1 //===- llvm/Support/KnownBits.h - Stores known zeros/ones -------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file contains a class for representing known zeros and ones used by 10 // computeKnownBits. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_SUPPORT_KNOWNBITS_H 15 #define LLVM_SUPPORT_KNOWNBITS_H 16 17 #include "llvm/ADT/APInt.h" 18 #include "llvm/ADT/Optional.h" 19 20 namespace llvm { 21 22 // Struct for tracking the known zeros and ones of a value. 23 struct KnownBits { 24 APInt Zero; 25 APInt One; 26 27 private: 28 // Internal constructor for creating a KnownBits from two APInts. KnownBitsKnownBits29 KnownBits(APInt Zero, APInt One) 30 : Zero(std::move(Zero)), One(std::move(One)) {} 31 32 public: 33 // Default construct Zero and One. KnownBitsKnownBits34 KnownBits() {} 35 36 /// Create a known bits object of BitWidth bits initialized to unknown. KnownBitsKnownBits37 KnownBits(unsigned BitWidth) : Zero(BitWidth, 0), One(BitWidth, 0) {} 38 39 /// Get the bit width of this value. getBitWidthKnownBits40 unsigned getBitWidth() const { 41 assert(Zero.getBitWidth() == One.getBitWidth() && 42 "Zero and One should have the same width!"); 43 return Zero.getBitWidth(); 44 } 45 46 /// Returns true if there is conflicting information. hasConflictKnownBits47 bool hasConflict() const { return Zero.intersects(One); } 48 49 /// Returns true if we know the value of all bits. isConstantKnownBits50 bool isConstant() const { 51 assert(!hasConflict() && "KnownBits conflict!"); 52 return Zero.countPopulation() + One.countPopulation() == getBitWidth(); 53 } 54 55 /// Returns the value when all bits have a known value. This just returns One 56 /// with a protective assertion. getConstantKnownBits57 const APInt &getConstant() const { 58 assert(isConstant() && "Can only get value when all bits are known"); 59 return One; 60 } 61 62 /// Returns true if we don't know any bits. isUnknownKnownBits63 bool isUnknown() const { return Zero.isZero() && One.isZero(); } 64 65 /// Resets the known state of all bits. resetAllKnownBits66 void resetAll() { 67 Zero.clearAllBits(); 68 One.clearAllBits(); 69 } 70 71 /// Returns true if value is all zero. isZeroKnownBits72 bool isZero() const { 73 assert(!hasConflict() && "KnownBits conflict!"); 74 return Zero.isAllOnes(); 75 } 76 77 /// Returns true if value is all one bits. isAllOnesKnownBits78 bool isAllOnes() const { 79 assert(!hasConflict() && "KnownBits conflict!"); 80 return One.isAllOnes(); 81 } 82 83 /// Make all bits known to be zero and discard any previous information. setAllZeroKnownBits84 void setAllZero() { 85 Zero.setAllBits(); 86 One.clearAllBits(); 87 } 88 89 /// Make all bits known to be one and discard any previous information. setAllOnesKnownBits90 void setAllOnes() { 91 Zero.clearAllBits(); 92 One.setAllBits(); 93 } 94 95 /// Returns true if this value is known to be negative. isNegativeKnownBits96 bool isNegative() const { return One.isSignBitSet(); } 97 98 /// Returns true if this value is known to be non-negative. isNonNegativeKnownBits99 bool isNonNegative() const { return Zero.isSignBitSet(); } 100 101 /// Returns true if this value is known to be non-zero. isNonZeroKnownBits102 bool isNonZero() const { return !One.isZero(); } 103 104 /// Returns true if this value is known to be positive. isStrictlyPositiveKnownBits105 bool isStrictlyPositive() const { 106 return Zero.isSignBitSet() && !One.isZero(); 107 } 108 109 /// Make this value negative. makeNegativeKnownBits110 void makeNegative() { 111 One.setSignBit(); 112 } 113 114 /// Make this value non-negative. makeNonNegativeKnownBits115 void makeNonNegative() { 116 Zero.setSignBit(); 117 } 118 119 /// Return the minimal unsigned value possible given these KnownBits. getMinValueKnownBits120 APInt getMinValue() const { 121 // Assume that all bits that aren't known-ones are zeros. 