[Flang][Test] Add support to change the default target triple for tests

[mnadeem]

Summary

In this patch I added support to change the default target triple used by flang tests using the cmake variable: -DFLANG_TEST_TARGET_TRIPLE="xxx".

The motivation for this is that we build our full toolchain for multiple targets e.g. aarch64, arm32 etc but we set arm32 as the default triple and we want to enable flang build in our CI. Since arm32 has no flang support, a bunch of tests are failing. To enable flang in our CI, changing the flang test triple using -DFLANG_TEST_TARGET_TRIPLE="aarch64-linux-gnu" works in the interim.

Please let me know if something like this has any value to the community.

[DavidTruby]

LGTM, if this supports getting more flang build bots up then I do think it has value
Thanks!

flang/README.md

cmake \
   -DLLVM_LIT_ARGS=-v \
   -DLLVM_ENABLE_PROJECTS="clang;mlir;flang;openmp" \
   -DLLVM_ENABLE_RUNTIMES="compiler-rt" \
   ../llvm-project/llvm
 
 ninja
 ```
 
+By default flang tests that do not specify an explicit `--target` flag use
+LLVM's default target triple. For these tests, if there is a need to test on a
+different triple by overriding the default, the following needs to be added to
+the cmake command above:
+`-DLLVM_TARGET_TRIPLE_ENV="<some string>" -DFLANG_TEST_TARGET_TRIPLE="<your triple>"`.
+
 To run the flang tests on this build, execute the command in the "build"
 directory:
 ```bash
 ninja check-flang
 ```
 
 To create the installed files:
 ```bash

flang/test/CMakeLists.txt

if (FLANG_STANDALONE_BUILD)
   add_lit_testsuites(FLANG ${CMAKE_CURRENT_BINARY_DIR}
     PARAMS ${FLANG_TEST_PARAMS}
     DEPENDS ${FLANG_TEST_DEPENDS})
 else()
   add_lit_testsuites(FLANG ${CMAKE_CURRENT_SOURCE_DIR}
     PARAMS ${FLANG_TEST_PARAMS}
     DEPENDS ${FLANG_TEST_DEPENDS})
 endif()
+
+# To modify the default target triple for flang tests.
+if (DEFINED FLANG_TEST_TARGET_TRIPLE)
+  if (NOT DEFINED LLVM_TARGET_TRIPLE_ENV OR LLVM_TARGET_TRIPLE_ENV STREQUAL "")
+    message(FATAL_ERROR "LLVM_TARGET_TRIPLE_ENV must also be defined in order "
+                        "to use FLANG_TEST_TARGET_TRIPLE.")
+  endif()
+endif()

flang/test/Unit/lit.cfg.py

 config.environment['PATH'] = path
 
 path = os.path.pathsep.join((config.flang_libs_dir, config.llvm_libs_dir,
                               config.environment.get('LD_LIBRARY_PATH','')))
 config.environment['LD_LIBRARY_PATH'] = path
 
 # Propagate PYTHON_EXECUTABLE into the environment
 #config.environment['PYTHON_EXECUTABLE'] = sys.executable
+
+# To modify the default target triple for flang tests.
+if config.flang_test_triple:
+    config.target_triple = config.flang_test_triple
+    config.environment[config.llvm_target_triple_env] = config.flang_test_triple

flang/test/Unit/lit.site.cfg.py.in

 @LIT_SITE_CFG_IN_HEADER@
 
 config.llvm_src_root = "@LLVM_SOURCE_DIR@"
 config.llvm_obj_root = "@LLVM_BINARY_DIR@"
+config.llvm_target_triple_env = "@LLVM_TARGET_TRIPLE_ENV@"
 config.llvm_tools_dir = lit_config.substitute("@LLVM_TOOLS_DIR@")
 config.llvm_libs_dir = lit_config.substitute("@LLVM_LIBS_DIR@")
 config.llvm_build_mode = lit_config.substitute("@LLVM_BUILD_MODE@")
 config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
 config.flang_obj_root = "@FLANG_BINARY_DIR@"
 config.flang_src_root = "@FLANG_SOURCE_DIR@"
 config.flang_libs_dir = "@LLVM_LIBRARY_OUTPUT_INTDIR@"
+config.flang_test_triple = "@FLANG_TEST_TARGET_TRIPLE@"
 config.flang_tools_dir = "@LLVM_RUNTIME_OUTPUT_INTDIR@"
 config.target_triple = "@LLVM_TARGET_TRIPLE@"
 config.python_executable = "@Python3_EXECUTABLE@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@FLANG_SOURCE_DIR@/test/Unit/lit.cfg.py")

flang/test/lit.cfg.py

 llvm_config.feature_config(
     [('--assertion-mode', {'ON': 'asserts'})])
 
 # Targets
 config.targets = frozenset(config.targets_to_build.split())
 for arch in config.targets_to_build.split():
     config.available_features.add(arch.lower() + '-registered-target')
 
+# To modify the default target triple for flang tests.
+if config.flang_test_triple:
+    config.target_triple = config.flang_test_triple
+    config.environment[config.llvm_target_triple_env] = config.flang_test_triple
+
 # excludes: A list of directories to exclude from the testsuite. The 'Inputs'
 # subdirectories contain auxiliary inputs for various tests in their parent
 # directories.
 config.excludes = ['Inputs', 'CMakeLists.txt', 'README.txt', 'LICENSE.txt']
 
 # If the flang examples are built, add examples to the config
 if config.flang_examples:
     config.available_features.add('examples')

flang/test/lit.site.cfg.py.in

 @LIT_SITE_CFG_IN_HEADER@
 
 import sys
 
 config.llvm_tools_dir = lit_config.substitute("@LLVM_TOOLS_DIR@")
 config.llvm_shlib_dir = lit_config.substitute(path(r"@SHLIBDIR@"))
 config.llvm_plugin_ext = "@LLVM_PLUGIN_EXT@"
+config.llvm_target_triple_env = "@LLVM_TARGET_TRIPLE_ENV@"
 config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
 config.errc_messages = "@LLVM_LIT_ERRC_MESSAGES@"
 config.flang_obj_root = "@FLANG_BINARY_DIR@"
 config.flang_src_dir = "@FLANG_SOURCE_DIR@"
 config.flang_tools_dir = lit_config.substitute("@FLANG_TOOLS_DIR@")
 config.flang_intrinsic_modules_dir = "@FLANG_INTRINSIC_MODULES_DIR@"
 config.flang_llvm_tools_dir = "@CMAKE_BINARY_DIR@/bin"
 config.flang_lib_dir = "@CMAKE_BINARY_DIR@/lib"
+config.flang_test_triple = "@FLANG_TEST_TARGET_TRIPLE@"
 config.flang_examples = @FLANG_BUILD_EXAMPLES@
 config.python_executable = "@PYTHON_EXECUTABLE@"
 config.flang_standalone_build = @FLANG_STANDALONE_BUILD@
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
 config.linked_bye_extension = @LLVM_BYE_LINK_INTO_TOOLS@
 config.cc = "@CMAKE_C_COMPILER@"
 config.targets_to_build = "@TARGETS_TO_BUILD@"
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@FLANG_SOURCE_DIR@/test/lit.cfg.py")