//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
#include "llvm/ParameterAttributes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
-#include "llvm/Intrinsics.h"
+#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringMap.h"
-#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
/// global) or not.
bool pointsToConstantMemory(const Value *P);
- virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
- std::vector<PointerAccessInfo> *Info);
-
private:
// CheckGEPInstructions - Check two GEP instructions with known
// must-aliasing base pointers. This checks to see if the index expressions
return new BasicAliasAnalysis();
}
-// getUnderlyingObject - This traverses the use chain to figure out what object
-// the specified value points to. If the value points to, or is derived from, a
-// unique object or an argument, return it.
+/// getUnderlyingObject - This traverses the use chain to figure out what object
+/// the specified value points to. If the value points to, or is derived from,
+/// a unique object or an argument, return it. This returns:
+/// Arguments, GlobalVariables, Functions, Allocas, Mallocs.
static const Value *getUnderlyingObject(const Value *V) {
if (!isa<PointerType>(V->getType())) return 0;
return true;
break; // next use.
case Instruction::BitCast:
- if (!isa<PointerType>(I->getType()))
- return true;
if (AddressMightEscape(I))
return true;
break; // next use
// If returned, the address will escape to calling functions, but no
// callees could modify it.
break; // next use
+ case Instruction::Call:
+ // If the call is to a few known safe intrinsics, we know that it does
+ // not escape
+ if (!isa<MemIntrinsic>(I))
+ return true;
+ break; // next use
default:
return true;
}
//
AliasAnalysis::ModRefResult
BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
- if (!isa<Constant>(P))
- if (const AllocationInst *AI =
- dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
- // Okay, the pointer is to a stack allocated object. If we can prove that
- // the pointer never "escapes", then we know the call cannot clobber it,
- // because it simply can't get its address.
- if (!AddressMightEscape(AI))
- return NoModRef;
+ if (!isa<Constant>(P)) {
+ const Value *Object = getUnderlyingObject(P);
+ // Allocations and byval arguments are "new" objects.
+ if (Object &&
+ (isa<AllocationInst>(Object) || isa<Argument>(Object))) {
+ // Okay, the pointer is to a stack allocated (or effectively so, for
+ // for noalias parameters) object. If the address of this object doesn't
+ // escape from this function body to a callee, then we know that no
+ // callees can mod/ref it unless they are actually passed it.
+ if (isa<AllocationInst>(Object) ||
+ cast<Argument>(Object)->hasByValAttr() ||
+ cast<Argument>(Object)->hasNoAliasAttr())
+ if (!AddressMightEscape(Object)) {
+ bool passedAsArg = false;
+ for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
+ CI != CE; ++CI)
+ if (isa<PointerType>((*CI)->getType()) &&
+ ( getUnderlyingObject(*CI) == P ||
+ alias(cast<Value>(CI), ~0ULL, P, ~0ULL) != NoAlias) )
+ passedAsArg = true;
+
+ if (!passedAsArg)
+ return NoModRef;
+ }
// If this is a tail call and P points to a stack location, we know that
// the tail call cannot access or modify the local stack.
- if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
- if (CI->isTailCall() && isa<AllocaInst>(AI))
- return NoModRef;
+ if (isa<AllocaInst>(Object) ||
+ (isa<Argument>(Object) && cast<Argument>(Object)->hasByValAttr()))
+ if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
+ if (CI->isTailCall())
+ return NoModRef;
}
+ }
// The AliasAnalysis base class has some smarts, lets use them.
return AliasAnalysis::getModRefInfo(CS, P, Size);
}
-static bool isNoAliasArgument(const Argument *Arg) {
- const Function *Func = Arg->getParent();
- const ParamAttrsList *Attr = Func->getParamAttrs();
- if (Attr) {
- unsigned Idx = 1;
- for (Function::const_arg_iterator I = Func->arg_begin(),
- E = Func->arg_end(); I != E; ++I, ++Idx) {
- if (&(*I) == Arg &&
- Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
- return true;
- }
- }
- return false;
-}
-
// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
// as array references. Note that this function is heavily tail recursive.
// Hopefully we have a smart C++ compiler. :)
// If they are two different objects, and one is a noalias argument
// then they do not alias.
