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() {} |
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.isNullValue() && One.isNullValue(); } |
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.isAllOnesValue(); |
75 | } |
76 | |
77 | /// Returns true if value is all one bits. |
78 | bool isAllOnes() const { |
79 | assert(!hasConflict() && "KnownBits conflict!" ); |
80 | return One.isAllOnesValue(); |
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.isNullValue(); } |
103 | |
104 | /// Returns true if this value is known to be positive. |
105 | bool isStrictlyPositive() const { return Zero.isSignBitSet() && !One.isNullValue(); } |
106 | |
107 | /// Make this value negative. |
108 | void makeNegative() { |
109 | One.setSignBit(); |
110 | } |
111 | |
112 | /// Make this value non-negative. |
113 | void makeNonNegative() { |
114 | Zero.setSignBit(); |
115 | } |
116 | |
117 | /// Return the minimal unsigned value possible given these KnownBits. |
118 | APInt getMinValue() const { |
119 | // Assume that all bits that aren't known-ones are zeros. |
120 | return One; |
121 | } |
122 | |
123 | /// Return the minimal signed value possible given these KnownBits. |
124 | APInt getSignedMinValue() const { |
125 | // Assume that all bits that aren't known-ones are zeros. |
126 | APInt Min = One; |
127 | // Sign bit is unknown. |
128 | if (Zero.isSignBitClear()) |
129 | Min.setSignBit(); |
130 | return Min; |
131 | } |
132 | |
133 | /// Return the maximal unsigned value possible given these KnownBits. |
134 | APInt getMaxValue() const { |
135 | // Assume that all bits that aren't known-zeros are ones. |
136 | return ~Zero; |
137 | } |
138 | |
139 | /// Return the maximal signed value possible given these KnownBits. |
140 | APInt getSignedMaxValue() const { |
141 | // Assume that all bits that aren't known-zeros are ones. |
142 | APInt Max = ~Zero; |
143 | // Sign bit is unknown. |
144 | if (One.isSignBitClear()) |
145 | Max.clearSignBit(); |
146 | return Max; |
147 | } |
148 | |
149 | /// Return known bits for a truncation of the value we're tracking. |
150 | KnownBits trunc(unsigned BitWidth) const { |
151 | return KnownBits(Zero.trunc(BitWidth), One.trunc(BitWidth)); |
152 | } |
153 | |
154 | /// Return known bits for an "any" extension of the value we're tracking, |
155 | /// where we don't know anything about the extended bits. |
156 | KnownBits anyext(unsigned BitWidth) const { |
157 | return KnownBits(Zero.zext(BitWidth), One.zext(BitWidth)); |
158 | } |
159 | |
160 | /// Return known bits for a zero extension of the value we're tracking. |
161 | KnownBits zext(unsigned BitWidth) const { |
162 | unsigned OldBitWidth = getBitWidth(); |
163 | APInt NewZero = Zero.zext(BitWidth); |
164 | NewZero.setBitsFrom(OldBitWidth); |
165 | return KnownBits(NewZero, One.zext(BitWidth)); |
166 | } |
167 | |
168 | /// Return known bits for a sign extension of the value we're tracking. |
169 | KnownBits sext(unsigned BitWidth) const { |
170 | return KnownBits(Zero.sext(BitWidth), One.sext(BitWidth)); |
171 | } |
172 | |
173 | /// Return known bits for an "any" extension or truncation of the value we're |
174 | /// tracking. |
175 | KnownBits anyextOrTrunc(unsigned BitWidth) const { |
176 | if (BitWidth > getBitWidth()) |
177 | return anyext(BitWidth); |
178 | if (BitWidth < getBitWidth()) |
179 | return trunc(BitWidth); |
180 | return *this; |
181 | } |
182 | |
183 | /// Return known bits for a zero extension or truncation of the value we're |
184 | /// tracking. |
185 | KnownBits zextOrTrunc(unsigned BitWidth) const { |
186 | if (BitWidth > getBitWidth()) |
187 | return zext(BitWidth); |
188 | if (BitWidth < getBitWidth()) |
189 | return trunc(BitWidth); |
190 | return *this; |
191 | } |
192 | |
193 | /// Return known bits for a sign extension or truncation of the value we're |
194 | /// tracking. |
195 | KnownBits sextOrTrunc(unsigned BitWidth) const { |
196 | if (BitWidth > getBitWidth()) |
197 | return sext(BitWidth); |
198 | if (BitWidth < getBitWidth()) |
199 | return trunc(BitWidth); |
200 | return *this; |
