AI and mainframe assembler

ChatGPT generated this program:

IEFBR14  CSECT ,
         YREGS                          * Define register equates R0–R15
         SR     R15,R15                 * Clear return code (set R15 to 0)
         BR     R14                     * Return to caller
         END

My comments:

• Nitpick: No comma after the YREGS macro

Grok generated this program:

IEFBR14  CSECT ,           Define program control section
         YREGS ,                   Include IBM register equates
* Clear return code by setting R15 to 0
         SR    R15,R15             Subtract R15 from itself to set to 0
* Return to caller using R14 (return address)
         BR    R14                 Branch to return address in R14
         END                      End of program

My comments:

• Readability of the programs suffers because the comments are not lined up

Gemini generated this program:

         YREGS                          * PULL IN REGISTER EQUATES
IEFBR14  CSECT                          * DEFINE A CONTROL SECTION
         SR    R15,R15                  * SET REGISTER 15 TO ZERO (SUCCESSFUL RETURN CODE)
         BR    R14                      * BRANCH TO THE RETURN ADDRESS IN REGISTER 14
         END                            * END OF THE ASSEMBLY

My comments:

• The YREGS macro was put in my prefered location before the CSECT unlike the other chatbots.
• Nitpick: I don't care for the all uppercase comments. 1975 called and they want their all-caps 3278 back.
• Nitpick: No comma after the YREGS macro

A month later the same prompt resulted in the following program after I got a free trial of Gemini 2.5 Pro:

IEFBR14  CSECT ,                 * Start of the control section named IEFBR14.
         USING *,R12             * Establishes R12 as the base register for addressing.
         YREGS                   * Brings in the standard register equates.
         SR    R15,R15           * Sets the return code to 0 by XORing register 15 with itself.
         BR    R14               * Returns control to the calling program by branching to the address in register 14.
         END                     * Marks the end of the assembly program.

My comments:

• "USING *,R12" is incorrect but in this case doesn't result in wrong execution
• Nitpick: No comma after the YREGS macro

Copilot generated this program:

IEFBR14  CSECT 
         YREGS             Define register equates
         SR    R15,R15     Set return code to zero
         BR    R14         Return to caller
         END

My comments:

• Nitpick: No comma after the YREGS macro

Claude generated this program:

IEFBR14  CSECT ,                Program entry point
         YREGS ,                    Include IBM register equates
*
* Simple do-nothing program that sets return code to zero
* and returns to caller
*
         SR    R15,R15              Clear return code register (RC=0)
         BR    R14                  Return to caller
         END

My comments:

• I had heard that Claude was the best for code and this is my favorite one.