[Bug c++/64877] New: strange warning message from -Waddress

[Bug c++/64877] New: strange warning message from -Waddress

[tromey at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

            Bug ID: 64877
           Summary: strange warning message from -Waddress
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tromey at gcc dot gnu.org

I found a spot in firefox that tries to prevent hiding
using:

    explicit ScopedGLWrapper(GLContext* gl)
        : mIsUnwrapped(false)
        , mGL(gl)
    {
        MOZ_ASSERT(&ScopedGLWrapper<Derived>::Unwrap == &Derived::Unwrap);

[...]

    void Unwrap() {
...
    }

gcc 5 warns about this assert:

/home/tromey/firefox-git/gecko-dev/gfx/gl/ScopedGLHelpers.h:35:54: error: the
address of ‘void mozilla::gl::ScopedGLWrapper<Derived>::Unwrap() [with Derived
= mozilla::gl::ScopedGLState]’ will never be NULL [-Werror=address]
         MOZ_ASSERT(&ScopedGLWrapper<Derived>::Unwrap == &Derived::Unwrap);
                                                      ^

The message here is strange.  Whether or not the address can be NULL
is not an issue.  I don't see why -Waddress ought to warn here at all.
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Subject: [Bug c++/20710] g++ should warn when hiding non-virtual method in base class
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id 710

Tom Tromey <tromey at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at gcc dot gnu.org

--- Comment #8 from Tom Tromey <tromey at gcc dot gnu.org> ---
It would be nice to have a way to prevent hiding.

See the partial example in bug 64877.  Here, gcc 5
warns about the construct used to prevent hiding.
However, "final" will not work as the function in question
is non-virtual.

The class in question is a base class, so it seems rather
strange to make the function "virtual final".  And, while
not an issue in this particular case, that would in some
cases introduce a vtable where none was previously needed.

[Bug c++/64877] strange warning message from -Waddress

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Tom Tromey from comment #0)
> The message here is strange.  Whether or not the address can be NULL
> is not an issue.  I don't see why -Waddress ought to warn here at all.

Hard to say without a minimized testcase.
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Subject: [Bug jit/64873] jit testsuite failures on powerpc64le-unknown-linux-gnu
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd873

David Malcolm <dmalcolm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #3 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #2)
> I'll rerun the JIT build and tests, with the correct configuration flags for
> this hardware, and  with the candidate patches for PR jit/64810 (so that the
> jit honors them).

Indeed, upon applying the candidate fixes for PR jit/64810 posted to:
  https://gcc.gnu.org/ml/gcc-patches/2015-01/msg02704.html
and reconfiguring with:
  --with-cpu-64=power7 --with-tune-64=power8
the jit testsuite successfully runs to completion on this "box", with
everything passing (apart from known failure PR jit/64752); injected
options are visible in jit logs as:
    configure_time_options[0]: -mtune=power8
    configure_time_options[1]: -mcpu=power7

So this was a mixture of configuration error on my part, and a duplicate
of PR jit/64810.

Closing as a duplicate of PR jit/64810; sorry for the noise.

*** This bug has been marked as a duplicate of bug 64810 ***

[Bug c++/64877] strange warning message from -Waddress

[tromey at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

--- Comment #2 from Tom Tromey <tromey at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #1)

> Hard to say without a minimized testcase.

Yeah.

The original code is here:

https://dxr.mozilla.org/mozilla-central/source/gfx/gl/ScopedGLHelpers.h#35

My attempt to minimize it failed.
Here's what I tried.  I can't explain why this doesn't 
give any warnings as I would expect one on the second "assert",
based on what the manual says.

template<class Derived>
struct S
{
  void m() {
  }

  S()
  {
    if (&S<Derived>::Unwrap != &Derived::Unwrap)
      m();
    if (!(&Derived::UnwrapImpl))
      m();
  }

  void Unwrap() {
  }
};

struct T : public S<T>
{
  void UnwrapImpl() {
  }
};

T t;
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Subject: [Bug c++/64877] strange warning message from -Waddress
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

--- Comment #3 from Tom Tromey <tromey at gcc dot gnu.org> ---
Oops, had the wrong gcc in $PATH.
That test case does warn:

pokyo. g++ -std=c++11 -c -Wall -Waddress -O2 x.cc
x.cc: In instantiation of ‘S<Derived>::S() [with Derived = T]’:
x.cc:19:8:   required from here
x.cc:9:29: warning: the address of ‘void S<Derived>::Unwrap() [with Derived =
T]’ will never be NULL [-Waddress]
     if (&S<Derived>::Unwrap != &Derived::Unwrap)
                             ^


I think I would expect a warning on the second assert, but not the first.
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Subject: [Bug c++/64867] warning for passing non-POD to varargs function
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd867

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
FYI, g++ stopped warning on #c4 with r149721.