201 | } |
202 | |
203 | /// Return known bits for a in-register sign extension of the value we're |
204 | /// tracking. |
205 | KnownBits sextInReg(unsigned SrcBitWidth) const; |
206 | |
207 | /// Return a KnownBits with the extracted bits |
208 | /// [bitPosition,bitPosition+numBits). |
209 | KnownBits (unsigned NumBits, unsigned BitPosition) const { |
210 | return KnownBits(Zero.extractBits(NumBits, BitPosition), |
211 | One.extractBits(NumBits, BitPosition)); |
212 | } |
213 | |
214 | /// Return KnownBits based on this, but updated given that the underlying |
215 | /// value is known to be greater than or equal to Val. |
216 | KnownBits makeGE(const APInt &Val) const; |
217 | |
218 | /// Returns the minimum number of trailing zero bits. |
219 | unsigned countMinTrailingZeros() const { |
220 | return Zero.countTrailingOnes(); |
221 | } |
222 | |
223 | /// Returns the minimum number of trailing one bits. |
224 | unsigned countMinTrailingOnes() const { |
225 | return One.countTrailingOnes(); |
226 | } |
227 | |
228 | /// Returns the minimum number of leading zero bits. |
229 | unsigned countMinLeadingZeros() const { |
230 | return Zero.countLeadingOnes(); |
231 | } |
232 | |
233 | /// Returns the minimum number of leading one bits. |
234 | unsigned countMinLeadingOnes() const { |
235 | return One.countLeadingOnes(); |
236 | } |
237 | |
238 | /// Returns the number of times the sign bit is replicated into the other |
239 | /// bits. |
240 | unsigned countMinSignBits() const { |
241 | if (isNonNegative()) |
242 | return countMinLeadingZeros(); |
243 | if (isNegative()) |
244 | return countMinLeadingOnes(); |
245 | return 0; |
246 | } |
247 | |
248 | /// Returns the maximum number of trailing zero bits possible. |
249 | unsigned countMaxTrailingZeros() const { |
250 | return One.countTrailingZeros(); |
251 | } |
252 | |
253 | /// Returns the maximum number of trailing one bits possible. |
254 | unsigned countMaxTrailingOnes() const { |
255 | return Zero.countTrailingZeros(); |
256 | } |
257 | |
258 | /// Returns the maximum number of leading zero bits possible. |
259 | unsigned countMaxLeadingZeros() const { |
260 | return One.countLeadingZeros(); |
261 | } |
262 | |
263 | /// Returns the maximum number of leading one bits possible. |
264 | unsigned countMaxLeadingOnes() const { |
265 | return Zero.countLeadingZeros(); |
266 | } |
267 | |
268 | /// Returns the number of bits known to be one. |
269 | unsigned countMinPopulation() const { |
270 | return One.countPopulation(); |
271 | } |
272 | |
273 | /// Returns the maximum number of bits that could be one. |
274 | unsigned countMaxPopulation() const { |
275 | return getBitWidth() - Zero.countPopulation(); |
276 | } |
277 | |
278 | /// Create known bits from a known constant. |
279 | static KnownBits makeConstant(const APInt &C) { |
280 | return KnownBits(~C, C); |
281 | } |
282 | |
283 | /// Compute known bits common to LHS and RHS. |
284 | static KnownBits commonBits(const KnownBits &LHS, const KnownBits &RHS) { |
285 | return KnownBits(LHS.Zero & RHS.Zero, LHS.One & RHS.One); |
286 | } |
287 | |
288 | /// Return true if LHS and RHS have no common bits set. |
289 | static bool haveNoCommonBitsSet(const KnownBits &LHS, const KnownBits &RHS) { |
290 | return (LHS.Zero | RHS.Zero).isAllOnesValue(); |
291 | } |
292 | |
293 | /// Compute known bits resulting from adding LHS, RHS and a 1-bit Carry. |
294 | static KnownBits computeForAddCarry( |
295 | const KnownBits &LHS, const KnownBits &RHS, const KnownBits &Carry); |
296 | |
297 | /// Compute known bits resulting from adding LHS and RHS. |
298 | static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS, |
299 | KnownBits RHS); |
300 | |
301 | /// Compute known bits resulting from multiplying LHS and RHS. |
302 | static KnownBits mul(const KnownBits &LHS, const KnownBits &RHS); |
303 | |
304 | /// Compute known bits from sign-extended multiply-hi. |
305 | static KnownBits mulhs(const KnownBits &LHS, const KnownBits &RHS); |
306 | |
307 | /// Compute known bits from zero-extended multiply-hi. |
