WM_NCOMPPROCS and full optimization

From OpenFOAMWiki

The problem is in my opinion not that CLang is that bad. On the contrary: I think the problem is that it tries to optimize the output of bison when other compilers don't. At least in the past a sure-fire way to get your code NOT (or only superficially) optimized was to add goto to it. Most optimization algorithms assume that there is only one way to enter a code block and if you use goto you break that promise and most compilers say "OK. I will not even try to optimize this garbage". The bison/flex code contains quite a number of AND the source files generated are quite large. CLang seems to try to optimize them with O3. The memory usage seems to vary for different versions of CLang. Ah. And by the way: the error messages of CLange are MUCH more readable than the stuff g++ prints

Bgschaid (talk)12:57, 6 October 2013

You do not have permission to edit this page, for the following reasons:

  • The action you have requested is limited to users in the group: Users.
  • You must confirm your email address before editing pages. Please set and validate your email address through your user preferences.
  • Your username or IP address has been blocked. The block was made by DNSBL. The reason given is Your IP address is listed as an open proxy in the DNSBL used by OpenFOAMWiki..
    • Start of block: 22:08, 17 May 2021
    • Expiry of block: 22:08, 17 May 2021
    • Intended blockee:
    You can contact DNSBL or another administrator to discuss the block. You cannot use the "email this user" feature unless a valid email address is specified in your account preferences and you have not been blocked from using it. Your current IP address is, and the block ID is #. Please include all above details in any queries you make.

You can view and copy the source of this page:

Return to Thread:Talk:Contrib/swak4Foam/WM NCOMPPROCS and full optimization/reply (3).

The problem is that optimizing the parser for swak is futile: the time spent doing the actual parsing is small compard to the actual "OF-work": calculations on the fields. That's why I added the special optimiziation switch for the parsers.

PS: and this "tries to optimize goto-stained code" is only a theory (I haven't looked at the source. But its behaviour - certain CLang versions freeze a 8 Gig machine when compiling FieldParser with O3 - make me pretty sure that this is the case)

Bgschaid (talk)14:11, 6 October 2013