MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0013469CMakeCMakepublic2012-08-14 05:282016-06-10 14:31
ReporterStefan Eilemann 
Assigned ToKitware Robot 
PrioritynormalSeveritymajorReproducibilityalways
StatusclosedResolutionmoved 
PlatformPPC64OSLinuxOS VersionSLES 10 / 2.6.16
Product VersionCMake-2-8 
Target VersionFixed in Version 
Summary0013469: OpenMP flags enable IPA optimization for IBM xlC compiler
DescriptionFindOpenMP sets '-qsmp' which turns on IPA, even in debug builds where it is extremely inconvenient.

Our temporary workaround is to switch it off again: https://github.com/Eyescale/CMake/commit/fbe0c8a87a1ba5fe683beeb697ecebaab26fd730 [^]

I'm new to xlC, but '-qsmp=noomp' looks better?
Steps To ReproduceCompile simple test program in debug with:

  find_package(OpenMP REQUIRED)
  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")


And observer ipa process running, or examine optimized program in debugger.
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Issue History
Date ModifiedUsernameFieldChange
2012-08-14 05:28Stefan EilemannNew Issue
2012-08-14 09:23Brad KingNote Added: 0030635
2012-08-14 09:36Stefan EilemannNote Added: 0030636
2012-08-14 09:37Stefan EilemannNote Edited: 0030636bug_revision_view_page.php?bugnote_id=30636#r772
2012-08-14 09:54Brad KingNote Added: 0030639
2012-08-14 09:57Stefan EilemannNote Added: 0030640
2012-08-14 10:02Stefan EilemannNote Added: 0030641
2012-08-14 10:05Brad KingNote Added: 0030642
2012-08-14 10:05Brad KingStatusnew => backlog
2012-08-14 14:08Stefan EilemannNote Added: 0030648
2012-08-15 04:09Stefan EilemannNote Added: 0030663
2016-06-10 14:28Kitware RobotNote Added: 0042104
2016-06-10 14:28Kitware RobotStatusbacklog => resolved
2016-06-10 14:28Kitware RobotResolutionopen => moved
2016-06-10 14:28Kitware RobotAssigned To => Kitware Robot
2016-06-10 14:31Kitware RobotStatusresolved => closed

Notes
(0030635)
Brad King   
2012-08-14 09:23   
According to the documentation of xlc on AIX the "-qsmp" option does not automatically imply "omp":

$ xlc -qversion
IBM XL C/C++ for AIX, V11.1 (5724-X13)
Version: 11.01.0000.0001
$ xlc
...
 -qsmp[=<suboptions_list>] | -qnosmp
  ...
  omp | noomp
    Enables strict OpenMP compliance. Only OpenMP
    parallelization pragmas are recognized.
    Default: noomp
  ...
  Specifying -qsmp without suboptions is equivalent
  to -qsmp=auto:explicit:opt:noomp:norec_locks:
  nonested_par:schedule=runtime:nostackcheck:threshold=100:ostls
...


What version of the compiler are you using? What do the docs say on the Linux version?
(0030636)
Stefan Eilemann   
2012-08-14 09:36   
(edited on: 2012-08-14 09:37)
IBM XL C/C++ Advanced Edition for Blue Gene/P, V9.0

The docs are the same. I couldn't quite figure out who actually activates ipa. Re-reading it looks like '-qmsp=noomp' would only enable OpenMP?
(0030639)
Brad King   
2012-08-14 09:54   
In release builds folks probably still want "-qsmp".

Can you just add "-qnoipa" when you don't want IPA?
(0030640)
Stefan Eilemann   
2012-08-14 09:57   
No, that didn't work. Same goes for -qnooptimize
(0030641)
Stefan Eilemann   
2012-08-14 10:02   
My feeling is that there is something broken with the way OpenMP is integrated. IPA is supposed only to be enabled by -O4/O5, but with -qsmp I see the xlc frontend running for a running for a reasonable amount of time, and the ipa takes over for a long time. One of our unit test didn't finish compiling within an hour.

If I find the time later to play around with the options, I'll update this ticket. I was hoping somebody else did figure this out already...
(0030642)
Brad King   
2012-08-14 10:05   
I wonder how "-qsmp=noomp" helps. It's already listed as the default in the docs.

Please bring this up with the compiler vendor first to find out the right flags.
(0030648)
Stefan Eilemann   
2012-08-14 14:08   
Yes, noomp is *one* of the default flags. I suspect that another one enables. I'll try to get feedback from IBM, but there is no guarantee this will happen.
(0030663)
Stefan Eilemann   
2012-08-15 04:09   
Ok, after hacking around a bit it seems that OpenMP and debug are mutually exclusive, since I can't figure out how to get OpenMP without ipa. Will try to get info from IBM.
(0042104)
Kitware Robot   
2016-06-10 14:28   
Resolving issue as `moved`.

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