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/ParameterAttributes.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/Intrinsics.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/StringMap.h"
29 #include "llvm/ADT/BitVector.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/Support/Compiler.h"
32 #include "llvm/Support/GetElementPtrTypeIterator.h"
33 #include "llvm/Support/ManagedStatic.h"
38 /// NoAA - This class implements the -no-aa pass, which always returns "I
39 /// don't know" for alias queries. NoAA is unlike other alias analysis
40 /// implementations, in that it does not chain to a previous analysis. As
41 /// such it doesn't follow many of the rules that other alias analyses must.
43 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
44 static char ID; // Class identification, replacement for typeinfo
45 NoAA() : ImmutablePass((intptr_t)&ID) {}
46 explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
48 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
49 AU.addRequired<TargetData>();
52 virtual void initializePass() {
53 TD = &getAnalysis<TargetData>();
56 virtual AliasResult alias(const Value *V1, unsigned V1Size,
57 const Value *V2, unsigned V2Size) {
61 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
62 std::vector<PointerAccessInfo> *Info) {
63 return UnknownModRefBehavior;
66 virtual void getArgumentAccesses(Function *F, CallSite CS,
67 std::vector<PointerAccessInfo> &Info) {
68 assert(0 && "This method may not be called on this function!");
71 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
72 virtual bool pointsToConstantMemory(const Value *P) { return false; }
73 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
76 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
79 virtual bool hasNoModRefInfoForCalls() const { return true; }
81 virtual void deleteValue(Value *V) {}
82 virtual void copyValue(Value *From, Value *To) {}
85 // Register this pass...
88 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
90 // Declare that we implement the AliasAnalysis interface
91 RegisterAnalysisGroup<AliasAnalysis> V(U);
92 } // End of anonymous namespace
94 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
97 /// BasicAliasAnalysis - This is the default alias analysis implementation.
98 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
99 /// derives from the NoAA class.
100 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
101 static char ID; // Class identification, replacement for typeinfo
102 BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
103 AliasResult alias(const Value *V1, unsigned V1Size,
104 const Value *V2, unsigned V2Size);
106 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
107 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
108 return NoAA::getModRefInfo(CS1,CS2);
111 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
112 /// non-escaping allocations.
113 virtual bool hasNoModRefInfoForCalls() const { return false; }
115 /// pointsToConstantMemory - Chase pointers until we find a (constant
117 bool pointsToConstantMemory(const Value *P);
119 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
120 std::vector<PointerAccessInfo> *Info);
123 // CheckGEPInstructions - Check two GEP instructions with known
124 // must-aliasing base pointers. This checks to see if the index expressions
125 // preclude the pointers from aliasing...
127 CheckGEPInstructions(const Type* BasePtr1Ty,
128 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
129 const Type *BasePtr2Ty,
130 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
133 // Register this pass...
134 char BasicAliasAnalysis::ID = 0;
135 RegisterPass<BasicAliasAnalysis>
136 X("basicaa", "Basic Alias Analysis (default AA impl)");
138 // Declare that we implement the AliasAnalysis interface
139 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
140 } // End of anonymous namespace
142 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
143 return new BasicAliasAnalysis();
146 // getUnderlyingObject - This traverses the use chain to figure out what object
147 // the specified value points to. If the value points to, or is derived from, a
148 // unique object or an argument, return it.
149 static const Value *getUnderlyingObject(const Value *V) {
150 if (!isa<PointerType>(V->getType())) return 0;
152 // If we are at some type of object, return it. GlobalValues and Allocations
153 // have unique addresses.
154 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
157 // Traverse through different addressing mechanisms...
158 if (const Instruction *I = dyn_cast<Instruction>(V)) {
159 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
160 return getUnderlyingObject(I->getOperand(0));
161 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
162 if (CE->getOpcode() == Instruction::BitCast ||
163 CE->getOpcode() == Instruction::GetElementPtr)
164 return getUnderlyingObject(CE->getOperand(0));
169 static const User *isGEP(const Value *V) {
170 if (isa<GetElementPtrInst>(V) ||
171 (isa<ConstantExpr>(V) &&
172 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
173 return cast<User>(V);
177 static const Value *GetGEPOperands(const Value *V,
178 SmallVector<Value*, 16> &GEPOps){
179 assert(GEPOps.empty() && "Expect empty list to populate!");
180 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
181 cast<User>(V)->op_end());
183 // Accumulate all of the chained indexes into the operand array
184 V = cast<User>(V)->getOperand(0);
186 while (const User *G = isGEP(V)) {
187 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
188 !cast<Constant>(GEPOps[0])->isNullValue())
189 break; // Don't handle folding arbitrary pointer offsets yet...
