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/Support/Compiler.h"
26 #include "llvm/Support/GetElementPtrTypeIterator.h"
27 #include "llvm/Support/ManagedStatic.h"
32 /// NoAA - This class implements the -no-aa pass, which always returns "I
33 /// don't know" for alias queries. NoAA is unlike other alias analysis
34 /// implementations, in that it does not chain to a previous analysis. As
35 /// such it doesn't follow many of the rules that other alias analyses must.
37 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
38 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
39 AU.addRequired<TargetData>();
42 virtual void initializePass() {
43 TD = &getAnalysis<TargetData>();
46 virtual AliasResult alias(const Value *V1, unsigned V1Size,
47 const Value *V2, unsigned V2Size) {
51 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
52 std::vector<PointerAccessInfo> *Info) {
53 return UnknownModRefBehavior;
56 virtual void getArgumentAccesses(Function *F, CallSite CS,
57 std::vector<PointerAccessInfo> &Info) {
58 assert(0 && "This method may not be called on this function!");
61 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
62 virtual bool pointsToConstantMemory(const Value *P) { return false; }
63 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
66 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
69 virtual bool hasNoModRefInfoForCalls() const { return true; }
71 virtual void deleteValue(Value *V) {}
72 virtual void copyValue(Value *From, Value *To) {}
75 // Register this pass...
77 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
79 // Declare that we implement the AliasAnalysis interface
80 RegisterAnalysisGroup<AliasAnalysis> V(U);
81 } // End of anonymous namespace
83 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
86 /// BasicAliasAnalysis - This is the default alias analysis implementation.
87 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
88 /// derives from the NoAA class.
89 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
90 AliasResult alias(const Value *V1, unsigned V1Size,
91 const Value *V2, unsigned V2Size);
93 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
94 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
95 return NoAA::getModRefInfo(CS1,CS2);
98 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
99 /// non-escaping allocations.
100 virtual bool hasNoModRefInfoForCalls() const { return false; }
102 /// pointsToConstantMemory - Chase pointers until we find a (constant
104 bool pointsToConstantMemory(const Value *P);
106 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
107 std::vector<PointerAccessInfo> *Info);
110 // CheckGEPInstructions - Check two GEP instructions with known
111 // must-aliasing base pointers. This checks to see if the index expressions
112 // preclude the pointers from aliasing...
114 CheckGEPInstructions(const Type* BasePtr1Ty,
115 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
116 const Type *BasePtr2Ty,
117 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
120 // Register this pass...
121 RegisterPass<BasicAliasAnalysis>
122 X("basicaa", "Basic Alias Analysis (default AA impl)");
124 // Declare that we implement the AliasAnalysis interface
125 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
126 } // End of anonymous namespace
128 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
129 return new BasicAliasAnalysis();
132 // getUnderlyingObject - This traverses the use chain to figure out what object
133 // the specified value points to. If the value points to, or is derived from, a
134 // unique object or an argument, return it.
135 static const Value *getUnderlyingObject(const Value *V) {
136 if (!isa<PointerType>(V->getType())) return 0;
138 // If we are at some type of object, return it. GlobalValues and Allocations
139 // have unique addresses.
140 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
143 // Traverse through different addressing mechanisms...
144 if (const Instruction *I = dyn_cast<Instruction>(V)) {
145 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
146 return getUnderlyingObject(I->getOperand(0));
147 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
148 if (CE->getOpcode() == Instruction::BitCast ||
149 CE->getOpcode() == Instruction::GetElementPtr)
150 return getUnderlyingObject(CE->getOperand(0));
155 static const User *isGEP(const Value *V) {
156 if (isa<GetElementPtrInst>(V) ||
157 (isa<ConstantExpr>(V) &&
158 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
159 return cast<User>(V);
163 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
164 assert(GEPOps.empty() && "Expect empty list to populate!");
165 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
166 cast<User>(V)->op_end());
168 // Accumulate all of the chained indexes into the operand array
169 V = cast<User>(V)->getOperand(0);
171 while (const User *G = isGEP(V)) {
172 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
173 !cast<Constant>(GEPOps[0])->isNullValue())
174 break; // Don't handle folding arbitrary pointer offsets yet...
175 GEPOps.erase(GEPOps.begin()); // Drop the zero index
176 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
177 V = G->getOperand(0);
182 /// pointsToConstantMemory - Chase pointers until we find a (constant
184 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
185 if (const Value *V = getUnderlyingObject(P))
186 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
187 return GV->isConstant();
191 // Determine if an AllocationInst instruction escapes from the function it is
192 // contained in. If it does not escape, there is no way for another function to
193 // mod/ref it. We do this by looking at its uses and determining if the uses
194 // can escape (recursively).
