[cmake] Add minor version to library SONAME (llvm#79376)

We need to do this now that we are bumping the minor release number when
we create the release branch.

This also results in a slight change to the library names for LLVM. The
main library now has a more convential library name:
'libLLVM.so.$major.$minor'. The old library name: libLLVM-$major.so is
now a symlink that points to the new library. However, the symlink is
not present in the build directory. It is only present in the install
directory.

The library name was changed because it helped to keep the CMake changes
more simple.

Fixes llvm#76273

llvm/CMakeLists.txt

@@ -35,7 +35,7 @@ endif()
 
 if(NOT DEFINED LLVM_SHLIB_SYMBOL_VERSION)
   # "Symbol version prefix for libLLVM.so"
-  set(LLVM_SHLIB_SYMBOL_VERSION "LLVM_${LLVM_VERSION_MAJOR}")
+  set(LLVM_SHLIB_SYMBOL_VERSION "LLVM_${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}")
 endif()
 
 if ((CMAKE_GENERATOR MATCHES "Visual Studio") AND (MSVC_TOOLSET_VERSION LESS 142) AND (CMAKE_GENERATOR_TOOLSET STREQUAL ""))

llvm/cmake/modules/AddLLVM.cmake

@@ -108,7 +108,7 @@ function(add_llvm_symbol_exports target_name export_file)
       COMMAND "${Python3_EXECUTABLE}" "-c"
       "import sys; \
        lines = ['    ' + l.rstrip() for l in sys.stdin] + ['  local: *;']; \
-       print('LLVM_${LLVM_VERSION_MAJOR} {'); \
+       print('LLVM_${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR} {'); \
        print('  global:') if len(lines) > 1 else None; \
        print(';\\n'.join(lines) + '\\n};')"
       < ${export_file} > ${native_export_file}
@@ -646,9 +646,9 @@ function(llvm_add_library name)
     if(UNIX AND NOT APPLE AND NOT ARG_SONAME)
       set_target_properties(${name}
         PROPERTIES
-        # Since 4.0.0, the ABI version is indicated by the major version
-        SOVERSION ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}
-        VERSION ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX})
+        # Since 18.1.0, the ABI version is indicated by the major and minor version.
+        SOVERSION ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}${LLVM_VERSION_SUFFIX}
+        VERSION ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}${LLVM_VERSION_SUFFIX})
     endif()
   endif()
 

llvm/tools/llvm-shlib/CMakeLists.txt

@@ -33,7 +33,10 @@ if(LLVM_BUILD_LLVM_DYLIB)
   if (LLVM_LINK_LLVM_DYLIB)
     set(INSTALL_WITH_TOOLCHAIN INSTALL_WITH_TOOLCHAIN)
   endif()
-  add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB SONAME ${INSTALL_WITH_TOOLCHAIN} ${SOURCES})
+  add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB OUTPUT_NAME LLVM ${INSTALL_WITH_TOOLCHAIN} ${SOURCES})
+  # Add symlink for backwards compatibility with old library name
+  get_target_property(LLVM_DYLIB_FILENAME LLVM OUTPUT_NAME)
+  llvm_install_library_symlink(LLVM-${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX} ${LLVM_DYLIB_FILENAME} SHARED COMPONENT LLVM)
 
   list(REMOVE_DUPLICATES LIB_NAMES)
   if("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")