void GraphBuilder::visitGetElementPtrInst(User &GEP) {
//
// Ensure that the indexed pointer has a DSNode.
//
DSNodeHandle Value = getValueDest(GEP.getOperand(0));
if (Value.isNull())
Value = createNode();
//
// There are a few quick and easy cases to handle. If the DSNode of the
// indexed pointer is already folded, then we know that the result of the
// GEP will have the same offset into the same DSNode
// as the indexed pointer.
//
if (!Value.isNull() &&
Value.getNode()->isNodeCompletelyFolded()) {
setDestTo(GEP, Value);
return;
}
//
// Okay, no easy way out. Calculate the offset into the object being
// indexed.
//
int Offset = 0;
// FIXME: I am not sure if the code below is completely correct (especially
// if we start doing fancy analysis on non-constant array indices).
// What if the array is indexed using a larger index than its declared
// size? Does the LLVM verifier catch such issues?
//
//
// Determine the offset (in bytes) between the result of the GEP and the
// GEP's pointer operand.
//
// Note: All of these subscripts are indexing INTO the elements we have...
//
// FIXME: We can do better for array indexing. First, if the array index is
// constant, we can determine how much farther we're moving the
// pointer. Second, we can try to use the results of other analysis
// passes (e.g., ScalarEvolution) to find min/max values to do less
// conservative type-folding.
//
for (gep_type_iterator I = gep_type_begin(GEP), E = gep_type_end(GEP);
I != E; ++I)
if (StructType *STy = dyn_cast<StructType>(*I)) {
// indexing into a structure
// next index must be a constant
const ConstantInt* CUI = cast<ConstantInt>(I.getOperand());
int FieldNo = CUI->getSExtValue();
// increment the offset by the actual byte offset being accessed
unsigned requiredSize = TD.getTypeAllocSize(STy) + Value.getOffset() + Offset;
if(!Value.getNode()->isArrayNode() || Value.getNode()->getSize() <= 0){
if (requiredSize > Value.getNode()->getSize())
Value.getNode()->growSize(requiredSize);
}
Offset += (unsigned)TD.getStructLayout(STy)->getElementOffset(FieldNo);
if(TypeInferenceOptimize) {
if(ArrayType* AT = dyn_cast<ArrayType>(STy->getTypeAtIndex(FieldNo))) {
Value.getNode()->mergeTypeInfo(AT, Value.getOffset() + Offset);
if((++I) == E) {
break;
}
// Check if we are still indexing into an array.
// We only record the topmost array type of any nested array.
// Keep skipping indexes till we reach a non-array type.
// J is the type of the next index.
// Uncomment the line below to get all the nested types.
gep_type_iterator J = I;
while(isa<ArrayType>(*(++J))) {
// Value.getNode()->mergeTypeInfo(AT1, Value.getOffset() + Offset);
if((++I) == E) {
break;
}
J = I;
}
if((I) == E) {
break;
}
}
}
} else if(ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
// indexing into an array.
Value.getNode()->setArrayMarker();
Type *CurTy = ATy->getElementType();
if(!isa<ArrayType>(CurTy) &&
Value.getNode()->getSize() <= 0) {
Value.getNode()->growSize(TD.getTypeAllocSize(CurTy));
} else if(isa<ArrayType>(CurTy) && Value.getNode()->getSize() <= 0){
Type *ETy = (cast<ArrayType>(CurTy))->getElementType();
while(isa<ArrayType>(ETy)) {
ETy = (cast<ArrayType>(ETy))->getElementType();
}
Value.getNode()->growSize(TD.getTypeAllocSize(ETy));
}
// Find if the DSNode belongs to the array
// If not fold.
if((Value.getOffset() || Offset != 0)
|| (!isa<ArrayType>(CurTy)
&& (Value.getNode()->getSize() != TD.getTypeAllocSize(CurTy)))) {
Value.getNode()->foldNodeCompletely();
Value.getNode();
Offset = 0;
break;
}
} else if (const PointerType *PtrTy = dyn_cast<PointerType>(*I)) {
Type *CurTy = PtrTy->getElementType();
//
// Unless we're advancing the pointer by zero bytes via array indexing,
// fold the node (i.e., mark it type-unknown) and indicate that we're
// indexing zero bytes into the object.
//
// Note that we break out of the loop if we fold the node. Once
// something is folded, all values within it are considered to alias.
//
if (!isa<Constant>(I.getOperand()) ||
!cast<Constant>(I.getOperand())->isNullValue()) {
Value.getNode()->setArrayMarker();
if(!isa<ArrayType>(CurTy) && Value.getNode()->getSize() <= 0){
Value.getNode()->growSize(TD.getTypeAllocSize(CurTy));
} else if(isa<ArrayType>(CurTy) && Value.getNode()->getSize() <= 0){
Type *ETy = (cast<ArrayType>(CurTy))->getElementType();
while(isa<ArrayType>(ETy)) {
ETy = (cast<ArrayType>(ETy))->getElementType();
}
Value.getNode()->growSize(TD.getTypeAllocSize(ETy));
}
if(Value.getOffset() || Offset != 0
|| (!isa<ArrayType>(CurTy)
&& (Value.getNode()->getSize() != TD.getTypeAllocSize(CurTy)))) {
Value.getNode()->foldNodeCompletely();
Value.getNode();
Offset = 0;
break;
}
}
}
// Add in the offset calculated...
Value.setOffset(Value.getOffset()+Offset);
// Check the offset
DSNode *N = Value.getNode();
if (N) N->checkOffsetFoldIfNeeded(Value.getOffset());
// Value is now the pointer we want to GEP to be...
setDestTo(GEP, Value);
}