195 static bool AddressMightEscape(const Value *V) {
196 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
198 const Instruction *I = cast<Instruction>(*UI);
199 switch (I->getOpcode()) {
200 case Instruction::Load:
202 case Instruction::Store:
203 if (I->getOperand(0) == V)
204 return true; // Escapes if the pointer is stored.
206 case Instruction::GetElementPtr:
207 if (AddressMightEscape(I))
209 case Instruction::BitCast:
210 if (!isa<PointerType>(I->getType()))
212 if (AddressMightEscape(I))
215 case Instruction::Ret:
216 // If returned, the address will escape to calling functions, but no
217 // callees could modify it.
226 // getModRefInfo - Check to see if the specified callsite can clobber the
227 // specified memory object. Since we only look at local properties of this
228 // function, we really can't say much about this query. We do, however, use
229 // simple "address taken" analysis on local objects.
231 AliasAnalysis::ModRefResult
232 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
233 if (!isa<Constant>(P))
234 if (const AllocationInst *AI =
235 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
236 // Okay, the pointer is to a stack allocated object. If we can prove that
237 // the pointer never "escapes", then we know the call cannot clobber it,
238 // because it simply can't get its address.
239 if (!AddressMightEscape(AI))
242 // If this is a tail call and P points to a stack location, we know that
243 // the tail call cannot access or modify the local stack.
244 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
245 if (CI->isTailCall() && isa<AllocaInst>(AI))
249 // The AliasAnalysis base class has some smarts, lets use them.
250 return AliasAnalysis::getModRefInfo(CS, P, Size);
253 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
254 // as array references. Note that this function is heavily tail recursive.
255 // Hopefully we have a smart C++ compiler. :)
257 AliasAnalysis::AliasResult
258 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
259 const Value *V2, unsigned V2Size) {
260 // Strip off any constant expression casts if they exist
261 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
262 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
263 V1 = CE->getOperand(0);
264 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
265 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
266 V2 = CE->getOperand(0);
268 // Are we checking for alias of the same value?
269 if (V1 == V2) return MustAlias;
271 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
272 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
273 return NoAlias; // Scalars cannot alias each other
275 // Strip off cast instructions...
276 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
277 return alias(I->getOperand(0), V1Size, V2, V2Size);
278 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
279 return alias(V1, V1Size, I->getOperand(0), V2Size);
281 // Figure out what objects these things are pointing to if we can...
282 const Value *O1 = getUnderlyingObject(V1);
283 const Value *O2 = getUnderlyingObject(V2);
285 // Pointing at a discernible object?
288 if (isa<Argument>(O1)) {
289 // Incoming argument cannot alias locally allocated object!
290 if (isa<AllocationInst>(O2)) return NoAlias;
291 // Otherwise, nothing is known...
292 } else if (isa<Argument>(O2)) {
293 // Incoming argument cannot alias locally allocated object!
294 if (isa<AllocationInst>(O1)) return NoAlias;
295 // Otherwise, nothing is known...
296 } else if (O1 != O2) {
297 // If they are two different objects, we know that we have no alias...
301 // If they are the same object, they we can look at the indexes. If they
302 // index off of the object is the same for both pointers, they must alias.
303 // If they are provably different, they must not alias. Otherwise, we
304 // can't tell anything.
308 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
309 return NoAlias; // Unique values don't alias null
311 if (isa<GlobalVariable>(O1) ||
312 (isa<AllocationInst>(O1) &&
313 !cast<AllocationInst>(O1)->isArrayAllocation()))
314 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
315 // If the size of the other access is larger than the total size of the
316 // global/alloca/malloc, it cannot be accessing the global (it's
317 // undefined to load or store bytes before or after an object).
318 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
319 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
320 if (GlobalSize < V2Size && V2Size != ~0U)
326 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
327 return NoAlias; // Unique values don't alias null
329 if (isa<GlobalVariable>(O2) ||
330 (isa<AllocationInst>(O2) &&
331 !cast<AllocationInst>(O2)->isArrayAllocation()))
332 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
333 // If the size of the other access is larger than the total size of the
334 // global/alloca/malloc, it cannot be accessing the object (it's
335 // undefined to load or store bytes before or after an object).
336 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
337 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
338 if (GlobalSize < V1Size && V1Size != ~0U)
343 // If we have two gep instructions with must-alias'ing base pointers, figure
344 // out if the indexes to the GEP tell us anything about the derived pointer.