190 GEPOps.erase(GEPOps.begin()); // Drop the zero index
191 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
192 V = G->getOperand(0);
197 /// pointsToConstantMemory - Chase pointers until we find a (constant
199 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
200 if (const Value *V = getUnderlyingObject(P))
201 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
202 return GV->isConstant();
206 // Determine if an AllocationInst instruction escapes from the function it is
207 // contained in. If it does not escape, there is no way for another function to
208 // mod/ref it. We do this by looking at its uses and determining if the uses
209 // can escape (recursively).
210 static bool AddressMightEscape(const Value *V) {
211 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
213 const Instruction *I = cast<Instruction>(*UI);
214 switch (I->getOpcode()) {
215 case Instruction::Load:
217 case Instruction::Store:
218 if (I->getOperand(0) == V)
219 return true; // Escapes if the pointer is stored.
221 case Instruction::GetElementPtr:
222 if (AddressMightEscape(I))
225 case Instruction::BitCast:
226 if (!isa<PointerType>(I->getType()))
228 if (AddressMightEscape(I))
231 case Instruction::Ret:
232 // If returned, the address will escape to calling functions, but no
233 // callees could modify it.
242 // getModRefInfo - Check to see if the specified callsite can clobber the
243 // specified memory object. Since we only look at local properties of this
244 // function, we really can't say much about this query. We do, however, use
245 // simple "address taken" analysis on local objects.
247 AliasAnalysis::ModRefResult
248 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
249 if (!isa<Constant>(P))
250 if (const AllocationInst *AI =
251 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
252 // Okay, the pointer is to a stack allocated object. If we can prove that
253 // the pointer never "escapes", then we know the call cannot clobber it,
254 // because it simply can't get its address.
255 if (!AddressMightEscape(AI))
258 // If this is a tail call and P points to a stack location, we know that
259 // the tail call cannot access or modify the local stack.
260 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
261 if (CI->isTailCall() && isa<AllocaInst>(AI))
265 // The AliasAnalysis base class has some smarts, lets use them.
266 return AliasAnalysis::getModRefInfo(CS, P, Size);
269 static bool isNoAliasArgument(const Argument *Arg) {
270 const Function *Func = Arg->getParent();
271 const ParamAttrsList *Attr = Func->getParamAttrs();
274 for (Function::const_arg_iterator I = Func->arg_begin(),
275 E = Func->arg_end(); I != E; ++I, ++Idx) {
277 Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
284 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
285 // as array references. Note that this function is heavily tail recursive.
286 // Hopefully we have a smart C++ compiler. :)
288 AliasAnalysis::AliasResult
289 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
290 const Value *V2, unsigned V2Size) {
291 // Strip off any constant expression casts if they exist
292 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
293 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
294 V1 = CE->getOperand(0);
295 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
296 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
297 V2 = CE->getOperand(0);
299 // Are we checking for alias of the same value?
300 if (V1 == V2) return MustAlias;
302 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
303 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
304 return NoAlias; // Scalars cannot alias each other
306 // Strip off cast instructions...
307 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
308 return alias(I->getOperand(0), V1Size, V2, V2Size);
309 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
310 return alias(V1, V1Size, I->getOperand(0), V2Size);
312 // Figure out what objects these things are pointing to if we can...
313 const Value *O1 = getUnderlyingObject(V1);
314 const Value *O2 = getUnderlyingObject(V2);
316 // Pointing at a discernible object?
319 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
320 // Incoming argument cannot alias locally allocated object!
321 if (isa<AllocationInst>(O2)) return NoAlias;
323 // If they are two different objects, and one is a noalias argument
324 // then they do not alias.
325 if (O1 != O2 && isNoAliasArgument(O1Arg))
328 // Otherwise, nothing is known...
331 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
332 // Incoming argument cannot alias locally allocated object!
333 if (isa<AllocationInst>(O1)) return NoAlias;
335 // If they are two different objects, and one is a noalias argument
336 // then they do not alias.
337 if (O1 != O2 && isNoAliasArgument(O2Arg))
340 // Otherwise, nothing is known...
342 } else if (O1 != O2) {
343 if (!isa<Argument>(O1))
344 // If they are two different objects, and neither is an argument,
345 // we know that we have no alias...
349 // If they are the same object, they we can look at the indexes. If they
350 // index off of the object is the same for both pointers, they must alias.
351 // If they are provably different, they must not alias. Otherwise, we
352 // can't tell anything.
