way. 582 if (Offset == 0) 583 Offset = EmitGEPOffset(GEPLHS); 584 return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset, 585 Constant::getNullValue(Offset->getType())); 586 } else if (GEPOperator *GEPRHS = dyn_cast<GEPOperator>(RHS)) { 587 // If the base pointers are different, but the indices are the same, just 588 // compare the base pointer. 589 if (PtrBase != GEPRHS->getOperand(0)) { 590 bool IndicesTheSame = GEPLHS->getNumOperands()==GEPRHS->getNumOperands(); 591 IndicesTheSame &= GEPLHS->getOperand(0)->getType() == 592 GEPRHS->getOperand(0)->getType(); 593 if (IndicesTheSame) 594 for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i) 595 if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) { 596 IndicesTheSame = false; 597 break; 598 } 599 600 // If all indices are the same, just compare the base pointers. 601 if (IndicesTheSame) 602 return new ICmpInst(ICmpInst::getSignedPredicate(Cond), 603 GEPLHS->getOperand(0), GEPRHS->getOperand(0)); 604 605 // Otherwise, the base pointers are different and the indices are 606 // different, bail out. 607 return 0; 608 } 609 610 // If one of the GEPs has all zero indices, recurse. 611 bool AllZeros = true; 612 for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i) 613 if (!isa<Constant>(GEPLHS->getOperand(i)) || 614 !cast<Constant>(GEPLHS->getOperand(i))->isNullValue()) { 615 AllZeros = false; 616 break; 617 } 618 if (AllZeros) 619 return FoldGEPICmp(GEPRHS, GEPLHS->getOperand(0), 620 ICmpInst::getSwappedPredicate(Cond), I); 621 622 // If the other GEP has all zero indices, recurse. 623 AllZeros = true; 624 for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i) 625 if (!isa<Constant>(GEPRHS->getOperand(i)) || 626 !cast<Constant>(GEPRHS->getOperand(i))->isNullValue()) { 627 AllZeros = false; 628 break; 629 } 630 if (AllZeros) 631 return FoldGEPICmp(GEPLHS, GEPRHS->getOperand(0), Cond, I); 632 633 if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) { 634 // If the GEPs only differ by one index, compare it. 635 unsigned NumDifferences = 0; // Keep track of # differences. 636 unsigned DiffOperand = 0; // The operand that differs. 637 for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i) 638 if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) { 639 if (GEPLHS->getOperand(i)->getType()->getPrimitiveSizeInBits() != 640 GEPRHS->getOperand(i)->getType()->getPrimitiveSizeInBits()) { 641 // Irreconcilable differences. 642 NumDifferences = 2; 643 break; 644 } else { 645 if (NumDifferences++) break; 646 DiffOperand = i; 647 } 648 } 649 650 if (NumDifferences == 0) // SAME GEP? 651 return ReplaceInstUsesWith(I, // No comparison is needed here. 652 ConstantInt::get(Type::getInt1Ty(I.getContext()), 653 ICmpInst::isTrueWhenEqual(Cond))); 654 655 else if (NumDifferences == 1) { 656 Value *LHSV = GEPLHS->getOperand(DiffOperand); 657 Value *RHSV = GEPRHS->getOperand(DiffOperand); 658 // Make sure we do a signed comparison here. 659 return new ICmpInst(ICmpInst::getSignedPredicate(Cond), LHSV, RHSV); 660 } 661 } 662 663 // Only lower this if the icmp is the only user of the GEP or if we expect 664 // the result to fold to a constant! 665 if (TD && 666 (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) && 667 (isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) { 668 // ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2) 669 Value *L = EmitGEPOffset(GEPLHS); 670 Value *R = EmitGEPOffset(GEPRHS); 671 return new ICmpInst(ICmpInst::getSignedPredicate(Cond), L, R); 672 } 673 } 674 return 0; 675} 676 677/// FoldICmpAddOpCst - Fold "icmp pred (X+CI), X". 678Instruction *InstCombiner::FoldICmpAddOpCst(ICmpInst &ICI, 679 Value *X, ConstantInt *CI, 680 ICmpInst::Predicate Pred, 681 Value *TheAdd) { 682 // If we have X+0, exit early (simplifying logic below) and let it get folded 683 // elsewhere. icmp X+0, X -> icmp X, X 684 if (CI->isZero()) { 685 bool isTrue = ICmpInst::isTrueWhenEqual(Pred); 686 return ReplaceInstUsesWith(ICI, ConstantInt::get(ICI.getType(), isTrue)); 687 } 688 689 // (X+4) == X -> false. 690 if (Pred == ICmpInst::ICMP_EQ) 691 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(X->getContext())); 692 693 // (X+4) != X -> true. 694 if (Pred == ICmpInst::ICMP_NE) 695 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(X->getContext())); 696 697 // If this is an instruction (as opposed to constantexpr) get NUW/NSW info. 698 bool isNUW = false, isNSW = false; 699 if (BinaryOperator *Add = dyn_cast<BinaryOperator>(TheAdd)) { 700 isNUW = Add->hasNoUnsignedWrap(); 701 isNSW = Add->hasNoSignedWrap(); 702 } 703 704 // From this point on, we know that (X+C <= X) --> (X+C < X) because C != 0, 705 // so the values can never be equal. Similiarly for all other "or equals" 706 // operators. 707 708 // (X+1) <u X --> X >u (MAXUINT-1) --> X == 255 709 // (X+2) <u X --> X >u (MAXUINT-2) --> X > 253 710 // (X+MAXUINT) <u X --> X >u (MAXUINT-MAXUINT) --> X != 0 711 if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) { 712 // If this is an NUW add, then this is always false. 713 if (isNUW) 714 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(X->getContext())); 715 716 Value *R = 717 ConstantExpr::getSub(ConstantInt::getAllOnesValue(CI->getType()), CI); 718 return new ICmpInst(ICmpInst::ICMP_UGT, X, R); 719 } 720 721 // (X+1) >u X --> X <u (0-1) --> X != 255 722 // (X+2) >u X --> X <u (0-2) --> X <u 254 723 // (X+MAXUINT) >u X --> X <u (0-MAXUINT) --> X <u 1 --> X == 0 724 if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) { 725 // If this is an NUW add, then this is always true. 726 if (isNUW) 727 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(X->getContext())); 728 return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantExpr::getNeg(CI)); 729 } 730 731 unsigned BitWidth = CI->getType()->getPrimitiveSizeInBits(); 732 ConstantInt *SMax = ConstantInt::get(X->getContext(), 733 APInt::getSignedMaxValue(BitWidth)); 734 735 // (X+ 1) <s X --> X >s (MAXSINT-1) --> X == 127 736 // (X+ 2) <s X --> X >s (MAXSINT-2) --> X >s 125 737 // (X+MAXSINT) <s X --> X >s (MAXSINT-MAXSINT) --> X >s 0 738 // (X+MINSINT) <s X --> X >s (MAXSINT-MINSINT) --> X >s -1 739 // (X+ -2) <s X --> X >s (MAXSINT- -2) --> X >s 126 740 // (X+ -1) <s X --> X >s (MAXSINT- -1) --> X != 127 741 if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE) { 742 // If this is an NSW add, then we have two cases: if the constant is 743 // positive, then this is always false, if negative, this is always true. 744 if (isNSW) { 745 bool isTrue = CI->getValue().isNegative(); 746 return ReplaceInstUsesWith(ICI, ConstantInt::get(ICI.getType(), isTrue)); 747 } 748 749 return new ICmpInst(ICmpInst::ICMP_SGT, X, ConstantExpr::getSub(SMax, CI)); 750 } 751 752 // (X+ 1) >s X --> X <s (MAXSINT-(1-1)) --> X != 127 753 // (X+ 2) >s X --> X <s (MAXSINT-(2-1)) --> X <s 126 754 // (X+MAXSINT) >s X --> X <s (MAXSINT-(MAXSINT-1)) --> X <s 1 755 // (X+MINSINT) >s X --> X <s (MAXSINT-(MINSINT-1)) --> X <s -2 756 // (X+ -2) >s X --> X <s (MAXSINT-(-2-1)) --> X <s -126 757 // (X+ -1) >s X --> X <s (MAXSINT-(-1-1)) --> X == -128 758 759 // If this is an NSW add, then we have two cases: if the constant is 760 // positive, then this is always true, if negative, this is always false. 761 if (isNSW) { 762 bool isTrue = !CI->getValue().isNegative(); 763 return ReplaceInstUsesWith(ICI, ConstantInt::get(ICI.getType(), isTrue)); 764 } 765 766 assert(Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE); 767 Constant *C = ConstantInt::get(X->getContext(), CI->getValue()-1); 768 return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C)); 769} 770 771/// FoldICmpDivCst - Fold "icmp pred, ([su]div X, DivRHS), CmpRHS" where DivRHS 772/// and CmpRHS are both known to be integer constants. 773Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI, 774 ConstantInt *DivRHS) { 775 ConstantInt *CmpRHS = cast<ConstantInt>(ICI.getOperand(1)); 776 const APInt &CmpRHSV = CmpRHS->getValue(); 777 778 // FIXME: If the operand types don't match the type of the divide 779 // then don't attempt this transform. The code below doesn't have the 780 // logic to deal with a signed divide and an unsigned compare (and 781 // vice versa). This is because (x /s C1) <s C2 produces different 782 // results than (x /s C1) <u C2 or (x /u C1) <s C2 or even 783 // (x /u C1) <u C2. Simply casting the operands and result won't 784 // work. :( The if statement below tests that condition and bails 785 // if it finds it. 786 bool DivIsSigned = DivI->getOpcode() == Instruction::SDiv; 787 if (!ICI.isEquality() && DivIsSigned != ICI.isSigned()) 788 return 0; 789 if (DivRHS->isZero()) 790 return 0; // The ProdOV computation fails on divide by zero. 791 if (DivIsSigned && DivRHS->isAllOnesValue()) 792 return 0; // The overflow computation also screws up here 793 if (DivRHS->isOne()) 794 return 0; // Not worth bothering, and eliminates some funny cases 795 // with INT_MIN. 796 797 // Compute Prod = CI * DivRHS. We are essentially solving an equation 798 // of form X/C1=C2. We solve for X by multiplying C1 (DivRHS) and 799 // C2 (CI). By solving for X we can turn this into a range check 800 // instead of computing a divide. 801 Constant *Prod = ConstantExpr::getMul(CmpRHS, DivRHS); 802 803 // Determine if the product overflows by seeing if the product is 804 // not equal to the divide. Make sure we do the same kind of divide 805 // as in the LHS instruction that we're folding. 806 bool ProdOV = (DivIsSigned ? ConstantExpr::getSDiv(Prod, DivRHS) : 807 ConstantExpr::getUDiv(Prod, DivRHS)) != CmpRHS; 808 809 // Get the ICmp opcode 810 ICmpInst::Predicate Pred = ICI.getPredicate(); 811 812 // Figure out the interval that is being checked. For example, a comparison 813 // like "X /u 5 == 0" is really checking that X is in the interval [0, 5). 