Re: [C]: Unnecessary int(16)->long(32) promotion: Bug in C front end?

[Ian Lance Taylor <iant at google dot com>]

Georg-Johann Lay writes:

> extern char *grub_scratch_mem;
> int testload_func (char *arg, int flags)
> {
>   int i;
>   for (i = 0; i < 0x10ac0; i++)
>     if (*((unsigned char *) ((0x200000 + i + (int) grub_scratch_mem)))
>         != *((unsigned char *) ((0x300000 + i + (int) grub_scratch_mem))))
>       return 0;
>   return 1;
> }
>
> And compiled with the command line
>
>> avr-gcc pr30338.c -S -Os -dp -mmcu=atmega128 -fdump-tree-original
>
> pr30338.c: In function 'testload_func':
> pr30338.c:9:11: warning: cast to pointer from integer of different
> size [-Wint-to-pointer-cast]
> pr30338.c:10:14: warning: cast to pointer from integer of different
> size [-Wint-to-pointer-cast]
>
> Frist of all, the warning is incorrect because Pmode=HImode=int on AVR.

The constant 0x200000 does not fit in a 16-bit integer.  Therefore the
compiler gives it the type long, as the C standard requires.  The
arithmetic promotion rules then cause the compiler to cast i and
grub_scratch_mem to long, and to do the operation in long.  The warning
then occurs when casting from long to a pointer type.

Ian