Figure out how to handle index vectors in getelementptr instructions and constant expressions about llvm HOT 6 CLOSED

// gepType returns the pointer type to the element at the position in the type
// specified by the given indices, as calculated by the getelementptr
// instruction.
func gepType(elemType types.Type, indices []value.Value) types.Type {
	e := elemType
	for i, index := range indices {
		if i == 0 {
			// Ignore checking the 0th index as it simply follows the pointer of
			// src.
			//
			// ref: http://llvm.org/docs/GetElementPtr.html#why-is-the-extra-0-index-required
			continue
		}
		switch t := e.(type) {
		case *types.PointerType:
			// ref: http://llvm.org/docs/GetElementPtr.html#what-is-dereferenced-by-gep
			panic(fmt.Errorf("unable to index into element of pointer type `%v`; for more information, see http://llvm.org/docs/GetElementPtr.html#what-is-dereferenced-by-gep", elemType))
		case *types.VectorType:
			e = t.ElemType
		case *types.ArrayType:
			e = t.ElemType
		case *types.StructType:
			idx, ok := index.(*constant.Int)
			if !ok {
				panic(fmt.Errorf("invalid index type for structure element; expected *constant.Int, got %T", index))
			}
			e = t.Fields[idx.X.Int64()]
		default:
			panic(fmt.Errorf("support for indexing element type %T not yet implemented", e))
		}
	}
	// TODO: Validate how index vectors in gep are supposed to work.
	//
	// Example from dir.ll:
	//    %113 = getelementptr inbounds %struct.fileinfo, %struct.fileinfo* %96, <2 x i64> %110, !dbg !4736
	//    %116 = bitcast i8** %115 to <2 x %struct.fileinfo*>*, !dbg !4738
	//    store <2 x %struct.fileinfo*> %113, <2 x %struct.fileinfo*>* %116, align 8, !dbg !4738, !tbaa !1793
	if len(indices) > 0 {
		if t, ok := indices[0].Type().(*types.VectorType); ok {
			return types.NewVector(t.Len, types.NewPointer(e))
		}
	}
	return types.NewPointer(e)
}

// TODO: investigate why we are able to parse `return i32* %gep`, should not be possible as there is no `return` token in the grammar.
//{path: "../testdata/llvm/test/Assembler/getelementptr_invalid_ptr.ll"},
// TODO: fix computation of gep type. We currently do not update the return type to vector if the first gep index is a scalar, but the second (or later) indices is a vector. As such, we currently compute the type `i32*` where `<4 x i32*>` should have been computed.
//{path: "../testdata/llvm/test/Assembler/getelementptr_vec_ce.ll"},
// TODO: fix computation of gep type. We currently do not update the return type to vector if the first gep index is a scalar, but the second (or later) indices is a vector. As such, we currently compute the type `i32*` where `<4 x i32*>` should have been computed.
//{path: "../testdata/llvm/test/Assembler/getelementptr_vec_ce2.ll"},
// TODO: fix gep type computation.
//{path: "../testdata/llvm/test/Assembler/getelementptr_vec_idx1.ll"},
// TODO: fix gep type computation.
//{path: "../testdata/llvm/test/Assembler/getelementptr_vec_idx2.ll"},
// TODO: fix gep type computation.
//{path: "../testdata/llvm/test/Assembler/getelementptr_vec_idx3.ll"},