814 // Compute this interval based on the constants involved and the signedness of 815 // the compare/divide. This computes a half-open interval, keeping track of 816 // whether either value in the interval overflows. After analysis each 817 // overflow variable is set to 0 if it's corresponding bound variable is valid 818 // -1 if overflowed off the bottom end, or +1 if overflowed off the top end. 819 int LoOverflow = 0, HiOverflow = 0; 820 Constant *LoBound = 0, *HiBound = 0; 821 822 if (!DivIsSigned) { // udiv 823 // e.g. X/5 op 3 --> [15, 20) 824 LoBound = Prod; 825 HiOverflow = LoOverflow = ProdOV; 826 if (!HiOverflow) 827 HiOverflow = AddWithOverflow(HiBound, LoBound, DivRHS, false); 828 } else if (DivRHS->getValue().isStrictlyPositive()) { // Divisor is > 0. 829 if (CmpRHSV == 0) { // (X / pos) op 0 830 // Can't overflow. e.g. X/2 op 0 --> [-1, 2) 831 LoBound = cast<ConstantInt>(ConstantExpr::getNeg(SubOne(DivRHS))); 832 HiBound = DivRHS; 833 } else if (CmpRHSV.isStrictlyPositive()) { // (X / pos) op pos 834 LoBound = Prod; // e.g. X/5 op 3 --> [15, 20) 835 HiOverflow = LoOverflow = ProdOV; 836 if (!HiOverflow) 837 HiOverflow = AddWithOverflow(HiBound, Prod, DivRHS, true); 838 } else { // (X / pos) op neg 839 // e.g. X/5 op -3 --> [-15-4, -15+1) --> [-19, -14) 840 HiBound = AddOne(Prod); 841 LoOverflow = HiOverflow = ProdOV ? -1 : 0; 842 if (!LoOverflow) { 843 ConstantInt* DivNeg = 844 cast<ConstantInt>(ConstantExpr::getNeg(DivRHS)); 845 LoOverflow = AddWithOverflow(LoBound, HiBound, DivNeg, true) ? -1 : 0; 846 } 847 } 848 } else if (DivRHS->getValue().isNegative()) { // Divisor is < 0. 849 if (CmpRHSV == 0) { // (X / neg) op 0 850 // e.g. X/-5 op 0 --> [-4, 5) 851 LoBound = AddOne(DivRHS); 852 HiBound = cast<ConstantInt>(ConstantExpr::getNeg(DivRHS)); 853 if (HiBound == DivRHS) { // -INTMIN = INTMIN 854 HiOverflow = 1; // [INTMIN+1, overflow) 855 HiBound = 0; // e.g. X/INTMIN = 0 --> X > INTMIN 856 } 857 } else if (CmpRHSV.isStrictlyPositive()) { // (X / neg) op pos 858 // e.g. X/-5 op 3 --> [-19, -14) 859 HiBound = AddOne(Prod); 860 HiOverflow = LoOverflow = ProdOV ? -1 : 0; 861 if (!LoOverflow) 862 LoOverflow = AddWithOverflow(LoBound, HiBound, DivRHS, true) ? -1 : 0; 863 } else { // (X / neg) op neg 864 LoBound = Prod; // e.g. X/-5 op -3 --> [15, 20) 865 LoOverflow = HiOverflow = ProdOV; 866 if (!HiOverflow) 867 HiOverflow = SubWithOverflow(HiBound, Prod, DivRHS, true); 868 } 869 870 // Dividing by a negative swaps the condition. LT <-> GT 871 Pred = ICmpInst::getSwappedPredicate(Pred); 872 } 873 874 Value *X = DivI->getOperand(0); 875 switch (Pred) { 876 default: llvm_unreachable("Unhandled icmp opcode!"); 877 case ICmpInst::ICMP_EQ: 878 if (LoOverflow && HiOverflow) 879 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); 880 if (HiOverflow) 881 return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE : 882 ICmpInst::ICMP_UGE, X, LoBound); 883 if (LoOverflow) 884 return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT : 885 ICmpInst::ICMP_ULT, X, HiBound); 886 return ReplaceInstUsesWith(ICI, 887 InsertRangeTest(X, LoBound, HiBound, DivIsSigned, 888 true)); 889 case ICmpInst::ICMP_NE: 890 if (LoOverflow && HiOverflow) 891 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); 892 if (HiOverflow) 893 return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT : 894 ICmpInst::ICMP_ULT, X, LoBound); 895 if (LoOverflow) 896 return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE : 897 ICmpInst::ICMP_UGE, X, HiBound); 898 return ReplaceInstUsesWith(ICI, InsertRangeTest(X, LoBound, HiBound, 899 DivIsSigned, false)); 900 case ICmpInst::ICMP_ULT: 901 case ICmpInst::ICMP_SLT: 902 if (LoOverflow == +1) // Low bound is greater than input range. 903 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); 904 if (LoOverflow == -1) // Low bound is less than input range. 905 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); 906 return new ICmpInst(Pred, X, LoBound); 907 case ICmpInst::ICMP_UGT: 908 case ICmpInst::ICMP_SGT: 909 if (HiOverflow == +1) // High bound greater than input range. 910 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); 911 else if (HiOverflow == -1) // High bound less than input range. 912 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); 913 if (Pred == ICmpInst::ICMP_UGT) 914 return new ICmpInst(ICmpInst::ICMP_UGE, X, HiBound); 915 else 916 return new ICmpInst(ICmpInst::ICMP_SGE, X, HiBound); 917 } 918} 919 920 921/// visitICmpInstWithInstAndIntCst - Handle "icmp (instr, intcst)". 922/// 923Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI, 924 Instruction *LHSI, 925 ConstantInt *RHS) { 926 const APInt &RHSV = RHS->getValue(); 927 928 switch (LHSI->getOpcode()) { 929 case Instruction::Trunc: 930 if (ICI.isEquality() && LHSI->hasOneUse()) { 931 // Simplify icmp eq (trunc x to i8), 42 -> icmp eq x, 42|highbits if all 932 // of the high bits truncated out of x are known. 933 unsigned DstBits = LHSI->getType()->getPrimitiveSizeInBits(), 934 SrcBits = LHSI->getOperand(0)->getType()->getPrimitiveSizeInBits(); 935 APInt Mask(APInt::getHighBitsSet(SrcBits, SrcBits-DstBits)); 936 APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0); 937 ComputeMaskedBits(LHSI->getOperand(0), Mask, KnownZero, KnownOne); 938 939 // If all the high bits are known, we can do this xform. 940 if ((KnownZero|KnownOne).countLeadingOnes() >= SrcBits-DstBits) { 941 // Pull in the high bits from known-ones set. 942 APInt NewRHS = RHS->getValue().zext(SrcBits); 943 NewRHS |= KnownOne; 944 return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0), 945 ConstantInt::get(ICI.getContext(), NewRHS)); 946 } 947 } 948 break; 949 950 case Instruction::Xor: // (icmp pred (xor X, XorCST), CI) 951 if (ConstantInt *XorCST = dyn_cast<ConstantInt>(LHSI->getOperand(1))) { 952 // If this is a comparison that tests the signbit (X < 0) or (x > -1), 953 // fold the xor. 954 if ((ICI.getPredicate() == ICmpInst::ICMP_SLT && RHSV == 0) || 955 (ICI.getPredicate() == ICmpInst::ICMP_SGT && RHSV.isAllOnesValue())) { 956 Value *CompareVal = LHSI->getOperand(0); 957 958 // If the sign bit of the XorCST is not set, there is no change to 959 // the operation, just stop using the Xor. 960 if (!XorCST->getValue().isNegative()) { 961 ICI.setOperand(0, CompareVal); 962 Worklist.Add(LHSI); 963 return &ICI; 964 } 965 966 // Was the old condition true if the operand is positive? 967 bool isTrueIfPositive = ICI.getPredicate() == ICmpInst::ICMP_SGT; 968 969 // If so, the new one isn't. 970 isTrueIfPositive ^= true; 971 972 if (isTrueIfPositive) 973 return new ICmpInst(ICmpInst::ICMP_SGT, CompareVal, 974 SubOne(RHS)); 975 else 976 return new ICmpInst(ICmpInst::ICMP_SLT, CompareVal, 977 AddOne(RHS)); 978 } 979 980 if (LHSI->hasOneUse()) { 981 // (icmp u/s (xor A SignBit), C) -> (icmp s/u A, (xor C SignBit)) 982 if (!ICI.isEquality() && XorCST->getValue().isSignBit()) { 983 const APInt &SignBit = XorCST->getValue(); 984 ICmpInst::Predicate Pred = ICI.isSigned() 985 ? ICI.getUnsignedPredicate() 986 : ICI.getSignedPredicate(); 987 return new ICmpInst(Pred, LHSI->getOperand(0), 988 ConstantInt::get(ICI.getContext(), 989 RHSV ^ SignBit)); 990 } 991 992 // (icmp u/s (xor A ~SignBit), C) -> (icmp s/u (xor C ~SignBit), A) 993 if (!ICI.isEquality() && XorCST->getValue().isMaxSignedValue()) { 994 const APInt &NotSignBit = XorCST->getValue(); 995 ICmpInst::Predicate Pred = ICI.isSigned() 996 ? ICI.getUnsignedPredicate() 997 : ICI.getSignedPredicate(); 998 Pred = ICI.getSwappedPredicate(Pred); 999 return new ICmpInst(Pred, LHSI->getOperand(0), 1000 ConstantInt::get(ICI.getContext(), 1001 RHSV ^ NotSignBit)); 1002 } 1003 } 1004 } 1005 break; 1006 case Instruction::And: // (icmp pred (and X, AndCST), RHS) 1007 if (LHSI->hasOneUse() && isa<ConstantInt>(LHSI->getOperand(1)) && 1008 LHSI->getOperand(0)->hasOneUse()) { 1009 ConstantInt *AndCST = cast<ConstantInt>(LHSI->getOperand(1)); 1010 1011 // If the LHS is an AND of a truncating cast, we can widen the 1012 // and/compare to be the input width without changing the value 1013 // produced, eliminating a cast. 1014 if (TruncInst *Cast = dyn_cast<TruncInst>(LHSI->getOperand(0))) { 1015 // We can do this transformation if either the AND constant does not 1016 // have its sign bit set or if it is an equality comparison. 1017 // Extending a relational comparison when we're checking the sign 1018 // bit would not work. 1019 if (Cast->hasOneUse() && 1020 (ICI.isEquality() || 1021 (AndCST->getValue().isNonNegative() && RHSV.isNonNegative()))) { 1022 uint32_t BitWidth = 1023 cast<IntegerType>(Cast->getOperand(0)->getType())->getBitWidth(); 1024 APInt NewCST = AndCST->getValue().zext(BitWidth); 1025 APInt NewCI = RHSV.zext(BitWidth); 1026 Value *NewAnd = 1027 Builder->CreateAnd(Cast->getOperand(0), 1028 ConstantInt::get(ICI.getContext(), NewCST), 1029 LHSI->getName()); 1030 return new ICmpInst(ICI.getPredicate(), NewAnd, 1031 ConstantInt::get(ICI.getContext(), NewCI)); 1032 } 1033 } 1034 1035 // If this is: (X >> C1) & C2 != C3 (where any shift and any compare 1036 // could exist), turn it into (X & (C2 << C1)) != (C3 << C1). This 1037 // happens a LOT in code produced by the C front-end, for bitfield 1038 // access. 1039 BinaryOperator *Shift = dyn_cast<BinaryOperator>(LHSI->getOperand(0)); 1040 if (Shift && !Shift->isShift()) 1041 Shift = 0; 1042 1043 ConstantInt *ShAmt; 1044 ShAmt = Shift ? dyn_cast<ConstantInt>(Shift->getOperand(1)) : 0; 1045 const Type *Ty = Shift ? Shift->getType() : 0; // Type of the shift. 