Re: [PATCH] Emit -Waddress warnings for comparing address of reference against NULL

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Sun, May 3, 2015 at 5:29 PM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> On Sun, Apr 26, 2015 at 8:56 PM, Patrick Palka <patrick@parcs.ath.cx> wrote:
>> Here is an updated version of the patch with, hopefully, all your
>> suggestions made.  I decided to add calls to STRIP_NOPS before emitting
>> the warning so that we properly warn for cases where there's a cast in
>> between the whole thing, e.g.
>>
>>   if (!&(int &)a)
>>
>> I also added guards to emit the warnings only when the stripped operand
>> is actually a decl so that we don't pass a non-decl argument to
>> warning_at() which can happen in a case like
>>
>>   if (!&(int &)*(int *)0)
>>
>> Does this look OK now after testing?
>>
>> gcc/c-family/ChangeLog:
>>
>>         PR c++/65168
>>         * c-common.c (c_common_truthvalue_conversion): Warn when
>>         converting an address of a reference to a truth value.
>>
>> gcc/cp/ChangeLog:
>>
>>         PR c++/65168
>>         * typeck.c (cp_build_binary_op): Warn when comparing an address
>>         of a reference against NULL.
>>
>> gcc/testsuite/ChangeLog:
>>
>>         PR c++/65168
>>         g++.dg/warn/Walways-true-3.C: New test.
>> ---
>>  gcc/c-family/c-common.c                    | 14 ++++++++++
>>  gcc/cp/typeck.c                            | 34 ++++++++++++++++++++++
>>  gcc/testsuite/g++.dg/warn/Walways-true-3.C | 45 ++++++++++++++++++++++++++++++
>>  3 files changed, 93 insertions(+)
>>  create mode 100644 gcc/testsuite/g++.dg/warn/Walways-true-3.C
>>
>> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
>> index 9797e17..c353c72 100644
>> --- a/gcc/c-family/c-common.c
>> +++ b/gcc/c-family/c-common.c
>> @@ -4806,6 +4806,20 @@ c_common_truthvalue_conversion (location_t location, tree expr)
>>         tree totype = TREE_TYPE (expr);
>>         tree fromtype = TREE_TYPE (TREE_OPERAND (expr, 0));
>>
>> +       if (POINTER_TYPE_P (totype)
>> +           && TREE_CODE (fromtype) == REFERENCE_TYPE)
>> +         {
>> +           tree inner = expr;
>> +           STRIP_NOPS (inner);
>> +
>> +           if (DECL_P (inner))
>> +             warning_at (location,
>> +                         OPT_Waddress,
>> +                         "the compiler can assume that the address of "
>> +                         "%qD will always evaluate to %<true%>",
>> +                         inner);
>> +         }
>> +
>>         /* Don't cancel the effect of a CONVERT_EXPR from a REFERENCE_TYPE,
>>            since that affects how `default_conversion' will behave.  */
>>         if (TREE_CODE (totype) == REFERENCE_TYPE
>> diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
>> index 91db32a..13fb401 100644
>> --- a/gcc/cp/typeck.c
>> +++ b/gcc/cp/typeck.c
>> @@ -4423,6 +4423,23 @@ cp_build_binary_op (location_t location,
>>                 warning (OPT_Waddress, "the address of %qD will never be NULL",
>>                          TREE_OPERAND (op0, 0));
>>             }
>> +
>> +         if (CONVERT_EXPR_P (op0)
>> +             && TREE_CODE (TREE_TYPE (TREE_OPERAND (op0, 0)))
>> +                == REFERENCE_TYPE)
>> +           {
>> +             tree inner_op0 = op0;
>> +             STRIP_NOPS (inner_op0);
>> +
>> +             if ((complain & tf_warning)
>> +                 && c_inhibit_evaluation_warnings == 0
>> +                 && !TREE_NO_WARNING (op0)
>> +                 && DECL_P (inner_op0))
>> +               warning (OPT_Waddress,
>> +                        "the compiler can assume that the address of "
>> +                        "%qD will never be NULL",
>> +                        inner_op0);
>> +           }
>>         }
>>        else if (((code1 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type1))
>>                 && null_ptr_cst_p (op0))
>> @@ -4445,6 +4462,23 @@ cp_build_binary_op (location_t location,
>>                 warning (OPT_Waddress, "the address of %qD will never be NULL",
>>                          TREE_OPERAND (op1, 0));
>>             }
>> +
>> +         if (CONVERT_EXPR_P (op1)
>> +             && TREE_CODE (TREE_TYPE (TREE_OPERAND (op1, 0)))
>> +                == REFERENCE_TYPE)
>> +           {
>> +             tree inner_op1 = op1;
>> +             STRIP_NOPS (inner_op1);
>> +
>> +             if ((complain & tf_warning)
>> +                 && c_inhibit_evaluation_warnings == 0
>> +                 && !TREE_NO_WARNING (op1)
>> +                 && DECL_P (inner_op1))
>> +               warning (OPT_Waddress,
>> +                        "the compiler can assume that the address of "
>> +                        "%qD will never be NULL",
>> +                        inner_op1);
>> +           }
>>         }
>>        else if ((code0 == POINTER_TYPE && code1 == POINTER_TYPE)
>>                || (TYPE_PTRDATAMEM_P (type0) && TYPE_PTRDATAMEM_P (type1)))
>> diff --git a/gcc/testsuite/g++.dg/warn/Walways-true-3.C b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
>> new file mode 100644
>> index 0000000..0d13d3f
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
>> @@ -0,0 +1,45 @@
>> +// { dg-options "-Waddress" }
>> +
>> +void foo (void);
>> +
>> +int d;
>> +int &c = d;
>> +
>> +void
>> +bar (int &a)
>> +{
>> +  int &b = a;
>> +
>> +  if ((int *)&a) // { dg-warning "address of" }
>> +    foo ();
>> +
>> +  if (&b) // { dg-warning "address of" }
>> +    foo ();
>> +
>> +  if (!&c) // { dg-warning "address of" }
>> +    foo ();
>> +
>> +  if (!&(int &)(int &)a) // { dg-warning "address of" }
>> +    foo ();
>> +
>> +  if (&a == 0) // { dg-warning "never be NULL" }
>> +    foo ();
>> +
>> +  if (&b != 0) // { dg-warning "never be NULL" }
>> +    foo ();
>> +
>> +  if (0 == &(int &)(int &)c) // { dg-warning "never be NULL" }
>> +    foo ();
>> +
>> +  if (&a != (int *)0) // { dg-warning "never be NULL" }
>> +    foo ();
>> +}
>> +
>> +bool
>> +bar_1 (int &a)
>> +{
>> +  if (d == 5)
>> +    return &a; // { dg-warning "address of" }
>> +  else
>> +    return !&(int &)(int &)a; // { dg-warning "address of" }
>> +}
>> --
>> 2.4.0.rc2.31.g7c597ef
>>
>
> Ping.

Ping.