1 //===- MergeFunctions.cpp - Merge identical functions ---------------------===//
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 pass looks for equivalent functions that are mergable and folds them.
12 // A hash is computed from the function, based on its type and number of
15 // Once all hashes are computed, we perform an expensive equality comparison
16 // on each function pair. This takes n^2/2 comparisons per bucket, so it's
17 // important that the hash function be high quality. The equality comparison
18 // iterates through each instruction in each basic block.
20 // When a match is found the functions are folded. If both functions are
21 // overridable, we move the functionality into a new internal function and
22 // leave two overridable thunks to it.
24 //===----------------------------------------------------------------------===//
28 // * virtual functions.
30 // Many functions have their address taken by the virtual function table for
31 // the object they belong to. However, as long as it's only used for a lookup
32 // and call, this is irrelevant, and we'd like to fold such functions.
34 // * switch from n^2 pair-wise comparisons to an n-way comparison for each
37 // * be smarter about bitcasts.
39 // In order to fold functions, we will sometimes add either bitcast instructions
40 // or bitcast constant expressions. Unfortunately, this can confound further
41 // analysis since the two functions differ where one has a bitcast and the
42 // other doesn't. We should learn to look through bitcasts.
44 //===----------------------------------------------------------------------===//
46 #include "llvm/Transforms/IPO.h"
47 #include "llvm/ADT/DenseSet.h"
48 #include "llvm/ADT/FoldingSet.h"
49 #include "llvm/ADT/STLExtras.h"
50 #include "llvm/ADT/SmallSet.h"
51 #include "llvm/ADT/Statistic.h"
52 #include "llvm/IR/CallSite.h"
53 #include "llvm/IR/Constants.h"
54 #include "llvm/IR/DataLayout.h"
55 #include "llvm/IR/IRBuilder.h"
56 #include "llvm/IR/InlineAsm.h"
57 #include "llvm/IR/Instructions.h"
58 #include "llvm/IR/LLVMContext.h"
59 #include "llvm/IR/Module.h"
60 #include "llvm/IR/Operator.h"
61 #include "llvm/IR/ValueHandle.h"
62 #include "llvm/Pass.h"
63 #include "llvm/Support/Debug.h"
64 #include "llvm/Support/ErrorHandling.h"
65 #include "llvm/Support/raw_ostream.h"
69 #define DEBUG_TYPE "mergefunc"
71 STATISTIC(NumFunctionsMerged, "Number of functions merged");
72 STATISTIC(NumThunksWritten, "Number of thunks generated");
73 STATISTIC(NumAliasesWritten, "Number of aliases generated");
74 STATISTIC(NumDoubleWeak, "Number of new functions created");
76 /// Returns the type id for a type to be hashed. We turn pointer types into
77 /// integers here because the actual compare logic below considers pointers and
78 /// integers of the same size as equal.
79 static Type::TypeID getTypeIDForHash(Type *Ty) {
80 if (Ty->isPointerTy())
81 return Type::IntegerTyID;
82 return Ty->getTypeID();
85 /// Creates a hash-code for the function which is the same for any two
86 /// functions that will compare equal, without looking at the instructions
87 /// inside the function.
88 static unsigned profileFunction(const Function *F) {
89 FunctionType *FTy = F->getFunctionType();
92 ID.AddInteger(F->size());
93 ID.AddInteger(F->getCallingConv());
94 ID.AddBoolean(F->hasGC());
95 ID.AddBoolean(FTy->isVarArg());
96 ID.AddInteger(getTypeIDForHash(FTy->getReturnType()));
97 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
98 ID.AddInteger(getTypeIDForHash(FTy->getParamType(i)));
99 return ID.ComputeHash();
104 /// ComparableFunction - A struct that pairs together functions with a
105 /// DataLayout so that we can keep them together as elements in the DenseSet.
106 class ComparableFunction {
108 static const ComparableFunction EmptyKey;
109 static const ComparableFunction TombstoneKey;
110 static DataLayout * const LookupOnly;
112 ComparableFunction(Function *Func, const DataLayout *DL)
113 : Func(Func), Hash(profileFunction(Func)), DL(DL) {}
115 Function *getFunc() const { return Func; }
116 unsigned getHash() const { return Hash; }
117 const DataLayout *getDataLayout() const { return DL; }
119 // Drops AssertingVH reference to the function. Outside of debug mode, this
123 "Attempted to release function twice, or release empty/tombstone!");
128 explicit ComparableFunction(unsigned Hash)
129 : Func(nullptr), Hash(Hash), DL(nullptr) {}
131 AssertingVH<Function> Func;
133 const DataLayout *DL;
136 const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0);
137 const ComparableFunction ComparableFunction::TombstoneKey =
138 ComparableFunction(1);
139 DataLayout *const ComparableFunction::LookupOnly = (DataLayout*)(-1);
145 struct DenseMapInfo<ComparableFunction> {
146 static ComparableFunction getEmptyKey() {
147 return ComparableFunction::EmptyKey;
149 static ComparableFunction getTombstoneKey() {
150 return ComparableFunction::TombstoneKey;
152 static unsigned getHashValue(const ComparableFunction &CF) {
155 static bool isEqual(const ComparableFunction &LHS,
156 const ComparableFunction &RHS);
162 /// FunctionComparator - Compares two functions to determine whether or not
163 /// they will generate machine code with the same behaviour. DataLayout is
164 /// used if available. The comparator always fails conservatively (erring on the
165 /// side of claiming that two functions are different).
166 class FunctionComparator {
168 FunctionComparator(const DataLayout *DL, const Function *F1,
170 : F1(F1), F2(F2), DL(DL) {}
172 /// Test whether the two functions have equivalent behaviour.
176 /// Test whether two basic blocks have equivalent behaviour.
177 bool compare(const BasicBlock *BB1, const BasicBlock *BB2);
179 /// Constants comparison.
180 /// Its analog to lexicographical comparison between hypothetical numbers
182 /// <bitcastability-trait><raw-bit-contents>
184 /// 1. Bitcastability.
185 /// Check whether L's type could be losslessly bitcasted to R's type.
186 /// On this stage method, in case when lossless bitcast is not possible
187 /// method returns -1 or 1, thus also defining which type is greater in
188 /// context of bitcastability.
189 /// Stage 0: If types are equal in terms of cmpTypes, then we can go straight
190 /// to the contents comparison.