1046 const Type *AndTy = AndCST->getType(); // Type of the and. 1047 1048 // We can fold this as long as we can't shift unknown bits 1049 // into the mask. This can only happen with signed shift 1050 // rights, as they sign-extend. 1051 if (ShAmt) { 1052 bool CanFold = Shift->isLogicalShift(); 1053 if (!CanFold) { 1054 // To test for the bad case of the signed shr, see if any 1055 // of the bits shifted in could be tested after the mask. 1056 uint32_t TyBits = Ty->getPrimitiveSizeInBits(); 1057 int ShAmtVal = TyBits - ShAmt->getLimitedValue(TyBits); 1058 1059 uint32_t BitWidth = AndTy->getPrimitiveSizeInBits(); 1060 if ((APInt::getHighBitsSet(BitWidth, BitWidth-ShAmtVal) & 1061 AndCST->getValue()) == 0) 1062 CanFold = true; 1063 } 1064 1065 if (CanFold) { 1066 Constant *NewCst; 1067 if (Shift->getOpcode() == Instruction::Shl) 1068 NewCst = ConstantExpr::getLShr(RHS, ShAmt); 1069 else 1070 NewCst = ConstantExpr::getShl(RHS, ShAmt); 1071 1072 // Check to see if we are shifting out any of the bits being 1073 // compared. 1074 if (ConstantExpr::get(Shift->getOpcode(), 1075 NewCst, ShAmt) != RHS) { 1076 // If we shifted bits out, the fold is not going to work out. 1077 // As a special case, check to see if this means that the 1078 // result is always true or false now. 1079 if (ICI.getPredicate() == ICmpInst::ICMP_EQ) 1080 return ReplaceInstUsesWith(ICI, 1081 ConstantInt::getFalse(ICI.getContext())); 1082 if (ICI.getPredicate() == ICmpInst::ICMP_NE) 1083 return ReplaceInstUsesWith(ICI, 1084 ConstantInt::getTrue(ICI.getContext())); 1085 } else { 1086 ICI.setOperand(1, NewCst); 1087 Constant *NewAndCST; 1088 if (Shift->getOpcode() == Instruction::Shl) 1089 NewAndCST = ConstantExpr::getLShr(AndCST, ShAmt); 1090 else 1091 NewAndCST = ConstantExpr::getShl(AndCST, ShAmt); 1092 LHSI->setOperand(1, NewAndCST); 1093 LHSI->setOperand(0, Shift->getOperand(0)); 1094 Worklist.Add(Shift); // Shift is dead. 1095 return &ICI; 1096 } 1097 } 1098 } 1099 1100 // Turn ((X >> Y) & C) == 0 into (X & (C << Y)) == 0. The later is 1101 // preferable because it allows the C<<Y expression to be hoisted out 1102 // of a loop if Y is invariant and X is not. 1103 if (Shift && Shift->hasOneUse() && RHSV == 0 && 1104 ICI.isEquality() && !Shift->isArithmeticShift() && 1105 !isa<Constant>(Shift->getOperand(0))) { 1106 // Compute C << Y. 1107 Value *NS; 1108 if (Shift->getOpcode() == Instruction::LShr) { 1109 NS = Builder->CreateShl(AndCST, Shift->getOperand(1), "tmp"); 1110 } else { 1111 // Insert a logical shift. 1112 NS = Builder->CreateLShr(AndCST, Shift->getOperand(1), "tmp"); 1113 } 1114 1115 // Compute X & (C << Y). 1116 Value *NewAnd = 1117 Builder->CreateAnd(Shift->getOperand(0), NS, LHSI->getName()); 1118 1119 ICI.setOperand(0, NewAnd); 1120 return &ICI; 1121 } 1122 } 1123 1124 // Try to optimize things like "A[i]&42 == 0" to index computations. 1125 if (LoadInst *LI = dyn_cast<LoadInst>(LHSI->getOperand(0))) { 1126 if (GetElementPtrInst *GEP = 1127 dyn_cast<GetElementPtrInst>(LI->getOperand(0))) 1128 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0))) 1129 if (GV->isConstant() && GV->hasDefinitiveInitializer() && 1130 !LI->isVolatile() && isa<ConstantInt>(LHSI->getOperand(1))) { 1131 ConstantInt *C = cast<ConstantInt>(LHSI->getOperand(1)); 1132 if (Instruction *Res = FoldCmpLoadFromIndexedGlobal(GEP, GV,ICI, C)) 1133 return Res; 1134 } 1135 } 1136 break; 1137 1138 case Instruction::Or: { 1139 if (!ICI.isEquality() || !RHS->isNullValue() || !LHSI->hasOneUse()) 1140 break; 1141 Value *P, *Q; 1142 if (match(LHSI, m_Or(m_PtrToInt(m_Value(P)), m_PtrToInt(m_Value(Q))))) { 1143 // Simplify icmp eq (or (ptrtoint P), (ptrtoint Q)), 0 1144 // -> and (icmp eq P, null), (icmp eq Q, null). 1145 1146 Value *ICIP = Builder->CreateICmp(ICI.getPredicate(), P, 1147 Constant::getNullValue(P->getType())); 1148 Value *ICIQ = Builder->CreateICmp(ICI.getPredicate(), Q, 1149 Constant::getNullValue(Q->getType())); 1150 Instruction *Op; 1151 if (ICI.getPredicate() == ICmpInst::ICMP_EQ) 1152 Op = BinaryOperator::CreateAnd(ICIP, ICIQ); 1153 else 1154 Op = BinaryOperator::CreateOr(ICIP, ICIQ); 1155 return Op; 1156 } 1157 break; 1158 } 1159 1160 case Instruction::Shl: { // (icmp pred (shl X, ShAmt), CI) 1161 ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1)); 1162 if (!ShAmt) break; 1163 1164 uint32_t TypeBits = RHSV.getBitWidth(); 1165 1166 // Check that the shift amount is in range. If not, don't perform 1167 // undefined shifts. When the shift is visited it will be 1168 // simplified. 1169 if (ShAmt->uge(TypeBits)) 1170 break; 1171 1172 if (ICI.isEquality()) { 1173 // If we are comparing against bits always shifted out, the 1174 // comparison cannot succeed. 1175 Constant *Comp = 1176 ConstantExpr::getShl(ConstantExpr::getLShr(RHS, ShAmt), 1177 ShAmt); 1178 if (Comp != RHS) {// Comparing against a bit that we know is zero. 1179 bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE; 1180 Constant *Cst = 1181 ConstantInt::get(Type::getInt1Ty(ICI.getContext()), IsICMP_NE); 1182 return ReplaceInstUsesWith(ICI, Cst); 1183 } 1184 1185 if (LHSI->hasOneUse()) { 1186 // Otherwise strength reduce the shift into an and. 1187 uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits); 1188 Constant *Mask = 1189 ConstantInt::get(ICI.getContext(), APInt::getLowBitsSet(TypeBits, 1190 TypeBits-ShAmtVal)); 1191 1192 Value *And = 1193 Builder->CreateAnd(LHSI->getOperand(0),Mask, LHSI->getName()+".mask"); 1194 return new ICmpInst(ICI.getPredicate(), And, 1195 ConstantInt::get(ICI.getContext(), 1196 RHSV.lshr(ShAmtVal))); 1197 } 1198 } 1199 1200 // Otherwise, if this is a comparison of the sign bit, simplify to and/test. 1201 bool TrueIfSigned = false; 1202 if (LHSI->hasOneUse() && 1203 isSignBitCheck(ICI.getPredicate(), RHS, TrueIfSigned)) { 1204 // (X << 31) <s 0 --> (X&1) != 0 1205 Constant *Mask = ConstantInt::get(ICI.getContext(), APInt(TypeBits, 1) << 1206 (TypeBits-ShAmt->getZExtValue()-1)); 1207 Value *And = 1208 Builder->CreateAnd(LHSI->getOperand(0), Mask, LHSI->getName()+".mask"); 1209 return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ, 1210 And, Constant::getNullValue(And->getType())); 1211 } 1212 break; 1213 } 1214 1215 case Instruction::LShr: // (icmp pred (shr X, ShAmt), CI) 1216 case Instruction::AShr: { 1217 // Only handle equality comparisons of shift-by-constant. 1218 ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1)); 1219 if (!ShAmt || !ICI.isEquality()) break; 1220 1221 // Check that the shift amount is in range. If not, don't perform 1222 // undefined shifts. When the shift is visited it will be 1223 // simplified. 1224 uint32_t TypeBits = RHSV.getBitWidth(); 1225 if (ShAmt->uge(TypeBits)) 1226 break; 1227 1228 uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits); 1229 1230 // If we are comparing against bits always shifted out, the 1231 // comparison cannot succeed. 1232 APInt Comp = RHSV << ShAmtVal; 1233 if (LHSI->getOpcode() == Instruction::LShr) 1234 Comp = Comp.lshr(ShAmtVal); 1235 else 1236 Comp = Comp.ashr(ShAmtVal); 1237 1238 if (Comp != RHSV) { // Comparing against a bit that we know is zero. 1239 bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE; 1240 Constant *Cst = ConstantInt::get(Type::getInt1Ty(ICI.getContext()), 1241 IsICMP_NE); 1242 return ReplaceInstUsesWith(ICI, Cst); 1243 } 1244 1245 // Otherwise, check to see if the bits shifted out are known to be zero. 1246 // If so, we can compare against the unshifted value: 1247 // (X & 4) >> 1 == 2 --> (X & 4) == 4. 1248 if (LHSI->hasOneUse() && 1249 MaskedValueIsZero(LHSI->getOperand(0), 1250 APInt::getLowBitsSet(Comp.getBitWidth(), ShAmtVal))) { 1251 return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0), 1252 ConstantExpr::getShl(RHS, ShAmt)); 1253 } 1254 1255 if (LHSI->hasOneUse()) { 1256 // Otherwise strength reduce the shift into an and. 1257 APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal)); 1258 Constant *Mask = ConstantInt::get(ICI.getContext(), Val); 1259 1260 Value *And = Builder->CreateAnd(LHSI->getOperand(0), 1261 Mask, LHSI->getName()+".mask"); 1262 return new ICmpInst(ICI.getPredicate(), And, 1263 ConstantExpr::getShl(RHS, ShAmt)); 1264 } 1265 break; 1266 } 1267 1268 case Instruction::SDiv: 1269 case Instruction::UDiv: 1270 // Fold: icmp pred ([us]div X, C1), C2 -> range test 1271 // Fold this div into the comparison, producing a range check. 1272 // Determine, based on the divide type, what the range is being 1273 // checked. If there is an overflow on the low or high side, remember 1274 // it, otherwise compute the range [low, hi) bounding the new value. 1275 // See: InsertRangeTest above for the kinds of replacements possible. 