Method for speculative execution of instructions and a device having speculative execution capabilities
View Patent ↗A method for speculative execution of instructions, the method includes: decoding a compare instruction; speculatively executing, in a continuous manner, conditional instructions that are conditioned by a condition that is related to a resolution of the compare instruction and are decoded during a speculation window that starts at the decoding of the compare instruction and ends when the compare instruction is resolved; and stalling an execution of a non-conditional instruction that is dependent upon an outcome of at least one of the conditional instructions, until the speculation window ends.
1. A method for speculative execution of instructions, the method comprising: decoding a compare instruction; speculatively executing, in a continuous manner, conditional instructions that are conditioned by a condition that is related to a resolution of the compare instruction and are decoded during a speculation window that starts at the decoding of the compare instruction and ends when the compare instruction is resolved; and stalling an execution of a non-conditional instruction that is dependent upon an outcome of at least one of the conditional instructions, until the speculation window ends.
2. The method according to claim 1 comprising ignoring an outcome of an execution of at least one conditional instruction if the resolution of the compare instruction indicates that a condition associated with the at least one conditional instruction was not fulfilled.
3. The method according to claim 1 wherein the speculatively executing comprises executing a conditional instruction that depends upon an outcome of another conditional instruction that is decoded during the speculation window.
4. The method according to claim 1 wherein the speculatively executing comprises:
executing a first conditional instruction that replaces an old value of a certain register by a new value; and
executing a second conditional instruction that uses the new value of the register if the first and second conditional instructions have the same dependency on the resolution of the compare instruction.
5. The method according to claim 1 wherein the speculatively execution comprises:
executing a first conditional instruction that replaces an old value of a certain register by a new value; and
executing a second conditional instruction that uses the old value of the register if the first and second conditional instructions have opposing dependencies on the resolution of the compare instruction.
6. The method according to claim 1 comprising executing, in parallel, conditional instructions that have opposing dependencies on the resolution of the compare instruction and selecting, in response to a resolution of the compare instruction, an outcome of one conditional instruction out of the conditional instructions.
7. The method according to claim 1 comprising updating status data that indicates which registers are affected by the non-conditional instructions and indicates registers are affected by the conditional instructions.
8. The method according to claim 1 wherein the speculatively executing comprises forwarding values of registers affected by the conditional instructions during the speculation window.
9. The method according to claim 1 wherein the conditional instructions are part of very long instruction words.
10. The method according to claim 1 wherein the conditional instructions are selected from a group consisting of load store instructions and pointer arithmetic instructions.
11. A device having speculative execution capabilities, the device comprises:
a first sequence of pipelined stages that is configured to execute a compare instruction; wherein the pipelined stages comprises a decoding stage, multiple intermediate pipeline stages and an execution stage;
a speculative execution module that is configured to:
speculatively execute, in a continuous manner, conditional instructions that are conditioned by a condition that is related to a resolution of the compare instruction and are decoded during a speculation window that starts at the decoding of the compare instruction and ends when the compare instruction is resolved; and
stall an execution of a non-conditional instruction that is dependent upon an outcome of at least one of the conditional instructions, until the speculation window ends.
12. The device according to claim 11 comprising wherein the device ignores an outcome of an execution of at least one conditional instruction if the resolution of the compare instruction indicates that a condition associated with the at least one conditional instruction was not fulfilled.
13. The device according to claim 11 wherein the speculative execution module is configured to executing a conditional instruction that depends upon an outcome of another conditional instruction that is decoded during the speculation window.
14. The device according to claim 11 wherein speculative execution module is configured to:
execute a first conditional instruction that replaces an old value of a certain register by a new value; and
execute a second conditional instruction that uses the new value of the register if the first and second conditional instructions have the same dependency on the resolution of the compare instruction.
15. The device according to claim 11 wherein the speculative execution module is configured to:
execute a first conditional instruction that replaces an old value of a certain register by a new value; and
execute a second conditional instruction that uses the old value of the register if the first and second conditional instructions have opposing dependencies on the resolution of the compare instruction.
16. The device according to claim 11 comprising multiple speculative execution modules that are configured to execute, in parallel, conditional instructions that have opposing dependencies on the resolution of the compare instruction; and
wherein the device is configured to select, in response to a resolution of the compare instruction, an outcome of one conditional instruction out of the conditional instructions.
17. The device according to claim 11 wherein the speculative execution module is configured to update status data that indicates which registers are affected by the non-conditional instructions and indicates registers that are affected by the conditional instructions.
18. The device according to claim 11 wherein the speculative execution module is configured to forward values of registers affected by the conditional instructions during the speculation window.
19. The device according to claim 11 wherein the device comprises multiple sequences of pipelined stages and at least one speculative execution module for executing very long instruction words.
20. The device according to claim 11 wherein the conditional instructions are selected from a group consisting of load store instructions and pointer arithmetic instructions.