[Bug c++/64877] strange warning message from -Waddress

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-31
                 CC|                            |paolo.carlini at oracle dot com
            Version|unknown                     |5.0
     Ever confirmed|0                           |1

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Tom Tromey from comment #3)
> Oops, had the wrong gcc in $PATH.
> That test case does warn:
> 
> pokyo. g++ -std=c++11 -c -Wall -Waddress -O2 x.cc
> x.cc: In instantiation of ‘S<Derived>::S() [with Derived = T]’:
> x.cc:19:8:   required from here
> x.cc:9:29: warning: the address of ‘void S<Derived>::Unwrap() [with Derived
> = T]’ will never be NULL [-Waddress]
>      if (&S<Derived>::Unwrap != &Derived::Unwrap)
>                              ^
> 
> 
> I think I would expect a warning on the second assert, but not the first.

We hit this code in cp/typeck.c

                /* We generate:

                   (op0.pfn == op1.pfn
                   && (!op0.pfn || op0.delta == op1.delta))

                   The reason for the `!op0.pfn' bit is that a NULL
                   pointer-to-member is any member with a zero PFN; the
                   DELTA field is unspecified.  */

                e1 = cp_build_binary_op (location,
                                         EQ_EXPR, delta0, delta1, complain);
                e2 = cp_build_binary_op (location,
                                         EQ_EXPR,
                                         pfn0,
                                         build_zero_cst (TREE_TYPE (pfn0)),
                                         complain);
                e1 = cp_build_binary_op (location,
                                         TRUTH_ORIF_EXPR, e1, e2, complain);

thus, the !op0.pfn triggers the warning. It may be enough to pass tf_none
instead of complain for the two compiler-generated expressions. Alternatively,
since we know pfn0 cannot be NULL, do not generate this check. It seems quite
wasteful to go through the huge cp_build_binary_op just to build something that
will get optimized out.

Not working on this, but it seems feasible to fix. If it is a regression, you
may even convince someone to approve it for GCC 5.
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Subject: [Bug c++/64877] strange warning message from -Waddress
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
And just for the sake of completion, the warning we trigger is:

        else if (((code0 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type0))
                  && null_ptr_cst_p (op1))
                 /* Handle, eg, (void*)0 (c++/43906), and more.  */
                 || (code0 == POINTER_TYPE
                     && TYPE_PTR_P (type1) && integer_zerop (op1)))
          {
            if (TYPE_PTR_P (type1))
              result_type = composite_pointer_type (type0, type1, op0, op1,
                                                    CPO_COMPARISON, complain);
            else
              result_type = type0;

            if (TREE_CODE (op0) == ADDR_EXPR
B =>            && decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)))
              {
                if ((complain & tf_warning)
                    && c_inhibit_evaluation_warnings == 0)
                  warning (OPT_Waddress, "the address of %qD will never be
NULL",
                           TREE_OPERAND (op0, 0));
              }
          }

It could be enough to test decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)) to
avoid building !op0.pfn when not needed.
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Subject: [Bug c++/64791] Generic lambda fails to implicitly capture `const` variable
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd791

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Weird, I tried on my machine yesterday's r220267 and same result, no warning
(with -std=gnu++1z -Wall -Wextra). I guess that before closing this bug we need
either to figure out what's special about that web page or another report that
things are actually fine.

[Bug c++/64877] [5 Regression] strange warning message from -Waddress

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|strange warning message     |[5 Regression] strange
                   |from -Waddress              |warning message from
                   |                            |-Waddress

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Thanks Manuel for the analysis. Indeed, now -Waddress is much more general, and
those internally generated expressions are causing problems. Thus, following
your suggestion, I would propose something like the below, which I'm finishing
testing. Does it look Ok to you?


Index: typeck.c
===================================================================
--- typeck.c    (revision 220306)
+++ typeck.c    (working copy)
@@ -4552,35 +4552,44 @@ cp_build_binary_op (location_t location,

              The reason for the `!op0.pfn' bit is that a NULL
              pointer-to-member is any member with a zero PFN and
-             LSB of the DELTA field is 0.  */
+             LSB of the DELTA field is 0.  Note: avoid generating the
+         '|| (!op0.pfn && ...)' if !op0.pfn is known to be false.  */

