[PicForth] Festive code generation bug

[Alex Holden]

Merry Christmas everybody.

I've found another code generation bug, this time involving nested if 
statements with 'exit' in them. Here's an example. It should exit with 
-1 on the stack if passed 1, exit with 0 on the stack if passed 2, and 
leave nothing on the stack if passed anything else. In fact, the else 
block is always skipped over, so it returns -1 when passed 1 and returns 
the number that was passed in if it was anything other than 1.

: test
         dup 1 = if
                 drop -1 exit
         else
                 2 = if
                         0 exit
                 then
         then
;

Here's the generated assembly:

         ; name: test
         ; max return-stack depth: 0
0x0006  0800    movf    0x00,w
0x0007  3A01    xorlw   0x01
0x0008  1D03    btfss   0x03,2
0x0009  280D    goto    0x00D   ; test + 0x007
0x000A  30FF    movlw   0xFF
0x000B  0080    movwf   0x00
0x000C  0008    return
0x000D  2816    goto    0x016   ; test + 0x010
0x000E  0600    xorwf   0x00,w
0x000F  0A84    incf    0x04,f
0x0010  3800    iorlw   0x00
0x0011  1D03    btfss   0x03,2
0x0012  2816    goto    0x016   ; test + 0x010
0x0013  0384    decf    0x04,f
0x0014  0180    clrf    0x00
0x0015  0008    return
0x0016  0008    return

-- 
------------ Alex Holden - http://www.linuxhacker.org ------------
If it doesn't work, you're not hitting it with a big enough hammer