1276 if (ConstantInt *DivRHS = dyn_cast<ConstantInt>(LHSI->getOperand(1))) 1277 if (Instruction *R = FoldICmpDivCst(ICI, cast<BinaryOperator>(LHSI), 1278 DivRHS)) 1279 return R; 1280 break; 1281 1282 case Instruction::Add: 1283 // Fold: icmp pred (add X, C1), C2 1284 if (!ICI.isEquality()) { 1285 ConstantInt *LHSC = dyn_cast<ConstantInt>(LHSI->getOperand(1)); 1286 if (!LHSC) break; 1287 const APInt &LHSV = LHSC->getValue(); 1288 1289 ConstantRange CR = ICI.makeConstantRange(ICI.getPredicate(), RHSV) 1290 .subtract(LHSV); 1291 1292 if (ICI.isSigned()) { 1293 if (CR.getLower().isSignBit()) { 1294 return new ICmpInst(ICmpInst::ICMP_SLT, LHSI->getOperand(0), 1295 ConstantInt::get(ICI.getContext(),CR.getUpper())); 1296 } else if (CR.getUpper().isSignBit()) { 1297 return new ICmpInst(ICmpInst::ICMP_SGE, LHSI->getOperand(0), 1298 ConstantInt::get(ICI.getContext(),CR.getLower())); 1299 } 1300 } else { 1301 if (CR.getLower().isMinValue()) { 1302 return new ICmpInst(ICmpInst::ICMP_ULT, LHSI->getOperand(0), 1303 ConstantInt::get(ICI.getContext(),CR.getUpper())); 1304 } else if (CR.getUpper().isMinValue()) { 1305 return new ICmpInst(ICmpInst::ICMP_UGE, LHSI->getOperand(0), 1306 ConstantInt::get(ICI.getContext(),CR.getLower())); 1307 } 1308 } 1309 } 1310 break; 1311 } 1312 1313 // Simplify icmp_eq and icmp_ne instructions with integer constant RHS. 1314 if (ICI.isEquality()) { 1315 bool isICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE; 1316 1317 // If the first operand is (add|sub|and|or|xor|rem) with a constant, and 1318 // the second operand is a constant, simplify a bit. 1319 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(LHSI)) { 1320 switch (BO->getOpcode()) { 1321 case Instruction::SRem: 1322 // If we have a signed (X % (2^c)) == 0, turn it into an unsigned one. 1323 if (RHSV == 0 && isa<ConstantInt>(BO->getOperand(1)) &&BO->hasOneUse()){ 1324 const APInt &V = cast<ConstantInt>(BO->getOperand(1))->getValue(); 1325 if (V.sgt(1) && V.isPowerOf2()) { 1326 Value *NewRem = 1327 Builder->CreateURem(BO->getOperand(0), BO->getOperand(1), 1328 BO->getName()); 1329 return new ICmpInst(ICI.getPredicate(), NewRem, 1330 Constant::getNullValue(BO->getType())); 1331 } 1332 } 1333 break; 1334 case Instruction::Add: 1335 // Replace ((add A, B) != C) with (A != C-B) if B & C are constants. 1336 if (ConstantInt *BOp1C = dyn_cast<ConstantInt>(BO->getOperand(1))) { 1337 if (BO->hasOneUse()) 1338 return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), 1339 ConstantExpr::getSub(RHS, BOp1C)); 1340 } else if (RHSV == 0) { 1341 // Replace ((add A, B) != 0) with (A != -B) if A or B is 1342 // efficiently invertible, or if the add has just this one use. 1343 Value *BOp0 = BO->getOperand(0), *BOp1 = BO->getOperand(1); 1344 1345 if (Value *NegVal = dyn_castNegVal(BOp1)) 1346 return new ICmpInst(ICI.getPredicate(), BOp0, NegVal); 1347 else if (Value *NegVal = dyn_castNegVal(BOp0)) 1348 return new ICmpInst(ICI.getPredicate(), NegVal, BOp1); 1349 else if (BO->hasOneUse()) { 1350 Value *Neg = Builder->CreateNeg(BOp1); 1351 Neg->takeName(BO); 1352 return new ICmpInst(ICI.getPredicate(), BOp0, Neg); 1353 } 1354 } 1355 break; 1356 case Instruction::Xor: 1357 // For the xor case, we can xor two constants together, eliminating 1358 // the explicit xor. 1359 if (Constant *BOC = dyn_cast<Constant>(BO->getOperand(1))) 1360 return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), 1361 ConstantExpr::getXor(RHS, BOC)); 1362 1363 // FALLTHROUGH 1364 case Instruction::Sub: 1365 // Replace (([sub|xor] A, B) != 0) with (A != B) 1366 if (RHSV == 0) 1367 return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), 1368 BO->getOperand(1)); 1369 break; 1370 1371 case Instruction::Or: 1372 // If bits are being or'd in that are not present in the constant we 1373 // are comparing against, then the comparison could never succeed! 1374 if (ConstantInt *BOC = dyn_cast<ConstantInt>(BO->getOperand(1))) { 1375 Constant *NotCI = ConstantExpr::getNot(RHS); 1376 if (!ConstantExpr::getAnd(BOC, NotCI)->isNullValue()) 1377 return ReplaceInstUsesWith(ICI, 1378 ConstantInt::get(Type::getInt1Ty(ICI.getContext()), 1379 isICMP_NE)); 1380 } 1381 break; 1382 1383 case Instruction::And: 1384 if (ConstantInt *BOC = dyn_cast<ConstantInt>(BO->getOperand(1))) { 1385 // If bits are being compared against that are and'd out, then the 1386 // comparison can never succeed! 1387 if ((RHSV & ~BOC->getValue()) != 0) 1388 return ReplaceInstUsesWith(ICI, 1389 ConstantInt::get(Type::getInt1Ty(ICI.getContext()), 1390 isICMP_NE)); 1391 1392 // If we have ((X & C) == C), turn it into ((X & C) != 0). 1393 if (RHS == BOC && RHSV.isPowerOf2()) 1394 return new ICmpInst(isICMP_NE ? ICmpInst::ICMP_EQ : 1395 ICmpInst::ICMP_NE, LHSI, 1396 Constant::getNullValue(RHS->getType())); 1397 1398 // Replace (and X, (1 << size(X)-1) != 0) with x s< 0 1399 if (BOC->getValue().isSignBit()) { 1400 Value *X = BO->getOperand(0); 1401 Constant *Zero = Constant::getNullValue(X->getType()); 1402 ICmpInst::Predicate pred = isICMP_NE ? 1403 ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE; 1404 return new ICmpInst(pred, X, Zero); 1405 } 1406 1407 // ((X & ~7) == 0) --> X < 8 1408 if (RHSV == 0 && isHighOnes(BOC)) { 1409 Value *X = BO->getOperand(0); 1410 Constant *NegX = ConstantExpr::getNeg(BOC); 1411 ICmpInst::Predicate pred = isICMP_NE ? 1412 ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT; 1413 return new ICmpInst(pred, X, NegX); 1414 } 1415 } 1416 default: break; 1417 } 1418 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(LHSI)) { 1419 // Handle icmp {eq|ne} <intrinsic>, intcst. 1420 switch (II->getIntrinsicID()) { 1421 case Intrinsic::bswap: 1422 Worklist.Add(II); 1423 ICI.setOperand(0, II->getArgOperand(0)); 1424 ICI.setOperand(1, ConstantInt::get(II->getContext(), RHSV.byteSwap())); 1425 return &ICI; 1426 case Intrinsic::ctlz: 1427 case Intrinsic::cttz: 1428 // ctz(A) == bitwidth(a) -> A == 0 and likewise for != 1429 if (RHSV == RHS->getType()->getBitWidth()) { 1430 Worklist.Add(II); 1431 ICI.setOperand(0, II->getArgOperand(0)); 1432 ICI.setOperand(1, ConstantInt::get(RHS->getType(), 0)); 1433 return &ICI; 1434 } 1435 break; 1436 case Intrinsic::ctpop: 1437 // popcount(A) == 0 -> A == 0 and likewise for != 1438 if (RHS->isZero()) { 1439 Worklist.Add(II); 1440 ICI.setOperand(0, II->getArgOperand(0)); 1441 ICI.setOperand(1, RHS); 1442 return &ICI; 1443 } 1444 break; 1445 default: 1446 break; 1447 } 1448 } 1449 } 1450 return 0; 1451} 1452 1453/// visitICmpInstWithCastAndCast - Handle icmp (cast x to y), (cast/cst). 1454/// We only handle extending casts so far. 1455/// 1456Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) { 1457 const CastInst *LHSCI = cast<CastInst>(ICI.getOperand(0)); 1458 Value *LHSCIOp = LHSCI->getOperand(0); 1459 const Type *SrcTy = LHSCIOp->getType(); 1460 const Type *DestTy = LHSCI->getType(); 1461 Value *RHSCIOp; 1462 1463 // Turn icmp (ptrtoint x), (ptrtoint/c) into a compare of the input if the 1464 // integer type is the same size as the pointer type. 1465 if (TD && LHSCI->getOpcode() == Instruction::PtrToInt && 1466 TD->getPointerSizeInBits() == 1467 cast<IntegerType>(DestTy)->getBitWidth()) { 1468 Value *RHSOp = 0; 1469 if (Constant *RHSC = dyn_cast<Constant>(ICI.getOperand(1))) { 1470 RHSOp = ConstantExpr::getIntToPtr(RHSC, SrcTy); 1471 } else if (PtrToIntInst *RHSC = dyn_cast<PtrToIntInst>(ICI.getOperand(1))) { 1472 RHSOp = RHSC->getOperand(0); 1473 // If the pointer types don't match, insert a bitcast. 1474 if (LHSCIOp->getType() != RHSOp->getType()) 1475 RHSOp = Builder->CreateBitCast(RHSOp, LHSCIOp->getType()); 1476 } 1477 1478 if (RHSOp) 1479 return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSOp); 1480 } 1481 1482 // The code below only handles extension cast instructions, so far. 1483 // Enforce this. 1484 if (LHSCI->getOpcode() != Instruction::ZExt && 1485 LHSCI->getOpcode() != Instruction::SExt) 1486 return 0; 1487 1488 bool isSignedExt = LHSCI->getOpcode() == Instruction::SExt; 1489 bool isSignedCmp = ICI.isSigned(); 1490 1491 if (CastInst *CI = dyn_cast<CastInst>(ICI.getOperand(1))) { 1492 // Not an extension from the same type? 1493 RHSCIOp = CI->getOperand(0); 1494 if (RHSCIOp->getType() != LHSCIOp->getType()) 1495 return 0; 1496 1497 // If the signedness of the two casts doesn't agree (i.e. one is a sext 1498 // and the other is a zext), then we can't handle this. 1499 if (CI->getOpcode() != LHSCI->getOpcode()) 1500 return 0; 1501 1502 // Deal with equality cases early. 1503 if (ICI.isEquality()) 1504 return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp); 1505 1506 // A signed comparison of sign extended values simplifies into a 1507 // signed comparison. 1508 if (isSignedCmp && isSignedExt) 1509 return new ICmpInst(ICI.getPredicate(), LHSCIOp, RHSCIOp); 1510 1511 // The other three cases all fold into an unsigned comparison. 1512 return new ICmpInst(ICI.getUnsignedPredicate(), LHSCIOp, RHSCIOp); 1513 } 1514 1515 // If we aren't dealing with a constant on the RHS, exit early 1516 ConstantInt *CI = dyn_cast<ConstantInt>(ICI.getOperand(1)); 1517 if (!CI) 1518 return 0; 1519 1520 // Compute the constant that would happen if we truncated to SrcTy then 1521 // reextended to DestTy. 1522 Constant *Res1 = ConstantExpr::getTrunc(CI, SrcTy); 1523 Constant *Res2 = ConstantExpr::getCast(LHSCI->getOpcode(), 1524 Res1, DestTy); 1525 1526 // If the re-extended constant didn't change... 1527 if (Res2 == CI) { 1528 // Deal with equality cases early. 1529 if (ICI.isEquality()) 1530 return new ICmpInst(ICI.getPredicate(), LHSCIOp, Res1); 1531 1532 // A signed comparison of sign extended values simplifies into a 1533 // signed comparison. 1534 if (isSignedExt && isSignedCmp) 1535 return new ICmpInst(ICI.getPredicate(), LHSCIOp, Res1); 1536 1537 // The other three cases all fold into an unsigned comparison. 1538 return new ICmpInst(ICI.getUnsignedPredicate(), LHSCIOp, Res1); 1539 } 1540 1541 // The re-extended constant changed so the constant cannot be represented 1542 // in the shorter type. Consequently, we cannot emit a simple comparison. 1543 1544 // First, handle some easy cases. We know the result cannot be equal at this 1545 // point so handle the ICI.isEquality() cases 1546 if (ICI.getPredicate() == ICmpInst::ICMP_EQ) 1547 return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(ICI.getContext())); 1548 if (ICI.getPredicate() == ICmpInst::ICMP_NE) 1549 return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(ICI.getContext())); 1550 1551 // Evaluate the comparison for LT (we invert for GT below). LE and GE cases 1552 // should have been folded away previously and not enter in here. 1553 Value *Result; 1554 if (isSignedCmp) { 1555 // We're performing a signed comparison. 