[lldb] Add LTO dependency to lldb test suite

[augusto2112]

Summary

Make the lldb test target depend on LTO, since TestFullLtoStepping
needs it.

[DavidSpickett]

If you don't have LTO, does this mean that only that one test won't run, or will the whole suite not run?

Perhaps I misunderstand the purpose of add_lldb_test_dependency.

[augusto2112]

@DavidSpickett right now if you don't have LTO the test will run but fail.

[DavidSpickett]

Sorry I should have been specific. With this change applied, when you don't have LTO, we'll just skip the individual test, or we'll not do testing at all?

Wondering if this is an all or nothing situation, which would be unfortunate for a single test.

[aprantl]

@DavidSpickett Is it possible to configure LLVM to not build with libLTO? Which CMake flag controls this?

[DavidSpickett]

Well that was my confusion, no there isn't an option. So how does one end up with a build that doesn't include it. Perhaps a standalone build of lldb, built with a prebuilt llvm that didn't package libLTO?

Which sounds perfectly legitimate and the test should be skipped. I'd just like to see whatever the use case is added to the commit message.

[aprantl]

Well that was my confusion, no there isn't an option. So how does one end up with a build that doesn't include it. Perhaps a standalone build of lldb, built with a prebuilt llvm that didn't package libLTO?

This is just about adding a dependency between lldb-test-deps and libLTO. If you just run ninja check-lldb prior to this patch libLTO would not be built. Now it is. This is not about a build setting, just about a build dependency. Without this dependency why would we expect libLTO get built?

[DavidSpickett]

If you just run ninja check-lldb prior to this patch libLTO would not be built.

Great, put that in the commit message.

What I was trying to get at was the meaning of depends on:

• depends on thing, so we should build the thing
• depends on thing, so we shouldn't run the test if thing isn't present

And confirm that the former was your intent, but we do a lot of the latter elsewhere.

[augusto2112]

@DavidSpickett thanks for the review, I've updated the commit message to be clearer.

lldb/test/CMakeLists.txt

if(NOT LLDB_BUILT_STANDALONE)
   )
 endif()
 
 # Add dependencies if we test with the in-tree clang.
 # This works with standalone builds as they import the clang target.
 if(TARGET clang)
   add_lldb_test_dependency(clang)
 
+  # TestFullLtoStepping depends on LTO, and only runs when the compiler is clang.
+  add_lldb_test_dependency(LTO)
+
   if (TARGET libcxx OR ("libcxx" IN_LIST LLVM_ENABLE_RUNTIMES))
     set(LLDB_HAS_LIBCXX ON)
     if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
       set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE})
       set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
       set(LIBCXX_GENERATED_INCLUDE_TARGET_DIR "${LLVM_BINARY_DIR}/include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1")
     else()
       set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})