There is no even simple peephole optimizations in LuaJIT

check.disasm

01:20 $ luajit -jdump -O3 -Ohotloop=9 -Ocse -Ofold ../days_ffi.lua 
---- TRACE 1 start days_ffi.lua:14
0015  MOV      9   3
0016  MOV     10   2
0017  CALL     9   2   2
0000  . FUNCF    3          ; days_ffi.lua:9
0001  . GGET     1   0      ; "tonumber"
0002  . TGETS    2   0   1  ; "secs"
0003  . CALL     1   2   2
0000  . . FUNCC               ; tonumber
0004  . TGETS    2   0   2  ; "nsec"
0005  . DIVVN    2   2   0  ; 1000000000
0006  . ADDVV    1   1   2
0007  . DIVVN    1   1   1  ; 3600
0008  . DIVVN    1   1   2  ; 24
0009  . RET1     1   2
0018  MOV      4   9
0019  FORL     5 => 0015
---- TRACE 1 IR
0001    int SLOAD  #6    CI
0002 >  fun SLOAD  #4    T
0003 >  tab SLOAD  #3    T
0004 >  fun EQ     0002  days_ffi.lua:9
0005    tab FLOAD  days_ffi.lua:9  func.env
0006    int FLOAD  0005  tab.hmask
0007 >  int EQ     0006  +63 
0008    p32 FLOAD  0005  tab.node
0009 >  p32 HREFK  0008  "tonumber" @8
0010 >  fun HLOAD  0009
0011    int FLOAD  0003  tab.hmask
0012 >  int EQ     0011  +1  
0013    p32 FLOAD  0003  tab.node
0014 >  p32 HREFK  0013  "secs" @0
0015 >  num HLOAD  0014
0016 >  fun EQ     0010  tonumber
0017 >  p32 HREFK  0013  "nsec" @1
0018 >  num HLOAD  0017
0019    num DIV    0018  +1000000000
0020    num ADD    0019  0015
0021    num DIV    0020  +3600
0022    num DIV    0021  +24 
0023  + int ADD    0001  +1  
0024 >  int LE     0023  +60 
0025 ------ LOOP ------------
0026  + int ADD    0023  +1  
0027 >  int LE     0026  +60 
0028    int PHI    0023  0026
---- TRACE 1 mcode 278
5560db79fee7  mov dword [0x41453410], 0x1
5560db79fef2  mov esi, edx
5560db79fef4  movsd xmm3, [0x41464718]
5560db79fefd  movsd xmm2, [0x41464700]
5560db79ff06  movsd xmm1, [0x414646e8]
5560db79ff0f  cvttsd2si ebp, [rsi+0x28]
5560db79ff14  cmp dword [rsi+0x1c], -0x09
5560db79ff18  jnz 0x5560db790010        ->0
5560db79ff1e  cmp dword [rsi+0x14], -0x0c
5560db79ff22  jnz 0x5560db790010        ->0
5560db79ff28  mov edx, [rsi+0x10]
5560db79ff2b  cmp dword [rsi+0x18], 0x4145df58
5560db79ff32  jnz 0x5560db790010        ->0
5560db79ff38  mov ebx, [0x4145df60]
5560db79ff3f  cmp dword [rbx+0x1c], +0x3f
5560db79ff43  jnz 0x5560db790010        ->0
5560db79ff49  mov ecx, [rbx+0x14]
5560db79ff4c  mov rdi, 0xfffffffb41456380
5560db79ff56  cmp rdi, [rcx+0xc8]
5560db79ff5d  jnz 0x5560db790010        ->0
5560db79ff63  cmp dword [rcx+0xc4], -0x09
5560db79ff6a  jnz 0x5560db790010        ->0
5560db79ff70  cmp dword [rdx+0x1c], +0x01
5560db79ff74  jnz 0x5560db790010        ->0
5560db79ff7a  mov eax, [rdx+0x14]
5560db79ff7d  mov rdi, 0xfffffffb4145d8e8
5560db79ff87  cmp rdi, [rax+0x8]
5560db79ff8b  jnz 0x5560db790010        ->0
5560db79ff91  cmp dword [rax+0x4], 0xfffeffff
5560db79ff98  jnb 0x5560db790010        ->0
5560db79ff9e  cmp dword [rcx+0xc0], 0x41456358
5560db79ffa8  jnz 0x5560db790010        ->0
5560db79ffae  mov rdi, 0xfffffffb41456df8
5560db79ffb8  cmp rdi, [rax+0x20]
5560db79ffbc  jnz 0x5560db790010        ->0
5560db79ffc2  cmp dword [rax+0x1c], 0xfffeffff
5560db79ffc9  jnb 0x5560db790010        ->0
5560db79ffcf  movsd xmm0, [rax+0x18]
5560db79ffd4  divsd xmm0, xmm3
5560db79ffd8  addsd xmm0, [rax]
5560db79ffdc  divsd xmm0, xmm2
5560db79ffe0  divsd xmm0, xmm1
5560db79ffe4  add ebp, +0x01
5560db79ffe7  cmp ebp, +0x3c
5560db79ffea  jg 0x5560db790014 ->1
->LOOP:
5560db79fff0  add ebp, +0x01
5560db79fff3  cmp ebp, +0x3c
5560db79fff6  jle 0x5560db79fff0        ->LOOP
5560db79fff8  jmp 0x5560db79001c        ->3
---- TRACE 1 stop -> loop

check.lua

local ffi = require 'ffi'

local date_mt = {
        secs = 0,
        nsec = 0,
}
local date = setmetatable({ secs = 123, nsec = 456}, date_mt)

local days = function(self)
       return (tonumber(self.secs) + self.nsec / 1e9) / (60 * 60) / 24
end

local foo
for _=1,10 do
	foo = days(date)
end

run-check-luajit.sh

luajit -jdump -O3 -Ohotloop=9 -Ocse -Ofold ../days_ffi.lua
# / (60 * 60) / 24 ==  / (60 * 60 * 24)
# but nobody folded this expression