122 return One; 123 } 124 125 /// Return the minimal signed value possible given these KnownBits. getSignedMinValueKnownBits126 APInt getSignedMinValue() const { 127 // Assume that all bits that aren't known-ones are zeros. 128 APInt Min = One; 129 // Sign bit is unknown. 130 if (Zero.isSignBitClear()) 131 Min.setSignBit(); 132 return Min; 133 } 134 135 /// Return the maximal unsigned value possible given these KnownBits. getMaxValueKnownBits136 APInt getMaxValue() const { 137 // Assume that all bits that aren't known-zeros are ones. 138 return ~Zero; 139 } 140 141 /// Return the maximal signed value possible given these KnownBits. getSignedMaxValueKnownBits142 APInt getSignedMaxValue() const { 143 // Assume that all bits that aren't known-zeros are ones. 144 APInt Max = ~Zero; 145 // Sign bit is unknown. 146 if (One.isSignBitClear()) 147 Max.clearSignBit(); 148 return Max; 149 } 150 151 /// Return known bits for a truncation of the value we're tracking. truncKnownBits152 KnownBits trunc(unsigned BitWidth) const { 153 return KnownBits(Zero.trunc(BitWidth), One.trunc(BitWidth)); 154 } 155 156 /// Return known bits for an "any" extension of the value we're tracking, 157 /// where we don't know anything about the extended bits. anyextKnownBits158 KnownBits anyext(unsigned BitWidth) const { 159 return KnownBits(Zero.zext(BitWidth), One.zext(BitWidth)); 160 } 161 162 /// Return known bits for a zero extension of the value we're tracking. zextKnownBits163 KnownBits zext(unsigned BitWidth) const { 164 unsigned OldBitWidth = getBitWidth(); 165 APInt NewZero = Zero.zext(BitWidth); 166 NewZero.setBitsFrom(OldBitWidth); 167 return KnownBits(NewZero, One.zext(BitWidth)); 168 } 169 170 /// Return known bits for a sign extension of the value we're tracking. sextKnownBits171 KnownBits sext(unsigned BitWidth) const { 172 return KnownBits(Zero.sext(BitWidth), One.sext(BitWidth)); 173 } 174 175 /// Return known bits for an "any" extension or truncation of the value we're 176 /// tracking. anyextOrTruncKnownBits177 KnownBits anyextOrTrunc(unsigned BitWidth) const { 178 if (BitWidth > getBitWidth()) 179 return anyext(BitWidth); 180 if (BitWidth < getBitWidth()) 181 return trunc(BitWidth); 182 return *this; 183 } 184 185 /// Return known bits for a zero extension or truncation of the value we're 186 /// tracking. zextOrTruncKnownBits187 KnownBits zextOrTrunc(unsigned BitWidth) const { 188 if (BitWidth > getBitWidth()) 189 return zext(BitWidth); 190 if (BitWidth < getBitWidth()) 191 return trunc(BitWidth); 192 return *this; 193 } 194 195 /// Return known bits for a sign extension or truncation of the value we're 196 /// tracking. sextOrTruncKnownBits197 KnownBits sextOrTrunc(unsigned BitWidth) const { 198 if (BitWidth > getBitWidth()) 199 return sext(BitWidth); 200 if (BitWidth < getBitWidth()) 201 return trunc(BitWidth); 202 return *this; 203 } 204 205 /// Return known bits for a in-register sign extension of the value we're 206 /// tracking. 207 KnownBits sextInReg(unsigned SrcBitWidth) const; 208 209 /// Insert the bits from a smaller known bits starting at bitPosition. insertBitsKnownBits210 void insertBits(const KnownBits &SubBits, unsigned BitPosition) { 211 Zero.insertBits(SubBits.Zero, BitPosition); 212 One.insertBits(SubBits.One, BitPosition); 213 } 214 215 /// Return a subset of the known bits from [bitPosition,bitPosition+numBits). extractBitsKnownBits216 KnownBits extractBits(unsigned NumBits, unsigned BitPosition) const { 217 return KnownBits(Zero.extractBits(NumBits, BitPosition), 218 One.extractBits(NumBits, BitPosition)); 219 } 220 221 /// Return KnownBits based on this, but updated given that the underlying 222 /// value is known to be greater than or equal to Val. 223 KnownBits makeGE(const APInt &Val) const; 224 225 /// Returns the minimum number of trailing zero bits. countMinTrailingZerosKnownBits226 unsigned countMinTrailingZeros() const { 227 return Zero.countTrailingOnes(); 228 } 229 230 /// Returns the minimum