1. A computer program product for providing diagnostic information on transaction aborts, the computer program product comprising: a non-transitory computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: executing a transaction, the transaction effectively delaying committing transactional stores to main memory until completion of a selected transaction; based on executing the transaction, determining whether the transaction includes one or more branching instructions; based on determining the transaction includes one or more branching instructions, setting one or more indicators corresponding to the one or more branching instructions, wherein an indicator corresponds to a branching instruction and indicates whether a branch was taken by the branching instruction, wherein the setting of the indicator includes setting the indicator to a first value based on the branching instruction corresponding to the indicator taking a branch, and setting the indicator to a second value based on the branching instruction corresponding to the indicator not taking the branch; determining that the transaction has aborted; and based on determining the transaction has aborted, storing the one or more indicators in a transaction diagnostic block (TDB) associated with the transaction, wherein the transaction diagnostic block provides a branch history that indicates which branching instructions have taken the branch and which branching instructions have not taken the branch during a transactional execution mode that includes the transaction.