I noticed in disassembly for G1 barriers that we have are missing a few easy things for code density in our hand-written assembly for G1 barriers:
 *) cmpptr(reg, 0) -> testptr(reg, reg)
 *) jcc -> jccb for forward branches, where obvious
 *) jmp -> jmpb for forward jumps, where obvious

A simple patch already gives me about 1.2% savings even without compiling a lot of code.

for I in `seq 1 3`; do build/linux-x86_64-server-release/images/jdk/bin/java -Xcomp -XX:+CITime 2>&1 | grep "nmethod code"; done

# Before
  nmethod code size : 5764304 bytes
  nmethod code size : 5764336 bytes
  nmethod code size : 5764480 bytes

# After
  nmethod code size : 5691032 bytes
  nmethod code size : 5691032 bytes
  nmethod code size : 5691000 bytes