1556 if (cast<ConstantInt>(CI)->getValue().isNegative()) 1557 Result = ConstantInt::getFalse(ICI.getContext()); // X < (small) --> false 1558 else 1559 Result = ConstantInt::getTrue(ICI.getContext()); // X < (large) --> true 1560 } else { 1561 // We're performing an unsigned comparison. 1562 if (isSignedExt) { 1563 // We're performing an unsigned comp with a sign extended value. 1564 // This is true if the input is >= 0. [aka >s -1] 1565 Constant *NegOne = Constant::getAllOnesValue(SrcTy); 1566 Result = Builder->CreateICmpSGT(LHSCIOp, NegOne, ICI.getName()); 1567 } else { 1568 // Unsigned extend & unsigned compare -> always true. 1569 Result = ConstantInt::getTrue(ICI.getContext()); 1570 } 1571 } 1572 1573 // Finally, return the value computed. 1574 if (ICI.getPredicate() == ICmpInst::ICMP_ULT || 1575 ICI.getPredicate() == ICmpInst::ICMP_SLT) 1576 return ReplaceInstUsesWith(ICI, Result); 1577 1578 assert((ICI.getPredicate()==ICmpInst::ICMP_UGT || 1579 ICI.getPredicate()==ICmpInst::ICMP_SGT) && 1580 "ICmp should be folded!"); 1581 if (Constant *CI = dyn_cast<Constant>(Result)) 1582 return ReplaceInstUsesWith(ICI, ConstantExpr::getNot(CI)); 1583 return BinaryOperator::CreateNot(Result); 1584} 1585 1586 1587 1588Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { 1589 bool Changed = false; 1590 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 1591 1592 /// Orders the operands of the compare so that they are listed from most 1593 /// complex to least complex. This puts constants before unary operators, 1594 /// before binary operators. 1595 if (getComplexity(Op0) < getComplexity(Op1)) { 1596 I.swapOperands(); 1597 std::swap(Op0, Op1); 1598 Changed = true; 1599 } 1600 1601 if (Value *V = SimplifyICmpInst(I.getPredicate(), Op0, Op1, TD)) 1602 return ReplaceInstUsesWith(I, V); 1603 1604 const Type *Ty = Op0->getType(); 1605 1606 // icmp's with boolean values can always be turned into bitwise operations 1607 if (Ty->isIntegerTy(1)) { 1608 switch (I.getPredicate()) { 1609 default: llvm_unreachable("Invalid icmp instruction!"); 1610 case ICmpInst::ICMP_EQ: { // icmp eq i1 A, B -> ~(A^B) 1611 Value *Xor = Builder->CreateXor(Op0, Op1, I.getName()+"tmp"); 1612 return BinaryOperator::CreateNot(Xor); 1613 } 1614 case ICmpInst::ICMP_NE: // icmp eq i1 A, B -> A^B 1615 return BinaryOperator::CreateXor(Op0, Op1); 1616 1617 case ICmpInst::ICMP_UGT: 1618 std::swap(Op0, Op1); // Change icmp ugt -> icmp ult 1619 // FALL THROUGH 1620 case ICmpInst::ICMP_ULT:{ // icmp ult i1 A, B -> ~A & B 1621 Value *Not = Builder->CreateNot(Op0, I.getName()+"tmp"); 1622 return BinaryOperator::CreateAnd(Not, Op1); 1623 } 1624 case ICmpInst::ICMP_SGT: 1625 std::swap(Op0, Op1); // Change icmp sgt -> icmp slt 1626 // FALL THROUGH 1627 case ICmpInst::ICMP_SLT: { // icmp slt i1 A, B -> A & ~B 1628 Value *Not = Builder->CreateNot(Op1, I.getName()+"tmp"); 1629 return BinaryOperator::CreateAnd(Not, Op0); 1630 } 1631 case ICmpInst::ICMP_UGE: 1632 std::swap(Op0, Op1); // Change icmp uge -> icmp ule 1633 // FALL THROUGH 1634 case ICmpInst::ICMP_ULE: { // icmp ule i1 A, B -> ~A | B 1635 Value *Not = Builder->CreateNot(Op0, I.getName()+"tmp"); 1636 return BinaryOperator::CreateOr(Not, Op1); 1637 } 1638 case ICmpInst::ICMP_SGE: 1639 std::swap(Op0, Op1); // Change icmp sge -> icmp sle 1640 // FALL THROUGH 1641 case ICmpInst::ICMP_SLE: { // icmp sle i1 A, B -> A | ~B 1642 Value *Not = Builder->CreateNot(Op1, I.getName()+"tmp"); 1643 return BinaryOperator::CreateOr(Not, Op0); 1644 } 1645 } 1646 } 1647 1648 unsigned BitWidth = 0; 1649 if (TD) 1650 BitWidth = TD->getTypeSizeInBits(Ty->getScalarType()); 1651 else if (Ty->isIntOrIntVectorTy()) 1652 BitWidth = Ty->getScalarSizeInBits(); 1653 1654 bool isSignBit = false; 1655 1656 // See if we are doing a comparison with a constant. 1657 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { 1658 Value *A = 0, *B = 0; 1659 1660 // (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B) 1661 if (I.isEquality() && CI->isZero() && 1662 match(Op0, m_Sub(m_Value(A), m_Value(B)))) { 1663 // (icmp cond A B) if cond is equality 1664 return new ICmpInst(I.getPredicate(), A, B); 1665 } 1666 1667 // If we have an icmp le or icmp ge instruction, turn it into the 1668 // appropriate icmp lt or icmp gt instruction. This allows us to rely on 1669 // them being folded in the code below. The SimplifyICmpInst code has 1670 // already handled the edge cases for us, so we just assert on them. 1671 switch (I.getPredicate()) { 1672 default: break; 1673 case ICmpInst::ICMP_ULE: 1674 assert(!CI->isMaxValue(false)); // A <=u MAX -> TRUE 1675 return new ICmpInst(ICmpInst::ICMP_ULT, Op0, 1676 ConstantInt::get(CI->getContext(), CI->getValue()+1)); 1677 case ICmpInst::ICMP_SLE: 1678 assert(!CI->isMaxValue(true)); // A <=s MAX -> TRUE 1679 return new ICmpInst(ICmpInst::ICMP_SLT, Op0, 1680 ConstantInt::get(CI->getContext(), CI->getValue()+1)); 1681 case ICmpInst::ICMP_UGE: 1682 assert(!CI->isMinValue(false)); // A >=u MIN -> TRUE 1683 return new ICmpInst(ICmpInst::ICMP_UGT, Op0, 1684 ConstantInt::get(CI->getContext(), CI->getValue()-1)); 1685 case ICmpInst::ICMP_SGE: 1686 assert(!CI->isMinValue(true)); // A >=s MIN -> TRUE 1687 return new ICmpInst(ICmpInst::ICMP_SGT, Op0, 1688 ConstantInt::get(CI->getContext(), CI->getValue()-1)); 1689 } 1690 1691 // If this comparison is a normal comparison, it demands all 1692 // bits, if it is a sign bit comparison, it only demands the sign bit. 1693 bool UnusedBit; 1694 isSignBit = isSignBitCheck(I.getPredicate(), CI, UnusedBit); 1695 } 1696 1697 // See if we can fold the comparison based on range information we can get 1698 // by checking whether bits are known to be zero or one in the input. 1699 if (BitWidth != 0) { 1700 APInt Op0KnownZero(BitWidth, 0), Op0KnownOne(BitWidth, 0); 1701 APInt Op1KnownZero(BitWidth, 0), Op1KnownOne(BitWidth, 0); 1702 1703 if (SimplifyDemandedBits(I.getOperandUse(0), 1704 isSignBit ? APInt::getSignBit(BitWidth) 1705 : APInt::getAllOnesValue(BitWidth), 1706 Op0KnownZero, Op0KnownOne, 0)) 1707 return &I; 1708 if (SimplifyDemandedBits(I.getOperandUse(1), 1709 APInt::getAllOnesValue(BitWidth), 1710 Op1KnownZero, Op1KnownOne, 0)) 1711 return &I; 1712 1713 // Given the known and unknown bits, compute a range that the LHS could be 1714 // in. Compute the Min, Max and RHS values based on the known bits. For the 1715 // EQ and NE we use unsigned values. 1716 APInt Op0Min(BitWidth, 0), Op0Max(BitWidth, 0); 1717 APInt Op1Min(BitWidth, 0), Op1Max(BitWidth, 0); 1718 if (I.isSigned()) { 1719 ComputeSignedMinMaxValuesFromKnownBits(Op0KnownZero, Op0KnownOne, 1720 Op0Min, Op0Max); 1721 ComputeSignedMinMaxValuesFromKnownBits(Op1KnownZero, Op1KnownOne, 1722 Op1Min, Op1Max); 1723 } else { 1724 ComputeUnsignedMinMaxValuesFromKnownBits(Op0KnownZero, Op0KnownOne, 1725 Op0Min, Op0Max); 1726 ComputeUnsignedMinMaxValuesFromKnownBits(Op1KnownZero, Op1KnownOne, 1727 Op1Min, Op1Max); 1728 } 1729 1730 // If Min and Max are known to be the same, then SimplifyDemandedBits 1731 // figured out that the LHS is a constant. Just constant fold this now so 1732 // that code below can assume that Min != Max. 1733 if (!isa<Constant>(Op0) && Op0Min == Op0Max) 1734 return new ICmpInst(I.getPredicate(), 1735 ConstantInt::get(I.getContext(), Op0Min), Op1); 1736 if (!isa<Constant>(Op1) && Op1Min == Op1Max) 1737 return new ICmpInst(I.getPredicate(), Op0, 1738 ConstantInt::get(I.getContext(), Op1Min)); 1739 1740 // Based on the range information we know about the LHS, see if we can 1741 // simplify this comparison. For example, (x&4) < 8 is always true. 1742 switch (I.getPredicate()) { 1743 default: llvm_unreachable("Unknown icmp opcode!"); 1744 case ICmpInst::ICMP_EQ: { 1745 if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max)) 1746 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1747 1748 // If all bits are known zero except for one, then we know at most one 1749 // bit is set. If the comparison is against zero, then this is a check 1750 // to see if *that* bit is set. 1751 APInt Op0KnownZeroInverted = ~Op0KnownZero; 1752 if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) { 1753 // If the LHS is an AND with the same constant, look through it. 1754 Value *LHS = 0; 1755 ConstantInt *LHSC = 0; 1756 if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) || 1757 LHSC->getValue() != Op0KnownZeroInverted) 1758 LHS = Op0; 1759 1760 // If the LHS is 1 << x, and we know the result is a power of 2 like 8, 1761 // then turn "((1 << x)&8) == 0" into "x != 3". 1762 Value *X = 0; 1763 if (match(LHS, m_Shl(m_One(), m_Value(X)))) { 1764 unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros(); 1765 return new ICmpInst(ICmpInst::ICMP_NE, X, 1766 ConstantInt::get(X->getType(), CmpVal)); 1767 } 1768 1769 // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1, 1770 // then turn "((8 >>u x)&1) == 0" into "x != 3". 1771 ConstantInt *CI = 0; 1772 if (Op0KnownZeroInverted == 1 && 1773 match(LHS, m_LShr(m_ConstantInt(CI), m_Value(X))) && 1774 CI->getValue().isPowerOf2()) { 1775 unsigned CmpVal = CI->getValue().countTrailingZeros(); 1776 return new ICmpInst(ICmpInst::ICMP_NE, X, 1777 ConstantInt::get(X->getType(), CmpVal)); 1778 } 1779 } 1780 1781 break; 1782 } 1783 case ICmpInst::ICMP_NE: { 1784 if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max)) 1785 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1786 1787 // If all bits are known zero except for one, then we know at most one 1788 // bit is set. If the comparison is against zero, then this is a check 1789 // to see if *that* bit is set. 1790 APInt Op0KnownZeroInverted = ~Op0KnownZero; 1791 if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) { 1792 // If the LHS is an AND with the same constant, look through it. 1793 Value *LHS = 0; 1794 ConstantInt *LHSC = 0; 1795 if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) || 1796 LHSC->getValue() != Op0KnownZeroInverted) 1797 LHS = Op0; 1798 1799 // If the LHS is 1 << x, and we know the result is a power of 2 like 8, 1800 // then turn "((1 << x)&8) != 0" into "x == 3". 