[LLVM][CMake] Build examples for llvm-test-depends

Build examples and example plug-ins by default when running tests. If
examples are unwanted, they can still be disabled completely using
LLVM_INCLUDE_EXAMPLES=OFF. Plugin tests depend on examples and it is
beneficial to test them by default. By default, Examples will still not
be included in the default target or be installed, this remains
controlled by LLVM_BUILD_EXAMPLES (which defaults to OFF).

The additional cost for building examples for tests is 17 compilation
units (12 C++, 5 C), which should be tolerable.

I don't know how broken the examples currently are in the various build
configurations, but if we find breakage, it would be good to fix it.

Pull Request: #171998

Author: aengelke

llvm/docs/CMake.rst

@@ -366,9 +366,10 @@ its enabled sub-projects. Nearly all of these variable names begin with
   ``LLVM_ENABLE_SPHINX`` and ``LLVM_ENABLE_DOXYGEN``.
 
 **LLVM_BUILD_EXAMPLES**:BOOL
-  Build LLVM examples. Defaults to OFF. Targets for building each example are
-  generated in any case. See documentation for *LLVM_BUILD_TOOLS* above for more
-  details.
+  Include LLVM examples in the 'all' build target and install them as part of
+  the ``install`` target. Defaults to OFF. Targets for building examples are
+  still generated, this is controlled by *LLVM_INCLUDE_EXAMPLES*. Note that some
+  examples might still be built as dependencies for tests.
 
 **LLVM_BUILD_INSTRUMENTED_COVERAGE**:BOOL
   If enabled, `source-based code coverage

llvm/test/CMakeLists.txt

@@ -13,7 +13,7 @@ llvm_canonicalize_cmake_booleans(
   LLVM_LINK_LLVM_DYLIB
   LLVM_TOOL_LTO_BUILD
   LLVM_USE_INTEL_JITEVENTS
-  LLVM_BUILD_EXAMPLES
+  LLVM_INCLUDE_EXAMPLES
   LLVM_ENABLE_PLUGINS
   LLVM_BYE_LINK_INTO_TOOLS
   LLVM_EXAMPLEIRTRANSFORMS_LINK_INTO_TOOLS
@@ -186,7 +186,7 @@ if (TARGET llvm-mt)
   list(APPEND LLVM_TEST_DEPENDS llvm-mt)
 endif ()
 
-if(LLVM_BUILD_EXAMPLES)
+if(LLVM_INCLUDE_EXAMPLES)
   list(APPEND LLVM_TEST_DEPENDS
     Kaleidoscope-Ch3
     Kaleidoscope-Ch4

llvm/test/Examples/lit.local.cfg

@@ -1,4 +1,4 @@
-if not config.build_examples or sys.platform in ["win32"]:
+if not config.include_examples or sys.platform in ["win32"]:
     config.unsupported = True
 
 # Test discovery should ignore subdirectories that contain test inputs.

llvm/test/lit.cfg.py

@@ -511,7 +511,7 @@ def enable_ptxas(ptxas_executable):
 if config.has_plugins:
     config.available_features.add("plugins")
 
-if config.build_examples:
+if config.include_examples:
     config.available_features.add("examples")
 
 if config.linked_bye_extension:

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

@@ -40,7 +40,7 @@ config.have_curl = @LLVM_ENABLE_CURL@
 config.have_httplib = @LLVM_ENABLE_HTTPLIB@
 config.have_dia_sdk = @LLVM_ENABLE_DIA_SDK@
 config.enable_ffi = @LLVM_ENABLE_FFI@
-config.build_examples = @LLVM_BUILD_EXAMPLES@
+config.include_examples = @LLVM_INCLUDE_EXAMPLES@
 config.enable_backtrace = @ENABLE_BACKTRACES@
 config.enable_threads = @LLVM_ENABLE_THREADS@
 config.build_shared_libs = @BUILD_SHARED_LIBS@