356 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
357 return NoAlias; // Unique values don't alias null
359 if (isa<GlobalVariable>(O1) ||
360 (isa<AllocationInst>(O1) &&
361 !cast<AllocationInst>(O1)->isArrayAllocation()))
362 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
363 // If the size of the other access is larger than the total size of the
364 // global/alloca/malloc, it cannot be accessing the global (it's
365 // undefined to load or store bytes before or after an object).
366 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
367 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
368 if (GlobalSize < V2Size && V2Size != ~0U)
374 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
375 return NoAlias; // Unique values don't alias null
377 if (isa<GlobalVariable>(O2) ||
378 (isa<AllocationInst>(O2) &&
379 !cast<AllocationInst>(O2)->isArrayAllocation()))
380 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
381 // If the size of the other access is larger than the total size of the
382 // global/alloca/malloc, it cannot be accessing the object (it's
383 // undefined to load or store bytes before or after an object).
384 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
385 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
386 if (GlobalSize < V1Size && V1Size != ~0U)
391 // If we have two gep instructions with must-alias'ing base pointers, figure
392 // out if the indexes to the GEP tell us anything about the derived pointer.
393 // Note that we also handle chains of getelementptr instructions as well as
394 // constant expression getelementptrs here.
396 if (isGEP(V1) && isGEP(V2)) {
397 // Drill down into the first non-gep value, to test for must-aliasing of
398 // the base pointers.
399 const Value *BasePtr1 = V1, *BasePtr2 = V2;
401 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
402 } while (isGEP(BasePtr1) &&
403 cast<User>(BasePtr1)->getOperand(1) ==
404 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
406 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
407 } while (isGEP(BasePtr2) &&
408 cast<User>(BasePtr2)->getOperand(1) ==
409 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
411 // Do the base pointers alias?
412 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
413 if (BaseAlias == NoAlias) return NoAlias;
414 if (BaseAlias == MustAlias) {
415 // If the base pointers alias each other exactly, check to see if we can
416 // figure out anything about the resultant pointers, to try to prove
419 // Collect all of the chained GEP operands together into one simple place
420 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
421 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
422 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
424 // If GetGEPOperands were able to fold to the same must-aliased pointer,
425 // do the comparison.
426 if (BasePtr1 == BasePtr2) {
428 CheckGEPInstructions(BasePtr1->getType(),
429 &GEP1Ops[0], GEP1Ops.size(), V1Size,
431 &GEP2Ops[0], GEP2Ops.size(), V2Size);
432 if (GAlias != MayAlias)
438 // Check to see if these two pointers are related by a getelementptr
439 // instruction. If one pointer is a GEP with a non-zero index of the other
440 // pointer, we know they cannot alias.
444 std::swap(V1Size, V2Size);
447 if (V1Size != ~0U && V2Size != ~0U)
449 SmallVector<Value*, 16> GEPOperands;
450 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
452 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
453 if (R == MustAlias) {
454 // If there is at least one non-zero constant index, we know they cannot
456 bool ConstantFound = false;
457 bool AllZerosFound = true;
458 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
459 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
460 if (!C->isNullValue()) {
461 ConstantFound = true;
462 AllZerosFound = false;
466 AllZerosFound = false;
469 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
470 // the ptr, the end result is a must alias also.
475 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
478 // Otherwise we have to check to see that the distance is more than
479 // the size of the argument... build an index vector that is equal to
480 // the arguments provided, except substitute 0's for any variable
481 // indexes we find...
482 if (cast<PointerType>(
483 BasePtr->getType())->getElementType()->isSized()) {
484 for (unsigned i = 0; i != GEPOperands.size(); ++i)
485 if (!isa<ConstantInt>(GEPOperands[i]))
487 Constant::getNullValue(GEPOperands[i]->getType());
489 getTargetData().getIndexedOffset(BasePtr->getType(),
493 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
503 // This function is used to determin if the indices of two GEP instructions are
504 // equal. V1 and V2 are the indices.
505 static bool IndexOperandsEqual(Value *V1, Value *V2) {
506 if (V1->getType() == V2->getType())
508 if (Constant *C1 = dyn_cast<Constant>(V1))
509 if (Constant *C2 = dyn_cast<Constant>(V2)) {
510 // Sign extend the constants to long types, if necessary
511 if (C1->getType() != Type::Int64Ty)
512 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
513 if (C2->getType() != Type::Int64Ty)
514 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
520 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
521 /// base pointers. This checks to see if the index expressions preclude the
522 /// pointers from aliasing...
