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

[Jason Merrill <jason@redhat.com>]

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