number of trailing one bits. countMinTrailingOnesKnownBits231 unsigned countMinTrailingOnes() const { 232 return One.countTrailingOnes(); 233 } 234 235 /// Returns the minimum number of leading zero bits. countMinLeadingZerosKnownBits236 unsigned countMinLeadingZeros() const { 237 return Zero.countLeadingOnes(); 238 } 239 240 /// Returns the minimum number of leading one bits. countMinLeadingOnesKnownBits241 unsigned countMinLeadingOnes() const { 242 return One.countLeadingOnes(); 243 } 244 245 /// Returns the number of times the sign bit is replicated into the other 246 /// bits. countMinSignBitsKnownBits247 unsigned countMinSignBits() const { 248 if (isNonNegative()) 249 return countMinLeadingZeros(); 250 if (isNegative()) 251 return countMinLeadingOnes(); 252 return 0; 253 } 254 255 /// Returns the maximum number of trailing zero bits possible. countMaxTrailingZerosKnownBits256 unsigned countMaxTrailingZeros() const { 257 return One.countTrailingZeros(); 258 } 259 260 /// Returns the maximum number of trailing one bits possible. countMaxTrailingOnesKnownBits261 unsigned countMaxTrailingOnes() const { 262 return Zero.countTrailingZeros(); 263 } 264 265 /// Returns the maximum number of leading zero bits possible. countMaxLeadingZerosKnownBits266 unsigned countMaxLeadingZeros() const { 267 return One.countLeadingZeros(); 268 } 269 270 /// Returns the maximum number of leading one bits possible. countMaxLeadingOnesKnownBits271 unsigned countMaxLeadingOnes() const { 272 return Zero.countLeadingZeros(); 273 } 274 275 /// Returns the number of bits known to be one. countMinPopulationKnownBits276 unsigned countMinPopulation() const { 277 return One.countPopulation(); 278 } 279 280 /// Returns the maximum number of bits that could be one. countMaxPopulationKnownBits281 unsigned countMaxPopulation() const { 282 return getBitWidth() - Zero.countPopulation(); 283 } 284 countMaxActiveBitsKnownBits285 unsigned countMaxActiveBits() const { 286 return getBitWidth() - countMinLeadingZeros(); 287 } 288 289 /// Create known bits from a known constant. makeConstantKnownBits290 static KnownBits makeConstant(const APInt &C) { 291 return KnownBits(~C, C); 292 } 293 294 /// Compute known bits common to LHS and RHS. commonBitsKnownBits295 static KnownBits commonBits(const KnownBits &LHS, const KnownBits &RHS) { 296 return KnownBits(LHS.Zero & RHS.Zero, LHS.One & RHS.One); 297 } 298 299 /// Return true if LHS and RHS have no common bits set. haveNoCommonBitsSetKnownBits300 static bool haveNoCommonBitsSet(const KnownBits &LHS, const KnownBits &RHS) { 301 return (LHS.Zero | RHS.Zero).isAllOnes(); 302 } 303 304 /// Compute known bits resulting from adding LHS, RHS and a 1-bit Carry. 305 static KnownBits computeForAddCarry( 306 const KnownBits &LHS, const KnownBits &RHS, const KnownBits &Carry); 307 308 /// Compute known bits resulting from adding LHS and RHS. 309 static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS, 310 KnownBits RHS); 311 312 /// Compute known bits resulting from multiplying LHS and RHS. 313 static KnownBits mul(const KnownBits &LHS, const KnownBits &RHS, 314 bool SelfMultiply = false); 315 316 /// Compute known bits from sign-extended multiply-hi. 317 static KnownBits mulhs(const KnownBits &LHS, const KnownBits &RHS); 318 319 /// Compute known bits from zero-extended multiply-hi. 320 static KnownBits mulhu(const KnownBits &LHS, const KnownBits &RHS); 321 322 /// Compute known bits for udiv(LHS, RHS). 323 static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS); 324 325 /// Compute known bits for urem(LHS, RHS). 326 static KnownBits urem(const KnownBits &LHS, const KnownBits &RHS); 327 328 /// Compute known bits for srem(LHS, RHS). 329 static KnownBits srem(const KnownBits &LHS, const KnownBits &RHS); 330 331 /// Compute known bits for umax(LHS, RHS). 332 static KnownBits umax(const KnownBits &LHS, const KnownBits &RHS); 333 334 /// Compute known bits for umin(LHS, RHS). 