Make sure z3 can be disabled from outside, even if detected on the system.

[LocutusOfBorg]

Summary

This fix build failures e.g. in Ubuntu, where z3 is disabled, but we don't want support for it because z3 is not in main archive

[LocutusOfBorg]

hello, ping?

[lebedev.ri]

Makes sense to me.

[mgorny]

Are you sure about this? FWIU right now the default is to "use Z3 if available". If I read the patch right, it will be "default to requiring Z3, unless explicitly disabled". Not that I mind but I suppose it's a semantic change.

[mikhail.ramalho]

I'm not cmake expert but does

option(LLVM_ENABLE_Z3_SOLVER
  "Enable Support for the Z3 constraint solver in LLVM."
  ON
)

means that it's enabled by default?

If so, I'd suggest making it disabled by default.

[LocutusOfBorg]

thanks for merging! looks done in fb34345e363ae00e6a2f7979ef524f4a4ffae582

llvm/CMakeLists.txt

 option(LLVM_ENABLE_LIBPFM "Use libpfm for performance counters if available." ON)
 
 option(LLVM_ENABLE_THREADS "Use threads if available." ON)
 
 set(LLVM_ENABLE_ZLIB "ON" CACHE STRING "Use zlib for compression/decompression if available. Can be ON, OFF, or FORCE_ON")
 
 set(LLVM_Z3_INSTALL_DIR "" CACHE STRING "Install directory of the Z3 solver.")
 
+option(LLVM_ENABLE_Z3_SOLVER
+  "Enable Support for the Z3 constraint solver in LLVM."
+  ON
+)
+
+if (LLVM_ENABLE_Z3_SOLVER)
   find_package(Z3 4.7.1)
 
   if (LLVM_Z3_INSTALL_DIR)
     if (NOT Z3_FOUND)
       message(FATAL_ERROR "Z3 >= 4.7.1 has not been found in LLVM_Z3_INSTALL_DIR: ${LLVM_Z3_INSTALL_DIR}.")
     endif()
-endif()
-
-set(LLVM_ENABLE_Z3_SOLVER_DEFAULT "${Z3_FOUND}")
-
-option(LLVM_ENABLE_Z3_SOLVER
-  "Enable Support for the Z3 constraint solver in LLVM."
-  ${LLVM_ENABLE_Z3_SOLVER_DEFAULT}
-)
-
-if (LLVM_ENABLE_Z3_SOLVER)
+  else()
     if (NOT Z3_FOUND)
       message(FATAL_ERROR "LLVM_ENABLE_Z3_SOLVER cannot be enabled when Z3 is not available.")
     endif()
+  endif()
 
   set(LLVM_WITH_Z3 1)
 endif()
 
 if( LLVM_TARGETS_TO_BUILD STREQUAL "all" )
   set( LLVM_TARGETS_TO_BUILD ${LLVM_ALL_TARGETS} )
 endif()