1 //===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the default implementation of the Alias Analysis interface
11 // that simply implements a few identities (two different globals cannot alias,
12 // etc), but otherwise does no analysis.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Function.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Instructions.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/Support/Compiler.h"
27 #include "llvm/Support/GetElementPtrTypeIterator.h"
28 #include "llvm/Support/ManagedStatic.h"
33 /// NoAA - This class implements the -no-aa pass, which always returns "I
34 /// don't know" for alias queries. NoAA is unlike other alias analysis
35 /// implementations, in that it does not chain to a previous analysis. As
36 /// such it doesn't follow many of the rules that other alias analyses must.
38 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
39 static const char ID; // Class identification, replacement for typeinfo
40 NoAA() : ImmutablePass((intptr_t)&ID) {}
42 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
43 AU.addRequired<TargetData>();
46 virtual void initializePass() {
47 TD = &getAnalysis<TargetData>();
50 virtual AliasResult alias(const Value *V1, unsigned V1Size,
51 const Value *V2, unsigned V2Size) {
55 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
56 std::vector<PointerAccessInfo> *Info) {
57 return UnknownModRefBehavior;
60 virtual void getArgumentAccesses(Function *F, CallSite CS,
61 std::vector<PointerAccessInfo> &Info) {
62 assert(0 && "This method may not be called on this function!");
65 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
66 virtual bool pointsToConstantMemory(const Value *P) { return false; }
67 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
70 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
73 virtual bool hasNoModRefInfoForCalls() const { return true; }
75 virtual void deleteValue(Value *V) {}
76 virtual void copyValue(Value *From, Value *To) {}
79 // Register this pass...
80 const char NoAA::ID = 0;
82 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
84 // Declare that we implement the AliasAnalysis interface
85 RegisterAnalysisGroup<AliasAnalysis> V(U);
86 } // End of anonymous namespace
88 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
91 /// BasicAliasAnalysis - This is the default alias analysis implementation.
92 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
93 /// derives from the NoAA class.
94 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
95 static const char ID; // Class identification, replacement for typeinfo
96 AliasResult alias(const Value *V1, unsigned V1Size,
97 const Value *V2, unsigned V2Size);
99 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
100 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
101 return NoAA::getModRefInfo(CS1,CS2);
104 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
105 /// non-escaping allocations.
106 virtual bool hasNoModRefInfoForCalls() const { return false; }
108 /// pointsToConstantMemory - Chase pointers until we find a (constant
110 bool pointsToConstantMemory(const Value *P);
112 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
113 std::vector<PointerAccessInfo> *Info);
116 // CheckGEPInstructions - Check two GEP instructions with known
117 // must-aliasing base pointers. This checks to see if the index expressions
118 // preclude the pointers from aliasing...
120 CheckGEPInstructions(const Type* BasePtr1Ty,
121 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
122 const Type *BasePtr2Ty,
123 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
126 // Register this pass...
127 const char BasicAliasAnalysis::ID = 0;
128 RegisterPass<BasicAliasAnalysis>
129 X("basicaa", "Basic Alias Analysis (default AA impl)");
131 // Declare that we implement the AliasAnalysis interface
132 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
133 } // End of anonymous namespace
135 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
136 return new BasicAliasAnalysis();
139 // getUnderlyingObject - This traverses the use chain to figure out what object
140 // the specified value points to. If the value points to, or is derived from, a
141 // unique object or an argument, return it.
142 static const Value *getUnderlyingObject(const Value *V) {
143 if (!isa<PointerType>(V->getType())) return 0;
145 // If we are at some type of object, return it. GlobalValues and Allocations
146 // have unique addresses.
147 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
150 // Traverse through different addressing mechanisms...
