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(RHS: 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(width: BitWidth), One.trunc(width: 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(width: BitWidth), One.zext(width: 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(width: BitWidth); |
166 | NewZero.setBitsFrom(OldBitWidth); |
167 | return KnownBits(NewZero, One.zext(width: 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(width: BitWidth), One.sext(width: 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: SubBits.Zero, bitPosition: BitPosition); |
212 | One.insertBits(SubBits: SubBits.One, bitPosition: BitPosition); |
213 | } |
214 | |
215 | /// Return a subset of the known bits from [bitPosition,bitPosition+numBits). |
216 | KnownBits (unsigned NumBits, unsigned BitPosition) const { |
217 | return KnownBits(Zero.extractBits(numBits: NumBits, bitPosition: BitPosition), |
218 | One.extractBits(numBits: NumBits, bitPosition: 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(NewLSB: Lo.Zero), One.concat(NewLSB: 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 known bits results from subtracting RHS from LHS with 1-bit |
336 | /// Borrow. |
337 | static KnownBits computeForSubBorrow(const KnownBits &LHS, KnownBits RHS, |
338 | const KnownBits &Borrow); |
339 | |
340 | /// Compute knownbits resulting from llvm.sadd.sat(LHS, RHS) |
341 | static KnownBits sadd_sat(const KnownBits &LHS, const KnownBits &RHS); |
342 | |
343 | /// Compute knownbits resulting from llvm.uadd.sat(LHS, RHS) |
344 | static KnownBits uadd_sat(const KnownBits &LHS, const KnownBits &RHS); |
345 | |
346 | /// Compute knownbits resulting from llvm.ssub.sat(LHS, RHS) |
347 | static KnownBits ssub_sat(const KnownBits &LHS, const KnownBits &RHS); |
348 | |
349 | /// Compute knownbits resulting from llvm.usub.sat(LHS, RHS) |
350 | static KnownBits usub_sat(const KnownBits &LHS, const KnownBits &RHS); |
351 | |
352 | /// Compute known bits resulting from multiplying LHS and RHS. |
353 | static KnownBits mul(const KnownBits &LHS, const KnownBits &RHS, |
354 | bool NoUndefSelfMultiply = false); |
355 | |
356 | /// Compute known bits from sign-extended multiply-hi. |
357 | static KnownBits mulhs(const KnownBits &LHS, const KnownBits &RHS); |
358 | |
359 | /// Compute known bits from zero-extended multiply-hi. |
360 | static KnownBits mulhu(const KnownBits &LHS, const KnownBits &RHS); |
361 | |
362 | /// Compute known bits for sdiv(LHS, RHS). |
363 | static KnownBits sdiv(const KnownBits &LHS, const KnownBits &RHS, |
364 | bool Exact = false); |
365 | |
366 | /// Compute known bits for udiv(LHS, RHS). |
367 | static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS, |
368 | bool Exact = false); |
369 | |
370 | /// Compute known bits for urem(LHS, RHS). |
371 | static KnownBits urem(const KnownBits &LHS, const KnownBits &RHS); |
372 | |
373 | /// Compute known bits for srem(LHS, RHS). |
374 | static KnownBits srem(const KnownBits &LHS, const KnownBits &RHS); |
375 | |
376 | /// Compute known bits for umax(LHS, RHS). |
377 | static KnownBits umax(const KnownBits &LHS, const KnownBits &RHS); |
378 | |
379 | /// Compute known bits for umin(LHS, RHS). |
380 | static KnownBits umin(const KnownBits &LHS, const KnownBits &RHS); |
381 | |
382 | /// Compute known bits for smax(LHS, RHS). |
383 | static KnownBits smax(const KnownBits &LHS, const KnownBits &RHS); |
384 | |
385 | /// Compute known bits for smin(LHS, RHS). |
386 | static KnownBits smin(const KnownBits &LHS, const KnownBits &RHS); |
387 | |
388 | /// Compute known bits for shl(LHS, RHS). |
389 | /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. |
390 | static KnownBits shl(const KnownBits &LHS, const KnownBits &RHS, |
391 | bool NUW = false, bool NSW = false, |
392 | bool ShAmtNonZero = false); |
393 | |
394 | /// Compute known bits for lshr(LHS, RHS). |
395 | /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. |
396 | static KnownBits lshr(const KnownBits &LHS, const KnownBits &RHS, |
397 | bool ShAmtNonZero = false); |
398 | |
399 | /// Compute known bits for ashr(LHS, RHS). |
400 | /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. |
401 | static KnownBits ashr(const KnownBits &LHS, const KnownBits &RHS, |
402 | bool ShAmtNonZero = false); |
403 | |
404 | /// Determine if these known bits always give the same ICMP_EQ result. |
