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Status Not under consideration
Workspace PL/I Compilers
Created by Guest
Created on Feb 16, 2015

RELATED IDEAS

EPLI V4.3 generated code compares badly to OS PL/I V2.3 generated code

In a very grey past, I was taught that the best way to initialize an array of structures was to use either

array_of_struc(1) = '';
array_of_struct(*) = array_of_struct(1);

or, if this initialisation had to be done multiple times, to create a STATIC copy of "struct" with all fields initialised and perform the initialisation by

array_of_struct(*) = static_init_copy_of_struct(1);

Idea priority High
  • Guest
    Reply
    |     Sep 14, 2015

    Due to processing by IBM, this request was reassigned to have the following updated attributes:
    Brand - Servers and Systems Software
    Product family - Programming Languages
    Product - PL/I Compilers

    For recording keeping, the previous attributes were:
    Brand - Rational
    Product family - Design & development
    Product - PL/I Compilers

  • Guest
    Reply
    |     Mar 27, 2015

    We did some testing to compare the old and new code, and the new code actually runs faster on current hardware (which doesn't like MVC instructions where the source and target overlap). So, we will not be changing the compiler for this

  • Guest
    Reply
    |     Mar 3, 2015

    I apologize for the description, if it is possible to change the one-line description into "Some EPLI V4.3 generated code compares badly to OS PL/I V2.3 generated code" (i.e. add Some), I would not mind, but I can no longer do this myself.

    The comment that "although it is possible only on z" is somewhat mysterious, as the x86 architecture would allow such initialisations to be done using REP MOVS(B/W/D), which is very fast on the latest AMD and Intel CPU's.

    For what it's worth, given that Enterprise PL/I is, correct me if I'm wrong, a direct descendant of Visual Age PL/I, which was developed for OS/2 on Intel, it seems that some types of code-generation constructions were copied somewhat indiscriminately from the severely register-constrained code generator in the VA compiler, and some of the code generated by that compiler is, to express myself rather politely, not optimal.

  • Guest
    Reply
    |     Mar 3, 2015

    This is indeed an optimization and will be considered although it is possible only on z. However, the brief one-line description of this RFE is misleading as it implies that the performance of the code generated by the new compiler is overall worse than that from the old compiler. That is not the case from the measurements we have or from measurements reported by customers at public user conferences.

  • Guest
    Reply
    |     Feb 24, 2015

    Hi
    Multiple use of MVC is better than one MVC in a loop.

    But, alot of the (new) instructions are immediate and Register only so they use about a bit more than nothing of the CPU, while a MVC is using Memory access (slow).

    I actualy say to our customers to use a STATIC initialized copy of the structure and use PLIMOVE to initialize the normal (AUTOMATIC) structure.

    Also, our customers are not allowed to initialize arrays, they have to set an indicator to 0 and the program has to be designed to use that indicator.

    This is because we sometime have arrays (and structures with arrays) of about 20 or more Megabytes and we get in performance Problems if they are always initialized (in any way); at least in transactional programms (IMS/CICS).

    So, i don't know if the extra code from the newer compiler is really be less performant. Maybe related to the complexity of the structure.

    Patrick

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