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 <optional> 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.popcount() + One.popcount() == 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 /// Concatenate the bits from \p Lo onto the bottom of *this. This is 222 /// equivalent to: 223 /// (this->zext(NewWidth) << Lo.getBitWidth()) | Lo.zext(NewWidth) 224 KnownBits concat(const KnownBits &Lo) const { 225 return KnownBits(Zero.concat(Lo.Zero), One.concat(Lo.One)); 226 } 227 228 /// Return KnownBits based on this, but updated given that the underlying 229 /// value is known to be greater than or equal to Val. 230 KnownBits makeGE(const APInt &Val) const; 231 232 /// Returns the minimum number of trailing zero bits. 233 unsigned countMinTrailingZeros() const { return Zero.countr_one(); } 234 235 /// Returns the minimum number of trailing one bits. 236 unsigned countMinTrailingOnes() const { return One.countr_one(); } 237 238 /// Returns the minimum number of leading zero bits. 239 unsigned countMinLeadingZeros() const { return Zero.countl_one(); } 240 241 /// Returns the minimum number of leading one bits. 242 unsigned countMinLeadingOnes() const { return One.countl_one(); } 243 244 /// Returns the number of times the sign bit is replicated into the other 245 /// bits. 246 unsigned countMinSignBits() const { 247 if (isNonNegative()) 248 return countMinLeadingZeros(); 249 if (isNegative()) 250 return countMinLeadingOnes(); 251 // Every value has at least 1 sign bit. 252 return 1; 253 } 254 255 /// Returns the maximum number of bits needed to represent all possible 256 /// signed values with these known bits. This is the inverse of the minimum 257 /// number of known sign bits. Examples for bitwidth 5: 258 /// 110?? --> 4 259 /// 0000? --> 2 260 unsigned countMaxSignificantBits() const { 261 return getBitWidth() - countMinSignBits() + 1; 262 } 263 264 /// Returns the maximum number of trailing zero bits possible. 265 unsigned countMaxTrailingZeros() const { return One.countr_zero(); } 266 267 /// Returns the maximum number of trailing one bits possible. 268 unsigned countMaxTrailingOnes() const { return Zero.countr_zero(); } 269 270 /// Returns the maximum number of leading zero bits possible. 271 unsigned countMaxLeadingZeros() const { return One.countl_zero(); } 272 273 /// Returns the maximum number of leading one bits possible. 274 unsigned countMaxLeadingOnes() const { return Zero.countl_zero(); } 275 276 /// Returns the number of bits known to be one. 277 unsigned countMinPopulation() const { return One.popcount(); } 278 279 /// Returns the maximum number of bits that could be one. 280 unsigned countMaxPopulation() const { 281 return getBitWidth() - Zero.popcount(); 282 } 283 284 /// Returns the maximum number of bits needed to represent all possible 285 /// unsigned values with these known bits. This is the inverse of the 286 /// minimum number of leading zeros. 287 unsigned countMaxActiveBits() const { 288 return getBitWidth() - countMinLeadingZeros(); 289 } 290 291 /// Create known bits from a known constant. 292 static KnownBits makeConstant(const APInt &C) { 293 return KnownBits(~C, C); 294 } 295 296 /// Returns KnownBits information that is known to be true for both this and 297 /// RHS. 298 /// 299 /// When an operation is known to return one of its operands, this can be used 300 /// to combine information about the known bits of the operands to get the 301 /// information that must be true about the result. 302 KnownBits intersectWith(const KnownBits &RHS) const { 303 return KnownBits(Zero & RHS.Zero, One & RHS.One); 304 } 305 306 /// Returns KnownBits information that is known to be true for either this or 307 /// RHS or both. 308 /// 309 /// This can be used to combine different sources of information about the 310 /// known bits of a single value, e.g. information about the low bits and the 311 /// high bits of the result of a multiplication. 