Instruction cache behavior and branch prediction

A computer-implemented method, comprising:

• identifying a branching instruction associated with:
• a cold block starting with a cold target that the branching instruction flows to when a routing condition is a first one of true or false;
• and
• a hot block located before the branching instruction in an instruction cache that starts at a hot target that flows to a subsequent instruction and that the branching instruction jumps to when the routing condition is a second one of true or false, wherein, based on historical data, the branching instruction is more likely to proceed to the hot target than to the cold target at execution;
• inserting a space between the branching instruction and the cold target;
• inserting a duplicate hot block and a jump instruction in the space, wherein the duplicate hot block flows to the jump instruction and the jump instruction jumps to the subsequent instruction;
• and
• reversing the routing condition in the branching instruction to flow to the duplicate hot block when the routing condition is the second one of true or false and to jump to the cold target when the routing condition is the first one of true or false.

A computer-implemented method, comprising:

• profiling branching instructions in an instruction cache to identify likelihoods of proceeding to a plurality of targets from the branching instructions;
• identifying a hot path in the instruction cache based on the identified likelihoods;
• and
• rearranging the plurality of targets relative to one another and associated branching instructions so that a first branching instruction that has a higher likelihood of proceeding to a first hot target than to a first cold target and that previously flowed to the first cold target and jumped to the first hot target instead flows to the first hot target and jumps to the first cold target.

A system, comprising:

• a processor, including an instruction cache;
• a memory including instructions that when executed by the processor perform an operation comprising:
• profiling branching instructions in the instruction cache to identify likelihoods of proceeding to a plurality of targets from the branching instructions;
• identifying a hot path in the instruction cache based on the identified likelihoods;
• and
• rearranging the plurality of targets relative to one another and associated branching instructions so that a first branching instruction that has a higher likelihood of proceeding to a first hot target than to a first cold target and that previously flowed to the first cold target and jumped to the first hot target instead flows to the first hot target and jumps to the first cold target.

A computer-readable storage medium having computer-readable program code embodied therewith, the computer-readable program code executable by one or more computer processors to:

• profile branching instructions in an instruction cache to identify likelihoods of proceeding to a plurality of targets from the branching instructions;
• identify a hot path in the instruction cache based on the identified likelihoods;
• and
• rearrange the plurality of targets relative to one another and associated branching instructions so that a first branching instruction that has a higher likelihood of proceeding to a first hot target than to a first cold target and that previously flowed to the first cold target and jumped to the first hot target instead flows to the first hot target and jumps to the first cold target.