[CMake] Fix build with -DLLVM_TOOL_LLVM_{MCA/EXEGESIS}_BUILD=OFF

[arichardson]

Summary

I have been trying to reduce our Jenkins build times by not building tools
that aren't used in dependent jobs and noticed that not building llvm-mca
or llvm-exegesis broke the CMake configure for tests.

llvm-mca and llvm-exegesis seem to be the only tools worth disabling to
save build time since they contain more than just a couple of source files
and are not needed for any of the other tests.

[michaelplatings]

Out of interest, how are you disabling tools?

Just an idea, but how about making all the targets optional? It's less code and gives you more flexibility should you wish to disable more of them in future.

set(LLVM_TEST_DEPENDS_CANDIDATES
          BugpointPasses
[...]
          yaml2obj
        )

foreach(candidate ${LLVM_TEST_DEPENDS_CANDIDATES})
  if(TARGET ${candidate})
    list(APPEND LLVM_TEST_DEPENDS ${candidate})
  endif()
endforeach()

[beanz]

How are you instructing lit to not run the tests that rely on these tools? Doesn't seem like you are, so I would expect check-llvm to fail on a clean build configuration due to missing tools.

test/CMakeLists.txt

set(LLVM_TEST_DEPENDS
           llvm-cxxfilt
           llvm-cxxmap
           llvm-diff
           llvm-dis
           llvm-dlltool
           dsymutil
           llvm-dwarfdump
           llvm-dwp
-          llvm-exegesis
           llvm-extract
           llvm-isel-fuzzer
           llvm-lib
           llvm-link
           llvm-lto2
           llvm-mc
-          llvm-mca
           llvm-modextract
           llvm-mt
           llvm-nm
           llvm-objcopy
           llvm-objdump
           llvm-opt-fuzzer
           llvm-opt-report
           llvm-pdbutil
set(LLVM_TEST_DEPENDS
           opt
           sancov
           sanstats
           verify-uselistorder
           yaml-bench
           yaml2obj
         )
 
+if(TARGET llvm-mca)
+  list(APPEND LLVM_TEST_DEPENDS llvm-mca)
+endif()
+if(TARGET llvm-exegesis)
+  list(APPEND LLVM_TEST_DEPENDS llvm-exegesis)
+endif()
 if(TARGET llvm-lto)
-  set(LLVM_TEST_DEPENDS ${LLVM_TEST_DEPENDS} llvm-lto)
+  list(APPEND LLVM_TEST_DEPENDS llvm-lto)
 endif()
 
 # If Intel JIT events are supported, depend on a tool that tests the listener.
 if( LLVM_USE_INTEL_JITEVENTS )
   set(LLVM_TEST_DEPENDS ${LLVM_TEST_DEPENDS} llvm-jitlistener)
 endif( LLVM_USE_INTEL_JITEVENTS )
 
 if(TARGET LLVMgold)

unittests/tools/CMakeLists.txt

 if(LLVM_TARGETS_TO_BUILD MATCHES "X86")
   add_subdirectory(
     llvm-cfi-verify
   )
 endif()
 
-add_subdirectory(
-  llvm-exegesis
-)
+if(TARGET llvm-exegesis)
+  add_subdirectory(llvm-exegesis)
+endif()