The mesa_vulkan_overlay renders broken font with recent radv-git, 18.3.3 works fine (both build against LLVM 7.0.1). GPU is a RX580. Bisected to:

commit da2959463616756e89cece39f2bae1d437df4bbd
Author: Jason Ekstrand <jason.ekstrand@intel.com>
Date:   Wed Jan 16 11:52:03 2019 -0600

    spirv: Only split blocks
    
    Instead of splitting every per-vertex struct, just split the ones that
    are actually blocks.  The reason for the split is so that we have
    separate variables for separate locations, qualifiers, and builtin
    decorations.  The vulkan spec only allows these on members of blocks.
    
    Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>