Re: C/C++ PATCH to implement -Wpointer-compare warning (PR c++/64767)

[Eric Gallager <egall@gwmail.gwu.edu>]

On 10/2/16, Jason Merrill <jason@redhat.com> wrote:
> OK, thanks.
>
> On Sat, Oct 1, 2016 at 10:16 AM, Marek Polacek <polacek@redhat.com> wrote:
>> On Fri, Sep 30, 2016 at 05:48:03PM -0400, Jason Merrill wrote:
>>> On Fri, Sep 30, 2016 at 12:43 PM, Marek Polacek <polacek@redhat.com>
>>> wrote:
>>> > On Fri, Sep 23, 2016 at 10:31:33AM -0400, Jason Merrill wrote:
>>> >> On Fri, Sep 23, 2016 at 9:15 AM, Marek Polacek <polacek@redhat.com>
>>> >> wrote:
>>> >> > On Wed, Sep 21, 2016 at 03:52:09PM -0400, Jason Merrill wrote:
>>> >> >> On Mon, Sep 19, 2016 at 2:49 PM, Jason Merrill <jason@redhat.com>
>>> >> >> wrote:
>>> >> >> > I suppose that an INTEGER_CST of character type is necessarily a
>>> >> >> > character constant, so adding a check for !char_type_p ought to
>>> >> >> > do the
>>> >> >> > trick.
>>> >> >>
>>> >> >> Indeed it does.  I'm checking this in:
>>> >> >
>>> >> > Nice, thanks.  What about the original patch?  We still need to
>>> >> > warn
>>> >> > (or error for C++11) for pointer comparisons.
>>> >>
>>> >> If we still accept pointer comparisons in C++, that's another bug
>>> >> with
>>> >> treating \0 as a null pointer constant.  This seems to be because
>>> >> ocp_convert of \0 to int produces an INTEGER_CST indistinguishable
>>> >> from literal 0.
>>> >
>>> > I was trying to fix this in ocp_convert, by using NOP_EXPRs, but that
>>> > wasn't
>>> > successful.  But since we're interested in ==/!=, I think this can be
>>> > fixed
>>> > easily in cp_build_binary_op.  Actually, all that seems to be needed is
>>> > using
>>> > orig_op as the argument to null_ptr_cst_p, but that wouldn't give the
>>> > correct
>>> > diagnostics, so I did this.  By checking orig_op we can see if the
>>> > operands are
>>> > character literals or not, because orig_op is an operand before the
>>> > default
>>> > conversions.
>>>
>>> What is wrong about the diagnostic from just using orig_op?  "ISO C++
>>> forbids comparison between pointer and integer" seems fine to me, and
>>> will help the user to realize that they need to index off the pointer.
>>>
>>> I see that some of the calls to null_ptr_cst_p in cp_build_binary_op
>>> have already been changed to check orig_op*, but not all.  Let's
>>> update the remaining calls, that should do the trick without adding a
>>> new error.
>>
>> Here you go:
>>
>> Bootstrapped/regtested on x86_64-linux and ppc64-linux, ok for trunk?
>>
>> 2016-10-01  Marek Polacek  <polacek@redhat.com>
>>
>>         Core 903
>>         * typeck.c (cp_build_binary_op): Pass original operands to
>>         null_ptr_cst_p, not those after the default conversions.
>>
>>         * g++.dg/cpp0x/nullptr37.C: New test.
>>
>> diff --git gcc/cp/typeck.c gcc/cp/typeck.c
>> index 617ca55..8b780be 100644
>> --- gcc/cp/typeck.c
>> +++ gcc/cp/typeck.c
>> @@ -4573,7 +4573,7 @@ cp_build_binary_op (location_t location,
>>               || code1 == COMPLEX_TYPE || code1 == ENUMERAL_TYPE))
>>         short_compare = 1;
>>        else if (((code0 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type0))
>> -               && null_ptr_cst_p (op1))
>> +               && null_ptr_cst_p (orig_op1))
>>                /* Handle, eg, (void*)0 (c++/43906), and more.  */
>>                || (code0 == POINTER_TYPE
>>                    && TYPE_PTR_P (type1) && integer_zerop (op1)))
>> @@ -4587,7 +4587,7 @@ cp_build_binary_op (location_t location,
>>           warn_for_null_address (location, op0, complain);
>>         }
>>        else if (((code1 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type1))
>> -               && null_ptr_cst_p (op0))
>> +               && null_ptr_cst_p (orig_op0))
>>                /* Handle, eg, (void*)0 (c++/43906), and more.  */
>>                || (code1 == POINTER_TYPE
>>                    && TYPE_PTR_P (type0) && integer_zerop (op0)))
>> @@ -4604,7 +4604,7 @@ cp_build_binary_op (location_t location,
>>                || (TYPE_PTRDATAMEM_P (type0) && TYPE_PTRDATAMEM_P
>> (type1)))
>>         result_type = composite_pointer_type (type0, type1, op0, op1,
>>                                               CPO_COMPARISON, complain);
>> -      else if (null_ptr_cst_p (op0) && null_ptr_cst_p (op1))
>> +      else if (null_ptr_cst_p (orig_op0) && null_ptr_cst_p (orig_op1))
>>         /* One of the operands must be of nullptr_t type.  */
>>          result_type = TREE_TYPE (nullptr_node);
>>        else if (code0 == POINTER_TYPE && code1 == INTEGER_TYPE)
>> @@ -4623,7 +4623,7 @@ cp_build_binary_op (location_t location,
>>            else
>>              return error_mark_node;
>>         }
>> -      else if (TYPE_PTRMEMFUNC_P (type0) && null_ptr_cst_p (op1))
>> +      else if (TYPE_PTRMEMFUNC_P (type0) && null_ptr_cst_p (orig_op1))
>>         {
>>           if (TARGET_PTRMEMFUNC_VBIT_LOCATION
>>               == ptrmemfunc_vbit_in_delta)
>> @@ -4664,7 +4664,7 @@ cp_build_binary_op (location_t location,
>>             }
>>           result_type = TREE_TYPE (op0);
>>         }
>> -      else if (TYPE_PTRMEMFUNC_P (type1) && null_ptr_cst_p (op0))
>> +      else if (TYPE_PTRMEMFUNC_P (type1) && null_ptr_cst_p (orig_op0))
