1 //===- FunctionComparator.h - Function Comparator ---------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the FunctionComparator and GlobalNumberState classes which
11 // are used by the MergeFunctions pass for comparing functions.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_TRANSFORMS_UTILS_FUNCTIONCOMPARATOR_H
16 #define LLVM_TRANSFORMS_UTILS_FUNCTIONCOMPARATOR_H
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/ValueMap.h"
23 #include "llvm/IR/Operator.h"
24 #include "llvm/Support/AtomicOrdering.h"
25 #include "llvm/Support/Casting.h"
31 class GetElementPtrInst;
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 class GlobalNumberState {
46 struct Config : ValueMapConfig<GlobalValue*> {
47 enum { FollowRAUW = false };
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;
58 GlobalNumberState() = default;
60 uint64_t getNumber(GlobalValue* Global) {
61 ValueNumberMap::iterator MapIter;
63 std::tie(MapIter, Inserted) = GlobalNumbers.insert({Global, NextNumber});
66 return MapIter->second;
70 GlobalNumbers.clear();
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 class FunctionComparator {
80 FunctionComparator(const Function *F1, const Function *F2,
81 GlobalNumberState* GN)
82 : FnL(F1), FnR(F2), GlobalNumbers(GN) {}
84 /// Test whether the two functions have equivalent behaviour.
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 &);
92 /// Start the comparison.
98 /// Compares the signature and other general attributes of the two functions.
99 int compareSignature() const;
101 /// Test whether two basic blocks have equivalent behaviour.
102 int cmpBasicBlocks(const BasicBlock *BBL, const BasicBlock *BBR) const;
104 /// Constants comparison.
105 /// Its analog to lexicographical comparison between hypothetical numbers
107 /// <bitcastability-trait><raw-bit-contents>
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 non-vector.
121 /// If both types are vectors, then vector with greater bitwidth is
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
126 /// Stage 3: Pointer types are greater than non-pointers. 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
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).
135 /// Just for clearance, let's see how the set of constants could look
136 /// on single dimension axis:
138 /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
139 /// Where: NFCT - Not a FirstClassType
140 /// FCT - FirstClassTyp:
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.
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]
156 /// Now look, what could be inside [FCT, "others"], for example:
157 /// [FCT, "others"] =
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
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.
178 /// Bitcastable constants.
179 /// Let's assume, that some constant, belongs to some group of
180 /// "so-called-equal" values with different types, and at the same time
181 /// belongs to another group of constants with equal types
182 /// and "really" equal values.
184 /// Now, prove that this is impossible:
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
191 /// 2. All constants with non-equal, 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.
202 /// In another words, for pointers and vectors, we ignore top-level type and
203 /// look at their particular properties (bit-width 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;
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;
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
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
219 /// Stage 1: Constants are greater than non-constants.
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;
232 /// Compare two Instructions for equivalence, similar to
233 /// Instruction::isSameOperationAs.
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 non-equal, we assign parts comparison
238 /// result to the operation comparison result and exit from method.
239 /// Otherwise we proceed to the next stage.
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: synch-scope (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 10-15
256 /// strings for particular instruction, and could change sometimes.
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;
264 /// cmpType - compares two types,
265 /// defines total ordering among the types set.
268 /// 0 if types are equal,
269 /// -1 if Left is less than Right,
270 /// +1 if Left is greater than Right.
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.
277 /// 0. Before comparison we coerce pointer types of 0 address space to
279 /// We also don't bother with same type at left and right, so
280 /// just return 0 in this case.
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:
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;
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;
311 // The two functions undergoing comparison.
312 const Function *FnL, *FnR;
315 int cmpOrderings(AtomicOrdering L, AtomicOrdering R) const;
316 int cmpInlineAsm(const InlineAsm *L, const InlineAsm *R) const;
317 int cmpAttrs(const AttributeSet L, const AttributeSet R) const;
318 int cmpRangeMetadata(const MDNode *L, const MDNode *R) const;
319 int cmpOperandBundlesSchema(const Instruction *L, const Instruction *R) const;
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 return cmpGEPs(cast<GEPOperator>(GEPL), cast<GEPOperator>(GEPR));
335 /// Assign serial numbers to values from left function, and values from
338 /// Being comparing functions we need to compare values we meet at left and
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).
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.
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;
370 // The global state we will use
371 GlobalNumberState* GlobalNumbers;
374 } // end namespace llvm
376 #endif // LLVM_TRANSFORMS_UTILS_FUNCTIONCOMPARATOR_H