[llvm-bugs] [Bug 51095] New: Variable not globalized on the device when nested inside parallel region.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51095

            Bug ID: 51095
           Summary: Variable not globalized on the device when nested
                    inside parallel region.
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: OpenMP
          Assignee: a.bataev at hotmail.com
          Reporter: huberjn at ornl.gov
                CC: jdoerfert at anl.gov, llvm-bugs at lists.llvm.org

In this example (https://godbolt.org/z/W4WMPr5xq) the variable `x` is shared
between all the threads by writing its pointer to a global value that is read
by all the threads. This should be legal according to OpenMP, but when the
variable is placed directly inside the parallel region, rather than inside of a
function that's called in parallel, it will not be globalized. When I compile
and the first version on my nvptx64 machine I get the following:

$ clang++ version1.cpp -fopenmp-targets=nvptx64 -fopenmp
$ ./a.out

Thread 0: 1
Thread 1: 1
Thread 2: 1
...
Thread 125: 1
Thread 126: 1
Thread 127: 1

The second version where `x` is directly in the parallel region gives me this:

$ clang++ version1.cpp -fopenmp-targets=nvptx64 -fopenmp
$ ./a.out

Thread 0: 0
Thread 1: 1
Thread 2: 2
...
Thread 125: 125
Thread 126: 126
Thread 127: 127

A call to `__kmpc_alloc_shared` is not inserted for the variable `x` in the
second version, leading to the value not being sharable between the threads.

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