CMake support RelWithDebInfo build_type that enables upcxx runtime assertions

So on Dan’s advice to build with -g and -O3 I ran into a few snags while attempting to bludgeon CMake to properly do this for which I’ll document my issues and workaround here. I think that supporting this standard-but-mostly-unused RelWithDebInfo CMAKE_BUILD_TYPE is something achievable and relatively easy to do.

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So first off just adding “-g” to a Release build options breaks because upcxx complains that you cannot set -g and -O at the same time without UPCXX_CODEMODE set or adding the -codemode={opt|debug} option. Similarly adding -O3 to a Debug build breaks. Nor is adding either really sustainable because an environmental variable is not necessarily propagated to the subsequent make calls and adding “-codemode=..” to the CMAKE_CXX_FLAGS variable breaks any normal code.

In my (pretty new server Mar 2020) with an arguable old cmake version (3.10) from a not-very old linux install (Ubuntu 18.04.05 LTS), I found that I could not even see UPCXX_OPTIONS to modify it. Nor would setting ENV{UPCXX_CODEMODE} (which is what “share/cmake/UPCXX/UPCXXConfig.cmake” does) hold over to the make step. Note that this does seem to work for cmake > 3.12 though, and that is my temporary workaround (i.e. use a custom build of cmake 3.18 on my dev machine and add “set(ENV{UPCXX_CODEMODE} debug)” in the CMakeLists.txt )

Note, that I also found that in 3.10 the CMAKE_CXX_FLAGS were not set at all in RelWithDebInfo whereas Release and Debug set those flags just fine… I may file a bug with CMake on this because CMAKE_CXX_FLAGS_RELWITHDEBINFO is fully proper.

The upshot is that I believe that including -codemode=debug in the UPCXX_OPTIONS variable is a better solution than setting the ENV{UPCXX_CODEMODE} variable.

So, I think that changing share/cmake/UPCXX/UPCXXConfig.cmake from:

  if ((NOT DEFINED ENV{UPCXX_CODEMODE}) OR ("$ENV{UPCXX_CODEMODE}" STREQUAL "unset"))
    string(TOUPPER "${CMAKE_BUILD_TYPE}" uc_CMAKE_BUILD_TYPE)
    if (uc_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
      set(ENV{UPCXX_CODEMODE} "debug" )
    else()
      set(ENV{UPCXX_CODEMODE} "O3" ) # O3 is compatible with any version
    endif()
    unset(uc_CMAKE_BUILD_TYPE)
  endif()

To this

    string(TOUPPER "${CMAKE_BUILD_TYPE}" uc_CMAKE_BUILD_TYPE)
    if (uc_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
      list(APPEND UPCXX_OPTIONS "-codemode=debug" )
    elseif(uc_CMAKE_BUILD_TYPE STREQUAL "RELWITHDEBINFO")
      list(APPEND UPCXX_OPTIONS "-codemode=debug" )
    else()
      list(APPEND UPCXX_OPTIONS "-codemode=opt" )
    endif()
    unset(uc_CMAKE_BUILD_TYPE)

is all that is needed to make this stick in all CMake versions and enable this standard but new-to-upcxx build_mode.

And for backwards compatibility, this code can be protected with some new upcxx cmake option (with documentation) which one can set before the call to find_package(upcxx)

as motivation for this change here are the timing differences for a toy dataset of mhmxx on my single desktop, and I confirmed that both the Debug and RelWithDebInfo versions throw assertion errors from upcxx.

53.57s  Release (-O3)
77.60s  RelWithDebInfo (-O2 -g)
244.19s Debug (-g)

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