Conditional compare instruction

A data processing apparatus comprising:

• processing means for processing data;
• an instruction decoder means for generating control signals in response to program instructions, said control signals being for controlling said processing means to process said data;
• status storage means for storing a current condition state of said processing means, said current condition state being modifiable during processing of said data;
• wherein said program instructions include a conditional compare instruction, and said instruction decoder means is responsive to said conditional compare instruction to generate control signals for controlling said processing means to perform a conditional compare operation comprising:
• (i) if said current condition state passes a test condition, then performing a compare operation on a first operand and a second operand and setting said current condition state to a result condition state generated during said compare operation;
• and
• (ii) if said current condition state fails said test condition, then setting said current condition state to a fail condition state specified by said conditional compare instruction.

A data processing method comprising the steps of:

• in response to program instructions including a conditional compare instruction, generating control signals for controlling processing circuitry to process data;
• storing a current condition state of said processing circuitry, said current condition state being modifiable during processing of said data;
• in response to said conditional compare instruction, generating control signals for controlling said processing circuitry to perform a conditional compare operation comprising:
• (i) if said current condition state passes a test condition, then performing a compare operation on a first operand and a second operand and setting said current condition state to a result condition state generated during said compare operation;
• and
• (ii) if said current condition state fails said test condition, then setting said current condition state to a fail condition state specified by said conditional compare instruction.

A method of compiling a sequence of program instructions for execution by a data processing apparatus, the sequence of program instructions including an unconditional compare instruction for controlling said data processing apparatus to perform an unconditional compare operation on two operands and set a current condition state of said data processing apparatus to a result condition state generated during said unconditional compare operation, and at least one conditional compare instruction for controlling said data processing apparatus to perform a conditional compare operation comprising:

• (i) if said current condition state of said data processing apparatus passes a test condition, then performing a compare operation on a first operand and a second operand and setting said current condition state to a result condition state generated during said compare operation;
• and (ii) if said current condition state fails said test condition, then setting said current condition state to a fail condition state specified by said conditional compare instruction;
• said method comprising the steps of:
• (a) receiving input of data defining a chained sequence of N comparison operations logically combined using one or more AND or OR operations, where N is an integer greater than 1, each of said N comparison operations testing whether respective operands satisfy a respective predetermined criterion;
• (b) generating a said unconditional compare instruction corresponding to the first comparison operation of said chained sequence;
• (c) for each integer value of i between 2 and N, performing the steps of:
• (i) determining whether an comparison operation of said chained sequence is logically combined with a result of a partial chained sequence using an AND operation or an OR operation, said partial chained sequence comprising the first to (i−1)1 comparison operations of said chained sequence;
• (ii) if said il comparison operation is logically combined with said result of said partial chained sequence using an AND operation, generating a conditional compare instruction corresponding to said i comparison operation, said conditional compare instruction specifying as said test condition a condition which is passed when said predetermined criterion of said (i−1)th comparison operation is satisfied and specifying as said fail condition state a condition state corresponding to said predetermined criterion of said i comparison operation not being satisfied;
• (iii) if said i comparison operation is logically combined with said result of said partial chained sequence using an OR operation, generating a conditional compare instruction corresponding to said comparison operation, said conditional compare instruction specifying as said test condition a condition which is passed when said predetermined criterion of said (i−1)1 comparison operation is not satisfied and specifying as said fail condition state a condition state corresponding to said predetermined criterion of said comparison operation being satisfied;
• (d) outputting at least said unconditional compare instruction generated in step (b) and (N−1) said conditional compare instructions generated in step (c) as said sequence of program instructions.