191 /// If types differ, remember types comparison result and check
192 /// whether we still can bitcast types.
193 /// Stage 1: Types that satisfies isFirstClassType conditions are always
194 /// greater then others.
195 /// Stage 2: Vector is greater then non-vector.
196 /// If both types are vectors, then vector with greater bitwidth is
198 /// If both types are vectors with the same bitwidth, then types
199 /// are bitcastable, and we can skip other stages, and go to contents
201 /// Stage 3: Pointer types are greater than non-pointers. If both types are
202 /// pointers of the same address space - go to contents comparison.
203 /// Different address spaces: pointer with greater address space is
205 /// Stage 4: Types are neither vectors, nor pointers. And they differ.
206 /// We don't know how to bitcast them. So, we better don't do it,
207 /// and return types comparison result (so it determines the
208 /// relationship among constants we don't know how to bitcast).
210 /// Just for clearance, let's see how the set of constants could look
211 /// on single dimension axis:
213 /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
214 /// Where: NFCT - Not a FirstClassType
215 /// FCT - FirstClassTyp:
217 /// 2. Compare raw contents.
218 /// It ignores types on this stage and only compares bits from L and R.
219 /// Returns 0, if L and R has equivalent contents.
220 /// -1 or 1 if values are different.
222 /// 2.1. If contents are numbers, compare numbers.
223 /// Ints with greater bitwidth are greater. Ints with same bitwidths
224 /// compared by their contents.
225 /// 2.2. "And so on". Just to avoid discrepancies with comments
226 /// perhaps it would be better to read the implementation itself.
227 /// 3. And again about overall picture. Let's look back at how the ordered set
228 /// of constants will look like:
229 /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
231 /// Now look, what could be inside [FCT, "others"], for example:
232 /// [FCT, "others"] =
234 /// [double 0.1], [double 1.23],
235 /// [i32 1], [i32 2],
236 /// { double 1.0 }, ; StructTyID, NumElements = 1
237 /// { i32 1 }, ; StructTyID, NumElements = 1
238 /// { double 1, i32 1 }, ; StructTyID, NumElements = 2
239 /// { i32 1, double 1 } ; StructTyID, NumElements = 2
242 /// Let's explain the order. Float numbers will be less than integers, just
243 /// because of cmpType terms: FloatTyID < IntegerTyID.
244 /// Floats (with same fltSemantics) are sorted according to their value.
245 /// Then you can see integers, and they are, like a floats,
246 /// could be easy sorted among each others.
247 /// The structures. Structures are grouped at the tail, again because of their
248 /// TypeID: StructTyID > IntegerTyID > FloatTyID.
249 /// Structures with greater number of elements are greater. Structures with
250 /// greater elements going first are greater.
251 /// The same logic with vectors, arrays and other possible complex types.
253 /// Bitcastable constants.
254 /// Let's assume, that some constant, belongs to some group of
255 /// "so-called-equal" values with different types, and at the same time
256 /// belongs to another group of constants with equal types
257 /// and "really" equal values.
259 /// Now, prove that this is impossible:
261 /// If constant A with type TyA is bitcastable to B with type TyB, then:
262 /// 1. All constants with equal types to TyA, are bitcastable to B. Since
263 /// those should be vectors (if TyA is vector), pointers
264 /// (if TyA is pointer), or else (if TyA equal to TyB), those types should
266 /// 2. All constants with non-equal, but bitcastable types to TyA, are
267 /// bitcastable to B.
268 /// Once again, just because we allow it to vectors and pointers only.
269 /// This statement could be expanded as below:
270 /// 2.1. All vectors with equal bitwidth to vector A, has equal bitwidth to
271 /// vector B, and thus bitcastable to B as well.
272 /// 2.2. All pointers of the same address space, no matter what they point to,
273 /// bitcastable. So if C is pointer, it could be bitcasted to A and to B.
274 /// So any constant equal or bitcastable to A is equal or bitcastable to B.
277 /// In another words, for pointers and vectors, we ignore top-level type and
278 /// look at their particular properties (bit-width for vectors, and
279 /// address space for pointers).
280 /// If these properties are equal - compare their contents.
281 int cmpConstants(const Constant *L, const Constant *R);
283 /// Assign or look up previously assigned numbers for the two values, and
284 /// return whether the numbers are equal. Numbers are assigned in the order
286 /// Comparison order:
287 /// Stage 0: Value that is function itself is always greater then others.
288 /// If left and right values are references to their functions, then
290 /// Stage 1: Constants are greater than non-constants.
291 /// If both left and right are constants, then the result of
292 /// cmpConstants is used as cmpValues result.
293 /// Stage 2: InlineAsm instances are greater than others. If both left and
294 /// right are InlineAsm instances, InlineAsm* pointers casted to
295 /// integers and compared as numbers.
296 /// Stage 3: For all other cases we compare order we meet these values in
297 /// their functions. If right value was met first during scanning,
298 /// then left value is greater.
299 /// In another words, we compare serial numbers, for more details
300 /// see comments for sn_mapL and sn_mapR.
301 int cmpValues(const Value *L, const Value *R);
303 bool enumerate(const Value *V1, const Value *V2) {
304 return cmpValues(V1, V2) == 0;
307 /// Compare two Instructions for equivalence, similar to
308 /// Instruction::isSameOperationAs but with modifications to the type
310 /// Stages are listed in "most significant stage first" order:
311 /// On each stage below, we do comparison between some left and right
312 /// operation parts. If parts are non-equal, we assign parts comparison
313 /// result to the operation comparison result and exit from method.
314 /// Otherwise we proceed to the next stage.
316 /// 1. Operations opcodes. Compared as numbers.
317 /// 2. Number of operands.
318 /// 3. Operation types. Compared with cmpType method.
319 /// 4. Compare operation subclass optional data as stream of bytes:
320 /// just convert it to integers and call cmpNumbers.
321 /// 5. Compare in operation operand types with cmpType in
322 /// most significant operand first order.
323 /// 6. Last stage. Check operations for some specific attributes.
324 /// For example, for Load it would be:
325 /// 6.1.Load: volatile (as boolean flag)
326 /// 6.2.Load: alignment (as integer numbers)
327 /// 6.3.Load: synch-scope (as integer numbers)
328 /// On this stage its better to see the code, since its not more than 10-15
329 /// strings for particular instruction, and could change sometimes.
