> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of Kirk Wolf > Sent: Wednesday, April 22, 2009 8:44 PM > To: [email protected] > Subject: Re: METAL C: CodeGen defeciency? <Snipped> > Interesting that they didn't use XC, isn't it? If you spend any time > looking at XLC generated code you will see lots of interesting stuff. > Of particular interest is some of the loop unwinding optimizations. > After a while you start to wonder if you should ever write in > assembler again, since only IBM knows what instruction heuristics > slide through the pipelines the best.
It seems to me to be counterproductive of IBM to "hide" (or simply fail to publish) knowledge or advice on effective assembler programming to take advantage of (or at least not to fall afoul of) the pipeline nature of today's z processors. Obviously a thorough reading of the z/Arch PoOP will give an experienced assembler programmer a few "don't do this, it flushes the pipeline" cautions, like the following that I recently ran across while researching something else entirely: In the notes under the Branch on Condition instruction in Chapter 7: "4. Execution of BCR 15,0 (that is, an instruction with a value of 07F0 hex) may result in significant performance degradation. To ensure optimum performance, the program should avoid use of BCR 15,0 except in cases when the serialization or checkpoint-synchronization function is actually required." But let's face it -- how many of us have the time to be "thorough" about reading the PoOP? So, does anyone who regularly reads the IBM Systems Journal or Redbooks/Redpapers or other IBM pubs know of anything that IBM may have published that consolidates and exposes such knowledge? I, for one, would be very happy to reduce my ignorance with a little such light reading. Peter This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