151 if (const Instruction *I = dyn_cast<Instruction>(V)) {
152 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
153 return getUnderlyingObject(I->getOperand(0));
154 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
155 if (CE->getOpcode() == Instruction::BitCast ||
156 CE->getOpcode() == Instruction::GetElementPtr)
157 return getUnderlyingObject(CE->getOperand(0));
162 static const User *isGEP(const Value *V) {
163 if (isa<GetElementPtrInst>(V) ||
164 (isa<ConstantExpr>(V) &&
165 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
166 return cast<User>(V);
170 static const Value *GetGEPOperands(const Value *V,
171 SmallVector<Value*, 16> &GEPOps){
172 assert(GEPOps.empty() && "Expect empty list to populate!");
173 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
174 cast<User>(V)->op_end());
176 // Accumulate all of the chained indexes into the operand array
177 V = cast<User>(V)->getOperand(0);
179 while (const User *G = isGEP(V)) {
180 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
181 !cast<Constant>(GEPOps[0])->isNullValue())
182 break; // Don't handle folding arbitrary pointer offsets yet...
183 GEPOps.erase(GEPOps.begin()); // Drop the zero index
184 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
185 V = G->getOperand(0);
190 /// pointsToConstantMemory - Chase pointers until we find a (constant
192 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
193 if (const Value *V = getUnderlyingObject(P))
194 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
195 return GV->isConstant();
199 // Determine if an AllocationInst instruction escapes from the function it is
200 // contained in. If it does not escape, there is no way for another function to
201 // mod/ref it. We do this by looking at its uses and determining if the uses
202 // can escape (recursively).
203 static bool AddressMightEscape(const Value *V) {
204 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
206 const Instruction *I = cast<Instruction>(*UI);
207 switch (I->getOpcode()) {
208 case Instruction::Load:
210 case Instruction::Store:
211 if (I->getOperand(0) == V)
212 return true; // Escapes if the pointer is stored.
214 case Instruction::GetElementPtr:
215 if (AddressMightEscape(I))
217 case Instruction::BitCast:
218 if (!isa<PointerType>(I->getType()))
220 if (AddressMightEscape(I))
223 case Instruction::Ret:
224 // If returned, the address will escape to calling functions, but no
225 // callees could modify it.
234 // getModRefInfo - Check to see if the specified callsite can clobber the
235 // specified memory object. Since we only look at local properties of this
236 // function, we really can't say much about this query. We do, however, use
237 // simple "address taken" analysis on local objects.
239 AliasAnalysis::ModRefResult
240 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
241 if (!isa<Constant>(P))
242 if (const AllocationInst *AI =
243 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
244 // Okay, the pointer is to a stack allocated object. If we can prove that
245 // the pointer never "escapes", then we know the call cannot clobber it,
246 // because it simply can't get its address.
247 if (!AddressMightEscape(AI))
250 // If this is a tail call and P points to a stack location, we know that
251 // the tail call cannot access or modify the local stack.
252 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
253 if (CI->isTailCall() && isa<AllocaInst>(AI))
257 // The AliasAnalysis base class has some smarts, lets use them.
258 return AliasAnalysis::getModRefInfo(CS, P, Size);
261 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
262 // as array references. Note that this function is heavily tail recursive.
263 // Hopefully we have a smart C++ compiler. :)
265 AliasAnalysis::AliasResult
266 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
267 const Value *V2, unsigned V2Size) {
268 // Strip off any constant expression casts if they exist
269 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
270 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
271 V1 = CE->getOperand(0);
272 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
273 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
274 V2 = CE->getOperand(0);
276 // Are we checking for alias of the same value?
277 if (V1 == V2) return MustAlias;
279 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
280 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
281 return NoAlias; // Scalars cannot alias each other
283 // Strip off cast instructions...
284 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
285 return alias(I->getOperand(0), V1Size, V2, V2Size);
286 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
287 return alias(V1, V1Size, I->getOperand(0), V2Size);
289 // Figure out what objects these things are pointing to if we can...
