[CodeGen] LLVM OpenMP Backend.

The ParallelLoopGenerator class is changed such that GNU OpenMP specific
code was removed, allowing to use it as super class in a
template-pattern. Therefore, the code has been reorganized and one may
not use the ParallelLoopGenerator directly anymore, instead specific
implementations have to be provided. These implementations contain the
library-specific code. As such, the "GOMP" (code completely taken from
the existing backend) and "KMP" variant were created.

For "check-polly" all tests that involved "GOMP": equivalents were added
that test the new functionalities, like static scheduling and different
chunk sizes. "docs/UsingPollyWithClang.rst" shows how the alternative
backend may be used.

Patch by Michael Halkenhäuser <michaelhalk@web.de>

Differential Revision: https://reviews.llvm.org/D59100

llvm-svn: 356434

1 files changed, 32 insertions, 0 deletions

diff --git a/polly/docs/UsingPollyWithClang.rst b/polly/docs/UsingPollyWithClang.rst
index 3198a417caa..b6f370502f6 100644
--- a/polly/docs/UsingPollyWithClang.rst
+++ b/polly/docs/UsingPollyWithClang.rst
@@ -37,6 +37,38 @@ also need to add -mllvm -polly-parallel -lgomp to your CFLAGS.
 
   clang -O3 -mllvm -polly -mllvm -polly-parallel -lgomp file.c
 
+Switching the OpenMP backend
+----------------------------
+
+The following CL switch allows to choose Polly's OpenMP-backend:
+
+       -polly-omp-backend[=BACKEND]
+              choose the OpenMP backend; BACKEND can be 'GNU' (the default) or 'LLVM';
+
+The OpenMP backends can be further influenced using the following CL switches:
+
+
+       -polly-num-threads[=NUM]
+              set the number of threads to use; NUM may be any positive integer (default: 0, which equals automatic/OMP runtime);
+
+       -polly-scheduling[=SCHED]
+              set the OpenMP scheduling type; SCHED can be 'static', 'dynamic', 'guided' or 'runtime' (the default);
+
+       -polly-scheduling-chunksize[=CHUNK]
+              set the chunksize (for the selected scheduling type); CHUNK may be any strictly positive integer (otherwise it will default to 1);
+
+Note that at the time of writing, the GNU backend may only use the
+`polly-num-threads` and `polly-scheduling` switches, where the latter also has
+to be set to "runtime".
+
+Example: Use alternative backend with dynamic scheduling, four threads and
+chunksize of one (additional switches).
+
+.. code-block:: console
+
+  -mllvm -polly-omp-backend=LLVM -mllvm -polly-num-threads=4
+  -mllvm -polly-scheduling=dynamic -mllvm -polly-scheduling-chunksize=1
+
 Automatic Vector code generation
 ================================