Fujitsu Corporation

Sunil W Savkar

Michael C Shebanow

Akira Katsuno

Niteen Aravind Patkar

A superscaler processor capable of executing multiple instructions concurrently. The processor includes a program counter which identifies instructions for execution by multiple execution units. Further included is a register file made up of multiple register window pointer selects one of the multiple register windows. In response to the value of the current window pointer, a return prediction table provides a speculative program counter value, indicative of a return address of an instruction for a subroutine, corresponding to the selected register window. A watchpoint register stores the speculative program counter value. A fetch program counter, in response to the speculative program counter value, stores the instructions for execution after they have been identified by the program counter.

Superscalar processor with multiple register windows and speculative

A method and apparatus accepts a relative control transfer instruction and generates a compact absolute control transfer instruction which may have a number of bits one greater than the relative control transfer instruction and including flags to rapidly construct the target address of the relative control transfer instruction. The compact absolute control transfer instruction is generated by sign extending the displacement of the relative control transfer instructions and adding it to a set of least significant bits from the control transfer instruction address, and optionally coupling some or all of the bits from the result with the original opcode or a different opcode. The target address of the relative control transfer instruction is determined by using, incrementing or decrementing, depending on the state of the flags, a group of the most significant bits from the relative control transfer instruction address and appending the result with the least significant bits from the result of the addition described above.

Method and apparatus for rapid computation of target addresses for

A clocked instruction flow is managed subject to issue and fetch constraints through a plurality of instruction latches which receive instructions from selected memory locations. By checking the number of instructions fetched and issued, the fetch program counter is adjusted responsive to the status of selected state variables indicating instructions issued and fetched. The instruction latches are fully scheduled from cycle to cycle with instructions, by fetching instructions in accordance with a fetch program counter.

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Palo Alto, CA, United States of America

Sunil W Savkar