1801 Value *X = 0; 1802 if (match(LHS, m_Shl(m_One(), m_Value(X)))) { 1803 unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros(); 1804 return new ICmpInst(ICmpInst::ICMP_EQ, X, 1805 ConstantInt::get(X->getType(), CmpVal)); 1806 } 1807 1808 // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1, 1809 // then turn "((8 >>u x)&1) != 0" into "x == 3". 1810 ConstantInt *CI = 0; 1811 if (Op0KnownZeroInverted == 1 && 1812 match(LHS, m_LShr(m_ConstantInt(CI), m_Value(X))) && 1813 CI->getValue().isPowerOf2()) { 1814 unsigned CmpVal = CI->getValue().countTrailingZeros(); 1815 return new ICmpInst(ICmpInst::ICMP_EQ, X, 1816 ConstantInt::get(X->getType(), CmpVal)); 1817 } 1818 } 1819 1820 break; 1821 } 1822 case ICmpInst::ICMP_ULT: 1823 if (Op0Max.ult(Op1Min)) // A <u B -> true if max(A) < min(B) 1824 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1825 if (Op0Min.uge(Op1Max)) // A <u B -> false if min(A) >= max(B) 1826 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1827 if (Op1Min == Op0Max) // A <u B -> A != B if max(A) == min(B) 1828 return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); 1829 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { 1830 if (Op1Max == Op0Min+1) // A <u C -> A == C-1 if min(A)+1 == C 1831 return new ICmpInst(ICmpInst::ICMP_EQ, Op0, 1832 ConstantInt::get(CI->getContext(), CI->getValue()-1)); 1833 1834 // (x <u 2147483648) -> (x >s -1) -> true if sign bit clear 1835 if (CI->isMinValue(true)) 1836 return new ICmpInst(ICmpInst::ICMP_SGT, Op0, 1837 Constant::getAllOnesValue(Op0->getType())); 1838 } 1839 break; 1840 case ICmpInst::ICMP_UGT: 1841 if (Op0Min.ugt(Op1Max)) // A >u B -> true if min(A) > max(B) 1842 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1843 if (Op0Max.ule(Op1Min)) // A >u B -> false if max(A) <= max(B) 1844 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1845 1846 if (Op1Max == Op0Min) // A >u B -> A != B if min(A) == max(B) 1847 return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); 1848 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { 1849 if (Op1Min == Op0Max-1) // A >u C -> A == C+1 if max(a)-1 == C 1850 return new ICmpInst(ICmpInst::ICMP_EQ, Op0, 1851 ConstantInt::get(CI->getContext(), CI->getValue()+1)); 1852 1853 // (x >u 2147483647) -> (x <s 0) -> true if sign bit set 1854 if (CI->isMaxValue(true)) 1855 return new ICmpInst(ICmpInst::ICMP_SLT, Op0, 1856 Constant::getNullValue(Op0->getType())); 1857 } 1858 break; 1859 case ICmpInst::ICMP_SLT: 1860 if (Op0Max.slt(Op1Min)) // A <s B -> true if max(A) < min(C) 1861 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1862 if (Op0Min.sge(Op1Max)) // A <s B -> false if min(A) >= max(C) 1863 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1864 if (Op1Min == Op0Max) // A <s B -> A != B if max(A) == min(B) 1865 return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); 1866 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { 1867 if (Op1Max == Op0Min+1) // A <s C -> A == C-1 if min(A)+1 == C 1868 return new ICmpInst(ICmpInst::ICMP_EQ, Op0, 1869 ConstantInt::get(CI->getContext(), CI->getValue()-1)); 1870 } 1871 break; 1872 case ICmpInst::ICMP_SGT: 1873 if (Op0Min.sgt(Op1Max)) // A >s B -> true if min(A) > max(B) 1874 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1875 if (Op0Max.sle(Op1Min)) // A >s B -> false if max(A) <= min(B) 1876 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1877 1878 if (Op1Max == Op0Min) // A >s B -> A != B if min(A) == max(B) 1879 return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1); 1880 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { 1881 if (Op1Min == Op0Max-1) // A >s C -> A == C+1 if max(A)-1 == C 1882 return new ICmpInst(ICmpInst::ICMP_EQ, Op0, 1883 ConstantInt::get(CI->getContext(), CI->getValue()+1)); 1884 } 1885 break; 1886 case ICmpInst::ICMP_SGE: 1887 assert(!isa<ConstantInt>(Op1) && "ICMP_SGE with ConstantInt not folded!"); 1888 if (Op0Min.sge(Op1Max)) // A >=s B -> true if min(A) >= max(B) 1889 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1890 if (Op0Max.slt(Op1Min)) // A >=s B -> false if max(A) < min(B) 1891 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1892 break; 1893 case ICmpInst::ICMP_SLE: 1894 assert(!isa<ConstantInt>(Op1) && "ICMP_SLE with ConstantInt not folded!"); 1895 if (Op0Max.sle(Op1Min)) // A <=s B -> true if max(A) <= min(B) 1896 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1897 if (Op0Min.sgt(Op1Max)) // A <=s B -> false if min(A) > max(B) 1898 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1899 break; 1900 case ICmpInst::ICMP_UGE: 1901 assert(!isa<ConstantInt>(Op1) && "ICMP_UGE with ConstantInt not folded!"); 1902 if (Op0Min.uge(Op1Max)) // A >=u B -> true if min(A) >= max(B) 1903 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1904 if (Op0Max.ult(Op1Min)) // A >=u B -> false if max(A) < min(B) 1905 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1906 break; 1907 case ICmpInst::ICMP_ULE: 1908 assert(!isa<ConstantInt>(Op1) && "ICMP_ULE with ConstantInt not folded!"); 1909 if (Op0Max.ule(Op1Min)) // A <=u B -> true if max(A) <= min(B) 1910 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 1911 if (Op0Min.ugt(Op1Max)) // A <=u B -> false if min(A) > max(B) 1912 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 1913 break; 1914 } 1915 1916 // Turn a signed comparison into an unsigned one if both operands 1917 // are known to have the same sign. 1918 if (I.isSigned() && 1919 ((Op0KnownZero.isNegative() && Op1KnownZero.isNegative()) || 1920 (Op0KnownOne.isNegative() && Op1KnownOne.isNegative()))) 1921 return new ICmpInst(I.getUnsignedPredicate(), Op0, Op1); 1922 } 1923 1924 // Test if the ICmpInst instruction is used exclusively by a select as 1925 // part of a minimum or maximum operation. If so, refrain from doing 1926 // any other folding. This helps out other analyses which understand 1927 // non-obfuscated minimum and maximum idioms, such as ScalarEvolution 1928 // and CodeGen. And in this case, at least one of the comparison 1929 // operands has at least one user besides the compare (the select), 1930 // which would often largely negate the benefit of folding anyway. 1931 if (I.hasOneUse()) 1932 if (SelectInst *SI = dyn_cast<SelectInst>(*I.use_begin())) 1933 if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) || 1934 (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1)) 1935 return 0; 1936 1937 // See if we are doing a comparison between a constant and an instruction that 1938 // can be folded into the comparison. 1939 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { 1940 // Since the RHS is a ConstantInt (CI), if the left hand side is an 1941 // instruction, see if that instruction also has constants so that the 1942 // instruction can be folded into the icmp 1943 if (Instruction *LHSI = dyn_cast<Instruction>(Op0)) 1944 if (Instruction *Res = visitICmpInstWithInstAndIntCst(I, LHSI, CI)) 1945 return Res; 1946 } 1947 1948 // Handle icmp with constant (but not simple integer constant) RHS 1949 if (Constant *RHSC = dyn_cast<Constant>(Op1)) { 1950 if (Instruction *LHSI = dyn_cast<Instruction>(Op0)) 1951 switch (LHSI->getOpcode()) { 1952 case Instruction::GetElementPtr: 1953 // icmp pred GEP (P, int 0, int 0, int 0), null -> icmp pred P, null 1954 if (RHSC->isNullValue() && 1955 cast<GetElementPtrInst>(LHSI)->hasAllZeroIndices()) 1956 return new ICmpInst(I.getPredicate(), LHSI->getOperand(0), 1957 Constant::getNullValue(LHSI->getOperand(0)->getType())); 1958 break; 1959 case Instruction::PHI: 1960 // Only fold icmp into the PHI if the phi and icmp are in the same 1961 // block. If in the same block, we're encouraging jump threading. If 1962 // not, we are just pessimizing the code by making an i1 phi. 1963 if (LHSI->getParent() == I.getParent()) 1964 if (Instruction *NV = FoldOpIntoPhi(I, true)) 1965 return NV; 1966 break; 1967 case Instruction::Select: { 1968 // If either operand of the select is a constant, we can fold the 1969 // comparison into the select arms, which will cause one to be 1970 // constant folded and the select turned into a bitwise or. 1971 Value *Op1 = 0, *Op2 = 0; 1972 if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) 1973 Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC); 1974 if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) 1975 Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC); 1976 1977 // We only want to perform this transformation if it will not lead to 1978 // additional code. This is true if either both sides of the select 1979 // fold to a constant (in which case the icmp is replaced with a select 1980 // which will usually simplify) or this is the only user of the 1981 // select (in which case we are trading a select+icmp for a simpler 1982 // select+icmp). 1983 if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) { 1984 if (!Op1) 1985 Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1), 1986 RHSC, I.getName()); 1987 if (!Op2) 1988 Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2), 1989 RHSC, I.getName()); 1990 return SelectInst::Create(LHSI->getOperand(0), Op1, Op2); 1991 } 1992 break; 1993 } 1994 case Instruction::IntToPtr: 1995 // icmp pred inttoptr(X), null -> icmp pred X, 0 1996 if (RHSC->isNullValue() && TD && 1997 TD->getIntPtrType(RHSC->getContext()) == 1998 LHSI->getOperand(0)->getType()) 1999 return new ICmpInst(I.getPredicate(), LHSI->getOperand(0), 2000 Constant::getNullValue(LHSI->getOperand(0)->getType())); 2001 break; 2002 2003 case Instruction::Load: 2004 // Try to optimize things like "A[i] > 4" to index computations. 