Method and apparatus for managing a speculative transaction in a processing unit

An apparatus for managing a speculative transaction in a processing unit, comprising:

• means for initiating the speculative transaction by dispatching a first instruction indicating start of the speculative transaction;
• means for identifying one or more register file (RF) entries storing data for the processing unit prior to initiating the speculative transaction;
• means for marking, in response to the initiating, the identified one or more RF entries by changing the state of a pre-transaction memory (PTM) bit associated with the one or more RF entries to indicate that the data stored in a respective RF entry is PTM;
• means for dispatching at least one second instruction targeting a first RF entry of the one or more RF entries, while the speculative transaction is active, the at least one second instruction writing new result data into the first RF entry;
• means for saving first previous result data evicted from the first RF entry by the new result data, into a first history buffer (HB) entry;
• means for marking the first HB entry as PTM by changing the state of a first PTM bit associated with the first HB entry, in response to the saving;
• means for dispatching a third instruction targeting the first RF entry, while the speculative transaction is active, the third instruction writing new result data into the first RF entry, and in response saving second previous result data evicted from the first RF entry into a second HB entry, without changing the state of a second PTM bit associated with the second HB entry;
• and
• means for, upon detecting a trigger, rolling back the processing unit to a state before the initiating the speculative transaction by restoring the first previous result data to the at first RF entry.

A computer program product for managing a speculative transaction in a processing unit, the computer program product comprising:

• a computer-readable storage medium having computer-readable program code embodied therewith for performing method steps comprising:
• initiating the speculative transaction by dispatching a first instruction indicating start of the speculative transaction;
• identifying one or more register file (RF) entries storing data for the processing unit prior to initiating the speculative transaction;
• marking, in response to the initiating, the identified one or more RF entries by changing the state of a pre-transaction memory (PTM) bit associated with the one or more RF entries to indicate that the data stored in a respective RF entry is PTM;
• dispatching at least one second instruction targeting a first RF entry of the one or more RF entries, while the speculative transaction is active, the at least one second instruction writing new result data into the first RF entry;
• saving first previous result data evicted from the first RF entry by the new result data, into a first history buffer (HB) entry;
• marking the first HB entry as PTM by changing the state of a first PTM bit associated with the first HB entry, in response to the saving;
• and
• dispatching a third instruction targeting the first RF entry, while the speculative transaction is active, the third instruction writing new result data into the first RF entry, and in response saving second previous result data evicted from the first RF entry into a second HB entry, without changing the state of a second PTM bit associated with the second HB entry,
• wherein the processing unit, upon detecting a trigger, is configured to rollback to a state before the initiating the speculative transaction by restoring the first previous result data to the first RF entry.