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1 : //=== FunctionComparator.h  Function Comparator * C++ *===//
2 : //
3 : // The LLVM Compiler Infrastructure
4 : //
5 : // This file is distributed under the University of Illinois Open Source
6 : // License. See LICENSE.TXT for details.
7 : //
8 : //======//
9 : //
10 : // This file defines the FunctionComparator and GlobalNumberState classes which
11 : // are used by the MergeFunctions pass for comparing functions.
12 : //
13 : //======//
14 :
15 : #ifndef LLVM_TRANSFORMS_UTILS_FUNCTIONCOMPARATOR_H
16 : #define LLVM_TRANSFORMS_UTILS_FUNCTIONCOMPARATOR_H
17 :
18 : #include "llvm/ADT/APFloat.h"
19 : #include "llvm/ADT/DenseMap.h"
20 : #include "llvm/ADT/StringRef.h"
21 : #include "llvm/IR/Function.h"
22 : #include "llvm/IR/Operator.h"
23 : #include "llvm/IR/ValueMap.h"
24 : #include "llvm/Support/AtomicOrdering.h"
25 : #include "llvm/Support/Casting.h"
26 : #include <cstdint>
27 : #include <tuple>
28 :
29 : namespace llvm {
30 :
31 : class GetElementPtrInst;
32 :
33 : /// GlobalNumberState assigns an integer to each global value in the program,
34 : /// which is used by the comparison routine to order references to globals. This
35 : /// state must be preserved throughout the pass, because Functions and other
36 : /// globals need to maintain their relative order. Globals are assigned a number
37 : /// when they are first visited. This order is deterministic, and so the
38 : /// assigned numbers are as well. When two functions are merged, neither number
39 : /// is updated. If the symbols are weak, this would be incorrect. If they are
40 : /// strong, then one will be replaced at all references to the other, and so
41 : /// direct callsites will now see one or the other symbol, and no update is
42 : /// necessary. Note that if we were guaranteed unique names, we could just
43 : /// compare those, but this would not work for stripped bitcodes or for those
44 : /// few symbols without a name.
45 46 : class GlobalNumberState {
46 : struct Config : ValueMapConfig<GlobalValue*> {
47 : enum { FollowRAUW = false };
48 : };
49 : // Each GlobalValue is mapped to an identifier. The Config ensures when RAUW
50 : // occurs, the mapping does not change. Tracking changes is unnecessary, and
51 : // also problematic for weak symbols (which may be overwritten).
52 : typedef ValueMap<GlobalValue *, uint64_t, Config> ValueNumberMap;
53 : ValueNumberMap GlobalNumbers;
54 : // The next unused serial number to assign to a global.
55 : uint64_t NextNumber = 0;
56 :
57 : public:
58 92 : GlobalNumberState() = default;
59 :
60 26 : uint64_t getNumber(GlobalValue* Global) {
61 26 : ValueNumberMap::iterator MapIter;
62 : bool Inserted;
63 104 : std::tie(MapIter, Inserted) = GlobalNumbers.insert({Global, NextNumber});
64 26 : if (Inserted)
65 11 : NextNumber++;
66 26 : return MapIter>second;
67 : }
68 :
69 : void clear() {
70 90 : GlobalNumbers.clear();
71 : }
72 : };
73 :
74 : /// FunctionComparator  Compares two functions to determine whether or not
75 : /// they will generate machine code with the same behaviour. DataLayout is
76 : /// used if available. The comparator always fails conservatively (erring on the
77 : /// side of claiming that two functions are different).
78 558 : class FunctionComparator {
79 : public:
80 : FunctionComparator(const Function *F1, const Function *F2,
81 : GlobalNumberState* GN)
82 558 : : FnL(F1), FnR(F2), GlobalNumbers(GN) {}
83 :
84 : /// Test whether the two functions have equivalent behaviour.
85 : int compare();
86 : /// Hash a function. Equivalent functions will have the same hash, and unequal
87 : /// functions will have different hashes with high probability.
88 : typedef uint64_t FunctionHash;
89 : static FunctionHash functionHash(Function &);
90 :
91 : protected:
92 : /// Start the comparison.
93 : void beginCompare() {
94 193 : sn_mapL.clear();
95 194 : sn_mapR.clear();
96 : }
97 :
98 : /// Compares the signature and other general attributes of the two functions.
99 : int compareSignature() const;
100 :
101 : /// Test whether two basic blocks have equivalent behaviour.
102 : int cmpBasicBlocks(const BasicBlock *BBL, const BasicBlock *BBR) const;
103 :
104 : /// Constants comparison.
