[OpenMP][NFC] lit: Allow setting default environment variables for test

Add CHECK_OPENMP_ENV environment variable which will be passed to environment
variables for test (make check-* target). This provides a handy way to
exercise various openmp code with different settings during development.

For example, to change default barrier pattern:
```
$ env CHECK_OPENMP_ENV="KMP_FORKJOIN_BARRIER_PATTERN=hier,hier \
KMP_PLAIN_BARRIER_PATTERN=hier,hier \
KMP_REDUCTION_BARRIER_PATTERN=hier,hier" \
ninja check-openmp
```

Even with this, each test can set appropriate environment variables if needed
as before.

Also, this commit adds missing documention about how to run tests in README.

Patch provided by t-msn

Differential Revision: https://reviews.llvm.org/D122645

openmp/README.rst

@@ -363,3 +363,35 @@ Advanced Builds with Various Options
 **Footnotes**
 
 .. [*] Other names and brands may be claimed as the property of others.
+
+How to Run Tests
+================
+
+There are following check-* make targets for tests.
+
+- ``check-ompt`` (ompt tests under runtime/test/ompt)
+- ``check-ompt-multiplex`` (ompt multiplex tests under tools/multiplex/tests)
+- ``check-libarcher`` (libarcher tests under tools/archer/tests)
+- ``check-libomp`` (libomp tests under runtime/test. This includes check-ompt tests too)
+- ``check-libomptarget-*`` (libomptarget tests for specific target under libomptarget/test)
+- ``check-libomptarget`` (all check-libomptarget-* tests)
+- ``check-openmp`` (combination of all above tests excluding duplicates)
+
+For example, to run all available tests, use ``make check-openmp``.
+
+Options for Tests
+------------------
+Tests use lit framework.
+See `lit documentation <https://llvm.org/docs/CommandGuide/lit.html>`_ for lit options.
+
+**CHECK_OPENMP_ENV** = ``""``
+  Default environment variables which test process uses for ``check-openmp``
+  separated by space.  This can be used for individual targets (``check-ompt``,
+  ``check-ompt-multiplex``, ``check-libarcher``, ``check-libomp`` and
+  ``check-libomptarget-*``) too.  Note that each test still overrides
+  environment variables if needed.  For example, to change barrier pattern to be
+  used from default hyper barrier to hierarchical barrier, run:
+
+.. code-block:: console
+
+  $ CHECK_OPENMP_ENV="KMP_PLAIN_BARRIER_PATTERN=hier,hier KMP_FORKJOIN_BARRIER_PATTERN=hier,hier KMP_REDUCTION_BARRIER_PATTERN=hier,hier" make check-openmp

openmp/libomptarget/test/lit.cfg

@@ -35,6 +35,14 @@ if 'LIBOMPTARGET_LOCK_MAPPED_HOST_BUFFERS' in os.environ:
 if 'OMP_TARGET_OFFLOAD' in os.environ:
     config.environment['OMP_TARGET_OFFLOAD'] = os.environ['OMP_TARGET_OFFLOAD']
 
+# set default environment variables for test
+if 'CHECK_OPENMP_ENV' in os.environ:
+    test_env = os.environ['CHECK_OPENMP_ENV'].split()
+    for env in test_env:
+        name = env.split('=')[0]
+        value = env.split('=')[1]
+        config.environment[name] = value
+
 def append_dynamic_library_path(name, value, sep):
     if name in config.environment:
         config.environment[name] = value + sep + config.environment[name]

openmp/runtime/test/lit.cfg

@@ -134,6 +134,14 @@ except NotImplementedError:
 if 'INTEL_LICENSE_FILE' in os.environ:
     config.environment['INTEL_LICENSE_FILE'] = os.environ['INTEL_LICENSE_FILE']
 
+# set default environment variables for test
+if 'CHECK_OPENMP_ENV' in os.environ:
+    test_env = os.environ['CHECK_OPENMP_ENV'].split()
+    for env in test_env:
+        name = env.split('=')[0]
+        value = env.split('=')[1]
+        config.environment[name] = value
+
 # substitutions
 config.substitutions.append(("%libomp-compile-and-run", \
     "%libomp-compile && %libomp-run"))

openmp/tools/archer/tests/lit.cfg

@@ -90,6 +90,14 @@ if config.has_tsan == True:
 if 'INTEL_LICENSE_FILE' in os.environ:
     config.environment['INTEL_LICENSE_FILE'] = os.environ['INTEL_LICENSE_FILE']
 
+# set default environment variables for test
+if 'CHECK_OPENMP_ENV' in os.environ:
+    test_env = os.environ['CHECK_OPENMP_ENV'].split()
+    for env in test_env:
+        name = env.split('=')[0]
+        value = env.split('=')[1]
+        config.environment[name] = value
+
 config.environment['ARCHER_OPTIONS'] = "report_data_leak=1"
 
 # Race Tests

openmp/tools/multiplex/tests/lit.cfg

@@ -54,6 +54,14 @@ config.test_flags = " -I " + config.test_source_root + "/.."\
 if 'INTEL_LICENSE_FILE' in os.environ:
     config.environment['INTEL_LICENSE_FILE'] = os.environ['INTEL_LICENSE_FILE']
 
+# set default environment variables for test
+if 'CHECK_OPENMP_ENV' in os.environ:
+    test_env = os.environ['CHECK_OPENMP_ENV'].split()
+    for env in test_env:
+        name = env.split('=')[0]
+        value = env.split('=')[1]
+        config.environment[name] = value
+
 # Allow XFAIL to work
 config.target_triple = [ ]
 for feature in config.test_compiler_features: