Branching in a computer system

A method of executing instructions in a computer system predicated on guard indicators included in the instructions, the instructions including normal instructions which are executed the guard indicator is true and branch instructions which are executed if the guard indicator is false, the method comprising:

• supplying instructions to at least one execution unit;
• detecting a branch instruction and, responsive to such detection, holding the guard indicator of the branch instruction and setting a branch shadow mode;
• in the branch shadow mode, comparing the guard indicator of the branch instructions with the guard indicator included in subsequent instructions and continuing to supply instructions if the guard indicators match, and preventing the supply of instructions if the guard indicators do not match;
• and
• disabling the branch shadow mode when the branch instruction has been determined such that the branch is taken or not by resolving the status of the guard indicator.

A computer system for executing instructions predicated on guard indicators included in the instructions, the instructions including normal instructions which are executed if the guard indicator is true and branch instructions which are executed if the guard indicator is false, the computer system comprising:

• instruction supply circuitry;
• at least one execution unit for receiving instructions from the supply circuitry:
• branch detection circuitry for detecting a branch instruction, for holding the guard indicator of the branch instruction and for setting a branch shadow mode;
• a comparer operable in the branch shadow mode for comparing the guard indicator of the branch instruction with the guard indicator included in subsequent instructions and for continuing to supply instructions if the guard indicators match and for preventing supply of instructions if the guard indicators do not match;
• and
• a disabler for disabling the branch shadow mode when the branch instruction has been determined such that the branch is taken or not by resolving the status of the guard indicator.