-
-// ConvertableToGEP - This function returns true if the specified value V is
-// a valid index into a pointer of type Ty. If it is valid, Idx is filled in
-// with the values that would be appropriate to make this a getelementptr
-// instruction. The type returned is the root type that the GEP would point to
-//
-const Type *ConvertableToGEP(const Type *Ty, Value *OffsetVal,
- vector<Value*> &Indices,
- BasicBlock::iterator *BI = 0) {
- const CompositeType *CompTy = getPointedToComposite(Ty);
- if (CompTy == 0) return 0;
-
- // See if the cast is of an integer expression that is either a constant,
- // or a value scaled by some amount with a possible offset.
- //
- analysis::ExprType Expr = analysis::ClassifyExpression(OffsetVal);
-
- // The expression must either be a constant, or a scaled index to be useful
- if (!Expr.Offset && !Expr.Scale)
- return 0;
-
- // Get the offset and scale now...
- unsigned Offset = 0, Scale = Expr.Var != 0;
-
- // Get the offset value if it exists...
- if (Expr.Offset) {
- int Val = getConstantValue(Expr.Offset);
- if (Val < 0) return false; // Don't mess with negative offsets
- Offset = (unsigned)Val;
- }
-
- // Get the scale value if it exists...
- if (Expr.Scale) {
- int Val = getConstantValue(Expr.Scale);
- if (Val < 0) return false; // Don't mess with negative scales
- Scale = (unsigned)Val;
- }
-
- // Check to make sure the offset is not negative or really large, outside the
- // scope of this structure...
- //
- if (!isa<ArrayType>(CompTy) || cast<ArrayType>(CompTy)->isSized())
- if (Offset >= TD.getTypeSize(CompTy))
- return 0;
-
- // Loop over the Scale and Offset values, filling in the Indices vector for
- // our final getelementptr instruction.
- //
- const Type *NextTy = CompTy;
- do {
- if (!isa<CompositeType>(NextTy))
- return 0; // Type must not be ready for processing...
- CompTy = cast<CompositeType>(NextTy);
-
- if (const StructType *StructTy = dyn_cast<StructType>(CompTy)) {
- const StructLayout *SL = TD.getStructLayout(StructTy);
- unsigned ActualOffset = Offset;
- NextTy = getStructOffsetType(StructTy, ActualOffset, Indices);
- Offset -= ActualOffset;
- } else {
- const ArrayType *AT = cast<ArrayType>(CompTy);
- const Type *ElTy = AT->getElementType();
- unsigned ElSize = TD.getTypeSize(ElTy);
-
- // See if the user is indexing into a different cell of this array...
- if (Scale && Scale >= ElSize) {
- // A scale n*ElSize might occur if we are not stepping through
- // array by one. In this case, we will have to insert math to munge
- // the index.
- //
- unsigned ScaleAmt = Scale/ElSize;
- if (Scale-ScaleAmt*ElSize)
- return 0; // Didn't scale by a multiple of element size, bail out
- Scale = ElSize;
-
- unsigned Index = Offset/ElSize; // is zero unless Offset > ElSize
- Offset -= Index*ElSize; // Consume part of the offset
-
- if (BI) { // Generate code?
- BasicBlock *BB = (**BI)->getParent();
- if (Expr.Var->getType() != Type::UIntTy) {
- CastInst *IdxCast = new CastInst(Expr.Var, Type::UIntTy);
- if (Expr.Var->hasName())
- IdxCast->setName(Expr.Var->getName()+"-idxcast");
- *BI = BB->getInstList().insert(*BI, IdxCast)+1;
- Expr.Var = IdxCast;
- }
-
- if (ScaleAmt) { // If we have to scale up our index, do so now
- Value *ScaleAmtVal = ConstantUInt::get(Type::UIntTy, ScaleAmt);
- Instruction *Scaler = BinaryOperator::create(Instruction::Mul,
- Expr.Var,ScaleAmtVal);
- if (Expr.Var->hasName())
- Scaler->setName(Expr.Var->getName()+"-scale");
-
- *BI = BB->getInstList().insert(*BI, Scaler)+1;
- Expr.Var = Scaler;
- }
-
- if (Index) { // Add an offset to the index
- Value *IndexAmt = ConstantUInt::get(Type::UIntTy, Index);
- Instruction *Offseter = BinaryOperator::create(Instruction::Add,
- Expr.Var, IndexAmt);
- if (Expr.Var->hasName())
- Offseter->setName(Expr.Var->getName()+"-offset");
- *BI = BB->getInstList().insert(*BI, Offseter)+1;
- Expr.Var = Offseter;
- }
- }
-
- Indices.push_back(Expr.Var);
- Scale = 0; // Consume scale factor!
- } else if (Offset >= ElSize) {
- // Calculate the index that we are entering into the array cell with
- unsigned Index = Offset/ElSize;
- Indices.push_back(ConstantUInt::get(Type::UIntTy, Index));
- Offset -= Index*ElSize; // Consume part of the offset
-
- } else {
- // Must be indexing a small amount into the first cell of the array
- // Just index into element zero of the array here.
- //
- Indices.push_back(ConstantUInt::get(Type::UIntTy, 0));
- }
- NextTy = ElTy;
- }
- } while (Offset || Scale); // Go until we're done!
-
- return NextTy;
-}