On Thu, Feb 1, 2018 at 6:42 PM, Aldy Hernandez <al...@redhat.com> wrote:
> Since my patch isn't the easy one liner I wanted it to be, perhaps we
> should concentrate on Martin's patch, which is more robust, and has
> testcases to boot! His patch from last week also fixes a couple other
> PRs.
>
> Richard, would this be acceptable? That is, could you or Jakub review
> Martin's all-encompassing patch? If so, I'll drop mine.
Sorry, no - this one looks way too complicated.
> Also, could someone pontificate on whether we want to fix
> -Warray-bounds regressions for this release cycle?
Remove bogus ones? Yes. Add "missing ones"? No.
Richard.
> Thanks.
>
> On Wed, Jan 31, 2018 at 6:05 AM, Richard Biener
> <richard.guent...@gmail.com> wrote:
>> On Tue, Jan 30, 2018 at 11:11 PM, Aldy Hernandez <al...@redhat.com> wrote:
>>> Hi!
>>>
>>> [Note: Jakub has mentioned that missing -Warray-bounds regressions should be
>>> punted to GCC 9. I think this particular one is easy pickings, but if this
>>> and/or the rest of the -Warray-bounds regressions should be marked as GCC 9
>>> material, please let me know so we can adjust all relevant PRs.]
>>>
>>> This is a -Warray-bounds regression that happens because the IL now has an
>>> MEM_REF instead on ARRAY_REF.
>>>
>>> Previously we had an ARRAY_REF we could diagnose:
>>>
>>> D.2720_5 = "12345678"[1073741824];
>>>
>>> But now this is represented as:
>>>
>>> _1 = MEM[(const char *)"12345678" + 1073741824B];
>>>
>>> I think we can just allow check_array_bounds() to handle MEM_REF's and
>>> everything should just work.
>>>
>>> The attached patch fixes both regressions mentioned in the PR.
>>>
>>> Tested on x86-64 Linux.
>>>
>>> OK?
>>
>> This doesn't look correct. You lump MEM_REF handling together with
>> ADDR_EXPR handling but for the above case you want to diagnose
>> _dereferences_ not address-taking.
>>
>> For the dereference case you need to amend the ARRAY_REF case, for example
>> via
>>
>> Index: gcc/tree-vrp.c
>> ===================================================================
>> --- gcc/tree-vrp.c (revision 257181)
>> +++ gcc/tree-vrp.c (working copy)
>> @@ -5012,6 +5012,13 @@ check_array_bounds (tree *tp, int *walk_
>> if (TREE_CODE (t) == ARRAY_REF)
>> vrp_prop->check_array_ref (location, t, false /*ignore_off_by_one*/);
>>
>> + else if (TREE_CODE (t) == MEM_REF
>> + && TREE_CODE (TREE_OPERAND (t, 0)) == ADDR_EXPR
>> + && TREE_CODE (TREE_OPERAND (TREE_OPERAND (t, 0), 0)) ==
>> STRING_CST)
>> + {
>> + call factored part of check_array_ref passing in STRING_CST and offset
>> + }
>> +
>> else if (TREE_CODE (t) == ADDR_EXPR)
>> {
>> vrp_prop->search_for_addr_array (t, location);
>>
>> note your patch will fail to warn for "1"[1] because taking that
>> address is valid but not
>> dereferencing it.
>>
>> Richard.