345 // Note that we also handle chains of getelementptr instructions as well as
346 // constant expression getelementptrs here.
348 if (isGEP(V1) && isGEP(V2)) {
349 // Drill down into the first non-gep value, to test for must-aliasing of
350 // the base pointers.
351 const Value *BasePtr1 = V1, *BasePtr2 = V2;
353 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
354 } while (isGEP(BasePtr1) &&
355 cast<User>(BasePtr1)->getOperand(1) ==
356 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
358 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
359 } while (isGEP(BasePtr2) &&
360 cast<User>(BasePtr2)->getOperand(1) ==
361 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
363 // Do the base pointers alias?
364 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
365 if (BaseAlias == NoAlias) return NoAlias;
366 if (BaseAlias == MustAlias) {
367 // If the base pointers alias each other exactly, check to see if we can
368 // figure out anything about the resultant pointers, to try to prove
371 // Collect all of the chained GEP operands together into one simple place
372 std::vector<Value*> GEP1Ops, GEP2Ops;
373 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
374 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
376 // If GetGEPOperands were able to fold to the same must-aliased pointer,
377 // do the comparison.
378 if (BasePtr1 == BasePtr2) {
380 CheckGEPInstructions(BasePtr1->getType(),
381 &GEP1Ops[0], GEP1Ops.size(), V1Size,
383 &GEP2Ops[0], GEP2Ops.size(), V2Size);
384 if (GAlias != MayAlias)
390 // Check to see if these two pointers are related by a getelementptr
391 // instruction. If one pointer is a GEP with a non-zero index of the other
392 // pointer, we know they cannot alias.
396 std::swap(V1Size, V2Size);
399 if (V1Size != ~0U && V2Size != ~0U)
401 std::vector<Value*> GEPOperands;
402 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
404 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
405 if (R == MustAlias) {
406 // If there is at least one non-zero constant index, we know they cannot
408 bool ConstantFound = false;
409 bool AllZerosFound = true;
410 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
411 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
412 if (!C->isNullValue()) {
413 ConstantFound = true;
414 AllZerosFound = false;
418 AllZerosFound = false;
421 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
422 // the ptr, the end result is a must alias also.
427 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
430 // Otherwise we have to check to see that the distance is more than
431 // the size of the argument... build an index vector that is equal to
432 // the arguments provided, except substitute 0's for any variable
433 // indexes we find...
434 if (cast<PointerType>(
435 BasePtr->getType())->getElementType()->isSized()) {
436 for (unsigned i = 0; i != GEPOperands.size(); ++i)
437 if (!isa<ConstantInt>(GEPOperands[i]))
439 Constant::getNullValue(GEPOperands[i]->getType());
441 getTargetData().getIndexedOffset(BasePtr->getType(),
445 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
455 // This function is used to determin if the indices of two GEP instructions are
456 // equal. V1 and V2 are the indices.
457 static bool IndexOperandsEqual(Value *V1, Value *V2) {
458 if (V1->getType() == V2->getType())
460 if (Constant *C1 = dyn_cast<Constant>(V1))
461 if (Constant *C2 = dyn_cast<Constant>(V2)) {
462 // Sign extend the constants to long types, if necessary
463 if (C1->getType() != Type::Int64Ty)
464 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
465 if (C2->getType() != Type::Int64Ty)
466 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
472 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
473 /// base pointers. This checks to see if the index expressions preclude the
474 /// pointers from aliasing...
475 AliasAnalysis::AliasResult
476 BasicAliasAnalysis::CheckGEPInstructions(
477 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
478 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
479 // We currently can't handle the case when the base pointers have different
480 // primitive types. Since this is uncommon anyway, we are happy being
481 // extremely conservative.
482 if (BasePtr1Ty != BasePtr2Ty)
485 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
487 // Find the (possibly empty) initial sequence of equal values... which are not
488 // necessarily constants.
489 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
490 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
491 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
492 unsigned UnequalOper = 0;
493 while (UnequalOper != MinOperands &&
494 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
495 // Advance through the type as we go...
497 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
498 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
500 // If all operands equal each other, then the derived pointers must
501 // alias each other...
503 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
504 "Ran out of type nesting, but not out of operands?");
509 // If we have seen all constant operands, and run out of indexes on one of the
510 // getelementptrs, check to see if the tail of the leftover one is all zeros.
511 // If so, return mustalias.
