Re: [RFC] evaluate: pointer arithmetics on plain void*

[Jan Pokorný <pokorny_jan@xxxxxxxxx>]

Hi again,

On 01/23/2012 11:32 AM, Jan Pokorný wrote:
> Hm, I was talking about post-ops only, the example showed a failing pre-op
> ...both is a single case as evaluate_preop boils down to evaluate_postop.
> 
> I went through evaluate.c again and I think these cases should be somehow
> unified (stating current state):
> 
> 1. evaluate_postop:
>   a. function: error ("bad argument type for ++/--")
>   b. void*:    nothing, but buggy evaluation (add/sub -1)

that "buggy evaluation" is a kind of regression that can be tracked down
to commit [1], which first started the "void != char" idea and which
missed that evaluate_postop function.

> 2. evaluate_ptr_add
>   a. function: warning ("arithmetics on pointers to functions")
>   b. void*:    nothing, sizeof(void) implicitly considered as 1
> 
> 3. evaluate_sizeof:
>   a. function: warning ("expression using sizeof on a function")
>   b. void:     warning ("expression using sizeof(void)")
>   (c. bool:     warning ("expression using sizeof bool"))
> 
> 4. evaluate_ptrsizeof:
>   - ?
> 
> 
> The original patch makes 1b. an equivalent to 1a.  The alternative
> is to handle 1b. in a similar way as 2b.  Maybe both would deserve
> a warning.

The most moderate alternative is to take what what used in
evaluate_ptr_add into evaluate_postop.

However, the question whether to follow assumptions that GCC makes
emerges.  I tried also clang -pedantic, I got:

	warning: arithmetic on a pointer to void is a GNU extension
	         [-pedantic,-Wpointer-arith]

> Still, there is at least one inconsistency: 1a. vs 2a. (error vs warning).

[1] http://git.kernel.org/?p=devel/sparse/sparse.git;a=commit;h=405cd6e

-- 
Jan
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