[compiler-rt] r253483 - [PGO] Runtime support for value profiling.

[Chris Bieneman via llvm-commits]

There is no equivalent to LLVM_HAS_ATOMICS in compiler-rt, and compiler-rt by design has no explicit dependencies on LLVM or Clang, so you can’t just use LLVM_HAS_ATOMICS.

Probably the best thing to do would be to implement a similar check in compiler-rt and populate a variable COMPILER_RT_HAS_ATOMICS.

-Chris

> On Dec 4, 2015, at 1:55 PM, Xinliang David Li <xinliangli at gmail.com> wrote:
> 
> Loop in Chris for advice.
> 
> Chris, I need a way to enable/disable use of atomic operations for profile library build. The cmake currently defines variable LLVM_HAS_ATOMICS which is set via 'CHECK_CXX_SOURCE_COMPILES(..)' call.  Can this variable be used in library CMakeLists file or is it for host compilation only? If not, what is the best alternatives? I am hesitant  to manually check each one of the arch variants ...
> 
> thanks,
> 
> David
> 
> 
> On Thu, Dec 3, 2015 at 3:55 PM, Xinliang David Li <xinliangli at gmail.com <mailto:xinliangli at gmail.com>> wrote:
> I have a pending patch to remove the need for sync_fetch_add operation. After that gets in, I will do more cleanups to make the problem go away.
> 
> David
> 
> 
> On Thu, Dec 3, 2015 at 3:38 PM, Joerg Sonnenberger via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> On Wed, Nov 18, 2015 at 06:12:35PM -0000, Betul Buyukkurt via llvm-commits wrote:
> > Author: betulb
> > Date: Wed Nov 18 12:12:35 2015
> > New Revision: 253483
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=253483&view=rev <http://llvm.org/viewvc/llvm-project?rev=253483&view=rev>
> > Log:
> > [PGO] Runtime support for value profiling.
> >
> > This change adds extends the data structures and adds in the routines
> > for handling runtime calls for value profiling. The profile data format
> > is modified and the version number is incremented.
> 
> This revision has introduced a serious portability regression. Now the
> instruction profiling code requires the present of 64bit atomics, which
> simple don't exist on many platforms.
> 
> Joerg
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