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. 29 KnownBits(APInt Zero, APInt One) 30 : Zero(std::move(Zero)), One(std::move(One)) {} 31 32 public: 33 // Default construct Zero and One. 34 KnownBits() = default; 35 36 /// Create a known bits object of BitWidth bits initialized to unknown. 37 KnownBits(unsigned BitWidth) : Zero(BitWidth, 0), One(BitWidth, 0) {} 38 39 /// Get the bit width of this value. 40 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. 47 bool hasConflict() const { return Zero.intersects(One); } 48 49 /// Returns true if we know the value of all bits. 50 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. 57 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. 63 bool isUnknown() const { return Zero.isZero() && One.isZero(); } 64 65 /// Resets the known state of all bits. 66 void resetAll() { 67 Zero.clearAllBits(); 68 One.clearAllBits(); 69 } 70 71 /// Returns true if value is all zero. 72 bool isZero() const { 73 assert(!hasConflict() && "KnownBits conflict!"); 74 return Zero.isAllOnes(); 75 } 76 77 /// Returns true if value is all one bits. 78 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. 84 void setAllZero() { 85 Zero.setAllBits(); 86 One.clearAllBits(); 87 } 88 89 /// Make all bits known to be one and discard any previous information. 90 void setAllOnes() { 91 Zero.clearAllBits(); 92 One.setAllBits(); 93 } 94 95 /// Returns true if this value is known to be negative. 96 bool isNegative() const { return One.isSignBitSet(); } 97 98 /// Returns true if this value is known to be non-negative. 99 bool isNonNegative() const { return Zero.isSignBitSet(); } 100 101 /// Returns true if this value is known to be non-zero. 102 bool isNonZero() const { return !One.isZero(); } 103 104 /// Returns true if this value is known to be positive. 105 bool isStrictlyPositive() const { 106 return Zero.isSignBitSet() && !One.isZero(); 107 } 108 109 /// Make this value negative. 110 void makeNegative() { 111 One.setSignBit(); 112 } 113 114 /// Make this value non-negative. 115 void makeNonNegative() { 116 Zero.setSignBit(); 117 } 118 119 /// Return the minimal unsigned value possible given these KnownBits. 120 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. 126 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. 136 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. 142 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. 152 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. 158 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. 163 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. 171 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. 177 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. 187 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. 197 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. 210 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). 216 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. 226 unsigned countMinTrailingZeros() const { 227 return Zero.countTrailingOnes(); 228 } 229 230 /// Returns the minimum number of trailing one bits. 231 unsigned countMinTrailingOnes() const { 232 return One.countTrailingOnes(); 233 } 234 235 /// Returns the minimum number of leading zero bits. 236 unsigned countMinLeadingZeros() const { 237 return Zero.countLeadingOnes(); 238 } 239 240 /// Returns the minimum number of leading one bits. 241 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. 247 unsigned countMinSignBits() const { 248 if (isNonNegative()) 249 return countMinLeadingZeros(); 250 if (isNegative()) 251 return countMinLeadingOnes(); 252 // Every value has at least 1 sign bit. 253 return 1; 254 } 255 256 /// Returns the maximum number of bits needed to represent all possible 257 /// signed values with these known bits. This is the inverse of the minimum 258 /// number of known sign bits. Examples for bitwidth 5: 259 /// 110?? --> 4 260 /// 0000? --> 2 261 unsigned countMaxSignificantBits() const { 262 return getBitWidth() - countMinSignBits() + 1; 263 } 264 265 /// Returns the maximum number of trailing zero bits possible. 266 unsigned countMaxTrailingZeros() const { 267 return One.countTrailingZeros(); 268 } 269 270 /// Returns the maximum number of trailing one bits possible. 271 unsigned countMaxTrailingOnes() const { 272 return Zero.countTrailingZeros(); 273 } 274 275 /// Returns the maximum number of leading zero bits possible. 276 unsigned countMaxLeadingZeros() const { 277 return One.countLeadingZeros(); 278 } 279 280 /// Returns the maximum number of leading one bits possible. 281 unsigned countMaxLeadingOnes() const { 282 return Zero.countLeadingZeros(); 283 } 284 285 /// Returns the number of bits known to be one. 286 unsigned countMinPopulation() const { 287 return One.countPopulation(); 288 } 289 290 /// Returns the maximum number of bits that could be one. 291 unsigned countMaxPopulation() const { 292 return getBitWidth() - Zero.countPopulation(); 293 } 294 295 /// Returns the maximum number of bits needed to represent all possible 296 /// unsigned values with these known bits. This is the inverse of the 297 /// minimum number of leading zeros. 298 unsigned countMaxActiveBits() const { 299 return getBitWidth() - countMinLeadingZeros(); 300 } 301 302 /// Create known bits from a known constant. 