Use data flow analysis to find constraints on transaction fields in a contract about tealer HOT 1 OPEN

The above dataflow equations do not work correctly when there's a backedge(loops). Because:

• For a field, each block is initialized with all possible values for that field.
• For a node to receive information, all of the predecessors must first receive the target information.
• For a loop header block to receive the information, the information must first reach the loop exit block. And the only way for the information to reach the loop exit block is from the loop header block. This results in a cycle, stopping the information from outside the loop from reaching the loop body blocks and stopping information computed within the loop body from reaching blocks outside the loop.

Ex:

information from instructions txn OnCompletion == int CloseOut in block 4 would not reach block 9 and 10. Similarly, information from instructions txn OnCompletion != int DeleteApplication in block 9 (inside the loop) would not reach block 4 and other blocks outside the loop.

An easy solution for this would be to:

• find back edges and ignore predecessors or successors connected with the back edge while combining information. As information is propagated from predecessors as well as successors information would reach all blocks even if we do this.

However, we are doing path-sensitive analysis. so, if the information is part of the back edge itself and is not part of the source or target block of the edge, we would lose that information. But, this should be fine for the use cases. Because, in practice, transaction constraints are not part of the loop conditions.

Another solution is to change the equations to follow GEN and KILL type analysis. And update the implementation accordingly.

from tealer.