105 : /// Its analog to lexicographical comparison between hypothetical numbers
106 : /// of next format:
107 : /// <bitcastabilitytrait><rawbitcontents>
108 : ///
109 : /// 1. Bitcastability.
110 : /// Check whether L's type could be losslessly bitcasted to R's type.
111 : /// On this stage method, in case when lossless bitcast is not possible
112 : /// method returns 1 or 1, thus also defining which type is greater in
113 : /// context of bitcastability.
114 : /// Stage 0: If types are equal in terms of cmpTypes, then we can go straight
115 : /// to the contents comparison.
116 : /// If types differ, remember types comparison result and check
117 : /// whether we still can bitcast types.
118 : /// Stage 1: Types that satisfies isFirstClassType conditions are always
119 : /// greater then others.
120 : /// Stage 2: Vector is greater then nonvector.
121 : /// If both types are vectors, then vector with greater bitwidth is
122 : /// greater.
123 : /// If both types are vectors with the same bitwidth, then types
124 : /// are bitcastable, and we can skip other stages, and go to contents
125 : /// comparison.
126 : /// Stage 3: Pointer types are greater than nonpointers. If both types are
127 : /// pointers of the same address space  go to contents comparison.
128 : /// Different address spaces: pointer with greater address space is
129 : /// greater.
130 : /// Stage 4: Types are neither vectors, nor pointers. And they differ.
131 : /// We don't know how to bitcast them. So, we better don't do it,
132 : /// and return types comparison result (so it determines the
133 : /// relationship among constants we don't know how to bitcast).
134 : ///
135 : /// Just for clearance, let's see how the set of constants could look
136 : /// on single dimension axis:
137 : ///
138 : /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
139 : /// Where: NFCT  Not a FirstClassType
140 : /// FCT  FirstClassTyp:
141 : ///
142 : /// 2. Compare raw contents.
143 : /// It ignores types on this stage and only compares bits from L and R.
144 : /// Returns 0, if L and R has equivalent contents.
145 : /// 1 or 1 if values are different.
146 : /// Pretty trivial:
147 : /// 2.1. If contents are numbers, compare numbers.
148 : /// Ints with greater bitwidth are greater. Ints with same bitwidths
149 : /// compared by their contents.
150 : /// 2.2. "And so on". Just to avoid discrepancies with comments
151 : /// perhaps it would be better to read the implementation itself.
152 : /// 3. And again about overall picture. Let's look back at how the ordered set
153 : /// of constants will look like:
154 : /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
155 : ///
156 : /// Now look, what could be inside [FCT, "others"], for example:
157 : /// [FCT, "others"] =
158 : /// [
159 : /// [double 0.1], [double 1.23],
160 : /// [i32 1], [i32 2],
161 : /// { double 1.0 }, ; StructTyID, NumElements = 1
162 : /// { i32 1 }, ; StructTyID, NumElements = 1
163 : /// { double 1, i32 1 }, ; StructTyID, NumElements = 2
164 : /// { i32 1, double 1 } ; StructTyID, NumElements = 2
165 : /// ]
166 : ///
167 : /// Let's explain the order. Float numbers will be less than integers, just
168 : /// because of cmpType terms: FloatTyID < IntegerTyID.
169 : /// Floats (with same fltSemantics) are sorted according to their value.
170 : /// Then you can see integers, and they are, like a floats,
171 : /// could be easy sorted among each others.
172 : /// The structures. Structures are grouped at the tail, again because of their
173 : /// TypeID: StructTyID > IntegerTyID > FloatTyID.
174 : /// Structures with greater number of elements are greater. Structures with
175 : /// greater elements going first are greater.
176 : /// The same logic with vectors, arrays and other possible complex types.
177 : ///
178 : /// Bitcastable constants.
179 : /// Let's assume, that some constant, belongs to some group of
180 : /// "socalledequal" values with different types, and at the same time
181 : /// belongs to another group of constants with equal types
182 : /// and "really" equal values.
183 : ///
184 : /// Now, prove that this is impossible:
185 : ///
186 : /// If constant A with type TyA is bitcastable to B with type TyB, then:
187 : /// 1. All constants with equal types to TyA, are bitcastable to B. Since
188 : /// those should be vectors (if TyA is vector), pointers
189 : /// (if TyA is pointer), or else (if TyA equal to TyB), those types should
190 : /// be equal to TyB.
191 : /// 2. All constants with nonequal, but bitcastable types to TyA, are
192 : /// bitcastable to B.
193 : /// Once again, just because we allow it to vectors and pointers only.