- if (O1 != O2 && isNoAliasArgument(O1Arg))
+ if (O1 != O2 && O1Arg->hasNoAliasAttr())
return NoAlias;
-
+
+ // Byval arguments can't alias globals or other arguments.
+ if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
+
// Otherwise, nothing is known...
}
// If they are two different objects, and one is a noalias argument
// then they do not alias.
- if (O1 != O2 && isNoAliasArgument(O2Arg))
+ if (O1 != O2 && O2Arg->hasNoAliasAttr())
return NoAlias;
+ // Byval arguments can't alias globals or other arguments.
+ if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
+
// Otherwise, nothing is known...
- } else if (O1 != O2) {
- if (!isa<Argument>(O1))
- // If they are two different objects, and neither is an argument,
- // we know that we have no alias...
- return NoAlias;
+ } else if (O1 != O2 && !isa<Argument>(O1)) {
+ // If they are two different objects, and neither is an argument,
+ // we know that we have no alias.
+ return NoAlias;
}
// If they are the same object, they we can look at the indexes. If they
// can't tell anything.
}
-
- if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
- return NoAlias; // Unique values don't alias null
+ // Unique values don't alias null, except non-byval arguments.
+ if (isa<ConstantPointerNull>(V2)) {
+ if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
+ if (O1Arg->hasByValAttr())
+ return NoAlias;
+ } else {
+ return NoAlias;
+ }
+ }
if (isa<GlobalVariable>(O1) ||
(isa<AllocationInst>(O1) &&
if (isGEP(V1) && isGEP(V2)) {
// Drill down into the first non-gep value, to test for must-aliasing of
// the base pointers.
- const Value *BasePtr1 = V1, *BasePtr2 = V2;
- do {
- BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
- } while (isGEP(BasePtr1) &&
- cast<User>(BasePtr1)->getOperand(1) ==
- Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
- do {
- BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
- } while (isGEP(BasePtr2) &&
- cast<User>(BasePtr2)->getOperand(1) ==
- Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
+ const User *G = cast<User>(V1);
+ while (isGEP(G->getOperand(0)) &&
+ G->getOperand(1) ==
+ Constant::getNullValue(G->getOperand(1)->getType()))
+ G = cast<User>(G->getOperand(0));
+ const Value *BasePtr1 = G->getOperand(0);
+
+ G = cast<User>(V2);
+ while (isGEP(G->getOperand(0)) &&
+ G->getOperand(1) ==
+ Constant::getNullValue(G->getOperand(1)->getType()))
+ G = cast<User>(G->getOperand(0));
+ const Value *BasePtr2 = G->getOperand(0);
// Do the base pointers alias?
AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
if (Op1C->getZExtValue() >= AT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
- } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
- if (Op1C->getZExtValue() >= PT->getNumElements())
+ } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
+ if (Op1C->getZExtValue() >= VT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
}
if (Op2) {
if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
// If this is an array index, make sure the array element is in range.
- if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
+ if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
if (Op2C->getZExtValue() >= AT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
- } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
+ } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
if (Op2C->getZExtValue() >= VT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
}
return MayAlias;
}
-static ManagedStatic<BitVector> NoMemoryIntrinsics;
-static ManagedStatic<BitVector> OnlyReadsMemoryIntrinsics;
-
-AliasAnalysis::ModRefBehavior
-BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
- std::vector<PointerAccessInfo> *Info) {
- if (!F->isDeclaration()) return UnknownModRefBehavior;
-
- static bool Initialized = false;
- if (!Initialized) {
- NoMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
- OnlyReadsMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
-#define GET_MODREF_BEHAVIOR
-#include "llvm/Intrinsics.gen"
-#undef GET_MODREF_BEHAVIOR
-
- Initialized = true;
- }
-
- // If this is an intrinsic, we can use lookup tables
- if (unsigned id = F->getIntrinsicID()) {
- if (NoMemoryIntrinsics->test(id))
- return DoesNotAccessMemory;
- if (OnlyReadsMemoryIntrinsics->test(id))
- return OnlyReadsMemory;
-
- return UnknownModRefBehavior;
- }
-
- return UnknownModRefBehavior;
-}
-
// Make sure that anything that uses AliasAnalysis pulls in this file...
DEFINING_FILE_FOR(BasicAliasAnalysis)
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