330 int cmpOperation(const Instruction *L, const Instruction *R) const;
332 bool isEquivalentOperation(const Instruction *I1,
333 const Instruction *I2) const {
334 return cmpOperation(I1, I2) == 0;
337 /// Compare two GEPs for equivalent pointer arithmetic.
338 /// Parts to be compared for each comparison stage,
339 /// most significant stage first:
340 /// 1. Address space. As numbers.
341 /// 2. Constant offset, (if "DataLayout *DL" field is not NULL,
342 /// using GEPOperator::accumulateConstantOffset method).
343 /// 3. Pointer operand type (using cmpType method).
344 /// 4. Number of operands.
345 /// 5. Compare operands, using cmpValues method.
346 int cmpGEP(const GEPOperator *GEPL, const GEPOperator *GEPR);
347 int cmpGEP(const GetElementPtrInst *GEPL, const GetElementPtrInst *GEPR) {
348 return cmpGEP(cast<GEPOperator>(GEPL), cast<GEPOperator>(GEPR));
351 bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2) {
352 return cmpGEP(GEP1, GEP2) == 0;
354 bool isEquivalentGEP(const GetElementPtrInst *GEP1,
355 const GetElementPtrInst *GEP2) {
356 return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
359 /// cmpType - compares two types,
360 /// defines total ordering among the types set.
363 /// 0 if types are equal,
364 /// -1 if Left is less than Right,
365 /// +1 if Left is greater than Right.
368 /// Comparison is broken onto stages. Like in lexicographical comparison
369 /// stage coming first has higher priority.
370 /// On each explanation stage keep in mind total ordering properties.
372 /// 0. Before comparison we coerce pointer types of 0 address space to
374 /// We also don't bother with same type at left and right, so
375 /// just return 0 in this case.
377 /// 1. If types are of different kind (different type IDs).
378 /// Return result of type IDs comparison, treating them as numbers.
379 /// 2. If types are vectors or integers, compare Type* values as numbers.
380 /// 3. Types has same ID, so check whether they belongs to the next group:
389 /// If so - return 0, yes - we can treat these types as equal only because
390 /// their IDs are same.
391 /// 4. If Left and Right are pointers, return result of address space
392 /// comparison (numbers comparison). We can treat pointer types of same
393 /// address space as equal.
394 /// 5. If types are complex.
395 /// Then both Left and Right are to be expanded and their element types will
396 /// be checked with the same way. If we get Res != 0 on some stage, return it.
397 /// Otherwise return 0.
398 /// 6. For all other cases put llvm_unreachable.
399 int cmpType(Type *TyL, Type *TyR) const;
401 bool isEquivalentType(Type *Ty1, Type *Ty2) const {
402 return cmpType(Ty1, Ty2) == 0;
405 int cmpNumbers(uint64_t L, uint64_t R) const;
407 int cmpAPInt(const APInt &L, const APInt &R) const;
408 int cmpAPFloat(const APFloat &L, const APFloat &R) const;
409 int cmpStrings(StringRef L, StringRef R) const;
410 int cmpAttrs(const AttributeSet L, const AttributeSet R) const;
412 // The two functions undergoing comparison.
413 const Function *F1, *F2;
415 const DataLayout *DL;
417 /// Assign serial numbers to values from left function, and values from
420 /// Being comparing functions we need to compare values we meet at left and
422 /// Its easy to sort things out for external values. It just should be
423 /// the same value at left and right.
424 /// But for local values (those were introduced inside function body)
425 /// we have to ensure they were introduced at exactly the same place,
426 /// and plays the same role.
427 /// Let's assign serial number to each value when we meet it first time.
428 /// Values that were met at same place will be with same serial numbers.
429 /// In this case it would be good to explain few points about values assigned
430 /// to BBs and other ways of implementation (see below).
432 /// 1. Safety of BB reordering.
433 /// It's safe to change the order of BasicBlocks in function.
434 /// Relationship with other functions and serial numbering will not be
435 /// changed in this case.
436 /// As follows from FunctionComparator::compare(), we do CFG walk: we start
437 /// from the entry, and then take each terminator. So it doesn't matter how in
438 /// fact BBs are ordered in function. And since cmpValues are called during
439 /// this walk, the numbering depends only on how BBs located inside the CFG.
440 /// So the answer is - yes. We will get the same numbering.
442 /// 2. Impossibility to use dominance properties of values.
443 /// If we compare two instruction operands: first is usage of local
444 /// variable AL from function FL, and second is usage of local variable AR
445 /// from FR, we could compare their origins and check whether they are
446 /// defined at the same place.
447 /// But, we are still not able to compare operands of PHI nodes, since those
448 /// could be operands from further BBs we didn't scan yet.
449 /// So it's impossible to use dominance properties in general.
450 DenseMap<const Value*, int> sn_mapL, sn_mapR;
455 int FunctionComparator::cmpNumbers(uint64_t L, uint64_t R) const {
456 if (L < R) return -1;
461 int FunctionComparator::cmpAPInt(const APInt &L, const APInt &R) const {
462 if (int Res = cmpNumbers(L.getBitWidth(), R.getBitWidth()))
464 if (L.ugt(R)) return 1;
465 if (R.ugt(L)) return -1;
469 int FunctionComparator::cmpAPFloat(const APFloat &L, const APFloat &R) const {
470 if (int Res = cmpNumbers((uint64_t)&L.getSemantics(),
471 (uint64_t)&R.getSemantics()))
473 return cmpAPInt(L.bitcastToAPInt(), R.bitcastToAPInt());
476 int FunctionComparator::cmpStrings(StringRef L, StringRef R) const {
477 // Prevent heavy comparison, compare sizes first.
478 if (int Res = cmpNumbers(L.size(), R.size()))
481 // Compare strings lexicographically only when it is necessary: only when
482 // strings are equal in size.
486 int FunctionComparator::cmpAttrs(const AttributeSet L,
487 const AttributeSet R) const {
488 if (int Res = cmpNumbers(L.getNumSlots(), R.getNumSlots()))
491 for (unsigned i = 0, e = L.getNumSlots(); i != e; ++i) {
492 AttributeSet::iterator LI = L.begin(i), LE = L.end(i), RI = R.begin(i),
494 for (; LI != LE && RI != RE; ++LI, ++RI) {
510 /// Constants comparison:
511 /// 1. Check whether type of L constant could be losslessly bitcasted to R
513 /// 2. Compare constant contents.
