llvm dev - Jan 2019 - Polybench llvm's IR -fopenmp

Hi all,

I'm trying to get the llvm's IR from the source code of Polybench (OMP)
https://github.com/cavazos-lab/PolyBench-ACC/tree/master/OpenMP.

I noticed a considerable difference between the IR generated using clang
-emit-llvm -fopenmp and clang -emit-llvm:

  *   using the -fopenmp flag I get a simplified IR in which I read a single
basic block where I can highlight a llvm.memcpy function
  *   without -fopenmp flag I get the expected IR in which I find a large number
of basic blocks (e.g. for loop --> for.begin, for.end ...)

Is there a way to avoid the insertion of llvm.memcpy when I'm using the
-fopenmp flag?
I've already tried -fno-builtin and -ffreestanding.

Thanks,
Best Regards,
Stefano Corda
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Detection and insertion of llvm.memcpy is done by the LoopIdiom
("-loop-idiom") pass. Currently, there is no way to disable this pass
in the pipeline other than using -O0, using opt to rebuild the pass
pipeline or editing the LLVM sources.

Michael

Am Sa., 12. Jan. 2019 um 10:23 Uhr schrieb Corda, S. via llvm-dev
<llvm-dev at lists.llvm.org>:
>
> Hi all,
>
> I'm trying to get the llvm's IR from the source code of Polybench
(OMP) https://github.com/cavazos-lab/PolyBench-ACC/tree/master/OpenMP.
>
> I noticed a considerable difference between the IR generated using clang
-emit-llvm -fopenmp and clang -emit-llvm:
>
> using the -fopenmp flag I get a simplified IR in which I read a single
basic block where I can highlight a llvm.memcpy function
> without -fopenmp flag I get the expected IR in which I find a large number
of basic blocks (e.g. for loop --> for.begin, for.end ...)
>
> Is there a way to avoid the insertion of llvm.memcpy when I'm using the
-fopenmp flag?
> I've already tried -fno-builtin and -ffreestanding.
>
> Thanks,
> Best Regards,
> Stefano Corda
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

>>>>> On Sun, 13 Jan 2019 19:07:07 -0600, Michael Kruse via
llvm-dev <llvm-dev at lists.llvm.org> said:
    Michael> Detection and insertion of llvm.memcpy is done by the
    Michael> LoopIdiom ("-loop-idiom") pass. Currently, there is no
way
    Michael> to disable this pass in the pipeline other than using -O0,
    Michael> using opt to rebuild the pass pipeline or editing the LLVM
    Michael> sources.

We had a similar problem in our SYCL compiler so we added a way to skip
the LoopIdiom pass...
https://github.com/triSYCL/triSYCL/blob/master/doc/architecture.rst#host-side-compilation-flow
https://github.com/triSYCL/clang/commit/16c2fc68cc
https://github.com/triSYCL/clang/commit/5508bf637a
-- 
  Ronan KERYELL