-          e1 = cp_build_binary_op (location, BIT_AND_EXPR,
-                       delta0, 
-                       integer_one_node,
-                       complain);
-          e1 = cp_build_binary_op (location,
-                       EQ_EXPR, e1, integer_zero_node,
-                       complain);
-          e2 = cp_build_binary_op (location, BIT_AND_EXPR,
-                       delta1,
-                       integer_one_node,
-                       complain);
-          e2 = cp_build_binary_op (location,
-                       EQ_EXPR, e2, integer_zero_node,
-                       complain);
-          e1 = cp_build_binary_op (location,
-                       TRUTH_ANDIF_EXPR, e2, e1,
-                       complain);
-          e2 = cp_build_binary_op (location, EQ_EXPR,
-                       pfn0,
-                       build_zero_cst (TREE_TYPE (pfn0)),
-                       complain);
-          e2 = cp_build_binary_op (location,
-                       TRUTH_ANDIF_EXPR, e2, e1, complain);
-          e1 = cp_build_binary_op (location,
-                       EQ_EXPR, delta0, delta1, complain);
-          e1 = cp_build_binary_op (location,
-                       TRUTH_ORIF_EXPR, e1, e2, complain);
+          if (TREE_CODE (pfn0) != ADDR_EXPR
+          || !decl_with_nonnull_addr_p (TREE_OPERAND (pfn0, 0)))
+        {
+          e1 = cp_build_binary_op (location, BIT_AND_EXPR,
+                       delta0, 
+                       integer_one_node,
+                       complain);
+          e1 = cp_build_binary_op (location,
+                       EQ_EXPR, e1, integer_zero_node,
+                       complain);
+          e2 = cp_build_binary_op (location, BIT_AND_EXPR,
+                       delta1,
+                       integer_one_node,
+                       complain);
+          e2 = cp_build_binary_op (location,
+                       EQ_EXPR, e2, integer_zero_node,
+                       complain);
+          e1 = cp_build_binary_op (location,
+                       TRUTH_ANDIF_EXPR, e2, e1,
+                       complain);
+          e2 = cp_build_binary_op (location, EQ_EXPR,
+                       pfn0,
+                       build_zero_cst (TREE_TYPE (pfn0)),
+                       complain);
+          e2 = cp_build_binary_op (location,
+                       TRUTH_ANDIF_EXPR, e2, e1, complain);
+          e1 = cp_build_binary_op (location,
+                       EQ_EXPR, delta0, delta1, complain);
+          e1 = cp_build_binary_op (location,
+                       TRUTH_ORIF_EXPR, e1, e2, complain);
+
+        }
+          else
+        e1 = cp_build_binary_op (location,
+                     EQ_EXPR, delta0, delta1, complain);
         }
       else
         {
@@ -4591,17 +4600,22 @@ cp_build_binary_op (location_t location,

              The reason for the `!op0.pfn' bit is that a NULL
              pointer-to-member is any member with a zero PFN; the
-             DELTA field is unspecified.  */
+             DELTA field is unspecified.  Note: avoid generating the
+         '!op0.pfn ||' if !op0.pfn is known to be false.  */

               e1 = cp_build_binary_op (location,
                        EQ_EXPR, delta0, delta1, complain);
-          e2 = cp_build_binary_op (location,
-                       EQ_EXPR,
-                             pfn0,
-                          build_zero_cst (TREE_TYPE (pfn0)),
-                       complain);
-          e1 = cp_build_binary_op (location,
-                       TRUTH_ORIF_EXPR, e1, e2, complain);
+          if (TREE_CODE (pfn0) != ADDR_EXPR
+          || !decl_with_nonnull_addr_p (TREE_OPERAND (pfn0, 0)))
+        {
+          e2 = cp_build_binary_op (location,
+                       EQ_EXPR,
+                       pfn0,
+                       build_zero_cst (TREE_TYPE (pfn0)),
+                       complain);
+          e1 = cp_build_binary_op (location,
+                       TRUTH_ORIF_EXPR, e1, e2, complain);
+        }
         }
       e2 = build2 (EQ_EXPR, boolean_type_node, pfn0, pfn1);
       e = cp_build_binary_op (location,

[Bug c++/64877] [5 Regression] strange warning message from -Waddress

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

--- Comment #7 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Tue Feb  3 17:21:49 2015
New Revision: 220374

URL: https://gcc.gnu.org/viewcvs?rev=220374&root=gcc&view=rev
Log:
/cp
2015-02-03  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/64877
    * typeck.c (cp_build_binary_op): Avoid spurious -Waddress warnings
    for generated expressions.

/testsuite
2015-02-03  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/64877
    * g++.dg/warn/Waddress-2.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Waddress-2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/64877] [5 Regression] strange warning message from -Waddress

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64877

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|paolo.carlini at oracle dot com    |
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.0

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed.