Add check-3c target with fewer dependencies than check-clang-3c. (#456)

This may significantly speed up the build.

Author: mattmccutchen-cci

clang/test/3C/CMakeLists.txt

@@ -0,0 +1,39 @@
+# Custom `check-3c` target that depends only on the tools used by the 3C
+# regression tests, unlike `check-clang-3c`, which depends on all of
+# CLANG_TEST_DEPS. This may significantly speed up the build.
+
+# If you want to run `lit` yourself, you can use `check-3c-deps` to build the
+# dependencies of the test suite without running it.
+add_custom_target(check-3c-deps
+  DEPENDS
+  # Tools actually used by our RUN lines.
+  3c
+  clang
+  FileCheck
+  # llvm_config.use_default_substitutions() in ../lit.cfg.py refuses to run if
+  # these do not exist.
+  count
+  not
+  # llvm_config.feature_config(...) in ../lit.cfg.py directly runs llvm-config
+  # to gather some information.
+  llvm-config
+  )
+
+# The llvm_config.add_tool_substitutions(...) call in ../lit.cfg.py looks for
+# some additional tools and warns if they don't exist. Currently, we allow these
+# warnings to be printed. If the warnings bother us, we could build the tools;
+# they account for a small fraction of the difference between check-3c-deps and
+# CLANG_TEST_DEPS.
+#
+# Note that lit.local.cfg runs after ../lit.cfg.py and thus cannot remove any of
+# the tool dependencies. We might be able to overcome that by defining our own
+# lit.cfg.py, but that doesn't seem worthwhile since it risks making the
+# configuration of the 3C tests diverge more seriously from that of the other
+# Clang tests, even when the 3C tests are run via check-clang-3c or the like.
+
+add_lit_testsuite(check-3c "Running the 3C regression tests"
+  ${CMAKE_CURRENT_BINARY_DIR}
+  PARAMS ${CLANG_TEST_PARAMS}
+  DEPENDS check-3c-deps
+  ARGS ${CLANG_TEST_EXTRA_ARGS}
+  )

clang/test/CMakeLists.txt

@@ -184,3 +184,7 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/debuginfo-tests)
     add_subdirectory(debuginfo-tests)
   endif()
 endif()
+
+# 3C has its own `check-3c` target that depends only on the tools it needs
+# rather than all of CLANG_TEST_DEPS.
+add_subdirectory(3C)