512 if (UnequalOper == MinOperands) {
513 if (NumGEP1Ops < NumGEP2Ops) {
514 std::swap(GEP1Ops, GEP2Ops);
515 std::swap(NumGEP1Ops, NumGEP2Ops);
518 bool AllAreZeros = true;
519 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
520 if (!isa<Constant>(GEP1Ops[i]) ||
521 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
525 if (AllAreZeros) return MustAlias;
529 // So now we know that the indexes derived from the base pointers,
530 // which are known to alias, are different. We can still determine a
531 // no-alias result if there are differing constant pairs in the index
532 // chain. For example:
533 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
535 // We have to be careful here about array accesses. In particular, consider:
536 // A[1][0] vs A[0][i]
537 // In this case, we don't *know* that the array will be accessed in bounds:
538 // the index could even be negative. Because of this, we have to
539 // conservatively *give up* and return may alias. We disregard differing
540 // array subscripts that are followed by a variable index without going
543 unsigned SizeMax = std::max(G1S, G2S);
544 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
546 // Scan for the first operand that is constant and unequal in the
547 // two getelementptrs...
548 unsigned FirstConstantOper = UnequalOper;
549 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
550 const Value *G1Oper = GEP1Ops[FirstConstantOper];
551 const Value *G2Oper = GEP2Ops[FirstConstantOper];
553 if (G1Oper != G2Oper) // Found non-equal constant indexes...
554 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
555 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
556 if (G1OC->getType() != G2OC->getType()) {
557 // Sign extend both operands to long.
558 if (G1OC->getType() != Type::Int64Ty)
559 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
560 if (G2OC->getType() != Type::Int64Ty)
561 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
562 GEP1Ops[FirstConstantOper] = G1OC;
563 GEP2Ops[FirstConstantOper] = G2OC;
567 // Handle the "be careful" case above: if this is an array/packed
568 // subscript, scan for a subsequent variable array index.
569 if (isa<SequentialType>(BasePtr1Ty)) {
571 cast<SequentialType>(BasePtr1Ty)->getElementType();
572 bool isBadCase = false;
574 for (unsigned Idx = FirstConstantOper+1;
575 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
576 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
577 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
581 NextTy = cast<SequentialType>(NextTy)->getElementType();
584 if (isBadCase) G1OC = 0;
587 // Make sure they are comparable (ie, not constant expressions), and
588 // make sure the GEP with the smaller leading constant is GEP1.
590 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
592 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
593 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
594 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
595 std::swap(NumGEP1Ops, NumGEP2Ops);
602 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
605 // No shared constant operands, and we ran out of common operands. At this
606 // point, the GEP instructions have run through all of their operands, and we
607 // haven't found evidence that there are any deltas between the GEP's.
608 // However, one GEP may have more operands than the other. If this is the
609 // case, there may still be hope. Check this now.
610 if (FirstConstantOper == MinOperands) {
611 // Make GEP1Ops be the longer one if there is a longer one.
612 if (NumGEP1Ops < NumGEP2Ops) {
613 std::swap(GEP1Ops, GEP2Ops);
614 std::swap(NumGEP1Ops, NumGEP2Ops);
617 // Is there anything to check?
618 if (NumGEP1Ops > MinOperands) {
619 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
620 if (isa<ConstantInt>(GEP1Ops[i]) &&
621 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
622 // Yup, there's a constant in the tail. Set all variables to
623 // constants in the GEP instruction to make it suiteable for
624 // TargetData::getIndexedOffset.
625 for (i = 0; i != MaxOperands; ++i)
626 if (!isa<ConstantInt>(GEP1Ops[i]))
627 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
628 // Okay, now get the offset. This is the relative offset for the full
630 const TargetData &TD = getTargetData();
631 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
634 // Now check without any constants at the end.
635 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
638 // If the tail provided a bit enough offset, return noalias!
639 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
644 // Couldn't find anything useful.
648 // If there are non-equal constants arguments, then we can figure
649 // out a minimum known delta between the two index expressions... at
650 // this point we know that the first constant index of GEP1 is less
651 // than the first constant index of GEP2.
653 // Advance BasePtr[12]Ty over this first differing constant operand.
654 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
655 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
656 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
657 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
659 // We are going to be using TargetData::getIndexedOffset to determine the
660 // offset that each of the GEP's is reaching. To do this, we have to convert
661 // all variable references to constant references. To do this, we convert the
662 // initial sequence of array subscripts into constant zeros to start with.
663 const Type *ZeroIdxTy = GEPPointerTy;
664 for (unsigned i = 0; i != FirstConstantOper; ++i) {
665 if (!isa<StructType>(ZeroIdxTy))
666 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
668 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
669 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
672 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
674 // Loop over the rest of the operands...