303 static KnownBits makeConstant(const APInt &C) { 304 return KnownBits(~C, C); 305 } 306 307 /// Compute known bits common to LHS and RHS. 308 static KnownBits commonBits(const KnownBits &LHS, const KnownBits &RHS) { 309 return KnownBits(LHS.Zero & RHS.Zero, LHS.One & RHS.One); 310 } 311 312 /// Return true if LHS and RHS have no common bits set. 313 static bool haveNoCommonBitsSet(const KnownBits &LHS, const KnownBits &RHS) { 314 return (LHS.Zero | RHS.Zero).isAllOnes(); 315 } 316 317 /// Compute known bits resulting from adding LHS, RHS and a 1-bit Carry. 318 static KnownBits computeForAddCarry( 319 const KnownBits &LHS, const KnownBits &RHS, const KnownBits &Carry); 320 321 /// Compute known bits resulting from adding LHS and RHS. 322 static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS, 323 KnownBits RHS); 324 325 /// Compute known bits resulting from multiplying LHS and RHS. 326 static KnownBits mul(const KnownBits &LHS, const KnownBits &RHS, 327 bool NoUndefSelfMultiply = false); 328 329 /// Compute known bits from sign-extended multiply-hi. 330 static KnownBits mulhs(const KnownBits &LHS, const KnownBits &RHS); 331 332 /// Compute known bits from zero-extended multiply-hi. 333 static KnownBits mulhu(const KnownBits &LHS, const KnownBits &RHS); 334 335 /// Compute known bits for udiv(LHS, RHS). 336 static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS); 337 338 /// Compute known bits for urem(LHS, RHS). 339 static KnownBits urem(const KnownBits &LHS, const KnownBits &RHS); 340 341 /// Compute known bits for srem(LHS, RHS). 342 static KnownBits srem(const KnownBits &LHS, const KnownBits &RHS); 343 344 /// Compute known bits for umax(LHS, RHS). 345 static KnownBits umax(const KnownBits &LHS, const KnownBits &RHS); 346 347 /// Compute known bits for umin(LHS, RHS). 348 static KnownBits umin(const KnownBits &LHS, const KnownBits &RHS); 349 350 /// Compute known bits for smax(LHS, RHS). 351 static KnownBits smax(const KnownBits &LHS, const KnownBits &RHS); 352 353 /// Compute known bits for smin(LHS, RHS). 354 static KnownBits smin(const KnownBits &LHS, const KnownBits &RHS); 355 356 /// Compute known bits for shl(LHS, RHS). 357 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 358 static KnownBits shl(const KnownBits &LHS, const KnownBits &RHS); 359 360 /// Compute known bits for lshr(LHS, RHS). 361 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 362 static KnownBits lshr(const KnownBits &LHS, const KnownBits &RHS); 363 364 /// Compute known bits for ashr(LHS, RHS). 365 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 366 static KnownBits ashr(const KnownBits &LHS, const KnownBits &RHS); 367 368 /// Determine if these known bits always give the same ICMP_EQ result. 369 static Optional<bool> eq(const KnownBits &LHS, const KnownBits &RHS); 370 371 /// Determine if these known bits always give the same ICMP_NE result. 372 static Optional<bool> ne(const KnownBits &LHS, const KnownBits &RHS); 373 374 /// Determine if these known bits always give the same ICMP_UGT result. 375 static Optional<bool> ugt(const KnownBits &LHS, const KnownBits &RHS); 376 377 /// Determine if these known bits always give the same ICMP_UGE result. 378 static Optional<bool> uge(const KnownBits &LHS, const KnownBits &RHS); 379 380 /// Determine if these known bits always give the same ICMP_ULT result. 381 static Optional<bool> ult(const KnownBits &LHS, const KnownBits &RHS); 382 383 /// Determine if these known bits always give the same ICMP_ULE result. 384 static Optional<bool> ule(const KnownBits &LHS, const KnownBits &RHS); 385 386 /// Determine if these known bits always give the same ICMP_SGT result. 387 static Optional<bool> sgt(const KnownBits &LHS, const KnownBits &RHS); 388 389 /// Determine if these known bits always give the same ICMP_SGE result. 390 static Optional<bool> sge(const KnownBits &LHS, const KnownBits &RHS); 391 392 /// Determine if these known bits always give the same ICMP_SLT result. 393 static Optional<bool> slt(const KnownBits &LHS, const KnownBits &RHS); 394 395 /// Determine if these known bits always give the same ICMP_SLE result. 396 static Optional<bool> sle(const KnownBits &LHS, const KnownBits &RHS); 397 398 /// Update known bits based on ANDing with RHS. 399 KnownBits &operator&=(const KnownBits &RHS); 400 401 /// Update known bits based on ORing with RHS. 402 KnownBits &operator|=(const KnownBits &RHS); 403 404 /// Update known bits based on XORing with RHS. 405 KnownBits &operator^=(const KnownBits &RHS); 406 407 /// Compute known bits for the absolute value. 408 KnownBits abs(bool IntMinIsPoison = false) const; 409 410 KnownBits byteSwap() { 411 return KnownBits(Zero.byteSwap(), One.byteSwap()); 412 } 413 414 KnownBits reverseBits() { 415 return KnownBits(Zero.reverseBits(), One.reverseBits()); 416 } 417 418 bool operator==(const KnownBits &Other) const { 419 return Zero == Other.Zero && One == Other.One; 420 } 421 422 bool operator!=(const KnownBits &Other) const { return !(*this == Other); } 423 424 void print(raw_ostream &OS) const; 425 void dump() const; 426 }; 427 428 inline KnownBits operator&(KnownBits LHS, const KnownBits &RHS) { 429 LHS &= RHS; 430 return LHS; 431 } 432 433 inline KnownBits operator&(const KnownBits &LHS, KnownBits &&RHS) { 434 RHS &= LHS; 435 return std::move(RHS); 436 } 437 438 inline KnownBits operator|(KnownBits LHS, const KnownBits &RHS) { 439 LHS |= RHS; 440 return LHS; 441 } 442 443 inline KnownBits operator|(const KnownBits &LHS, KnownBits &&RHS) { 444 RHS |= LHS; 445 return std::move(RHS); 446 } 447 448 inline KnownBits operator^(KnownBits LHS, const KnownBits &RHS) { 449 LHS ^= RHS; 450 return LHS; 451 } 452 453 inline KnownBits operator^(const KnownBits &LHS, KnownBits &&RHS) { 454 RHS ^= LHS; 455 return std::move(RHS); 456 } 457 458 } // end namespace llvm 459 460 #endif 461