2005 if (GetElementPtrInst *GEP = 2006 dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) { 2007 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0))) 2008 if (GV->isConstant() && GV->hasDefinitiveInitializer() && 2009 !cast<LoadInst>(LHSI)->isVolatile()) 2010 if (Instruction *Res = FoldCmpLoadFromIndexedGlobal(GEP, GV, I)) 2011 return Res; 2012 } 2013 break; 2014 } 2015 } 2016 2017 // If we can optimize a 'icmp GEP, P' or 'icmp P, GEP', do so now. 2018 if (GEPOperator *GEP = dyn_cast<GEPOperator>(Op0)) 2019 if (Instruction *NI = FoldGEPICmp(GEP, Op1, I.getPredicate(), I)) 2020 return NI; 2021 if (GEPOperator *GEP = dyn_cast<GEPOperator>(Op1)) 2022 if (Instruction *NI = FoldGEPICmp(GEP, Op0, 2023 ICmpInst::getSwappedPredicate(I.getPredicate()), I)) 2024 return NI; 2025 2026 // Test to see if the operands of the icmp are casted versions of other 2027 // values. If the ptr->ptr cast can be stripped off both arguments, we do so 2028 // now. 2029 if (BitCastInst *CI = dyn_cast<BitCastInst>(Op0)) { 2030 if (Op0->getType()->isPointerTy() && 2031 (isa<Constant>(Op1) || isa<BitCastInst>(Op1))) { 2032 // We keep moving the cast from the left operand over to the right 2033 // operand, where it can often be eliminated completely. 2034 Op0 = CI->getOperand(0); 2035 2036 // If operand #1 is a bitcast instruction, it must also be a ptr->ptr cast 2037 // so eliminate it as well. 2038 if (BitCastInst *CI2 = dyn_cast<BitCastInst>(Op1)) 2039 Op1 = CI2->getOperand(0); 2040 2041 // If Op1 is a constant, we can fold the cast into the constant. 2042 if (Op0->getType() != Op1->getType()) { 2043 if (Constant *Op1C = dyn_cast<Constant>(Op1)) { 2044 Op1 = ConstantExpr::getBitCast(Op1C, Op0->getType()); 2045 } else { 2046 // Otherwise, cast the RHS right before the icmp 2047 Op1 = Builder->CreateBitCast(Op1, Op0->getType()); 2048 } 2049 } 2050 return new ICmpInst(I.getPredicate(), Op0, Op1); 2051 } 2052 } 2053 2054 if (isa<CastInst>(Op0)) { 2055 // Handle the special case of: icmp (cast bool to X), <cst> 2056 // This comes up when you have code like 2057 // int X = A < B; 2058 // if (X) ... 2059 // For generality, we handle any zero-extension of any operand comparison 2060 // with a constant or another cast from the same type. 2061 if (isa<Constant>(Op1) || isa<CastInst>(Op1)) 2062 if (Instruction *R = visitICmpInstWithCastAndCast(I)) 2063 return R; 2064 } 2065 2066 // See if it's the same type of instruction on the left and right. 2067 if (BinaryOperator *Op0I = dyn_cast<BinaryOperator>(Op0)) { 2068 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1)) { 2069 if (Op0I->getOpcode() == Op1I->getOpcode() && Op0I->hasOneUse() && 2070 Op1I->hasOneUse() && Op0I->getOperand(1) == Op1I->getOperand(1)) { 2071 switch (Op0I->getOpcode()) { 2072 default: break; 2073 case Instruction::Add: 2074 case Instruction::Sub: 2075 case Instruction::Xor: 2076 if (I.isEquality()) // a+x icmp eq/ne b+x --> a icmp b 2077 return new ICmpInst(I.getPredicate(), Op0I->getOperand(0), 2078 Op1I->getOperand(0)); 2079 // icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b 2080 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0I->getOperand(1))) { 2081 if (CI->getValue().isSignBit()) { 2082 ICmpInst::Predicate Pred = I.isSigned() 2083 ? I.getUnsignedPredicate() 2084 : I.getSignedPredicate(); 2085 return new ICmpInst(Pred, Op0I->getOperand(0), 2086 Op1I->getOperand(0)); 2087 } 2088 2089 if (CI->getValue().isMaxSignedValue()) { 2090 ICmpInst::Predicate Pred = I.isSigned() 2091 ? I.getUnsignedPredicate() 2092 : I.getSignedPredicate(); 2093 Pred = I.getSwappedPredicate(Pred); 2094 return new ICmpInst(Pred, Op0I->getOperand(0), 2095 Op1I->getOperand(0)); 2096 } 2097 } 2098 break; 2099 case Instruction::Mul: 2100 if (!I.isEquality()) 2101 break; 2102 2103 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0I->getOperand(1))) { 2104 // a * Cst icmp eq/ne b * Cst --> a & Mask icmp b & Mask 2105 // Mask = -1 >> count-trailing-zeros(Cst). 2106 if (!CI->isZero() && !CI->isOne()) { 2107 const APInt &AP = CI->getValue(); 2108 ConstantInt *Mask = ConstantInt::get(I.getContext(), 2109 APInt::getLowBitsSet(AP.getBitWidth(), 2110 AP.getBitWidth() - 2111 AP.countTrailingZeros())); 2112 Value *And1 = Builder->CreateAnd(Op0I->getOperand(0), Mask); 2113 Value *And2 = Builder->CreateAnd(Op1I->getOperand(0), Mask); 2114 return new ICmpInst(I.getPredicate(), And1, And2); 2115 } 2116 } 2117 break; 2118 } 2119 } 2120 } 2121 } 2122 2123 // ~x < ~y --> y < x 2124 { Value *A, *B; 2125 if (match(Op0, m_Not(m_Value(A))) && 2126 match(Op1, m_Not(m_Value(B)))) 2127 return new ICmpInst(I.getPredicate(), B, A); 2128 } 2129 2130 if (I.isEquality()) { 2131 Value *A, *B, *C, *D; 2132 2133 // -x == -y --> x == y 2134 if (match(Op0, m_Neg(m_Value(A))) && 2135 match(Op1, m_Neg(m_Value(B)))) 2136 return new ICmpInst(I.getPredicate(), A, B); 2137 2138 if (match(Op0, m_Xor(m_Value(A), m_Value(B)))) { 2139 if (A == Op1 || B == Op1) { // (A^B) == A -> B == 0 2140 Value *OtherVal = A == Op1 ? B : A; 2141 return new ICmpInst(I.getPredicate(), OtherVal, 2142 Constant::getNullValue(A->getType())); 2143 } 2144 2145 if (match(Op1, m_Xor(m_Value(C), m_Value(D)))) { 2146 // A^c1 == C^c2 --> A == C^(c1^c2) 2147 ConstantInt *C1, *C2; 2148 if (match(B, m_ConstantInt(C1)) && 2149 match(D, m_ConstantInt(C2)) && Op1->hasOneUse()) { 2150 Constant *NC = ConstantInt::get(I.getContext(), 2151 C1->getValue() ^ C2->getValue()); 2152 Value *Xor = Builder->CreateXor(C, NC, "tmp"); 2153 return new ICmpInst(I.getPredicate(), A, Xor); 2154 } 2155 2156 // A^B == A^D -> B == D 2157 if (A == C) return new ICmpInst(I.getPredicate(), B, D); 2158 if (A == D) return new ICmpInst(I.getPredicate(), B, C); 2159 if (B == C) return new ICmpInst(I.getPredicate(), A, D); 2160 if (B == D) return new ICmpInst(I.getPredicate(), A, C); 2161 } 2162 } 2163 2164 if (match(Op1, m_Xor(m_Value(A), m_Value(B))) && 2165 (A == Op0 || B == Op0)) { 2166 // A == (A^B) -> B == 0 2167 Value *OtherVal = A == Op0 ? B : A; 2168 return new ICmpInst(I.getPredicate(), OtherVal, 2169 Constant::getNullValue(A->getType())); 2170 } 2171 2172 // (A-B) == A -> B == 0 2173 if (match(Op0, m_Sub(m_Specific(Op1), m_Value(B)))) 2174 return new ICmpInst(I.getPredicate(), B, 2175 Constant::getNullValue(B->getType())); 2176 2177 // A == (A-B) -> B == 0 2178 if (match(Op1, m_Sub(m_Specific(Op0), m_Value(B)))) 2179 return new ICmpInst(I.getPredicate(), B, 2180 Constant::getNullValue(B->getType())); 2181 2182 // (X&Z) == (Y&Z) -> (X^Y) & Z == 0 2183 if (Op0->hasOneUse() && Op1->hasOneUse() && 2184 match(Op0, m_And(m_Value(A), m_Value(B))) && 2185 match(Op1, m_And(m_Value(C), m_Value(D)))) { 2186 Value *X = 0, *Y = 0, *Z = 0; 2187 2188 if (A == C) { 2189 X = B; Y = D; Z = A; 2190 } else if (A == D) { 2191 X = B; Y = C; Z = A; 2192 } else if (B == C) { 2193 X = A; Y = D; Z = B; 2194 } else if (B == D) { 2195 X = A; Y = C; Z = B; 2196 } 2197 2198 if (X) { // Build (X^Y) & Z 2199 Op1 = Builder->CreateXor(X, Y, "tmp"); 2200 Op1 = Builder->CreateAnd(Op1, Z, "tmp"); 2201 I.setOperand(0, Op1); 2202 I.setOperand(1, Constant::getNullValue(Op1->getType())); 2203 return &I; 2204 } 2205 } 2206 } 2207 2208 { 2209 Value *X; ConstantInt *Cst; 2210 // icmp X+Cst, X 2211 if (match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op1 == X) 2212 return FoldICmpAddOpCst(I, X, Cst, I.getPredicate(), Op0); 2213 2214 // icmp X, X+Cst 2215 if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X) 2216 return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate(), Op1); 2217 } 2218 return Changed ? &I : 0; 2219} 2220 2221 2222 2223 2224 2225 2226/// FoldFCmp_IntToFP_Cst - Fold fcmp ([us]itofp x, cst) if possible. 2227/// 2228Instruction *InstCombiner::FoldFCmp_IntToFP_Cst(FCmpInst &I, 2229 Instruction *LHSI, 2230 Constant *RHSC) { 2231 if (!isa<ConstantFP>(RHSC)) return 0; 2232 const APFloat &RHS = cast<ConstantFP>(RHSC)->getValueAPF(); 2233 2234 // Get the width of the mantissa. We don't want to hack on conversions that 2235 // might lose information from the integer, e.g. "i64 -> float" 2236 int MantissaWidth = LHSI->getType()->getFPMantissaWidth(); 2237 if (MantissaWidth == -1) return 0; // Unknown. 2238 2239 // Check to see that the input is converted from an integer type that is small 2240 // enough that preserves all bits. TODO: check here for "known" sign bits. 2241 // This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e. 2242 unsigned InputSize = LHSI->getOperand(0)->getType()->getScalarSizeInBits(); 2243 2244 // If this is a uitofp instruction, we need an extra bit to hold the sign. 2245 bool LHSUnsigned = isa<UIToFPInst>(LHSI); 2246 if (LHSUnsigned) 2247 ++InputSize; 2248 2249 // If the conversion would lose info, don't hack on this. 2250 if ((int)InputSize > MantissaWidth) 2251 return 0; 2252 2253 // Otherwise, we can potentially simplify the comparison. We know that it 2254 // will always come through as an integer value and we know the constant is 2255 // not a NAN (it would have been previously simplified). 