675 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
676 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
677 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
678 // If they are equal, use a zero index...
679 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
680 if (!isa<ConstantInt>(Op1))
681 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
682 // Otherwise, just keep the constants we have.
685 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
686 // If this is an array index, make sure the array element is in range.
687 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
688 if (Op1C->getZExtValue() >= AT->getNumElements())
689 return MayAlias; // Be conservative with out-of-range accesses
690 } else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty)) {
691 if (Op1C->getZExtValue() >= PT->getNumElements())
692 return MayAlias; // Be conservative with out-of-range accesses
696 // GEP1 is known to produce a value less than GEP2. To be
697 // conservatively correct, we must assume the largest possible
698 // constant is used in this position. This cannot be the initial
699 // index to the GEP instructions (because we know we have at least one
700 // element before this one with the different constant arguments), so
701 // we know that the current index must be into either a struct or
702 // array. Because we know it's not constant, this cannot be a
703 // structure index. Because of this, we can calculate the maximum
706 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
707 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
708 else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty))
709 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
715 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
716 // If this is an array index, make sure the array element is in range.
717 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
718 if (Op2C->getZExtValue() >= AT->getNumElements())
719 return MayAlias; // Be conservative with out-of-range accesses
720 } else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty)) {
721 if (Op2C->getZExtValue() >= PT->getNumElements())
722 return MayAlias; // Be conservative with out-of-range accesses
724 } else { // Conservatively assume the minimum value for this index
725 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
730 if (BasePtr1Ty && Op1) {
731 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
732 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
737 if (BasePtr2Ty && Op2) {
738 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
739 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
745 if (GEPPointerTy->getElementType()->isSized()) {
747 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
749 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
750 assert(Offset1<Offset2 && "There is at least one different constant here!");
752 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
753 //cerr << "Determined that these two GEP's don't alias ["
754 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
762 struct VISIBILITY_HIDDEN StringCompare {
763 bool operator()(const char *LHS, const char *RHS) {
764 return strcmp(LHS, RHS) < 0;
769 // Note that this list cannot contain libm functions (such as acos and sqrt)
770 // that set errno on a domain or other error.
771 static const char *DoesntAccessMemoryFns[] = {
772 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
773 "trunc", "truncf", "truncl", "ldexp",
775 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
777 "cos", "cosf", "cosl",
778 "exp", "expf", "expl",
780 "sin", "sinf", "sinl",
781 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
783 "floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
786 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
787 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
790 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
791 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
793 "iswctype", "towctrans", "towlower", "towupper",
797 "isinf", "isnan", "finite",
799 // C99 math functions
800 "copysign", "copysignf", "copysignd",
801 "nexttoward", "nexttowardf", "nexttowardd",
802 "nextafter", "nextafterf", "nextafterd",
805 "__signbit", "__signbitf", "__signbitl",
809 static const char *OnlyReadsMemoryFns[] = {
810 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
811 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
814 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
815 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
819 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
820 "wcsrchr", "wcsspn", "wcsstr",
823 "alphasort", "alphasort64", "versionsort", "versionsort64",
826 "nan", "nanf", "nand",
829 "feof", "ferror", "fileno",
830 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
833 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
834 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
837 AliasAnalysis::ModRefBehavior
838 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
839 std::vector<PointerAccessInfo> *Info) {
840 if (!F->isDeclaration()) return UnknownModRefBehavior;
842 static bool Initialized = false;
844 NoMemoryTable->insert(NoMemoryTable->end(),
845 DoesntAccessMemoryFns,
846 DoesntAccessMemoryFns+
847 sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
849 OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
852 sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
853 #define GET_MODREF_BEHAVIOR
854 #include "llvm/Intrinsics.gen"
855 #undef GET_MODREF_BEHAVIOR
857 // Sort the table the first time through.
858 std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
859 std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
864 std::vector<const char*>::iterator Ptr =
865 std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
866 F->getName().c_str(), StringCompare());
867 if (Ptr != NoMemoryTable->end() && *Ptr == F->getName())
868 return DoesNotAccessMemory;
870 Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
871 OnlyReadsMemoryTable->end(),
872 F->getName().c_str(), StringCompare());
873 if (Ptr != OnlyReadsMemoryTable->end() && *Ptr == F->getName())
874 return OnlyReadsMemory;
876 return UnknownModRefBehavior;
879 // Make sure that anything that uses AliasAnalysis pulls in this file...
880 DEFINING_FILE_FOR(BasicAliasAnalysis)