523 AliasAnalysis::AliasResult
524 BasicAliasAnalysis::CheckGEPInstructions(
525 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
526 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
527 // We currently can't handle the case when the base pointers have different
528 // primitive types. Since this is uncommon anyway, we are happy being
529 // extremely conservative.
530 if (BasePtr1Ty != BasePtr2Ty)
533 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
535 // Find the (possibly empty) initial sequence of equal values... which are not
536 // necessarily constants.
537 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
538 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
539 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
540 unsigned UnequalOper = 0;
541 while (UnequalOper != MinOperands &&
542 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
543 // Advance through the type as we go...
545 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
546 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
548 // If all operands equal each other, then the derived pointers must
549 // alias each other...
551 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
552 "Ran out of type nesting, but not out of operands?");
557 // If we have seen all constant operands, and run out of indexes on one of the
558 // getelementptrs, check to see if the tail of the leftover one is all zeros.
559 // If so, return mustalias.
560 if (UnequalOper == MinOperands) {
561 if (NumGEP1Ops < NumGEP2Ops) {
562 std::swap(GEP1Ops, GEP2Ops);
563 std::swap(NumGEP1Ops, NumGEP2Ops);
566 bool AllAreZeros = true;
567 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
568 if (!isa<Constant>(GEP1Ops[i]) ||
569 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
573 if (AllAreZeros) return MustAlias;
577 // So now we know that the indexes derived from the base pointers,
578 // which are known to alias, are different. We can still determine a
579 // no-alias result if there are differing constant pairs in the index
580 // chain. For example:
581 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
583 // We have to be careful here about array accesses. In particular, consider:
584 // A[1][0] vs A[0][i]
585 // In this case, we don't *know* that the array will be accessed in bounds:
586 // the index could even be negative. Because of this, we have to
587 // conservatively *give up* and return may alias. We disregard differing
588 // array subscripts that are followed by a variable index without going
591 unsigned SizeMax = std::max(G1S, G2S);
592 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
594 // Scan for the first operand that is constant and unequal in the
595 // two getelementptrs...
596 unsigned FirstConstantOper = UnequalOper;
597 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
598 const Value *G1Oper = GEP1Ops[FirstConstantOper];
599 const Value *G2Oper = GEP2Ops[FirstConstantOper];
601 if (G1Oper != G2Oper) // Found non-equal constant indexes...
602 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
603 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
604 if (G1OC->getType() != G2OC->getType()) {
605 // Sign extend both operands to long.
606 if (G1OC->getType() != Type::Int64Ty)
607 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
608 if (G2OC->getType() != Type::Int64Ty)
609 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
610 GEP1Ops[FirstConstantOper] = G1OC;
611 GEP2Ops[FirstConstantOper] = G2OC;
615 // Handle the "be careful" case above: if this is an array/vector
616 // subscript, scan for a subsequent variable array index.
617 if (isa<SequentialType>(BasePtr1Ty)) {
619 cast<SequentialType>(BasePtr1Ty)->getElementType();
620 bool isBadCase = false;
622 for (unsigned Idx = FirstConstantOper+1;
623 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
624 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
625 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
629 NextTy = cast<SequentialType>(NextTy)->getElementType();
632 if (isBadCase) G1OC = 0;
635 // Make sure they are comparable (ie, not constant expressions), and
636 // make sure the GEP with the smaller leading constant is GEP1.
638 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
640 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
641 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
642 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
643 std::swap(NumGEP1Ops, NumGEP2Ops);
650 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
653 // No shared constant operands, and we ran out of common operands. At this
654 // point, the GEP instructions have run through all of their operands, and we
655 // haven't found evidence that there are any deltas between the GEP's.
656 // However, one GEP may have more operands than the other. If this is the
657 // case, there may still be hope. Check this now.
658 if (FirstConstantOper == MinOperands) {
659 // Make GEP1Ops be the longer one if there is a longer one.
660 if (NumGEP1Ops < NumGEP2Ops) {
661 std::swap(GEP1Ops, GEP2Ops);
662 std::swap(NumGEP1Ops, NumGEP2Ops);
665 // Is there anything to check?
666 if (NumGEP1Ops > MinOperands) {
667 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
668 if (isa<ConstantInt>(GEP1Ops[i]) &&
669 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
670 // Yup, there's a constant in the tail. Set all variables to
671 // constants in the GEP instruction to make it suiteable for
672 // TargetData::getIndexedOffset.
