On Fri, Jul 1, 2016 at 3:10 PM, Manish Goregaokar <man...@mozilla.com> wrote:
> Added a test:
Ok if this passed bootstrap/regtest.
Richard.
> gcc/ChangeLog:
> PR c/71699
> * fold-const.c (tree_binary_nonzero_warnv_p): Allow
> pointer addition to also be considered nonzero.
>
> gcc/testsuite/ChangeLog:
> PR c/71699
> * c-c++-common/pointer-addition-nonnull.c: New test for
> pointer addition.
> ---
> gcc/fold-const.c | 3 +++
> .../c-c++-common/pointer-addition-nonnull.c | 21
> +++++++++++++++++++++
> 2 files changed, 24 insertions(+)
> create mode 100644 gcc/testsuite/c-c++-common/pointer-addition-nonnull.c
>
> diff --git a/gcc/fold-const.c b/gcc/fold-const.c
> index 3b9500d..0d82018 100644
> --- a/gcc/fold-const.c
> +++ b/gcc/fold-const.c
> @@ -13199,6 +13199,9 @@ tree_binary_nonzero_warnv_p (enum tree_code code,
> switch (code)
> {
> case POINTER_PLUS_EXPR:
> + return flag_delete_null_pointer_checks
> + && (tree_expr_nonzero_warnv_p (op0, strict_overflow_p)
> + || tree_expr_nonzero_warnv_p (op1, strict_overflow_p));
> case PLUS_EXPR:
> if (ANY_INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_UNDEFINED (type))
> {
> diff --git a/gcc/testsuite/c-c++-common/pointer-addition-nonnull.c
> b/gcc/testsuite/c-c++-common/pointer-addition-nonnull.c
> new file mode 100644
> index 0000000..10bc04c
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/pointer-addition-nonnull.c
> @@ -0,0 +1,21 @@
> +/* { dg-options "-c -O2 -Wall" } */
> +
> +char *xstrdup (const char *) __attribute__ ((__returns_nonnull__));
> +
> +#define PREFIX "some "
> +
> +int
> +main ()
> +{
> + char *saveptr;
> + char *name = xstrdup (PREFIX "name");
> +
> + char *tail = name + sizeof (PREFIX) - 1;
> +
> + if (tail == 0)
> + tail = saveptr;
> + while (*tail == ' ')
> + ++tail;
> +
> + return 0;
> +}
> \ No newline at end of file
> --
> 2.8.3
>
> -Manish
>
>
> On Fri, Jul 1, 2016 at 1:40 PM, Richard Biener
> <richard.guent...@gmail.com> wrote:
>> On Thu, Jun 30, 2016 at 5:14 PM, Marc Glisse <marc.gli...@inria.fr> wrote:
>>> On Thu, 30 Jun 2016, Richard Biener wrote:
>>>
>>>> points-to analysis already has the constraint that POINTER_PLUS_EXPR
>>>> cannot leave the object op0 points to. Of course currently nothing uses
>>>> the
>>>> fact whether points-to computes pointed-to as nothing (aka NULL) - so the
>>>> argument may be moot.
>>>>
>>>> Anyway, one of my points to the original patch was that POINTER_PLUS_EXPR
>>>> handling should be clearly separate from PLUS_EXPR and that we have
>>>> flag_delete_null_pointer_checks to allow targest to declare that 0 is a
>>>> valid
>>>> object pointer (and thus you can do 4 + -4 and reach NULL).
>>>
>>>
>>> Thanks. So the tricky point is that we are not allowed to transform g into f
>>> below:
>>>
>>> char*f(char*p){return p+4;}
>>> char*g(char*p){return (char*)((intptr_t)p+4);}
>>>
>>> That makes sense and seems much easier to guarantee than I feared, nice.
>>>
>>> (on the other hand, only RTL is able to simplify (long)p+4-(long)(p+4))
>>
>> Hmm, yeah - we have some match.pd stuff to handle these kind of cases,
>> like p + ((long)p2 - (long)p1)) and also (long)(p + x) - (long)p.
>>
>> OTOH to handle (long)p + 4 - (long)(p + 4) the only thing we need is to
>> transform (long)(p + 4) to (long)p + 4 ... that would simplify things but
>> of course we cannot ever undo that canonicalization if the result is
>> ever converted back to a pointer. But maybe we can value-number it
>> the same with some tricks... (might be worth to file a bugreport)
>>
>> Richard.
>>
>>> --
>>> Marc Glisse