290 const Value *O1 = getUnderlyingObject(V1);
291 const Value *O2 = getUnderlyingObject(V2);
293 // Pointing at a discernible object?
296 if (isa<Argument>(O1)) {
297 // Incoming argument cannot alias locally allocated object!
298 if (isa<AllocationInst>(O2)) return NoAlias;
299 // Otherwise, nothing is known...
300 } else if (isa<Argument>(O2)) {
301 // Incoming argument cannot alias locally allocated object!
302 if (isa<AllocationInst>(O1)) return NoAlias;
303 // Otherwise, nothing is known...
304 } else if (O1 != O2) {
305 // If they are two different objects, we know that we have no alias...
309 // If they are the same object, they we can look at the indexes. If they
310 // index off of the object is the same for both pointers, they must alias.
311 // If they are provably different, they must not alias. Otherwise, we
312 // can't tell anything.
316 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
317 return NoAlias; // Unique values don't alias null
319 if (isa<GlobalVariable>(O1) ||
320 (isa<AllocationInst>(O1) &&
321 !cast<AllocationInst>(O1)->isArrayAllocation()))
322 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
323 // If the size of the other access is larger than the total size of the
324 // global/alloca/malloc, it cannot be accessing the global (it's
325 // undefined to load or store bytes before or after an object).
326 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
327 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
328 if (GlobalSize < V2Size && V2Size != ~0U)
334 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
335 return NoAlias; // Unique values don't alias null
337 if (isa<GlobalVariable>(O2) ||
338 (isa<AllocationInst>(O2) &&
339 !cast<AllocationInst>(O2)->isArrayAllocation()))
340 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
341 // If the size of the other access is larger than the total size of the
342 // global/alloca/malloc, it cannot be accessing the object (it's
343 // undefined to load or store bytes before or after an object).
344 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
345 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
346 if (GlobalSize < V1Size && V1Size != ~0U)
351 // If we have two gep instructions with must-alias'ing base pointers, figure
352 // out if the indexes to the GEP tell us anything about the derived pointer.
353 // Note that we also handle chains of getelementptr instructions as well as
354 // constant expression getelementptrs here.
356 if (isGEP(V1) && isGEP(V2)) {
357 // Drill down into the first non-gep value, to test for must-aliasing of
358 // the base pointers.
359 const Value *BasePtr1 = V1, *BasePtr2 = V2;
361 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
362 } while (isGEP(BasePtr1) &&
363 cast<User>(BasePtr1)->getOperand(1) ==
364 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
366 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
367 } while (isGEP(BasePtr2) &&
368 cast<User>(BasePtr2)->getOperand(1) ==
369 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
371 // Do the base pointers alias?
372 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
373 if (BaseAlias == NoAlias) return NoAlias;
374 if (BaseAlias == MustAlias) {
375 // If the base pointers alias each other exactly, check to see if we can
376 // figure out anything about the resultant pointers, to try to prove
379 // Collect all of the chained GEP operands together into one simple place
380 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
381 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
382 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
384 // If GetGEPOperands were able to fold to the same must-aliased pointer,
385 // do the comparison.
386 if (BasePtr1 == BasePtr2) {
388 CheckGEPInstructions(BasePtr1->getType(),
389 &GEP1Ops[0], GEP1Ops.size(), V1Size,
391 &GEP2Ops[0], GEP2Ops.size(), V2Size);
392 if (GAlias != MayAlias)
398 // Check to see if these two pointers are related by a getelementptr
399 // instruction. If one pointer is a GEP with a non-zero index of the other
400 // pointer, we know they cannot alias.
404 std::swap(V1Size, V2Size);
407 if (V1Size != ~0U && V2Size != ~0U)
409 SmallVector<Value*, 16> GEPOperands;
410 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
412 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
413 if (R == MustAlias) {
414 // If there is at least one non-zero constant index, we know they cannot
416 bool ConstantFound = false;
417 bool AllZerosFound = true;
418 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
419 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
420 if (!C->isNullValue()) {
421 ConstantFound = true;
422 AllZerosFound = false;
426 AllZerosFound = false;
429 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
430 // the ptr, the end result is a must alias also.