312 KnownBits unionWith(const KnownBits &RHS) const { 313 return KnownBits(Zero | RHS.Zero, One | RHS.One); 314 } 315 316 /// Compute known bits common to LHS and RHS. 317 LLVM_DEPRECATED("use intersectWith instead", "intersectWith") 318 static KnownBits commonBits(const KnownBits &LHS, const KnownBits &RHS) { 319 return LHS.intersectWith(RHS); 320 } 321 322 /// Return true if LHS and RHS have no common bits set. 323 static bool haveNoCommonBitsSet(const KnownBits &LHS, const KnownBits &RHS) { 324 return (LHS.Zero | RHS.Zero).isAllOnes(); 325 } 326 327 /// Compute known bits resulting from adding LHS, RHS and a 1-bit Carry. 328 static KnownBits computeForAddCarry( 329 const KnownBits &LHS, const KnownBits &RHS, const KnownBits &Carry); 330 331 /// Compute known bits resulting from adding LHS and RHS. 332 static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS, 333 KnownBits RHS); 334 335 /// Compute knownbits resulting from llvm.sadd.sat(LHS, RHS) 336 static KnownBits sadd_sat(const KnownBits &LHS, const KnownBits &RHS); 337 338 /// Compute knownbits resulting from llvm.uadd.sat(LHS, RHS) 339 static KnownBits uadd_sat(const KnownBits &LHS, const KnownBits &RHS); 340 341 /// Compute knownbits resulting from llvm.ssub.sat(LHS, RHS) 342 static KnownBits ssub_sat(const KnownBits &LHS, const KnownBits &RHS); 343 344 /// Compute knownbits resulting from llvm.usub.sat(LHS, RHS) 345 static KnownBits usub_sat(const KnownBits &LHS, const KnownBits &RHS); 346 347 /// Compute known bits resulting from multiplying LHS and RHS. 348 static KnownBits mul(const KnownBits &LHS, const KnownBits &RHS, 349 bool NoUndefSelfMultiply = false); 350 351 /// Compute known bits from sign-extended multiply-hi. 352 static KnownBits mulhs(const KnownBits &LHS, const KnownBits &RHS); 353 354 /// Compute known bits from zero-extended multiply-hi. 355 static KnownBits mulhu(const KnownBits &LHS, const KnownBits &RHS); 356 357 /// Compute known bits for sdiv(LHS, RHS). 358 static KnownBits sdiv(const KnownBits &LHS, const KnownBits &RHS, 359 bool Exact = false); 360 361 /// Compute known bits for udiv(LHS, RHS). 362 static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS, 363 bool Exact = false); 364 365 /// Compute known bits for urem(LHS, RHS). 366 static KnownBits urem(const KnownBits &LHS, const KnownBits &RHS); 367 368 /// Compute known bits for srem(LHS, RHS). 369 static KnownBits srem(const KnownBits &LHS, const KnownBits &RHS); 370 371 /// Compute known bits for umax(LHS, RHS). 372 static KnownBits umax(const KnownBits &LHS, const KnownBits &RHS); 373 374 /// Compute known bits for umin(LHS, RHS). 375 static KnownBits umin(const KnownBits &LHS, const KnownBits &RHS); 376 377 /// Compute known bits for smax(LHS, RHS). 378 static KnownBits smax(const KnownBits &LHS, const KnownBits &RHS); 379 380 /// Compute known bits for smin(LHS, RHS). 381 static KnownBits smin(const KnownBits &LHS, const KnownBits &RHS); 382 383 /// Compute known bits for shl(LHS, RHS). 384 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 385 static KnownBits shl(const KnownBits &LHS, const KnownBits &RHS, 386 bool NUW = false, bool NSW = false, 387 bool ShAmtNonZero = false); 388 389 /// Compute known bits for lshr(LHS, RHS). 390 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 391 static KnownBits lshr(const KnownBits &LHS, const KnownBits &RHS, 392 bool ShAmtNonZero = false); 393 394 /// Compute known bits for ashr(LHS, RHS). 395 /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. 396 static KnownBits ashr(const KnownBits &LHS, const KnownBits &RHS, 397 bool ShAmtNonZero = false); 398 399 /// Determine if these known bits always give the same ICMP_EQ result. 