194 : /// This statement could be expanded as below:
195 : /// 2.1. All vectors with equal bitwidth to vector A, has equal bitwidth to
196 : /// vector B, and thus bitcastable to B as well.
197 : /// 2.2. All pointers of the same address space, no matter what they point to,
198 : /// bitcastable. So if C is pointer, it could be bitcasted to A and to B.
199 : /// So any constant equal or bitcastable to A is equal or bitcastable to B.
200 : /// QED.
201 : ///
202 : /// In another words, for pointers and vectors, we ignore toplevel type and
203 : /// look at their particular properties (bitwidth for vectors, and
204 : /// address space for pointers).
205 : /// If these properties are equal  compare their contents.
206 : int cmpConstants(const Constant *L, const Constant *R) const;
207 :
208 : /// Compares two global values by number. Uses the GlobalNumbersState to
209 : /// identify the same gobals across function calls.
210 : int cmpGlobalValues(GlobalValue *L, GlobalValue *R) const;
211 :
212 : /// Assign or look up previously assigned numbers for the two values, and
213 : /// return whether the numbers are equal. Numbers are assigned in the order
214 : /// visited.
215 : /// Comparison order:
216 : /// Stage 0: Value that is function itself is always greater then others.
217 : /// If left and right values are references to their functions, then
218 : /// they are equal.
219 : /// Stage 1: Constants are greater than nonconstants.
220 : /// If both left and right are constants, then the result of
221 : /// cmpConstants is used as cmpValues result.
222 : /// Stage 2: InlineAsm instances are greater than others. If both left and
223 : /// right are InlineAsm instances, InlineAsm* pointers casted to
224 : /// integers and compared as numbers.
225 : /// Stage 3: For all other cases we compare order we meet these values in
226 : /// their functions. If right value was met first during scanning,
227 : /// then left value is greater.
228 : /// In another words, we compare serial numbers, for more details
229 : /// see comments for sn_mapL and sn_mapR.
230 : int cmpValues(const Value *L, const Value *R) const;
231 :
232 : /// Compare two Instructions for equivalence, similar to
233 : /// Instruction::isSameOperationAs.
234 : ///
235 : /// Stages are listed in "most significant stage first" order:
236 : /// On each stage below, we do comparison between some left and right
237 : /// operation parts. If parts are nonequal, we assign parts comparison
238 : /// result to the operation comparison result and exit from method.
239 : /// Otherwise we proceed to the next stage.
240 : /// Stages:
241 : /// 1. Operations opcodes. Compared as numbers.
242 : /// 2. Number of operands.
243 : /// 3. Operation types. Compared with cmpType method.
244 : /// 4. Compare operation subclass optional data as stream of bytes:
245 : /// just convert it to integers and call cmpNumbers.
246 : /// 5. Compare in operation operand types with cmpType in
247 : /// most significant operand first order.
248 : /// 6. Last stage. Check operations for some specific attributes.
249 : /// For example, for Load it would be:
250 : /// 6.1.Load: volatile (as boolean flag)
251 : /// 6.2.Load: alignment (as integer numbers)
252 : /// 6.3.Load: ordering (as underlying enum class value)
253 : /// 6.4.Load: synchscope (as integer numbers)
254 : /// 6.5.Load: range metadata (as integer ranges)
255 : /// On this stage its better to see the code, since its not more than 1015
256 : /// strings for particular instruction, and could change sometimes.
257 : ///
258 : /// Sets \p needToCmpOperands to true if the operands of the instructions
259 : /// still must be compared afterwards. In this case it's already guaranteed
260 : /// that both instructions have the same number of operands.
261 : int cmpOperations(const Instruction *L, const Instruction *R,
262 : bool &needToCmpOperands) const;
263 :
264 : /// cmpType  compares two types,
265 : /// defines total ordering among the types set.
266 : ///
267 : /// Return values:
268 : /// 0 if types are equal,
269 : /// 1 if Left is less than Right,
270 : /// +1 if Left is greater than Right.
271 : ///
272 : /// Description:
273 : /// Comparison is broken onto stages. Like in lexicographical comparison
274 : /// stage coming first has higher priority.
275 : /// On each explanation stage keep in mind total ordering properties.
276 : ///
277 : /// 0. Before comparison we coerce pointer types of 0 address space to
278 : /// integer.
279 : /// We also don't bother with same type at left and right, so
280 : /// just return 0 in this case.
281 : ///
282 : /// 1. If types are of different kind (different type IDs).
283 : /// Return result of type IDs comparison, treating them as numbers.
284 : /// 2. If types are integers, check that they have the same width. If they
285 : /// are vectors, check that they have the same count and subtype.