435 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
438 // Otherwise we have to check to see that the distance is more than
439 // the size of the argument... build an index vector that is equal to
440 // the arguments provided, except substitute 0's for any variable
441 // indexes we find...
442 if (cast<PointerType>(
443 BasePtr->getType())->getElementType()->isSized()) {
444 for (unsigned i = 0; i != GEPOperands.size(); ++i)
445 if (!isa<ConstantInt>(GEPOperands[i]))
447 Constant::getNullValue(GEPOperands[i]->getType());
449 getTargetData().getIndexedOffset(BasePtr->getType(),
453 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
463 // This function is used to determin if the indices of two GEP instructions are
464 // equal. V1 and V2 are the indices.
465 static bool IndexOperandsEqual(Value *V1, Value *V2) {
466 if (V1->getType() == V2->getType())
468 if (Constant *C1 = dyn_cast<Constant>(V1))
469 if (Constant *C2 = dyn_cast<Constant>(V2)) {
470 // Sign extend the constants to long types, if necessary
471 if (C1->getType() != Type::Int64Ty)
472 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
473 if (C2->getType() != Type::Int64Ty)
474 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
480 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
481 /// base pointers. This checks to see if the index expressions preclude the
482 /// pointers from aliasing...
483 AliasAnalysis::AliasResult
484 BasicAliasAnalysis::CheckGEPInstructions(
485 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
486 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
487 // We currently can't handle the case when the base pointers have different
488 // primitive types. Since this is uncommon anyway, we are happy being
489 // extremely conservative.
490 if (BasePtr1Ty != BasePtr2Ty)
493 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
495 // Find the (possibly empty) initial sequence of equal values... which are not
496 // necessarily constants.
497 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
498 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
499 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
500 unsigned UnequalOper = 0;
501 while (UnequalOper != MinOperands &&
502 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
503 // Advance through the type as we go...
505 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
506 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
508 // If all operands equal each other, then the derived pointers must
509 // alias each other...
511 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
512 "Ran out of type nesting, but not out of operands?");
517 // If we have seen all constant operands, and run out of indexes on one of the
518 // getelementptrs, check to see if the tail of the leftover one is all zeros.
519 // If so, return mustalias.
520 if (UnequalOper == MinOperands) {
521 if (NumGEP1Ops < NumGEP2Ops) {
522 std::swap(GEP1Ops, GEP2Ops);
523 std::swap(NumGEP1Ops, NumGEP2Ops);
526 bool AllAreZeros = true;
527 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
528 if (!isa<Constant>(GEP1Ops[i]) ||
529 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
533 if (AllAreZeros) return MustAlias;
537 // So now we know that the indexes derived from the base pointers,
538 // which are known to alias, are different. We can still determine a
539 // no-alias result if there are differing constant pairs in the index
540 // chain. For example:
541 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
543 // We have to be careful here about array accesses. In particular, consider:
544 // A[1][0] vs A[0][i]
545 // In this case, we don't *know* that the array will be accessed in bounds:
546 // the index could even be negative. Because of this, we have to
547 // conservatively *give up* and return may alias. We disregard differing
548 // array subscripts that are followed by a variable index without going
551 unsigned SizeMax = std::max(G1S, G2S);
552 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
554 // Scan for the first operand that is constant and unequal in the
555 // two getelementptrs...
556 unsigned FirstConstantOper = UnequalOper;
557 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
558 const Value *G1Oper = GEP1Ops[FirstConstantOper];
559 const Value *G2Oper = GEP2Ops[FirstConstantOper];
561 if (G1Oper != G2Oper) // Found non-equal constant indexes...
