clang/cmake: Require pre-built test dependencies for stand-alone builds

[tstellar]

Summary

If the FileCheck, count, and not tools are not found in
LLVM_TOOLS_BINARY_DIR, then tests will be disabled. CMake will
no longer try to build these tool from the llvm sources.

In theory, since stand-alone builds are meant to be done without
access to the llvm sources, this should be a no-op, but this
change will affect anyone trying to do stand-alone builds with
the full monorepo sources.

[mstorsjo]

This does, somewhat, coincide with what I'm trying to do in D131052. There, I don't point out the binaries for FileCheck and similar, but point out preexisting native llvm-tblgen, clang-tblgen etc (to avoid needing to build them in a nested native cmake when cross compiling) - but if they exist, they would probably be in the same directory. Would it make sense to try to settle on a common variable name for both of these? Or is there a case where we specifically need to be able to differentiate between the two?

CC @smeenai

(I haven't gotten around to refreshing that patch yet, unfortunately.)

[mgorny]

Could you issue a warning though? It's really annoying when targets disappear like that and you have to guess which of the checks failed.

[tstellar]

In D137669#3916493, @mgorny wrote:

Could you issue a warning though? It's really annoying when targets disappear like that and you have to guess which of the checks failed.

What about just making it an error if LLVM_INCLUDE_TESTS is set, but it kind find all the tools? I also don't like the silent disabling of features, but I'm not sure how visible the warning would be to users.

[mgorny]

I don't have a strong opinion. I'm happy as long as there is *anything* telling me "tests were disabled because ...".

[mstorsjo]

Also FYI, OpenMP has a bit of prior art in this area - see e.g. https://github.com/llvm/llvm-project/blob/main/openmp/cmake/OpenMPTesting.cmake#L27-L36. There it prints a warning at cmake time, disabling tests, saying why, and giving hints about how to fix it.

[tstellar]

In D137669#3915899, @mstorsjo wrote:

This does, somewhat, coincide with what I'm trying to do in D131052. There, I don't point out the binaries for FileCheck and similar, but point out preexisting native llvm-tblgen, clang-tblgen etc (to avoid needing to build them in a nested native cmake when cross compiling) - but if they exist, they would probably be in the same directory. Would it make sense to try to settle on a common variable name for both of these? Or is there a case where we specifically need to be able to differentiate between the two?

Do you mean creating a common variable name for the path to llvm utils?

[mstorsjo]

In D137669#3920309, @tstellar wrote:

In D137669#3915899, @mstorsjo wrote:

This does, somewhat, coincide with what I'm trying to do in D131052. There, I don't point out the binaries for FileCheck and similar, but point out preexisting native llvm-tblgen, clang-tblgen etc (to avoid needing to build them in a nested native cmake when cross compiling) - but if they exist, they would probably be in the same directory. Would it make sense to try to settle on a common variable name for both of these? Or is there a case where we specifically need to be able to differentiate between the two?

Do you mean creating a common variable name for the path to llvm utils?

Yes, exactly. The use cases are maybe slightly separate, but still, in both cases it'd be a path to a directory containing native versions of not, FileCheck, llvm-tblgen etc.

clang/CMakeLists.txt

if(LLVM_INCLUDE_TESTS)
 
     # Check prebuilt llvm/utils.
     if(EXISTS ${LLVM_TOOLS_BINARY_DIR}/FileCheck${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/count${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/not${CMAKE_EXECUTABLE_SUFFIX})
       set(LLVM_UTILS_PROVIDED ON)
     endif()
 
+    # Seek installed Lit.
+    find_program(LLVM_LIT
+                 NAMES llvm-lit lit.py lit
+                 PATHS "${LLVM_MAIN_SRC_DIR}/utils/lit"
+                 DOC "Path to lit.py")
+
+    if (LLVM_LIT AND LLVM_UTILS_PROVIDED)
       if(EXISTS ${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py)
         # Note: path not really used, except for checking if lit was found
-      set(LLVM_LIT ${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py)
         if(EXISTS ${LLVM_MAIN_SRC_DIR}/utils/llvm-lit)
           add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/llvm-lit utils/llvm-lit)
         endif()
-      if(NOT LLVM_UTILS_PROVIDED)
-        add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/FileCheck utils/FileCheck)
-        add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/count utils/count)
-        add_subdirectory(${LLVM_MAIN_SRC_DIR}/utils/not utils/not)
-        set(LLVM_UTILS_PROVIDED ON)
-        set(CLANG_TEST_DEPS FileCheck count not)
-      endif()
         set(UNITTEST_DIR ${LLVM_MAIN_SRC_DIR}/utils/unittest)
         if(EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h
             AND NOT EXISTS ${LLVM_LIBRARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}gtest${CMAKE_STATIC_LIBRARY_SUFFIX}
             AND EXISTS ${UNITTEST_DIR}/CMakeLists.txt)
           add_subdirectory(${UNITTEST_DIR} utils/unittest)
         endif()
-    else()
-      # Seek installed Lit.
-      find_program(LLVM_LIT
-                   NAMES llvm-lit lit.py lit
-                   PATHS "${LLVM_MAIN_SRC_DIR}/utils/lit"
-                   DOC "Path to lit.py")
       endif()
 
-    if(LLVM_LIT)
       # Define the default arguments to use with 'lit', and an option for the user
       # to override.
       set(LIT_ARGS_DEFAULT "-sv")
       if (MSVC OR XCODE)
         set(LIT_ARGS_DEFAULT "${LIT_ARGS_DEFAULT} --no-progress-bar")
       endif()
       set(LLVM_LIT_ARGS "${LIT_ARGS_DEFAULT}" CACHE STRING "Default options for lit")