286 : /// 3. Types have the same ID, so check whether they are one of:
287 : /// * Void
288 : /// * Float
289 : /// * Double
290 : /// * X86_FP80
291 : /// * FP128
292 : /// * PPC_FP128
293 : /// * Label
294 : /// * Metadata
295 : /// We can treat these types as equal whenever their IDs are same.
296 : /// 4. If Left and Right are pointers, return result of address space
297 : /// comparison (numbers comparison). We can treat pointer types of same
298 : /// address space as equal.
299 : /// 5. If types are complex.
300 : /// Then both Left and Right are to be expanded and their element types will
301 : /// be checked with the same way. If we get Res != 0 on some stage, return it.
302 : /// Otherwise return 0.
303 : /// 6. For all other cases put llvm_unreachable.
304 : int cmpTypes(Type *TyL, Type *TyR) const;
305 :
306 : int cmpNumbers(uint64_t L, uint64_t R) const;
307 : int cmpAPInts(const APInt &L, const APInt &R) const;
308 : int cmpAPFloats(const APFloat &L, const APFloat &R) const;
309 : int cmpMem(StringRef L, StringRef R) const;
310 :
311 : // The two functions undergoing comparison.
312 : const Function *FnL, *FnR;
313 :
314 : private:
315 : int cmpOrderings(AtomicOrdering L, AtomicOrdering R) const;
316 : int cmpInlineAsm(const InlineAsm *L, const InlineAsm *R) const;
317 : int cmpAttrs(const AttributeList L, const AttributeList R) const;
318 : int cmpRangeMetadata(const MDNode *L, const MDNode *R) const;
319 : int cmpOperandBundlesSchema(const Instruction *L, const Instruction *R) const;
320 :
321 : /// Compare two GEPs for equivalent pointer arithmetic.
322 : /// Parts to be compared for each comparison stage,
323 : /// most significant stage first:
324 : /// 1. Address space. As numbers.
325 : /// 2. Constant offset, (using GEPOperator::accumulateConstantOffset method).
326 : /// 3. Pointer operand type (using cmpType method).
327 : /// 4. Number of operands.
328 : /// 5. Compare operands, using cmpValues method.
329 : int cmpGEPs(const GEPOperator *GEPL, const GEPOperator *GEPR) const;
330 : int cmpGEPs(const GetElementPtrInst *GEPL,
331 : const GetElementPtrInst *GEPR) const {
332 70 : return cmpGEPs(cast<GEPOperator>(GEPL), cast<GEPOperator>(GEPR));
333 : }
334 :
335 : /// Assign serial numbers to values from left function, and values from
336 : /// right function.
337 : /// Explanation:
338 : /// Being comparing functions we need to compare values we meet at left and
339 : /// right sides.
340 : /// Its easy to sort things out for external values. It just should be
341 : /// the same value at left and right.
342 : /// But for local values (those were introduced inside function body)
343 : /// we have to ensure they were introduced at exactly the same place,
344 : /// and plays the same role.
345 : /// Let's assign serial number to each value when we meet it first time.
346 : /// Values that were met at same place will be with same serial numbers.
347 : /// In this case it would be good to explain few points about values assigned
348 : /// to BBs and other ways of implementation (see below).
349 : ///
350 : /// 1. Safety of BB reordering.
351 : /// It's safe to change the order of BasicBlocks in function.
352 : /// Relationship with other functions and serial numbering will not be
353 : /// changed in this case.
354 : /// As follows from FunctionComparator::compare(), we do CFG walk: we start
355 : /// from the entry, and then take each terminator. So it doesn't matter how in
356 : /// fact BBs are ordered in function. And since cmpValues are called during
357 : /// this walk, the numbering depends only on how BBs located inside the CFG.
358 : /// So the answer is  yes. We will get the same numbering.
359 : ///
360 : /// 2. Impossibility to use dominance properties of values.
361 : /// If we compare two instruction operands: first is usage of local
362 : /// variable AL from function FL, and second is usage of local variable AR
363 : /// from FR, we could compare their origins and check whether they are
364 : /// defined at the same place.
365 : /// But, we are still not able to compare operands of PHI nodes, since those
366 : /// could be operands from further BBs we didn't scan yet.
367 : /// So it's impossible to use dominance properties in general.
368 : mutable DenseMap<const Value*, int> sn_mapL, sn_mapR;
369 :
370 : // The global state we will use
371 : GlobalNumberState* GlobalNumbers;
372 : };
373 :
374 : } // end namespace llvm
375 :
376 : #endif // LLVM_TRANSFORMS_UTILS_FUNCTIONCOMPARATOR_H
