True about REGION size – the more you give it the faster it will be. Did you run both of those tests using the same REGION value on the same LPAR?
For the new compiler, have the standard library headers all been pre-compiled (suffix “.pch”)? I am told that those make a HUGE difference in C++ compile speeds. Peter From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Allan Staller Sent: Sunday, March 16, 2025 2:33 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Open XL C dramaticallly slower thant z/OS XL C compiler - expected? Classification: Confidential Region. The Optimizer takes a whole lot of virtual storage -----Original Message----- From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Charles Mills Sent: Friday, March 14, 2025 1:39 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Open XL C dramaticallly slower thant z/OS XL C compiler - expected? [CAUTION: This Email is from outside the Organization. Unless you trust the sender, Don’t click links or open attachments as it may be a Phishing email, which can steal your Information and compromise your Computer.] I am trying to get started with the new, "open," Clang-based XLC compiler. I am stunned at how noticeably slower it is than the legacy C compiler. I wasn't looking to benchmark -- the slow compile times just jumped out at me. Is this to be expected? I wish I had numbers for exactly the same source code but there are different userids involved and it's a little complicated. Different options for the two compiles because the option specifications are incompatible. Both modules are fairly vanilla source code written by the same author. Both of the following are on the same machine, the same virtual machine at IBM Dallas. It's a z16 A01. Compile under the legacy XL C compiler, a C++ compile of a 1886-line source module: 4 seconds elapsed, .36 CPU seconds. Compile under Open XL C compiler, a C++ compile of a 415-line source module: 26 seconds elapsed, 1.32 CPU seconds. Is this what others are seeing? Is this to be expected? IS anyone using the new compiler? Charles -- 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 lists...@listserv.ua.edu with the message: INFO IBM-MAIN