335 static KnownBits umin(const KnownBits &LHS, const KnownBits &RHS); 336 337 /// Compute known bits for smax(LHS, RHS). 338 static KnownBits smax(const KnownBits &LHS, const KnownBits &RHS); 339 340 /// Compute known bits for smin(LHS, RHS). 341 static KnownBits smin(const KnownBits &LHS, const KnownBits &RHS); 342 343 /// Compute known bits for shl(LHS, RHS). 344 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 345 static KnownBits shl(const KnownBits &LHS, const KnownBits &RHS); 346 347 /// Compute known bits for lshr(LHS, RHS). 348 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 349 static KnownBits lshr(const KnownBits &LHS, const KnownBits &RHS); 350 351 /// Compute known bits for ashr(LHS, RHS). 352 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 353 static KnownBits ashr(const KnownBits &LHS, const KnownBits &RHS); 354 355 /// Determine if these known bits always give the same ICMP_EQ result. 356 static Optional<bool> eq(const KnownBits &LHS, const KnownBits &RHS); 357 358 /// Determine if these known bits always give the same ICMP_NE result. 359 static Optional<bool> ne(const KnownBits &LHS, const KnownBits &RHS); 360 361 /// Determine if these known bits always give the same ICMP_UGT result. 362 static Optional<bool> ugt(const KnownBits &LHS, const KnownBits &RHS); 363 364 /// Determine if these known bits always give the same ICMP_UGE result. 365 static Optional<bool> uge(const KnownBits &LHS, const KnownBits &RHS); 366 367 /// Determine if these known bits always give the same ICMP_ULT result. 368 static Optional<bool> ult(const KnownBits &LHS, const KnownBits &RHS); 369 370 /// Determine if these known bits always give the same ICMP_ULE result. 371 static Optional<bool> ule(const KnownBits &LHS, const KnownBits &RHS); 372 373 /// Determine if these known bits always give the same ICMP_SGT result. 374 static Optional<bool> sgt(const KnownBits &LHS, const KnownBits &RHS); 375 376 /// Determine if these known bits always give the same ICMP_SGE result. 377 static Optional<bool> sge(const KnownBits &LHS, const KnownBits &RHS); 378 379 /// Determine if these known bits always give the same ICMP_SLT result. 380 static Optional<bool> slt(const KnownBits &LHS, const KnownBits &RHS); 381 382 /// Determine if these known bits always give the same ICMP_SLE result. 383 static Optional<bool> sle(const KnownBits &LHS, const KnownBits &RHS); 384 385 /// Update known bits based on ANDing with RHS. 386 KnownBits &operator&=(const KnownBits &RHS); 387 388 /// Update known bits based on ORing with RHS. 389 KnownBits &operator|=(const KnownBits &RHS); 390 391 /// Update known bits based on XORing with RHS. 392 KnownBits &operator^=(const KnownBits &RHS); 393 394 /// Compute known bits for the absolute value. 395 KnownBits abs(bool IntMinIsPoison = false) const; 396 byteSwapKnownBits397 KnownBits byteSwap() { 398 return KnownBits(Zero.byteSwap(), One.byteSwap()); 399 } 400 reverseBitsKnownBits401 KnownBits reverseBits() { 402 return KnownBits(Zero.reverseBits(), One.reverseBits()); 403 } 404 405 void print(raw_ostream &OS) const; 406 void dump() const; 407 }; 408 409 inline KnownBits operator&(KnownBits LHS, const KnownBits &RHS) { 410 LHS &= RHS; 411 return LHS; 412 } 413 414 inline KnownBits operator&(const KnownBits &LHS, KnownBits &&RHS) { 415 RHS &= LHS; 416 return std::move(RHS); 417 } 418 419 inline KnownBits operator|(KnownBits LHS, const KnownBits &RHS) { 420 LHS |= RHS; 421 return LHS; 422 } 423 424 inline KnownBits operator|(const KnownBits &LHS, KnownBits &&RHS) { 425 RHS |= LHS; 426 return std::move(RHS); 427 } 428 429 inline KnownBits operator^(KnownBits LHS, const KnownBits &RHS) { 430 LHS ^= RHS; 431 return LHS; 432 } 433 434 inline KnownBits operator^(const KnownBits &LHS, KnownBits &&RHS) { 435 RHS ^= LHS; 436 return std::move(RHS); 437 } 438 439 } // end namespace llvm 440 441 #endif 442