562 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
563 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
564 if (G1OC->getType() != G2OC->getType()) {
565 // Sign extend both operands to long.
566 if (G1OC->getType() != Type::Int64Ty)
567 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
568 if (G2OC->getType() != Type::Int64Ty)
569 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
570 GEP1Ops[FirstConstantOper] = G1OC;
571 GEP2Ops[FirstConstantOper] = G2OC;
575 // Handle the "be careful" case above: if this is an array/packed
576 // subscript, scan for a subsequent variable array index.
577 if (isa<SequentialType>(BasePtr1Ty)) {
579 cast<SequentialType>(BasePtr1Ty)->getElementType();
580 bool isBadCase = false;
582 for (unsigned Idx = FirstConstantOper+1;
583 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
584 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
585 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
589 NextTy = cast<SequentialType>(NextTy)->getElementType();
592 if (isBadCase) G1OC = 0;
595 // Make sure they are comparable (ie, not constant expressions), and
596 // make sure the GEP with the smaller leading constant is GEP1.
598 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
600 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
601 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
602 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
603 std::swap(NumGEP1Ops, NumGEP2Ops);
610 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
613 // No shared constant operands, and we ran out of common operands. At this
614 // point, the GEP instructions have run through all of their operands, and we
615 // haven't found evidence that there are any deltas between the GEP's.
616 // However, one GEP may have more operands than the other. If this is the
617 // case, there may still be hope. Check this now.
618 if (FirstConstantOper == MinOperands) {
619 // Make GEP1Ops be the longer one if there is a longer one.
620 if (NumGEP1Ops < NumGEP2Ops) {
621 std::swap(GEP1Ops, GEP2Ops);
622 std::swap(NumGEP1Ops, NumGEP2Ops);
625 // Is there anything to check?
626 if (NumGEP1Ops > MinOperands) {
627 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
628 if (isa<ConstantInt>(GEP1Ops[i]) &&
629 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
630 // Yup, there's a constant in the tail. Set all variables to
631 // constants in the GEP instruction to make it suiteable for
632 // TargetData::getIndexedOffset.
633 for (i = 0; i != MaxOperands; ++i)
634 if (!isa<ConstantInt>(GEP1Ops[i]))
635 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
636 // Okay, now get the offset. This is the relative offset for the full
638 const TargetData &TD = getTargetData();
639 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
642 // Now check without any constants at the end.
643 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
646 // If the tail provided a bit enough offset, return noalias!
647 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
652 // Couldn't find anything useful.
656 // If there are non-equal constants arguments, then we can figure
657 // out a minimum known delta between the two index expressions... at
658 // this point we know that the first constant index of GEP1 is less
659 // than the first constant index of GEP2.
661 // Advance BasePtr[12]Ty over this first differing constant operand.
662 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
663 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
664 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
665 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
667 // We are going to be using TargetData::getIndexedOffset to determine the
668 // offset that each of the GEP's is reaching. To do this, we have to convert
669 // all variable references to constant references. To do this, we convert the
670 // initial sequence of array subscripts into constant zeros to start with.
671 const Type *ZeroIdxTy = GEPPointerTy;
672 for (unsigned i = 0; i != FirstConstantOper; ++i) {
673 if (!isa<StructType>(ZeroIdxTy))
674 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
676 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
677 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
680 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
682 // Loop over the rest of the operands...
683 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
684 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
685 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
686 // If they are equal, use a zero index...
687 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
688 if (!isa<ConstantInt>(Op1))
689 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
690 // Otherwise, just keep the constants we have.
693 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
694 // If this is an array index, make sure the array element is in range.
