Lets try to estimate overhead of JIT compiler
I wrote simple perl script - it just counts redundant bytes for several cases:
- pair mov reg, rbp/add reg, imm (total length 7 bytes) can be replaced with lea reg, [rbp-imm] which is only 4 bytes
- pair mov reg, imm/add reg,imm can be replaced with just loading of right address so second instruction can be removed
- add reg, 1/sub reg, 1 (length 4 bytes) can be replaced to inc/dec reg (which has length 3 bytes)
etc etc
Results
total: 105374 odd 2439 2.3%
other samples shows similar overhead - between 2.3 and 3.4%
of course lots of code like
mov eax, 0x1 cmp r14, 0x2
jnz 0xc05674ab
xor eax, eax
c05674ab:
...
leave
ret
xor eax, eax
cmp r14, 0x2
setnz al
but it matters only in big IP filters
Unfortunately that's not all - we can see lots of repeated code like
mov [r13+0x58], blmov [r13+0x57], bl...
mov [r13+0x39], bl