>>         return cp_build_binary_op (location, code, op1, op0, complain);
>>        else if (TYPE_PTRMEMFUNC_P (type0) && TYPE_PTRMEMFUNC_P (type1))
>>         {
>> @@ -4877,21 +4877,21 @@ cp_build_binary_op (location_t location,
>>        else if (code0 == POINTER_TYPE && code1 == POINTER_TYPE)
>>         result_type = composite_pointer_type (type0, type1, op0, op1,
>>                                               CPO_COMPARISON, complain);
>> -      else if (code0 == POINTER_TYPE && null_ptr_cst_p (op1))
>> +      else if (code0 == POINTER_TYPE && null_ptr_cst_p (orig_op1))
>>         {
>>           result_type = type0;
>>           if (extra_warnings && (complain & tf_warning))
>>             warning (OPT_Wextra,
>>                      "ordered comparison of pointer with integer zero");
>>         }
>> -      else if (code1 == POINTER_TYPE && null_ptr_cst_p (op0))
>> +      else if (code1 == POINTER_TYPE && null_ptr_cst_p (orig_op0))
>>         {
>>           result_type = type1;
>>           if (extra_warnings && (complain & tf_warning))
>>             warning (OPT_Wextra,
>>                      "ordered comparison of pointer with integer zero");
>>         }
>> -      else if (null_ptr_cst_p (op0) && null_ptr_cst_p (op1))
>> +      else if (null_ptr_cst_p (orig_op0) && null_ptr_cst_p (orig_op1))
>>         /* One of the operands must be of nullptr_t type.  */
>>          result_type = TREE_TYPE (nullptr_node);
>>        else if (code0 == POINTER_TYPE && code1 == INTEGER_TYPE)
>> diff --git gcc/testsuite/g++.dg/cpp0x/nullptr37.C
>> gcc/testsuite/g++.dg/cpp0x/nullptr37.C
>> index e69de29..e746a28 100644
>> --- gcc/testsuite/g++.dg/cpp0x/nullptr37.C
>> +++ gcc/testsuite/g++.dg/cpp0x/nullptr37.C
>> @@ -0,0 +1,78 @@
>> +/* PR c++/64767 */
>> +// { dg-do compile { target c++11 } }
>> +
>> +int
>> +f1 (int *p, int **q)
>> +{
>> +  int r = 0;
>> +
>> +  r += p == '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p == L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p == u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p == U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p != '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p != L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p != u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += p != U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +
>> +  r += '\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += L'\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += u'\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += U'\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += '\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += L'\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += u'\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += U'\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +
>> +  r += q == '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q == L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q == u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q == U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q != '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q != L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q != u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += q != U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +
>> +  r += '\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += L'\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += u'\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += U'\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += '\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += L'\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += u'\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +  r += U'\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between
>> pointer and integer" }
>> +
>> +  return r;
>> +}
>> +
>> +int
>> +f2 (int *p)
>> +{
>> +  int r = 0;
>> +
>> +  r += p == (void *) 0;
>> +  r += p != (void *) 0;
>> +  r += (void *) 0 == p;
>> +  r += (void *) 0 != p;
>> +
>> +  r += p == 0;
>> +  r += p != 0;
>> +  r += 0 == p;
>> +  r += 0 != p;
>> +
>> +  return r;
>> +}
>> +
>> +int
>> +f3 (int *p)
>> +{
>> +  int r = 0;
>> +
>> +  r += p == (char) 0; // { dg-error "ISO C\\+\\+ forbids comparison
>> between pointer and integer" }
>> +  r += p != (char) 0; // { dg-error "ISO C\\+\\+ forbids comparison
>> between pointer and integer" }
>> +
>> +  r += (char) 0 == p; // { dg-error "ISO C\\+\\+ forbids comparison
>> between pointer and integer" }
>> +  r += (char) 0 != p; // { dg-error "ISO C\\+\\+ forbids comparison
>> between pointer and integer" }
>> +
>> +  return r;
>> +}
>>
>>         Marek
>

So I'm still kind of unclear as to what got committed as a result of
this thread. It seems like there's a new diagnostic for C++11, but
what about other language standards? Is there still going to be a
separate -Wpointer-compare flag usable in plain C? When I tried with
trunk from yesterday, it still didn't work:

$ /usr/local/bin/gcc -Wpointer-compare -c unexmacosx.c
gcc: error: unrecognized command line option ‘-Wpointer-compare’; did
you mean ‘-Wnonnull-compare’?
$

I hope a separate -Wpointer-compare flag can make it in in time for GCC 7.

Thanks,
Eric