673 for (i = 0; i != MaxOperands; ++i)
674 if (!isa<ConstantInt>(GEP1Ops[i]))
675 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
676 // Okay, now get the offset. This is the relative offset for the full
678 const TargetData &TD = getTargetData();
679 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
682 // Now check without any constants at the end.
683 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
686 // If the tail provided a bit enough offset, return noalias!
687 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
692 // Couldn't find anything useful.
696 // If there are non-equal constants arguments, then we can figure
697 // out a minimum known delta between the two index expressions... at
698 // this point we know that the first constant index of GEP1 is less
699 // than the first constant index of GEP2.
701 // Advance BasePtr[12]Ty over this first differing constant operand.
702 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
703 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
704 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
705 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
707 // We are going to be using TargetData::getIndexedOffset to determine the
708 // offset that each of the GEP's is reaching. To do this, we have to convert
709 // all variable references to constant references. To do this, we convert the
710 // initial sequence of array subscripts into constant zeros to start with.
711 const Type *ZeroIdxTy = GEPPointerTy;
712 for (unsigned i = 0; i != FirstConstantOper; ++i) {
713 if (!isa<StructType>(ZeroIdxTy))
714 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
716 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
717 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
720 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
722 // Loop over the rest of the operands...
723 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
724 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
725 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
726 // If they are equal, use a zero index...
727 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
728 if (!isa<ConstantInt>(Op1))
729 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
730 // Otherwise, just keep the constants we have.
733 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
734 // If this is an array index, make sure the array element is in range.
735 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
736 if (Op1C->getZExtValue() >= AT->getNumElements())
737 return MayAlias; // Be conservative with out-of-range accesses
738 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
739 if (Op1C->getZExtValue() >= PT->getNumElements())
740 return MayAlias; // Be conservative with out-of-range accesses
744 // GEP1 is known to produce a value less than GEP2. To be
745 // conservatively correct, we must assume the largest possible
746 // constant is used in this position. This cannot be the initial
747 // index to the GEP instructions (because we know we have at least one
748 // element before this one with the different constant arguments), so
749 // we know that the current index must be into either a struct or
750 // array. Because we know it's not constant, this cannot be a
751 // structure index. Because of this, we can calculate the maximum
754 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
755 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
756 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
757 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
762 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
763 // If this is an array index, make sure the array element is in range.
764 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
765 if (Op2C->getZExtValue() >= AT->getNumElements())
766 return MayAlias; // Be conservative with out-of-range accesses
767 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
768 if (Op2C->getZExtValue() >= VT->getNumElements())
769 return MayAlias; // Be conservative with out-of-range accesses
771 } else { // Conservatively assume the minimum value for this index
772 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
777 if (BasePtr1Ty && Op1) {
778 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
779 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
784 if (BasePtr2Ty && Op2) {
785 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
786 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
792 if (GEPPointerTy->getElementType()->isSized()) {
794 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
796 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
797 assert(Offset1 != Offset2 &&
798 "There is at least one different constant here!");
800 // Make sure we compare the absolute difference.
801 if (Offset1 > Offset2)
802 std::swap(Offset1, Offset2);
804 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
805 //cerr << "Determined that these two GEP's don't alias ["
806 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
813 static ManagedStatic<BitVector> NoMemoryIntrinsics;
814 static ManagedStatic<BitVector> OnlyReadsMemoryIntrinsics;
816 AliasAnalysis::ModRefBehavior
817 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
818 std::vector<PointerAccessInfo> *Info) {
819 if (!F->isDeclaration()) return UnknownModRefBehavior;
821 static bool Initialized = false;
823 NoMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
824 OnlyReadsMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
825 #define GET_MODREF_BEHAVIOR
826 #include "llvm/Intrinsics.gen"
827 #undef GET_MODREF_BEHAVIOR
832 // If this is an intrinsic, we can use lookup tables
833 if (unsigned id = F->getIntrinsicID()) {
834 if (NoMemoryIntrinsics->test(id))
835 return DoesNotAccessMemory;
836 if (OnlyReadsMemoryIntrinsics->test(id))
837 return OnlyReadsMemory;
839 return UnknownModRefBehavior;
842 const ParamAttrsList *Attrs = F->getParamAttrs();
843 if (Attrs && Attrs->paramHasAttr(0, ParamAttr::ReadNone))
844 return DoesNotAccessMemory;
845 if (Attrs && Attrs->paramHasAttr(0, ParamAttr::ReadOnly))
846 return OnlyReadsMemory;
848 return UnknownModRefBehavior;
851 // Make sure that anything that uses AliasAnalysis pulls in this file...
852 DEFINING_FILE_FOR(BasicAliasAnalysis)