514 /// For more details see declaration comments.
515 int FunctionComparator::cmpConstants(const Constant *L, const Constant *R) {
517 Type *TyL = L->getType();
518 Type *TyR = R->getType();
520 // Check whether types are bitcastable. This part is just re-factored
521 // Type::canLosslesslyBitCastTo method, but instead of returning true/false,
522 // we also pack into result which type is "less" for us.
523 int TypesRes = cmpType(TyL, TyR);
525 // Types are different, but check whether we can bitcast them.
526 if (!TyL->isFirstClassType()) {
527 if (TyR->isFirstClassType())
529 // Neither TyL nor TyR are values of first class type. Return the result
530 // of comparing the types
533 if (!TyR->isFirstClassType()) {
534 if (TyL->isFirstClassType())
539 // Vector -> Vector conversions are always lossless if the two vector types
540 // have the same size, otherwise not.
541 unsigned TyLWidth = 0;
542 unsigned TyRWidth = 0;
544 if (const VectorType *VecTyL = dyn_cast<VectorType>(TyL))
545 TyLWidth = VecTyL->getBitWidth();
546 if (const VectorType *VecTyR = dyn_cast<VectorType>(TyR))
547 TyRWidth = VecTyR->getBitWidth();
549 if (TyLWidth != TyRWidth)
550 return cmpNumbers(TyLWidth, TyRWidth);
552 // Zero bit-width means neither TyL nor TyR are vectors.
554 PointerType *PTyL = dyn_cast<PointerType>(TyL);
555 PointerType *PTyR = dyn_cast<PointerType>(TyR);
557 unsigned AddrSpaceL = PTyL->getAddressSpace();
558 unsigned AddrSpaceR = PTyR->getAddressSpace();
559 if (int Res = cmpNumbers(AddrSpaceL, AddrSpaceR))
567 // TyL and TyR aren't vectors, nor pointers. We don't know how to
573 // OK, types are bitcastable, now check constant contents.
575 if (L->isNullValue() && R->isNullValue())
577 if (L->isNullValue() && !R->isNullValue())
579 if (!L->isNullValue() && R->isNullValue())
582 if (int Res = cmpNumbers(L->getValueID(), R->getValueID()))
585 switch (L->getValueID()) {
586 case Value::UndefValueVal: return TypesRes;
587 case Value::ConstantIntVal: {
588 const APInt &LInt = cast<ConstantInt>(L)->getValue();
589 const APInt &RInt = cast<ConstantInt>(R)->getValue();
590 return cmpAPInt(LInt, RInt);
592 case Value::ConstantFPVal: {
593 const APFloat &LAPF = cast<ConstantFP>(L)->getValueAPF();
594 const APFloat &RAPF = cast<ConstantFP>(R)->getValueAPF();
595 return cmpAPFloat(LAPF, RAPF);
597 case Value::ConstantArrayVal: {
598 const ConstantArray *LA = cast<ConstantArray>(L);
599 const ConstantArray *RA = cast<ConstantArray>(R);
600 uint64_t NumElementsL = cast<ArrayType>(TyL)->getNumElements();
601 uint64_t NumElementsR = cast<ArrayType>(TyR)->getNumElements();
602 if (int Res = cmpNumbers(NumElementsL, NumElementsR))
604 for (uint64_t i = 0; i < NumElementsL; ++i) {
605 if (int Res = cmpConstants(cast<Constant>(LA->getOperand(i)),
606 cast<Constant>(RA->getOperand(i))))
611 case Value::ConstantStructVal: {
612 const ConstantStruct *LS = cast<ConstantStruct>(L);
613 const ConstantStruct *RS = cast<ConstantStruct>(R);
614 unsigned NumElementsL = cast<StructType>(TyL)->getNumElements();
615 unsigned NumElementsR = cast<StructType>(TyR)->getNumElements();
616 if (int Res = cmpNumbers(NumElementsL, NumElementsR))
618 for (unsigned i = 0; i != NumElementsL; ++i) {
619 if (int Res = cmpConstants(cast<Constant>(LS->getOperand(i)),
620 cast<Constant>(RS->getOperand(i))))
625 case Value::ConstantVectorVal: {
626 const ConstantVector *LV = cast<ConstantVector>(L);
627 const ConstantVector *RV = cast<ConstantVector>(R);
628 unsigned NumElementsL = cast<VectorType>(TyL)->getNumElements();
629 unsigned NumElementsR = cast<VectorType>(TyR)->getNumElements();
630 if (int Res = cmpNumbers(NumElementsL, NumElementsR))
632 for (uint64_t i = 0; i < NumElementsL; ++i) {
633 if (int Res = cmpConstants(cast<Constant>(LV->getOperand(i)),
634 cast<Constant>(RV->getOperand(i))))
639 case Value::ConstantExprVal: {
640 const ConstantExpr *LE = cast<ConstantExpr>(L);
641 const ConstantExpr *RE = cast<ConstantExpr>(R);
642 unsigned NumOperandsL = LE->getNumOperands();
643 unsigned NumOperandsR = RE->getNumOperands();
644 if (int Res = cmpNumbers(NumOperandsL, NumOperandsR))
646 for (unsigned i = 0; i < NumOperandsL; ++i) {
647 if (int Res = cmpConstants(cast<Constant>(LE->getOperand(i)),
648 cast<Constant>(RE->getOperand(i))))
653 case Value::FunctionVal:
654 case Value::GlobalVariableVal:
655 case Value::GlobalAliasVal:
656 default: // Unknown constant, cast L and R pointers to numbers and compare.
657 return cmpNumbers((uint64_t)L, (uint64_t)R);
661 /// cmpType - compares two types,
662 /// defines total ordering among the types set.
663 /// See method declaration comments for more details.
664 int FunctionComparator::cmpType(Type *TyL, Type *TyR) const {
666 PointerType *PTyL = dyn_cast<PointerType>(TyL);
667 PointerType *PTyR = dyn_cast<PointerType>(TyR);
670 if (PTyL && PTyL->getAddressSpace() == 0) TyL = DL->getIntPtrType(TyL);
671 if (PTyR && PTyR->getAddressSpace() == 0) TyR = DL->getIntPtrType(TyR);
677 if (int Res = cmpNumbers(TyL->getTypeID(), TyR->getTypeID()))
680 switch (TyL->getTypeID()) {
682 llvm_unreachable("Unknown type!");
683 // Fall through in Release mode.