2256 assert(!RHS.isNaN() && "NaN comparison not already folded!"); 2257 2258 ICmpInst::Predicate Pred; 2259 switch (I.getPredicate()) { 2260 default: llvm_unreachable("Unexpected predicate!"); 2261 case FCmpInst::FCMP_UEQ: 2262 case FCmpInst::FCMP_OEQ: 2263 Pred = ICmpInst::ICMP_EQ; 2264 break; 2265 case FCmpInst::FCMP_UGT: 2266 case FCmpInst::FCMP_OGT: 2267 Pred = LHSUnsigned ? ICmpInst::ICMP_UGT : ICmpInst::ICMP_SGT; 2268 break; 2269 case FCmpInst::FCMP_UGE: 2270 case FCmpInst::FCMP_OGE: 2271 Pred = LHSUnsigned ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_SGE; 2272 break; 2273 case FCmpInst::FCMP_ULT: 2274 case FCmpInst::FCMP_OLT: 2275 Pred = LHSUnsigned ? ICmpInst::ICMP_ULT : ICmpInst::ICMP_SLT; 2276 break; 2277 case FCmpInst::FCMP_ULE: 2278 case FCmpInst::FCMP_OLE: 2279 Pred = LHSUnsigned ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_SLE; 2280 break; 2281 case FCmpInst::FCMP_UNE: 2282 case FCmpInst::FCMP_ONE: 2283 Pred = ICmpInst::ICMP_NE; 2284 break; 2285 case FCmpInst::FCMP_ORD: 2286 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2287 case FCmpInst::FCMP_UNO: 2288 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2289 } 2290 2291 const IntegerType *IntTy = cast<IntegerType>(LHSI->getOperand(0)->getType()); 2292 2293 // Now we know that the APFloat is a normal number, zero or inf. 2294 2295 // See if the FP constant is too large for the integer. For example, 2296 // comparing an i8 to 300.0. 2297 unsigned IntWidth = IntTy->getScalarSizeInBits(); 2298 2299 if (!LHSUnsigned) { 2300 // If the RHS value is > SignedMax, fold the comparison. This handles +INF 2301 // and large values. 2302 APFloat SMax(RHS.getSemantics(), APFloat::fcZero, false); 2303 SMax.convertFromAPInt(APInt::getSignedMaxValue(IntWidth), true, 2304 APFloat::rmNearestTiesToEven); 2305 if (SMax.compare(RHS) == APFloat::cmpLessThan) { // smax < 13123.0 2306 if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SLT || 2307 Pred == ICmpInst::ICMP_SLE) 2308 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2309 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2310 } 2311 } else { 2312 // If the RHS value is > UnsignedMax, fold the comparison. This handles 2313 // +INF and large values. 2314 APFloat UMax(RHS.getSemantics(), APFloat::fcZero, false); 2315 UMax.convertFromAPInt(APInt::getMaxValue(IntWidth), false, 2316 APFloat::rmNearestTiesToEven); 2317 if (UMax.compare(RHS) == APFloat::cmpLessThan) { // umax < 13123.0 2318 if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_ULT || 2319 Pred == ICmpInst::ICMP_ULE) 2320 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2321 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2322 } 2323 } 2324 2325 if (!LHSUnsigned) { 2326 // See if the RHS value is < SignedMin. 2327 APFloat SMin(RHS.getSemantics(), APFloat::fcZero, false); 2328 SMin.convertFromAPInt(APInt::getSignedMinValue(IntWidth), true, 2329 APFloat::rmNearestTiesToEven); 2330 if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // smin > 12312.0 2331 if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SGT || 2332 Pred == ICmpInst::ICMP_SGE) 2333 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2334 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2335 } 2336 } 2337 2338 // Okay, now we know that the FP constant fits in the range [SMIN, SMAX] or 2339 // [0, UMAX], but it may still be fractional. See if it is fractional by 2340 // casting the FP value to the integer value and back, checking for equality. 2341 // Don't do this for zero, because -0.0 is not fractional. 2342 Constant *RHSInt = LHSUnsigned 2343 ? ConstantExpr::getFPToUI(RHSC, IntTy) 2344 : ConstantExpr::getFPToSI(RHSC, IntTy); 2345 if (!RHS.isZero()) { 2346 bool Equal = LHSUnsigned 2347 ? ConstantExpr::getUIToFP(RHSInt, RHSC->getType()) == RHSC 2348 : ConstantExpr::getSIToFP(RHSInt, RHSC->getType()) == RHSC; 2349 if (!Equal) { 2350 // If we had a comparison against a fractional value, we have to adjust 2351 // the compare predicate and sometimes the value. RHSC is rounded towards 2352 // zero at this point. 2353 switch (Pred) { 2354 default: llvm_unreachable("Unexpected integer comparison!"); 2355 case ICmpInst::ICMP_NE: // (float)int != 4.4 --> true 2356 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2357 case ICmpInst::ICMP_EQ: // (float)int == 4.4 --> false 2358 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2359 case ICmpInst::ICMP_ULE: 2360 // (float)int <= 4.4 --> int <= 4 2361 // (float)int <= -4.4 --> false 2362 if (RHS.isNegative()) 2363 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2364 break; 2365 case ICmpInst::ICMP_SLE: 2366 // (float)int <= 4.4 --> int <= 4 2367 // (float)int <= -4.4 --> int < -4 2368 if (RHS.isNegative()) 2369 Pred = ICmpInst::ICMP_SLT; 2370 break; 2371 case ICmpInst::ICMP_ULT: 2372 // (float)int < -4.4 --> false 2373 // (float)int < 4.4 --> int <= 4 2374 if (RHS.isNegative()) 2375 return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext())); 2376 Pred = ICmpInst::ICMP_ULE; 2377 break; 2378 case ICmpInst::ICMP_SLT: 2379 // (float)int < -4.4 --> int < -4 2380 // (float)int < 4.4 --> int <= 4 2381 if (!RHS.isNegative()) 2382 Pred = ICmpInst::ICMP_SLE; 2383 break; 2384 case ICmpInst::ICMP_UGT: 2385 // (float)int > 4.4 --> int > 4 2386 // (float)int > -4.4 --> true 2387 if (RHS.isNegative()) 2388 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2389 break; 2390 case ICmpInst::ICMP_SGT: 2391 // (float)int > 4.4 --> int > 4 2392 // (float)int > -4.4 --> int >= -4 2393 if (RHS.isNegative()) 2394 Pred = ICmpInst::ICMP_SGE; 2395 break; 2396 case ICmpInst::ICMP_UGE: 2397 // (float)int >= -4.4 --> true 2398 // (float)int >= 4.4 --> int > 4 2399 if (!RHS.isNegative()) 2400 return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext())); 2401 Pred = ICmpInst::ICMP_UGT; 2402 break; 2403 case ICmpInst::ICMP_SGE: 2404 // (float)int >= -4.4 --> int >= -4 2405 // (float)int >= 4.4 --> int > 4 2406 if (!RHS.isNegative()) 2407 Pred = ICmpInst::ICMP_SGT; 2408 break; 2409 } 2410 } 2411 } 2412 2413 // Lower this FP comparison into an appropriate integer version of the 2414 // comparison. 2415 return new ICmpInst(Pred, LHSI->getOperand(0), RHSInt); 2416} 2417 2418Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) { 2419 bool Changed = false; 2420 2421 /// Orders the operands of the compare so that they are listed from most 2422 /// complex to least complex. This puts constants before unary operators, 2423 /// before binary operators. 2424 if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) { 2425 I.swapOperands(); 2426 Changed = true; 2427 } 2428 2429 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 2430 2431 if (Value *V = SimplifyFCmpInst(I.getPredicate(), Op0, Op1, TD)) 2432 return ReplaceInstUsesWith(I, V); 2433 2434 // Simplify 'fcmp pred X, X' 2435 if (Op0 == Op1) { 2436 switch (I.getPredicate()) { 2437 default: llvm_unreachable("Unknown predicate!"); 2438 case FCmpInst::FCMP_UNO: // True if unordered: isnan(X) | isnan(Y) 2439 case FCmpInst::FCMP_ULT: // True if unordered or less than 2440 case FCmpInst::FCMP_UGT: // True if unordered or greater than 2441 case FCmpInst::FCMP_UNE: // True if unordered or not equal 2442 // Canonicalize these to be 'fcmp uno %X, 0.0'. 2443 I.setPredicate(FCmpInst::FCMP_UNO); 2444 I.setOperand(1, Constant::getNullValue(Op0->getType())); 2445 return &I; 2446 2447 case FCmpInst::FCMP_ORD: // True if ordered (no nans) 2448 case FCmpInst::FCMP_OEQ: // True if ordered and equal 2449 case FCmpInst::FCMP_OGE: // True if ordered and greater than or equal 2450 case FCmpInst::FCMP_OLE: // True if ordered and less than or equal 2451 // Canonicalize these to be 'fcmp ord %X, 0.0'. 2452 I.setPredicate(FCmpInst::FCMP_ORD); 2453 I.setOperand(1, Constant::getNullValue(Op0->getType())); 2454 return &I; 2455 } 2456 } 2457 2458 // Handle fcmp with constant RHS 2459 if (Constant *RHSC = dyn_cast<Constant>(Op1)) { 2460 if (Instruction *LHSI = dyn_cast<Instruction>(Op0)) 2461 switch (LHSI->getOpcode()) { 2462 case Instruction::PHI: 2463 // Only fold fcmp into the PHI if the phi and fcmp are in the same 2464 // block. If in the same block, we're encouraging jump threading. If 2465 // not, we are just pessimizing the code by making an i1 phi. 2466 if (LHSI->getParent() == I.getParent()) 2467 if (Instruction *NV = FoldOpIntoPhi(I, true)) 2468 return NV; 2469 break; 2470 case Instruction::SIToFP: 2471 case Instruction::UIToFP: 2472 if (Instruction *NV = FoldFCmp_IntToFP_Cst(I, LHSI, RHSC)) 2473 return NV; 2474 break; 2475 case Instruction::Select: { 2476 // If either operand of the select is a constant, we can fold the 2477 // comparison into the select arms, which will cause one to be 2478 // constant folded and the select turned into a bitwise or. 2479 Value *Op1 = 0, *Op2 = 0; 2480 if (LHSI->hasOneUse()) { 2481 if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) { 2482 // Fold the known value into the constant operand. 2483 Op1 = ConstantExpr::getCompare(I.getPredicate(), C, RHSC); 2484 // Insert a new FCmp of the other select operand. 2485 Op2 = Builder->CreateFCmp(I.getPredicate(), 2486 LHSI->getOperand(2), RHSC, I.getName()); 2487 } else if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) { 2488 // Fold the known value into the constant operand. 2489 Op2 = ConstantExpr::getCompare(I.getPredicate(), C, RHSC); 2490 // Insert a new FCmp of the other select operand. 2491 Op1 = Builder->CreateFCmp(I.getPredicate(), LHSI->getOperand(1), 2492 RHSC, I.getName()); 2493 } 2494 } 2495 2496 if (Op1) 2497 return SelectInst::Create(LHSI->getOperand(0), Op1, Op2); 2498 break; 2499 } 2500 case Instruction::Load: 2501 if (GetElementPtrInst *GEP = 2502 dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) { 2503 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0))) 2504 if (GV->isConstant() && GV->hasDefinitiveInitializer() && 2505 !cast<LoadInst>(LHSI)->isVolatile()) 2506 if (Instruction *Res = FoldCmpLoadFromIndexedGlobal(GEP, GV, I)) 2507 return Res; 2508 } 2509 break; 2510 } 2511 } 2512 2513 return Changed ? &I : 0; 2514} 2515