[Gm2] parameter range value overflow detected and integer division overflow

[Gaius Mulley]

Hi,

I'm almost about to push some changes to the trunk which will:

   (*)  detect integer overflow with ordinal operands.
        (Only div trunc currently -fpim2 -fpim3).  When I finish
         div ceil and div floor then -fpim4 and -fiso division will be
         fully detected.  I think the only remaining operator after this
         is modulus.  At that point all ordinal arithmetic overflow
         should be detected.
   (*)  detect parameter range value overflow.  For example see the
        following example.  Hopefully this additional check could be
        quite useful.

both tests will generate runtime checking code.  Both tests can also
under certain conditions be detected at compile time with the Modula-2
plugin (automatically run when gm2 is used).

Here it is in action:

$ cat overflow2.mod
MODULE overflow2 ;

FROM libc IMPORT printf ;


PROCEDURE func (x, y: CARDINAL) ;
VAR
   res: CARDINAL ;
BEGIN
   res := x DIV y ;
   printf ("res = %ud\n", res);
END func ;

VAR
   x, y: INTEGER ;
   u   : CARDINAL ;
BEGIN
   x := 1 ;
   y := -1 ;
   func (x, y) ;
END overflow2.
               
$ gm2 -O2 -fsoft-check-all overflow2.mod
overflow2.mod:20:3:inevitable runtime error will occur, an exception
will occur because the actual parameter is out of range of the formal
parameter


the message should be improved to say which parameter and maybe the
limits of the type.  But at least the detection logic is working :-)


regards,
Gaius