Method GetCodegendComputeFnImpl

be/src/exprs/slot-ref.cc:202–232

There are four possible cases we may generate: 1. Tuple is non-nullable and slot is non-nullable 2. Tuple is non-nullable and slot is nullable 3. Tuple is nullable and slot is non-nullable (when the aggregate output is the "nullable" side of an outer join). 4. Tuple is nullable and slot is nullable Resulting IR for a bigint slotref: (Note: some of the GEPs that look like no-ops are because certai

// TODO: We could generate a typed struct (and not a char*) for Tuple for llvm.  We know
// the types from the TupleDesc.  It will likely make this code simpler to reason about.
Status SlotRef::GetCodegendComputeFnImpl(LlvmCodeGen* codegen, llvm::Function** fn) {
  // SlotRefs are based on the slot_id and tuple_idx.  Combine them to make a
  // query-wide unique id. We also need to combine whether the tuple is nullable. For
  // example, in an outer join the scan node could have the same tuple id and slot id
  // as the join node. When the slot is being used in the scan-node, the tuple is
  // non-nullable. Used in the join node (and above in the plan tree), it is nullable.
  // TODO: can we do something better.
  constexpr int64_t TUPLE_NULLABLE_MASK = numeric_limits<int64_t>::min();
  int64_t unique_slot_id = slot_id_ | ((int64_t)tuple_idx_) << 32;
  DCHECK_EQ(unique_slot_id & TUPLE_NULLABLE_MASK, 0);
  if (tuple_is_nullable_) unique_slot_id |= TUPLE_NULLABLE_MASK;
  llvm::Function* ir_compute_fn_ = codegen->GetRegisteredExprFn(unique_slot_id);
  if (ir_compute_fn_ != NULL) {
    *fn = ir_compute_fn_;
    return Status::OK();
  }

  llvm::Value* args[2];
  *fn = CreateIrFunctionPrototype("GetSlotRef", codegen, &args);
  llvm::Value* eval_ptr = args[0];
  llvm::Value* row_ptr = args[1];

  LlvmBuilder builder(codegen->context());
  CodegenAnyVal result_value = CodegenValue(codegen, &builder, *fn, eval_ptr, row_ptr);
  builder.CreateRet(result_value.GetLoweredValue());

  *fn = codegen->FinalizeFunction(*fn);
  if (UNLIKELY(*fn == NULL)) return Status(TErrorCode::IR_VERIFY_FAILED, "SlotRef");
  codegen->RegisterExprFn(unique_slot_id, *fn);
  return Status::OK();
}

// Generates null checking code: null checking may be generated for the tuple and for the
// slot based on 'tuple_is_nullable' and 'slot_is_nullable'. If any one of the checks