[PATCH, PR 57748] Check for out of bounds access, Part 2

[Bernd Edlinger]

Hi,

On Thu, 26 Sep 2013 11:34:02, Eric Botcazou wrote:
>
>> So I still think my patch does the right thing.
>>
>> The rationale is:
>>
>> = expand_expr (tem,
>> (TREE_CODE (TREE_TYPE (tem)) == UNION_TYPE
>> && COMPLETE_TYPE_P (TREE_TYPE (tem))
>> && (TREE_CODE (TYPE_SIZE (TREE_TYPE (tem)))
>> != INTEGER_CST)
>> && modifier != EXPAND_STACK_PARM
>> ? target : NULL_RTX),
>> VOIDmode,
>> EXPAND_MEMORY);
>>
>> returns the address of the structure in question,
>> we can add offset, bitoffset, and access the memory
>> in the right mode and alignment information is
>> passed to the backend via MEM_ALIGN (op0).
>
> But there are conceptually no reasons to require a MEM here. Look at all the
> code just below the block. Given how hard it is to eliminate spills to memory
> in RTL once they are generated, this shouldn't be taken lightly.
>
> --
> Eric Botcazou

Sure, but the modifier is not meant to force something into memory,
especially when it is already in an register. Remember, we are only
talking of structures here, and we only want to access one member.

It is more the other way round:
It says: "You do not have to load the value in a register, if it is already in
memory I'm happy"

At least in my understanding.

Bernd.