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Re: [PATCH, PR 57748] Check for out of bounds access


> Doesn't that also apply to arithmetic on symbols when the offset is NULL?

This can presumably be retrofitted when the offset is null or constant.

> But yes, the codegen example posted shows this kind of difference
> (though it doesn't seem to save anything for that case).  I'd have expected
> a more explicit guarding of this case, like with MEM_P (to_rtx)
> && SYMBOL_REF_P (XEXP (to_rtx, 0)) though, eventually even looking
> whether the resulting address is legitimate.  But ... doesn't forwprop
> fix this up later anyway?

Not clear IMO, it would need to reassociate.

> The comment before it is also odd and likely only applies to later
> added restrictions.  Just to quote it again:
> 
>    if (offset != 0)
>      {
> ...
>           /* A constant address in TO_RTX can have VOIDmode, we must not try
> to call force_reg for that case.  Avoid that case.  */ if (MEM_P (to_rtx)
>               && GET_MODE (to_rtx) == BLKmode
>               && GET_MODE (XEXP (to_rtx, 0)) != VOIDmode
>               && bitsize > 0
>               && (bitpos % bitsize) == 0
>               && (bitsize % GET_MODE_ALIGNMENT (mode1)) == 0
>               && MEM_ALIGN (to_rtx) == GET_MODE_ALIGNMENT (mode1))
>             {
>               to_rtx = adjust_address (to_rtx, mode1, bitpos /
> BITS_PER_UNIT); bitpos = 0;
>             }
> 
>           to_rtx = offset_address (to_rtx, offset_rtx,
>                                    highest_pow2_factor_for_target (to,
>                                                                    offset));
> }

Yes, the comment is out-of-sync and not very informative.

-- 
Eric Botcazou


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