400 static std::optional<bool> eq(const KnownBits &LHS, const KnownBits &RHS); 401 402 /// Determine if these known bits always give the same ICMP_NE result. 403 static std::optional<bool> ne(const KnownBits &LHS, const KnownBits &RHS); 404 405 /// Determine if these known bits always give the same ICMP_UGT result. 406 static std::optional<bool> ugt(const KnownBits &LHS, const KnownBits &RHS); 407 408 /// Determine if these known bits always give the same ICMP_UGE result. 409 static std::optional<bool> uge(const KnownBits &LHS, const KnownBits &RHS); 410 411 /// Determine if these known bits always give the same ICMP_ULT result. 412 static std::optional<bool> ult(const KnownBits &LHS, const KnownBits &RHS); 413 414 /// Determine if these known bits always give the same ICMP_ULE result. 415 static std::optional<bool> ule(const KnownBits &LHS, const KnownBits &RHS); 416 417 /// Determine if these known bits always give the same ICMP_SGT result. 418 static std::optional<bool> sgt(const KnownBits &LHS, const KnownBits &RHS); 419 420 /// Determine if these known bits always give the same ICMP_SGE result. 421 static std::optional<bool> sge(const KnownBits &LHS, const KnownBits &RHS); 422 423 /// Determine if these known bits always give the same ICMP_SLT result. 424 static std::optional<bool> slt(const KnownBits &LHS, const KnownBits &RHS); 425 426 /// Determine if these known bits always give the same ICMP_SLE result. 427 static std::optional<bool> sle(const KnownBits &LHS, const KnownBits &RHS); 428 429 /// Update known bits based on ANDing with RHS. 430 KnownBits &operator&=(const KnownBits &RHS); 431 432 /// Update known bits based on ORing with RHS. 433 KnownBits &operator|=(const KnownBits &RHS); 434 435 /// Update known bits based on XORing with RHS. 436 KnownBits &operator^=(const KnownBits &RHS); 437 438 /// Compute known bits for the absolute value. 439 KnownBits abs(bool IntMinIsPoison = false) const; 440 441 KnownBits byteSwap() const { 442 return KnownBits(Zero.byteSwap(), One.byteSwap()); 443 } 444 445 KnownBits reverseBits() const { 446 return KnownBits(Zero.reverseBits(), One.reverseBits()); 447 } 448 449 /// Compute known bits for X & -X, which has only the lowest bit set of X set. 450 /// The name comes from the X86 BMI instruction 451 KnownBits blsi() const; 452 453 /// Compute known bits for X ^ (X - 1), which has all bits up to and including 454 /// the lowest set bit of X set. The name comes from the X86 BMI instruction. 455 KnownBits blsmsk() const; 456 457 bool operator==(const KnownBits &Other) const { 458 return Zero == Other.Zero && One == Other.One; 459 } 460 461 bool operator!=(const KnownBits &Other) const { return !(*this == Other); } 462 463 void print(raw_ostream &OS) const; 464 void dump() const; 465 466 private: 467 // Internal helper for getting the initial KnownBits for an `srem` or `urem` 468 // operation with the low-bits set. 469 static KnownBits remGetLowBits(const KnownBits &LHS, const KnownBits &RHS); 470 }; 471 472 inline KnownBits operator&(KnownBits LHS, const KnownBits &RHS) { 473 LHS &= RHS; 474 return LHS; 475 } 476 477 inline KnownBits operator&(const KnownBits &LHS, KnownBits &&RHS) { 478 RHS &= LHS; 479 return std::move(RHS); 480 } 481 482 inline KnownBits operator|(KnownBits LHS, const KnownBits &RHS) { 483 LHS |= RHS; 484 return LHS; 485 } 486 487 inline KnownBits operator|(const KnownBits &LHS, KnownBits &&RHS) { 488 RHS |= LHS; 489 return std::move(RHS); 490 } 491 492 inline KnownBits operator^(KnownBits LHS, const KnownBits &RHS) { 493 LHS ^= RHS; 494 return LHS; 495 } 496 497 inline KnownBits operator^(const KnownBits &LHS, KnownBits &&RHS) { 498 RHS ^= LHS; 499 return std::move(RHS); 500 } 501 502 inline raw_ostream &operator<<(raw_ostream &OS, const KnownBits &Known) { 503 Known.print(OS); 504 return OS; 505 } 506 507 } // end namespace llvm 508 509 #endif 510