695 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
696 if (Op1C->getZExtValue() >= AT->getNumElements())
697 return MayAlias; // Be conservative with out-of-range accesses
698 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
699 if (Op1C->getZExtValue() >= PT->getNumElements())
700 return MayAlias; // Be conservative with out-of-range accesses
704 // GEP1 is known to produce a value less than GEP2. To be
705 // conservatively correct, we must assume the largest possible
706 // constant is used in this position. This cannot be the initial
707 // index to the GEP instructions (because we know we have at least one
708 // element before this one with the different constant arguments), so
709 // we know that the current index must be into either a struct or
710 // array. Because we know it's not constant, this cannot be a
711 // structure index. Because of this, we can calculate the maximum
714 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
715 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
716 else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty))
717 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
723 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
724 // If this is an array index, make sure the array element is in range.
725 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
726 if (Op2C->getZExtValue() >= AT->getNumElements())
727 return MayAlias; // Be conservative with out-of-range accesses
728 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
729 if (Op2C->getZExtValue() >= PT->getNumElements())
730 return MayAlias; // Be conservative with out-of-range accesses
732 } else { // Conservatively assume the minimum value for this index
733 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
738 if (BasePtr1Ty && Op1) {
739 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
740 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
745 if (BasePtr2Ty && Op2) {
746 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
747 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
753 if (GEPPointerTy->getElementType()->isSized()) {
755 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
757 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
758 assert(Offset1<Offset2 && "There is at least one different constant here!");
760 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
761 //cerr << "Determined that these two GEP's don't alias ["
762 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
770 struct VISIBILITY_HIDDEN StringCompare {
771 bool operator()(const char *LHS, const char *RHS) {
772 return strcmp(LHS, RHS) < 0;
777 // Note that this list cannot contain libm functions (such as acos and sqrt)
778 // that set errno on a domain or other error.
779 static const char *DoesntAccessMemoryFns[] = {
780 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
781 "trunc", "truncf", "truncl", "ldexp",
783 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
785 "cos", "cosf", "cosl",
786 "exp", "expf", "expl",
788 "sin", "sinf", "sinl",
789 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
791 "floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
794 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
795 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
798 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
799 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
801 "iswctype", "towctrans", "towlower", "towupper",
805 "isinf", "isnan", "finite",
807 // C99 math functions
808 "copysign", "copysignf", "copysignd",
809 "nexttoward", "nexttowardf", "nexttowardd",
810 "nextafter", "nextafterf", "nextafterd",
813 "__signbit", "__signbitf", "__signbitl",
817 static const char *OnlyReadsMemoryFns[] = {
818 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
819 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
822 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
823 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
827 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
828 "wcsrchr", "wcsspn", "wcsstr",
831 "alphasort", "alphasort64", "versionsort", "versionsort64",
834 "nan", "nanf", "nand",
837 "feof", "ferror", "fileno",
838 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
841 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
842 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
845 AliasAnalysis::ModRefBehavior
846 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
847 std::vector<PointerAccessInfo> *Info) {
848 if (!F->isDeclaration()) return UnknownModRefBehavior;
850 static bool Initialized = false;
852 NoMemoryTable->insert(NoMemoryTable->end(),
853 DoesntAccessMemoryFns,
854 DoesntAccessMemoryFns+
855 sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
857 OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
860 sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
861 #define GET_MODREF_BEHAVIOR
862 #include "llvm/Intrinsics.gen"
863 #undef GET_MODREF_BEHAVIOR
865 // Sort the table the first time through.
866 std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
867 std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
872 std::vector<const char*>::iterator Ptr =
873 std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
874 F->getName().c_str(), StringCompare());
875 if (Ptr != NoMemoryTable->end() && *Ptr == F->getName())
876 return DoesNotAccessMemory;
878 Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
879 OnlyReadsMemoryTable->end(),
880 F->getName().c_str(), StringCompare());
881 if (Ptr != OnlyReadsMemoryTable->end() && *Ptr == F->getName())
882 return OnlyReadsMemory;
884 return UnknownModRefBehavior;
887 // Make sure that anything that uses AliasAnalysis pulls in this file...
888 DEFINING_FILE_FOR(BasicAliasAnalysis)