684 case Type::IntegerTyID:
685 case Type::VectorTyID:
686 // TyL == TyR would have returned true earlier.
687 return cmpNumbers((uint64_t)TyL, (uint64_t)TyR);
690 case Type::FloatTyID:
691 case Type::DoubleTyID:
692 case Type::X86_FP80TyID:
693 case Type::FP128TyID:
694 case Type::PPC_FP128TyID:
695 case Type::LabelTyID:
696 case Type::MetadataTyID:
699 case Type::PointerTyID: {
700 assert(PTyL && PTyR && "Both types must be pointers here.");
701 return cmpNumbers(PTyL->getAddressSpace(), PTyR->getAddressSpace());
704 case Type::StructTyID: {
705 StructType *STyL = cast<StructType>(TyL);
706 StructType *STyR = cast<StructType>(TyR);
707 if (STyL->getNumElements() != STyR->getNumElements())
708 return cmpNumbers(STyL->getNumElements(), STyR->getNumElements());
710 if (STyL->isPacked() != STyR->isPacked())
711 return cmpNumbers(STyL->isPacked(), STyR->isPacked());
713 for (unsigned i = 0, e = STyL->getNumElements(); i != e; ++i) {
714 if (int Res = cmpType(STyL->getElementType(i),
715 STyR->getElementType(i)))
721 case Type::FunctionTyID: {
722 FunctionType *FTyL = cast<FunctionType>(TyL);
723 FunctionType *FTyR = cast<FunctionType>(TyR);
724 if (FTyL->getNumParams() != FTyR->getNumParams())
725 return cmpNumbers(FTyL->getNumParams(), FTyR->getNumParams());
727 if (FTyL->isVarArg() != FTyR->isVarArg())
728 return cmpNumbers(FTyL->isVarArg(), FTyR->isVarArg());
730 if (int Res = cmpType(FTyL->getReturnType(), FTyR->getReturnType()))
733 for (unsigned i = 0, e = FTyL->getNumParams(); i != e; ++i) {
734 if (int Res = cmpType(FTyL->getParamType(i), FTyR->getParamType(i)))
740 case Type::ArrayTyID: {
741 ArrayType *ATyL = cast<ArrayType>(TyL);
742 ArrayType *ATyR = cast<ArrayType>(TyR);
743 if (ATyL->getNumElements() != ATyR->getNumElements())
744 return cmpNumbers(ATyL->getNumElements(), ATyR->getNumElements());
745 return cmpType(ATyL->getElementType(), ATyR->getElementType());
750 // Determine whether the two operations are the same except that pointer-to-A
751 // and pointer-to-B are equivalent. This should be kept in sync with
752 // Instruction::isSameOperationAs.
753 // Read method declaration comments for more details.
754 int FunctionComparator::cmpOperation(const Instruction *L,
755 const Instruction *R) const {
756 // Differences from Instruction::isSameOperationAs:
757 // * replace type comparison with calls to isEquivalentType.
758 // * we test for I->hasSameSubclassOptionalData (nuw/nsw/tail) at the top
759 // * because of the above, we don't test for the tail bit on calls later on
760 if (int Res = cmpNumbers(L->getOpcode(), R->getOpcode()))
763 if (int Res = cmpNumbers(L->getNumOperands(), R->getNumOperands()))
766 if (int Res = cmpType(L->getType(), R->getType()))
769 if (int Res = cmpNumbers(L->getRawSubclassOptionalData(),
770 R->getRawSubclassOptionalData()))
773 // We have two instructions of identical opcode and #operands. Check to see
774 // if all operands are the same type
775 for (unsigned i = 0, e = L->getNumOperands(); i != e; ++i) {
777 cmpType(L->getOperand(i)->getType(), R->getOperand(i)->getType()))
781 // Check special state that is a part of some instructions.
782 if (const LoadInst *LI = dyn_cast<LoadInst>(L)) {
783 if (int Res = cmpNumbers(LI->isVolatile(), cast<LoadInst>(R)->isVolatile()))
786 cmpNumbers(LI->getAlignment(), cast<LoadInst>(R)->getAlignment()))
789 cmpNumbers(LI->getOrdering(), cast<LoadInst>(R)->getOrdering()))
791 return cmpNumbers(LI->getSynchScope(), cast<LoadInst>(R)->getSynchScope());
793 if (const StoreInst *SI = dyn_cast<StoreInst>(L)) {
795 cmpNumbers(SI->isVolatile(), cast<StoreInst>(R)->isVolatile()))
798 cmpNumbers(SI->getAlignment(), cast<StoreInst>(R)->getAlignment()))
801 cmpNumbers(SI->getOrdering(), cast<StoreInst>(R)->getOrdering()))
803 return cmpNumbers(SI->getSynchScope(), cast<StoreInst>(R)->getSynchScope());
805 if (const CmpInst *CI = dyn_cast<CmpInst>(L))
806 return cmpNumbers(CI->getPredicate(), cast<CmpInst>(R)->getPredicate());
807 if (const CallInst *CI = dyn_cast<CallInst>(L)) {
808 if (int Res = cmpNumbers(CI->getCallingConv(),
809 cast<CallInst>(R)->getCallingConv()))
811 return cmpAttrs(CI->getAttributes(), cast<CallInst>(R)->getAttributes());
813 if (const InvokeInst *CI = dyn_cast<InvokeInst>(L)) {
814 if (int Res = cmpNumbers(CI->getCallingConv(),
815 cast<InvokeInst>(R)->getCallingConv()))
817 return cmpAttrs(CI->getAttributes(), cast<InvokeInst>(R)->getAttributes());
819 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(L)) {
820 ArrayRef<unsigned> LIndices = IVI->getIndices();
821 ArrayRef<unsigned> RIndices = cast<InsertValueInst>(R)->getIndices();
822 if (int Res = cmpNumbers(LIndices.size(), RIndices.size()))
824 for (size_t i = 0, e = LIndices.size(); i != e; ++i) {
825 if (int Res = cmpNumbers(LIndices[i], RIndices[i]))
829 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(L)) {
830 ArrayRef<unsigned> LIndices = EVI->getIndices();
831 ArrayRef<unsigned> RIndices = cast<ExtractValueInst>(R)->getIndices();
832 if (int Res = cmpNumbers(LIndices.size(), RIndices.size()))
834 for (size_t i = 0, e = LIndices.size(); i != e; ++i) {
835 if (int Res = cmpNumbers(LIndices[i], RIndices[i]))
839 if (const FenceInst *FI = dyn_cast<FenceInst>(L)) {
841 cmpNumbers(FI->getOrdering(), cast<FenceInst>(R)->getOrdering()))
843 return cmpNumbers(FI->getSynchScope(), cast<FenceInst>(R)->getSynchScope());
846 if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(L)) {
847 if (int Res = cmpNumbers(CXI->isVolatile(),
848 cast<AtomicCmpXchgInst>(R)->isVolatile()))
850 if (int Res = cmpNumbers(CXI->getSuccessOrdering(),
851 cast<AtomicCmpXchgInst>(R)->getSuccessOrdering()))
853 if (int Res = cmpNumbers(CXI->getFailureOrdering(),
854 cast<AtomicCmpXchgInst>(R)->getFailureOrdering()))
856 return cmpNumbers(CXI->getSynchScope(),
857 cast<AtomicCmpXchgInst>(R)->getSynchScope());
859 if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(L)) {
860 if (int Res = cmpNumbers(RMWI->getOperation(),
861 cast<AtomicRMWInst>(R)->getOperation()))
863 if (int Res = cmpNumbers(RMWI->isVolatile(),
864 cast<AtomicRMWInst>(R)->isVolatile()))
866 if (int Res = cmpNumbers(RMWI->getOrdering(),
867 cast<AtomicRMWInst>(R)->getOrdering()))
869 return cmpNumbers(RMWI->getSynchScope(),
870 cast<AtomicRMWInst>(R)->getSynchScope());
875 // Determine whether two GEP operations perform the same underlying arithmetic.
