[LLVMdev] llvm and openmp

[Duncan Sands]

Hi Karthik,

> I am new to llvm. Does llvm has support for openmp directives like #pragma
> openmp threadprivate(var)?

LLVM has no special support for openmp.  The LLVM front-ends that support
openmp, namely llvm-gcc and dragonegg, lower openmp constructs down to
library calls the same way GCC does.  This is no coincidence: both of those
front-ends are based on GCC and just let the GCC machinery take care of openmp.
The clang front-end does not support openmp.

  If so does the variable 'var' can be class objects
> instead of Plain Old Datatypes (POD) like int, float etc. g++ allows the #pragma
> openmp threadprivate(var) primitive only for the POD type. Please check the bug
> link at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27557 . Please let me know.

You are out of luck: if GCC rejects this then so will llvm-gcc and dragonegg.
That said, the GCC Ada front-end does support thread-local storage non-POD
types, so it can be done - but it jumps through a lot of hoops and the result
is not very efficient.  There's a big comment in gcc/ada/a-tasatt.adb explaining
how it is done and why that scheme was chosen.  You may enjoy these lines from
the start of the comment:

   The following notes are provided in case someone decides the implementation
   of this package is too complicated, or too slow. Please read this before
   making any "simplifications".

Ciao, Duncan.