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In a computer instruction set architecture (ISA), an execute instruction is a machine language instruction which treats data as a machine instruction and executes it. It can be considered a fourth mode of instruction sequencing after ordinary sequential execution , branching , and interrupting . [ 1 ]
[a] Branch (or branching, branched) may also refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction. Branch instructions are used to implement control flow in program loops and conditionals (i.e., executing a particular sequence of instructions only if certain conditions are ...
If it is zero, execution continues with the next instruction. One more sequencing option allowed on a branch instruction is the execute (XQ) option. When specified, the single instruction at the branch address is executed, but then execution continues after the original branch instruction. The IX option can be used with the XQ option.
Since the branch itself will generally not be the last instruction in an aligned group, instructions after the taken branch (or its delay slot) will be discarded. Once again, assuming a uniform distribution of branch instruction placements, 0.5, 1.5, and 3.5 instructions fetched are discarded.
Thus, instead of using a conditional branch to select an instruction or a sequence of instructions to execute based on the predicate that controls whether the branch occurs, the instructions to be executed are associated with that predicate, so that they will be executed, or not executed, based on whether that predicate is true or false. [1]
Speculative execution, which allows the execution of complete instructions or parts of instructions before being certain whether this execution should take place. A commonly used form of speculative execution is control flow speculation, where instructions past a control flow instruction (e.g., a branch) are executed before the target of the ...
An indirect branch (also known as a computed jump, indirect jump and register-indirect jump) is a type of program control instruction present in some machine language instruction sets. Rather than specifying the address of the next instruction to execute , as in a direct branch , the argument specifies where the address is located.
branching to an address made up of the base address of the branch table plus the just generated offset. This sometimes involves an addition of the offset onto the program counter register (unless, in some instruction sets, the branch instruction allows an extra index register). This final address usually points to one of a sequence of ...