Branch

Abstract: The present invention provides for the updating of both the instructions in a branch prediction cache and instructions recently provided to an instruction pipeline from the cache when an instruction being executed attempts to change such instructions ("Store-Into-Instruction-Stream"). The branch prediction cache (BPC) includes a tag identifying the address of instructions causing a branch, a record of the target address which was branched to on the last occurrence of each branch instruction, and a copy of the first several instructions beginning at this target address. A separate instruction cache is provided for normal execution of instructions, and all of the instructions written into the branch prediction cache from the system bus must also be stored in the instruction cache. The instruction cache monitors the system bus for attempts to write to the address of an instruction contained in the instruction cache. Upon such a detection, that entry in the instruction cache is invalidated, and the corresponding entry in the branch prediction cache is invalidated. A subsequent attempt to use an instruction in the branch prediction cache which has been invalidated will detect that it is not valid, and will instead go to main memory to fetch the instruction, where it has been modified.

Abstract: To increase the performance of a pipelined processor executing instructions, conditional instruction execution issues and executes instructions, including but not limited to branches, before the controlling conditions may be available and makes the decision to update the destination as late as possible in the pipeline Conditional instruction execution is further improved by a condition code mask field in instructions to choose those condition code bits to be involved in the decision; by a set condition code flag to enable or disable the setting of a condition code; by stale condition code handling to determine if the logically previous conditionally executing instruction was successful or unsuccessful in setting the condition code and to conditionally execute accordingly; by multiple condition codes so that independent instruction sequences can use condition codes in parallel; and by condition code reservation stations to capture a needed condition code as soon as it becomes available and hold that captured value until needed, thus freeing the condition code as soon as possible for use by other instructions Moving the conditional decision from the point of instruction issue to the point of instruction completion permits branch instructions to be eliminated in many cases; permits conditionally executing instructions directly in line; permits filling the branch umbra following a delayed branch with conditionally executing instructions; and reduces the latency from condition code generation to condition code use

Abstract: A method for programming a computer to execute a procedure is based on a graphical interface which utilizes data flow diagrams to represent the procedure. The method stores a plurality of executable functions, scheduling functions, and data types. A data flow diagram is assembled in response to the user input utilizing icons which correspond to the respective executable functions, scheduling functions, and data types which are interconnected by arcs on the screen. A panel, representative of an instrument fron panel having input and output formats is likewise assembled for the data flow diagram. An executable program is generated in response to the data flow diagram and the panel utilizing the executable functions, scheduling functions, and data types stored in the memory. Furthermore, the executable functions may include user defined functions that have been generated using the method for programming. In this manner, a hierarchy of procedures is implemented, each represented by a data flow diagram.

Abstract: In a parallel data processing system having a plurality of separately operating arithmetic processing units, a method and apparatus allows a plurality of branch instructions to be operated upon in a single machine cycle. The branch instructions have associated therewith a hierarchical priority system and the method and apparatus determine which branch, if any, should be taken. In particular, the method and apparatus simultaneously determine, during the parallel execution of the branch instructions, whether any branch test condition associated with a branch instruction is true, and independently, the target address for each branch instruction and a fall-through instruction address if a branch instruction is not taken.