876 // Read method declaration comments for more details.
877 int FunctionComparator::cmpGEP(const GEPOperator *GEPL,
878 const GEPOperator *GEPR) {
880 unsigned int ASL = GEPL->getPointerAddressSpace();
881 unsigned int ASR = GEPR->getPointerAddressSpace();
883 if (int Res = cmpNumbers(ASL, ASR))
886 // When we have target data, we can reduce the GEP down to the value in bytes
887 // added to the address.
889 unsigned BitWidth = DL->getPointerSizeInBits(ASL);
890 APInt OffsetL(BitWidth, 0), OffsetR(BitWidth, 0);
891 if (GEPL->accumulateConstantOffset(*DL, OffsetL) &&
892 GEPR->accumulateConstantOffset(*DL, OffsetR))
893 return cmpAPInt(OffsetL, OffsetR);
896 if (int Res = cmpNumbers((uint64_t)GEPL->getPointerOperand()->getType(),
897 (uint64_t)GEPR->getPointerOperand()->getType()))
900 if (int Res = cmpNumbers(GEPL->getNumOperands(), GEPR->getNumOperands()))
903 for (unsigned i = 0, e = GEPL->getNumOperands(); i != e; ++i) {
904 if (int Res = cmpValues(GEPL->getOperand(i), GEPR->getOperand(i)))
911 /// Compare two values used by the two functions under pair-wise comparison. If
912 /// this is the first time the values are seen, they're added to the mapping so
913 /// that we will detect mismatches on next use.
914 /// See comments in declaration for more details.
915 int FunctionComparator::cmpValues(const Value *L, const Value *R) {
916 // Catch self-reference case.
928 const Constant *ConstL = dyn_cast<Constant>(L);
929 const Constant *ConstR = dyn_cast<Constant>(R);
930 if (ConstL && ConstR) {
933 return cmpConstants(ConstL, ConstR);
941 const InlineAsm *InlineAsmL = dyn_cast<InlineAsm>(L);
942 const InlineAsm *InlineAsmR = dyn_cast<InlineAsm>(R);
944 if (InlineAsmL && InlineAsmR)
945 return cmpNumbers((uint64_t)L, (uint64_t)R);
951 auto LeftSN = sn_mapL.insert(std::make_pair(L, sn_mapL.size())),
952 RightSN = sn_mapR.insert(std::make_pair(R, sn_mapR.size()));
954 return cmpNumbers(LeftSN.first->second, RightSN.first->second);
956 // Test whether two basic blocks have equivalent behaviour.
957 bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) {
958 BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end();
959 BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end();
962 if (!enumerate(F1I, F2I))
965 if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) {
966 const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I);
970 if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand()))
973 if (!isEquivalentGEP(GEP1, GEP2))
976 if (!isEquivalentOperation(F1I, F2I))
979 assert(F1I->getNumOperands() == F2I->getNumOperands());
980 for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) {
981 Value *OpF1 = F1I->getOperand(i);
982 Value *OpF2 = F2I->getOperand(i);
984 if (!enumerate(OpF1, OpF2))
987 if (OpF1->getValueID() != OpF2->getValueID() ||
988 !isEquivalentType(OpF1->getType(), OpF2->getType()))
994 } while (F1I != F1E && F2I != F2E);
996 return F1I == F1E && F2I == F2E;
999 // Test whether the two functions have equivalent behaviour.
1000 bool FunctionComparator::compare() {
1001 // We need to recheck everything, but check the things that weren't included
1002 // in the hash first.
1007 if (F1->getAttributes() != F2->getAttributes())
1010 if (F1->hasGC() != F2->hasGC())
1013 if (F1->hasGC() && F1->getGC() != F2->getGC())
1016 if (F1->hasSection() != F2->hasSection())
1019 if (F1->hasSection() && F1->getSection() != F2->getSection())
1022 if (F1->isVarArg() != F2->isVarArg())
1025 // TODO: if it's internal and only used in direct calls, we could handle this
1027 if (F1->getCallingConv() != F2->getCallingConv())
1030 if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType()))
1033 assert(F1->arg_size() == F2->arg_size() &&
1034 "Identically typed functions have different numbers of args!");
1036 // Visit the arguments so that they get enumerated in the order they're
1038 for (Function::const_arg_iterator f1i = F1->arg_begin(),
1039 f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) {
1040 if (!enumerate(f1i, f2i))
1041 llvm_unreachable("Arguments repeat!");
1044 // We do a CFG-ordered walk since the actual ordering of the blocks in the
1045 // linked list is immaterial. Our walk starts at the entry block for both
1046 // functions, then takes each block from each terminator in order. As an
1047 // artifact, this also means that unreachable blocks are ignored.
