Following up on JDK-8374507, I noticed our build footprint is dominated by debug info files (and likely embedded to libjvm.so as well):

$ find build/linux-x86_64-server-fastdebug/ -type f -size +100M -printf "%s %p\n" | sort -n -r
1139416728 build/linux-x86_64-server-fastdebug/images/test/hotspot/gtest/server/libjvm.so
1139416728 build/linux-x86_64-server-fastdebug/hotspot/variant-server/libjvm/gtest/libjvm.so
994724125 build/linux-x86_64-server-fastdebug/support/interim-jmods/java.base.jmod
901019768 build/linux-x86_64-server-fastdebug/support/modules_libs/java.base/server/libjvm.debuginfo
901019768 build/linux-x86_64-server-fastdebug/support/interim-image/lib/server/libjvm.debuginfo
901019768 build/linux-x86_64-server-fastdebug/images/symbols/lib/server/libjvm.debuginfo
901019768 build/linux-x86_64-server-fastdebug/images/jdk/lib/server/libjvm.debuginfo
386479540 build/linux-x86_64-server-fastdebug/images/jmods/java.base.jmod
386479540 build/linux-x86_64-server-fastdebug/images/jdk/jmods/java.base.jmod
160335628 build/linux-x86_64-server-fastdebug/hotspot/variant-server/libjvm/gtest/objs/precompiled/precompiled.hpp.gch
160334141 build/linux-x86_64-server-fastdebug/hotspot/variant-server/libjvm/objs/precompiled/precompiled.hpp.gch
150099701 build/linux-x86_64-server-fastdebug/images/jdk/lib/modules

Now, at least these files are duplicates:

$ sha1sum build/linux-x86_64-server-fastdebug/images/test/hotspot/gtest/server/libjvm.so build/linux-x86_64-server-fastdebug/hotspot/variant-server/libjvm/gtest/libjvm.so
c1187c05479a6535c81bd455c35b18010d80a0a5 build/linux-x86_64-server-fastdebug/images/test/hotspot/gtest/server/libjvm.so
c1187c05479a6535c81bd455c35b18010d80a0a5 build/linux-x86_64-server-fastdebug/hotspot/variant-server/libjvm/gtest/libjvm.so

$ sha1sum build/linux-x86_64-server-fastdebug/support/modules_libs/java.base/server/libjvm.debuginfo build/linux-x86_64-server-fastdebug/support/interim-image/lib/server/libjvm.debuginfo build/linux-x86_64-server-fastdebug/images/symbols/lib/server/libjvm.debuginfo build/linux-x86_64-server-fastdebug/images/jdk/lib/server/libjvm.debuginfo
17fc72ce8a89c2de1fd64f993def4451af2b9c84 build/linux-x86_64-server-fastdebug/support/modules_libs/java.base/server/libjvm.debuginfo
17fc72ce8a89c2de1fd64f993def4451af2b9c84 build/linux-x86_64-server-fastdebug/support/interim-image/lib/server/libjvm.debuginfo
17fc72ce8a89c2de1fd64f993def4451af2b9c84 build/linux-x86_64-server-fastdebug/images/symbols/lib/server/libjvm.debuginfo
17fc72ce8a89c2de1fd64f993def4451af2b9c84 build/linux-x86_64-server-fastdebug/images/jdk/lib/server/libjvm.debuginfo


If we manage to hard-link them instead of copying, we could save about 4G out of 16G of build footprint.