[Yhc] FInfo->codesize woes.

[Tom Shackell]

Hi Stew,

> Hi YHC!
>   Greetings, and for those I haven't already pestered, my interest in 
> YHC pertains to my third year project, creating a JIT compiler for YHC's 
> bytecode.

Ah excellent :-)

> Does anyone know if the FInfo->codesize value is reliable? I am 
> presently compiling the _driver function which states a codesize of 
> 0x24, yet my JIT compiler shows the IP (when I reach an END_CODE op) 
> falls about 6 bytes short of this. 

The codesize is indeed reliable, though interestingly enough I get the 
codesize for _driver being 25 bytes rather than (0x24 = 36 bytes). I've 
just checked and 25 bytes is indeed correct (including 1 byte for the 
END_CODE itself). Here is a printout of the function, as loaded by the 
interpreter.

FInfo _driver [ arity: 2, consts: 7 ]{
     0.      [0x1b] ZAP_ARG 0
     2.      [0x01] NEED_HEAP_32
     3.      [0x25] PUSH_CONST_0
     4.      [0x30] MK_AP_1
     5.      [0x27] PUSH_CONST_2
     6.      [0x18] PUSH_ZAP_ARG_1
     7.      [0x28] PUSH_CONST_3
     8.      [0x41] APPLY 2
     10.     [0x01] NEED_HEAP_32
     11.     [0x33] MK_AP_4
     12.     [0x34] MK_AP_5
     13.     [0x0b] PUSH_ZAP_0
     14.     [0x5a] EVAL
     15.     [0x5c] TABLE_SWITCH [1] {0 -> 20}
     20.     [0x01] NEED_HEAP_32
     21.     [0x4a] UNPACK
     22.     [0x2b] PUSH_CONST_6
     23.     [0x5b] RETURN_EVAL
     24.     [0x00] END_CODE
     consts {
         0.      NODE 0xb6ca222c [(CExitSuccess)]
         1.      INFO FInfo 'reallyExit'[1]
         2.      NODE 0xb6ca223c [(FLAMBDA294/1)]
         3.      NODE 0xb6ca2748 [(Fcatch/0)]
         4.      INFO FInfo 'YHC.Internal.IO;Prelude.Monad;>>'[2]
         5.      INFO FInfo 'unsafePerformIO'[1]
         6.      NODE 0xb6ca2754 [(Fundefined/0)]
     }
}

> Also is every function guaranteed to 
> have an END_CODE op at the end? My current code works for a selection of 
> functions I have played with but I haven't had time to examine any more 
> than a modest selection.

Yes the compiler always places END_CODE at the end of every function. 
END_CODE crashes the interpreter if it's ever executed, it's designed to 
catch any problems with miscalculated jumps.


Hope that helps :-)



Tom