1048 SmallVector<const BasicBlock *, 8> F1BBs, F2BBs;
1049 SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1.
1051 F1BBs.push_back(&F1->getEntryBlock());
1052 F2BBs.push_back(&F2->getEntryBlock());
1054 VisitedBBs.insert(F1BBs[0]);
1055 while (!F1BBs.empty()) {
1056 const BasicBlock *F1BB = F1BBs.pop_back_val();
1057 const BasicBlock *F2BB = F2BBs.pop_back_val();
1059 if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB))
1062 const TerminatorInst *F1TI = F1BB->getTerminator();
1063 const TerminatorInst *F2TI = F2BB->getTerminator();
1065 assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors());
1066 for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) {
1067 if (!VisitedBBs.insert(F1TI->getSuccessor(i)))
1070 F1BBs.push_back(F1TI->getSuccessor(i));
1071 F2BBs.push_back(F2TI->getSuccessor(i));
1079 /// MergeFunctions finds functions which will generate identical machine code,
1080 /// by considering all pointer types to be equivalent. Once identified,
1081 /// MergeFunctions will fold them by replacing a call to one to a call to a
1082 /// bitcast of the other.
1084 class MergeFunctions : public ModulePass {
1088 : ModulePass(ID), HasGlobalAliases(false) {
1089 initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
1092 bool runOnModule(Module &M) override;
1095 typedef DenseSet<ComparableFunction> FnSetType;
1097 /// A work queue of functions that may have been modified and should be
1099 std::vector<WeakVH> Deferred;
1101 /// Insert a ComparableFunction into the FnSet, or merge it away if it's
1102 /// equal to one that's already present.
1103 bool insert(ComparableFunction &NewF);
1105 /// Remove a Function from the FnSet and queue it up for a second sweep of
1107 void remove(Function *F);
1109 /// Find the functions that use this Value and remove them from FnSet and
1110 /// queue the functions.
1111 void removeUsers(Value *V);
1113 /// Replace all direct calls of Old with calls of New. Will bitcast New if
1114 /// necessary to make types match.
1115 void replaceDirectCallers(Function *Old, Function *New);
1117 /// Merge two equivalent functions. Upon completion, G may be deleted, or may
1118 /// be converted into a thunk. In either case, it should never be visited
1120 void mergeTwoFunctions(Function *F, Function *G);
1122 /// Replace G with a thunk or an alias to F. Deletes G.
1123 void writeThunkOrAlias(Function *F, Function *G);
1125 /// Replace G with a simple tail call to bitcast(F). Also replace direct uses
1126 /// of G with bitcast(F). Deletes G.
1127 void writeThunk(Function *F, Function *G);
1129 /// Replace G with an alias to F. Deletes G.
1130 void writeAlias(Function *F, Function *G);
1132 /// The set of all distinct functions. Use the insert() and remove() methods
1136 /// DataLayout for more accurate GEP comparisons. May be NULL.
1137 const DataLayout *DL;
1139 /// Whether or not the target supports global aliases.
1140 bool HasGlobalAliases;
1143 } // end anonymous namespace
1145 char MergeFunctions::ID = 0;
1146 INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false)
1148 ModulePass *llvm::createMergeFunctionsPass() {
1149 return new MergeFunctions();
1152 bool MergeFunctions::runOnModule(Module &M) {
1153 bool Changed = false;
1154 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
1155 DL = DLP ? &DLP->getDataLayout() : nullptr;
1157 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
1158 if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage())
1159 Deferred.push_back(WeakVH(I));
1161 FnSet.resize(Deferred.size());
1164 std::vector<WeakVH> Worklist;
1165 Deferred.swap(Worklist);
1167 DEBUG(dbgs() << "size of module: " << M.size() << '\n');
1168 DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
1170 // Insert only strong functions and merge them. Strong function merging
1171 // always deletes one of them.
1172 for (std::vector<WeakVH>::iterator I = Worklist.begin(),
1173 E = Worklist.end(); I != E; ++I) {
1175 Function *F = cast<Function>(*I);
1176 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
1177 !F->mayBeOverridden()) {
1178 ComparableFunction CF = ComparableFunction(F, DL);
1179 Changed |= insert(CF);
1183 // Insert only weak functions and merge them. By doing these second we
1184 // create thunks to the strong function when possible. When two weak
1185 // functions are identical, we create a new strong function with two weak
1186 // weak thunks to it which are identical but not mergable.
1187 for (std::vector<WeakVH>::iterator I = Worklist.begin(),
1188 E = Worklist.end(); I != E; ++I) {
1190 Function *F = cast<Function>(*I);
1191 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
1192 F->mayBeOverridden()) {
1193 ComparableFunction CF = ComparableFunction(F, DL);
1194 Changed |= insert(CF);
1197 DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n');
1198 } while (!Deferred.empty());
1205 bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS,
1206 const ComparableFunction &RHS) {
1207 if (LHS.getFunc() == RHS.getFunc() &&
1208 LHS.getHash() == RHS.getHash())
1210 if (!LHS.getFunc() || !RHS.getFunc())
1213 // One of these is a special "underlying pointer comparison only" object.
1214 if (LHS.getDataLayout() == ComparableFunction::LookupOnly ||
1215 RHS.getDataLayout() == ComparableFunction::LookupOnly)
1218 assert(LHS.getDataLayout() == RHS.getDataLayout() &&
1219 "Comparing functions for different targets");
1221 return FunctionComparator(LHS.getDataLayout(), LHS.getFunc(),
1222 RHS.getFunc()).compare();
1225 // Replace direct callers of Old with New.
1226 void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
1227 Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType());
1228 for (auto UI = Old->use_begin(), UE = Old->use_end(); UI != UE;) {
1231 CallSite CS(U->getUser());
1232 if (CS && CS.isCallee(U)) {
1233 remove(CS.getInstruction()->getParent()->getParent());
1239 // Replace G with an alias to F if possible, or else a thunk to F. Deletes G.
1240 void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
1241 if (HasGlobalAliases && G->hasUnnamedAddr()) {
1242 if (G->hasExternalLinkage() || G->hasLocalLinkage() ||
1243 G->hasWeakLinkage()) {
1252 // Helper for writeThunk,
1253 // Selects proper bitcast operation,
1254 // but a bit simpler then CastInst::getCastOpcode.
