Variable branch target buffer (BTB) line size for compression

A computer-implemented method comprising:

• determining a branch target buffer (BTB) congruence class for a line of a first parent array of a BTB, wherein the BTB congruence class includes a hash, and
• wherein the BTB comprises at least two levels of associativity based on the BTB congruence class;
• setting a threshold indicative of a maximum number branches to be stored in the line;
• receiving a branch to store in the line of the first parent array;
• determining that storing the branch in the line would exceed the threshold;
• splitting the line into an even half line and an odd half line responsive to determining that storing the branch in the line would exceed the threshold, wherein the branch is stored in a second parent array based on an address of a branching mapping to either the even half line or the odd half line;
• and
• reinstalling entries to a newly allocated parent array when a branch is detected in a pipeline, which was not found by a branch predictor upon earlier searching of the pipeline.

A computer program product, the computer program product comprising:

• a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising:
• determining a branch target buffer (BTB) congruence class for a line of a first parent array of a BTB, wherein the BTB congruence class includes a hash, and
• wherein the BTB comprises at least two levels of associativity based on the BTB congruence class;
• setting a threshold indicative of a maximum number branches to be stored in the line;
• receiving a branch to store in the line of the first parent array;
• determining that storing the branch in the line would exceed the threshold;
• splitting the line into an even half line and an odd half line responsive to determining that storing the branch in the line would exceed the threshold, wherein the branch is stored in a second parent array based on an address of a branching mapping to either the even half line or the odd half line;
• and
• reinstalling entries to a newly allocated parent array when a branch is detected in a pipeline, which was not found by a branch predictor upon earlier searching of the pipeline.