• Debarshi Ray's avatar
    build: Restore optimized builds by default · cfc3985f
    Debarshi Ray authored
    Building with AX_CHECK_ENABLE_DEBUG([yes]), which is what happens by
    default for non-release builds, turns off compiler optimizations and
    overrides any optimization specified via CFLAGS in the build
    environment. This means that the nightly Flatpaks, and almost all
    other non-release builds, are built without any optimization. It's
    very likely that this has a negative impact on the image processing
    loops in the built-in GeglOperations.
    It can be useful to turn off compiler optimizations to get a better
    debugging experience, but it becomes a problem if it stomps over the
    build environment while doing so. The person doing the builds should
    should get to decide between ease of debugging and reasonable
    performance. After all, debugging is not the only thing that a
    developer does. Performance measurements are important too, and one can
    use GDB reasonably well with the Autoconf default, which also happens
    to be what most distributions use, of "-g O2".
    This wouldn't have been such a problem if AX_CHECK_ENABLE_DEBUG
    attached its flags before the values from the environment instead of
    after, because in case of multiple -O options, the last such option is
    the one that's effective.
    Thankfully, "no" doesn't override the environment, which is what
    happens for release builds, and distributions generally set their own
    CFLAGS. Otherwise every single user-facing build would have been
    broken. Note that any release build without CFLAGS set in the
    environment would neither get debug symbols (ie., no "-g") nor any
    compiler optimization because AX_CHECK_ENABLE_DEBUG always suppresses
    the Autoconf defaults of "-g -O2".
    One solution could have been to default to "info" for non-release
    builds and recommend the use of --enable-debug=info while building from
    Git, but that would not address release builds without CFLAGS.
    Given that the only other thing the macro does is to define the NDEBUG
    pre-processor macro when debugging is set to "no", which isn't widely
    used in the GLib-based GNOME platform [1], it seems better to just
    remove it altogether.
    Interestingly, this also seems to unmask some valid cases of
    -Wclobbered and -Wmaybe-uninitialized with Fedora's
    gcc-7.3.1-6.fc27.x86_64 build.
    Fallout from 8f6fb686. The deprecated
    GNOME_DEBUG_CHECK macro didn't set any debugging or optimization flags.
    [1] glib/gio/xdgmime is the only widely used code path where assert(3)
        is used. It's also used in gio/kqueue/dep-list.c, which is
        *BSD-specific and in GTK+'s Broadway backend. All those can
        probably be replaced with g_assert*.
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