[fpc-devel] bug: Inc(v,i)/Dec(v,i)

[Gerhard Scholz]

I've tried to submit this as a bug report, but after pressing on "Submit bug"
nothing happens on http://www.freepascal.org/bugs/add.php3



Inc ( v, i ) and Dec ( v, i ) produce rangecheck or overflow check with {$r+,q+}

Without checks the program runs corrctly.

The values and results are in range; the errors shold not occur.

Example program:

{$r+,q+,s+}
{ $r-,q-,s-}

program incdec ;

  uses
    sysutils ;

  var
    pre : 0..132 ;
    fra : -132..132 ;

  procedure init ; begin pre := 1 ; fra := -1 ; end ;

  begin
    init ; pre := pre + fra ;                       writeln ( pre ) ;
    init ; pre := pre - fra ;                       writeln ( pre ) ;
    init ; inc ( pre, fra ) ;   {Dec/Inc error? }   writeln ( pre ) ;
    init ; Dec ( pre, fra ) ;   {Dec/Inc error? }   writeln ( pre ) ;
   end.

The assembler code shows that Inc/Dec assumes that the second parameter
has the same type as the first. This is not true in this case.

Assembler code (shortened):

#...
# [18] init ; pre := pre + fra ;                       writeln ( pre ) ;
 call P$INCDEC_INIT
 movzbl U_P$INCDEC_PRE,%eax
 movswl U_P$INCDEC_FRA,%edx
 addl %eax,%edx
 jno .L18
 call FPC_OVERFLOW
.L18:
 movl %edx,%eax
 cmpl $132,%eax
 jbe .L19
 call FPC_RANGEERROR
.L19:
 movb %dl,U_P$INCDEC_PRE
#...
# [19] init ; pre := pre - fra ;                       writeln ( pre ) ;
 call P$INCDEC_INIT
 movzbl U_P$INCDEC_PRE,%edx
 movswl U_P$INCDEC_FRA,%eax
 subl %eax,%edx
 jno .L32
 call FPC_OVERFLOW
.L32:
 movl %edx,%eax
 cmpl $132,%eax
 jbe .L33
 call FPC_RANGEERROR
.L33:
 movb %dl,U_P$INCDEC_PRE
#...
# [20] init ; inc ( pre, fra ) ;   {Dec/Inc error? }   writeln ( pre ) ;
 call P$INCDEC_INIT
 movzbl U_P$INCDEC_PRE,%eax
 movzbl U_P$INCDEC_FRA,%edx
 addl %eax,%edx
 jae .L46
 call FPC_OVERFLOW
.L46:
 movl %edx,%eax
 cmpl $132,%eax
 jbe .L47
 call FPC_RANGEERROR
.L47:
#...
 movb %dl,U_P$INCDEC_PRE
# [21] init ; Dec ( pre, fra ) ;   {Dec/Inc error? }   writeln ( pre ) ;
 call P$INCDEC_INIT
 movzbl U_P$INCDEC_PRE,%edx
 movzbl U_P$INCDEC_FRA,%eax
 subl %eax,%edx
 jae .L60
 call FPC_OVERFLOW
.L60:
 movl %edx,%eax
 cmpl $132,%eax
 jbe .L61
 call FPC_RANGEERROR
.L61:
#...