308 | static KnownBits mulhu(const KnownBits &LHS, const KnownBits &RHS); |
309 | |
310 | /// Compute known bits for udiv(LHS, RHS). |
311 | static KnownBits udiv(const KnownBits &LHS, const KnownBits &RHS); |
312 | |
313 | /// Compute known bits for urem(LHS, RHS). |
314 | static KnownBits urem(const KnownBits &LHS, const KnownBits &RHS); |
315 | |
316 | /// Compute known bits for srem(LHS, RHS). |
317 | static KnownBits srem(const KnownBits &LHS, const KnownBits &RHS); |
318 | |
319 | /// Compute known bits for umax(LHS, RHS). |
320 | static KnownBits umax(const KnownBits &LHS, const KnownBits &RHS); |
321 | |
322 | /// Compute known bits for umin(LHS, RHS). |
323 | static KnownBits umin(const KnownBits &LHS, const KnownBits &RHS); |
324 | |
325 | /// Compute known bits for smax(LHS, RHS). |
326 | static KnownBits smax(const KnownBits &LHS, const KnownBits &RHS); |
327 | |
328 | /// Compute known bits for smin(LHS, RHS). |
329 | static KnownBits smin(const KnownBits &LHS, const KnownBits &RHS); |
330 | |
331 | /// Compute known bits for shl(LHS, RHS). |
332 | /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. |
333 | static KnownBits shl(const KnownBits &LHS, const KnownBits &RHS); |
334 | |
335 | /// Compute known bits for lshr(LHS, RHS). |
336 | /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. |
337 | static KnownBits lshr(const KnownBits &LHS, const KnownBits &RHS); |
338 | |
339 | /// Compute known bits for ashr(LHS, RHS). |
340 | /// NOTE: RHS (shift amount) bitwidth doesn't need to be the same as LHS. |
341 | static KnownBits ashr(const KnownBits &LHS, const KnownBits &RHS); |
342 | |
343 | /// Determine if these known bits always give the same ICMP_EQ result. |
344 | static Optional<bool> eq(const KnownBits &LHS, const KnownBits &RHS); |
345 | |
346 | /// Determine if these known bits always give the same ICMP_NE result. |
347 | static Optional<bool> ne(const KnownBits &LHS, const KnownBits &RHS); |
348 | |
349 | /// Determine if these known bits always give the same ICMP_UGT result. |
350 | static Optional<bool> ugt(const KnownBits &LHS, const KnownBits &RHS); |
351 | |
352 | /// Determine if these known bits always give the same ICMP_UGE result. |
353 | static Optional<bool> uge(const KnownBits &LHS, const KnownBits &RHS); |
354 | |
355 | /// Determine if these known bits always give the same ICMP_ULT result. |
356 | static Optional<bool> ult(const KnownBits &LHS, const KnownBits &RHS); |
357 | |
358 | /// Determine if these known bits always give the same ICMP_ULE result. |
359 | static Optional<bool> ule(const KnownBits &LHS, const KnownBits &RHS); |
360 | |
361 | /// Determine if these known bits always give the same ICMP_SGT result. |
362 | static Optional<bool> sgt(const KnownBits &LHS, const KnownBits &RHS); |
363 | |
364 | /// Determine if these known bits always give the same ICMP_SGE result. |
365 | static Optional<bool> sge(const KnownBits &LHS, const KnownBits &RHS); |
366 | |
367 | /// Determine if these known bits always give the same ICMP_SLT result. |
368 | static Optional<bool> slt(const KnownBits &LHS, const KnownBits &RHS); |
369 | |
370 | /// Determine if these known bits always give the same ICMP_SLE result. |
371 | static Optional<bool> sle(const KnownBits &LHS, const KnownBits &RHS); |
372 | |
373 | /// Insert the bits from a smaller known bits starting at bitPosition. |
374 | void insertBits(const KnownBits &SubBits, unsigned BitPosition) { |
375 | Zero.insertBits(SubBits.Zero, BitPosition); |
376 | One.insertBits(SubBits.One, BitPosition); |
377 | } |
378 | |
379 | /// Return a subset of the known bits from [bitPosition,bitPosition+numBits). |
380 | KnownBits (unsigned NumBits, unsigned BitPosition) { |
381 | return KnownBits(Zero.extractBits(NumBits, BitPosition), |
382 | One.extractBits(NumBits, BitPosition)); |
383 | } |
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 | |
397 | KnownBits byteSwap() { |
398 | return KnownBits(Zero.byteSwap(), One.byteSwap()); |
399 | } |
400 | |
401 | 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 | |