405 | static std::optional<bool> eq(const KnownBits &LHS, const KnownBits &RHS); |
406 | |
407 | /// Determine if these known bits always give the same ICMP_NE result. |
408 | static std::optional<bool> ne(const KnownBits &LHS, const KnownBits &RHS); |
409 | |
410 | /// Determine if these known bits always give the same ICMP_UGT result. |
411 | static std::optional<bool> ugt(const KnownBits &LHS, const KnownBits &RHS); |
412 | |
413 | /// Determine if these known bits always give the same ICMP_UGE result. |
414 | static std::optional<bool> uge(const KnownBits &LHS, const KnownBits &RHS); |
415 | |
416 | /// Determine if these known bits always give the same ICMP_ULT result. |
417 | static std::optional<bool> ult(const KnownBits &LHS, const KnownBits &RHS); |
418 | |
419 | /// Determine if these known bits always give the same ICMP_ULE result. |
420 | static std::optional<bool> ule(const KnownBits &LHS, const KnownBits &RHS); |
421 | |
422 | /// Determine if these known bits always give the same ICMP_SGT result. |
423 | static std::optional<bool> sgt(const KnownBits &LHS, const KnownBits &RHS); |
424 | |
425 | /// Determine if these known bits always give the same ICMP_SGE result. |
426 | static std::optional<bool> sge(const KnownBits &LHS, const KnownBits &RHS); |
427 | |
428 | /// Determine if these known bits always give the same ICMP_SLT result. |
429 | static std::optional<bool> slt(const KnownBits &LHS, const KnownBits &RHS); |
430 | |
431 | /// Determine if these known bits always give the same ICMP_SLE result. |
432 | static std::optional<bool> sle(const KnownBits &LHS, const KnownBits &RHS); |
433 | |
434 | /// Update known bits based on ANDing with RHS. |
435 | KnownBits &operator&=(const KnownBits &RHS); |
436 | |
437 | /// Update known bits based on ORing with RHS. |
438 | KnownBits &operator|=(const KnownBits &RHS); |
439 | |
440 | /// Update known bits based on XORing with RHS. |
441 | KnownBits &operator^=(const KnownBits &RHS); |
442 | |
443 | /// Compute known bits for the absolute value. |
444 | KnownBits abs(bool IntMinIsPoison = false) const; |
445 | |
446 | KnownBits byteSwap() const { |
447 | return KnownBits(Zero.byteSwap(), One.byteSwap()); |
448 | } |
449 | |
450 | KnownBits reverseBits() const { |
451 | return KnownBits(Zero.reverseBits(), One.reverseBits()); |
452 | } |
453 | |
454 | /// Compute known bits for X & -X, which has only the lowest bit set of X set. |
455 | /// The name comes from the X86 BMI instruction |
456 | KnownBits blsi() const; |
457 | |
458 | /// Compute known bits for X ^ (X - 1), which has all bits up to and including |
459 | /// the lowest set bit of X set. The name comes from the X86 BMI instruction. |
460 | KnownBits blsmsk() const; |
461 | |
462 | bool operator==(const KnownBits &Other) const { |
463 | return Zero == Other.Zero && One == Other.One; |
464 | } |
465 | |
466 | bool operator!=(const KnownBits &Other) const { return !(*this == Other); } |
467 | |
468 | void print(raw_ostream &OS) const; |
469 | void dump() const; |
470 | |
471 | private: |
472 | // Internal helper for getting the initial KnownBits for an `srem` or `urem` |
473 | // operation with the low-bits set. |
474 | static KnownBits remGetLowBits(const KnownBits &LHS, const KnownBits &RHS); |
475 | }; |
476 | |
477 | inline KnownBits operator&(KnownBits LHS, const KnownBits &RHS) { |
478 | LHS &= RHS; |
479 | return LHS; |
480 | } |
481 | |
482 | inline KnownBits operator&(const KnownBits &LHS, KnownBits &&RHS) { |
483 | RHS &= LHS; |
484 | return std::move(RHS); |
485 | } |
486 | |
487 | inline KnownBits operator|(KnownBits LHS, const KnownBits &RHS) { |
488 | LHS |= RHS; |
489 | return LHS; |
490 | } |
491 | |
492 | inline KnownBits operator|(const KnownBits &LHS, KnownBits &&RHS) { |
493 | RHS |= LHS; |
494 | return std::move(RHS); |
495 | } |
496 | |
497 | inline KnownBits operator^(KnownBits LHS, const KnownBits &RHS) { |
498 | LHS ^= RHS; |
499 | return LHS; |
500 | } |
501 | |
502 | inline KnownBits operator^(const KnownBits &LHS, KnownBits &&RHS) { |
503 | RHS ^= LHS; |
504 | return std::move(RHS); |
505 | } |
506 | |
507 | inline raw_ostream &operator<<(raw_ostream &OS, const KnownBits &Known) { |
508 | Known.print(OS); |
509 | return OS; |
510 | } |
511 | |
512 | } // end namespace llvm |
513 | |
514 | #endif |
515 | |