1255 static Value *createCast(IRBuilder<false> &Builder, Value *V, Type *DestTy) {
1256 Type *SrcTy = V->getType();
1257 if (SrcTy->isStructTy()) {
1258 assert(DestTy->isStructTy());
1259 assert(SrcTy->getStructNumElements() == DestTy->getStructNumElements());
1260 Value *Result = UndefValue::get(DestTy);
1261 for (unsigned int I = 0, E = SrcTy->getStructNumElements(); I < E; ++I) {
1262 Value *Element = createCast(
1263 Builder, Builder.CreateExtractValue(V, ArrayRef<unsigned int>(I)),
1264 DestTy->getStructElementType(I));
1267 Builder.CreateInsertValue(Result, Element, ArrayRef<unsigned int>(I));
1271 assert(!DestTy->isStructTy());
1272 if (SrcTy->isIntegerTy() && DestTy->isPointerTy())
1273 return Builder.CreateIntToPtr(V, DestTy);
1274 else if (SrcTy->isPointerTy() && DestTy->isIntegerTy())
1275 return Builder.CreatePtrToInt(V, DestTy);
1277 return Builder.CreateBitCast(V, DestTy);
1280 // Replace G with a simple tail call to bitcast(F). Also replace direct uses
1281 // of G with bitcast(F). Deletes G.
1282 void MergeFunctions::writeThunk(Function *F, Function *G) {
1283 if (!G->mayBeOverridden()) {
1284 // Redirect direct callers of G to F.
1285 replaceDirectCallers(G, F);
1288 // If G was internal then we may have replaced all uses of G with F. If so,
1289 // stop here and delete G. There's no need for a thunk.
1290 if (G->hasLocalLinkage() && G->use_empty()) {
1291 G->eraseFromParent();
1295 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
1297 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
1298 IRBuilder<false> Builder(BB);
1300 SmallVector<Value *, 16> Args;
1302 FunctionType *FFTy = F->getFunctionType();
1303 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
1305 Args.push_back(createCast(Builder, (Value*)AI, FFTy->getParamType(i)));
1309 CallInst *CI = Builder.CreateCall(F, Args);
1311 CI->setCallingConv(F->getCallingConv());
1312 if (NewG->getReturnType()->isVoidTy()) {
1313 Builder.CreateRetVoid();
1315 Builder.CreateRet(createCast(Builder, CI, NewG->getReturnType()));
1318 NewG->copyAttributesFrom(G);
1321 G->replaceAllUsesWith(NewG);
1322 G->eraseFromParent();
1324 DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n');
1328 // Replace G with an alias to F and delete G.
1329 void MergeFunctions::writeAlias(Function *F, Function *G) {
1330 PointerType *PTy = G->getType();
1331 auto *GA = GlobalAlias::create(PTy->getElementType(), PTy->getAddressSpace(),
1332 G->getLinkage(), "", F);
1333 F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
1335 GA->setVisibility(G->getVisibility());
1337 G->replaceAllUsesWith(GA);
1338 G->eraseFromParent();
1340 DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n');
1341 ++NumAliasesWritten;
1344 // Merge two equivalent functions. Upon completion, Function G is deleted.
1345 void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
1346 if (F->mayBeOverridden()) {
1347 assert(G->mayBeOverridden());
1349 if (HasGlobalAliases) {
1350 // Make them both thunks to the same internal function.
1351 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
1353 H->copyAttributesFrom(F);
1356 F->replaceAllUsesWith(H);
1358 unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
1363 F->setAlignment(MaxAlignment);
1364 F->setLinkage(GlobalValue::PrivateLinkage);
1366 // We can't merge them. Instead, pick one and update all direct callers
1367 // to call it and hope that we improve the instruction cache hit rate.
1368 replaceDirectCallers(G, F);
1373 writeThunkOrAlias(F, G);
1376 ++NumFunctionsMerged;
1379 // Insert a ComparableFunction into the FnSet, or merge it away if equal to one
1380 // that was already inserted.
1381 bool MergeFunctions::insert(ComparableFunction &NewF) {
1382 std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
1383 if (Result.second) {
1384 DEBUG(dbgs() << "Inserting as unique: " << NewF.getFunc()->getName() << '\n');
1388 const ComparableFunction &OldF = *Result.first;
1390 // Don't merge tiny functions, since it can just end up making the function
1392 // FIXME: Should still merge them if they are unnamed_addr and produce an
1394 if (NewF.getFunc()->size() == 1) {
1395 if (NewF.getFunc()->front().size() <= 2) {
1396 DEBUG(dbgs() << NewF.getFunc()->getName()
1397 << " is to small to bother merging\n");
1402 // Never thunk a strong function to a weak function.
1403 assert(!OldF.getFunc()->mayBeOverridden() ||
1404 NewF.getFunc()->mayBeOverridden());
1406 DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == "
1407 << NewF.getFunc()->getName() << '\n');
1409 Function *DeleteF = NewF.getFunc();
1411 mergeTwoFunctions(OldF.getFunc(), DeleteF);
1415 // Remove a function from FnSet. If it was already in FnSet, add it to Deferred
1416 // so that we'll look at it in the next round.
1417 void MergeFunctions::remove(Function *F) {
1418 // We need to make sure we remove F, not a function "equal" to F per the
1419 // function equality comparator.
1421 // The special "lookup only" ComparableFunction bypasses the expensive
1422 // function comparison in favour of a pointer comparison on the underlying
1424 ComparableFunction CF = ComparableFunction(F, ComparableFunction::LookupOnly);
1425 if (FnSet.erase(CF)) {
1426 DEBUG(dbgs() << "Removed " << F->getName() << " from set and deferred it.\n");
1427 Deferred.push_back(F);
1431 // For each instruction used by the value, remove() the function that contains
1432 // the instruction. This should happen right before a call to RAUW.
1433 void MergeFunctions::removeUsers(Value *V) {
1434 std::vector<Value *> Worklist;
1435 Worklist.push_back(V);
1436 while (!Worklist.empty()) {
1437 Value *V = Worklist.back();
1438 Worklist.pop_back();
1440 for (User *U : V->users()) {
1441 if (Instruction *I = dyn_cast<Instruction>(U)) {
1442 remove(I->getParent()->getParent());
1443 } else if (isa<GlobalValue>(U)) {
1445 } else if (Constant *C = dyn_cast<Constant>(U)) {
1446 for (User *UU : C->users())
1447 Worklist.push_back(UU);