[Bug middle-end/110091] New: bogus -Wdangling-pointer on non-pointer values

[Bug middle-end/110091] New: bogus -Wdangling-pointer on non-pointer values

[patrickdepinguin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110091

            Bug ID: 110091
           Summary: bogus -Wdangling-pointer on non-pointer values
           Product: gcc
           Version: 12.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrickdepinguin at gmail dot com
  Target Milestone: ---

Following reduced testcase gives a bogus -Wdangling-pointer:

struct tEntry
{
    int value;
};

struct tOut
{
    int outvalue;
};
extern struct tOut *out;

extern int otherfunc(struct tEntry *);
extern void anotherfunc(int val);

void bar()
{
    struct tEntry entry = { 0 };

    if (otherfunc(&entry) != 0)
    {
        return;
    }

    if (out)
    {
        out->outvalue = entry.value;
    }

    anotherfunc(5);
}

void foo()
{
    bar();
}



$ gcc -O2  -Wall -Werror /opt/test.c
/opt/test.c: In function 'bar':
/opt/test.c:26:30: error: dangling pointer to 'entry' may be used
[-Werror=dangling-pointer=]
   26 |         out->outvalue = entry.value;
      |                         ~~~~~^~~~~~
/opt/test.c:17:19: note: 'entry' declared here
   17 |     struct tEntry entry = { 0 };
      |                   ^~~~~
In function 'bar',
    inlined from 'foo' at /opt/test.c:34:5:
/opt/test.c:26:30: error: dangling pointer to 'entry' may be used
[-Werror=dangling-pointer=]
   26 |         out->outvalue = entry.value;
      |                         ~~~~~^~~~~~
/opt/test.c: In function 'foo':
/opt/test.c:17:19: note: 'entry' declared here
   17 |     struct tEntry entry = { 0 };
      |                   ^~~~~
cc1: all warnings being treated as errors


entry is a local struct, initialized to 0, and passed as pointer to an external
function.
But the use being warned about is not using any pointer.


Tested with 12.2.0 (Debian), 12.2.1 (Gentoo), 12.3.0 (official gcc docker
image), 13.1.0 (official gcc docker image).

[Bug tree-optimization/110091] bogus -Wdangling-pointer on non-pointer values

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110091

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-06-02
           Keywords|                            |compile-time-hog
          Component|middle-end                  |tree-optimization
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Function split decides to split out the call to anotherfunc (and the clobber of
the entry struct) from bar and then the diagnostic gets confused from that.

This is a bad split in the first place.
```
Splitting function at:
Split point at BB 6
  header time: 19.904000 header size: 12
  split time: 7.260000 split size: 2
  bbs: 6
  SSA names to pass: 
...

void bar.part.0 ()
{
  struct tEntry entry;

  <bb 4> [local count: 1073741824]:

  <bb 2> [local count: 1073741824]:
  anotherfunc (5);
  entry ={v} {CLOBBER(eol)};

  <bb 3> [local count: 1073741824]:
  return;

}
```

[Bug tree-optimization/110091] [12/13/14 Regression] bogus -Wdangling-pointer on non-pointer values

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110091

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|bogus -Wdangling-pointer on |[12/13/14 Regression] bogus
                   |non-pointer values          |-Wdangling-pointer on
                   |                            |non-pointer values
   Target Milestone|---                         |12.4

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The split started happening in GCC 12 too.

[Bug tree-optimization/110091] [12/13/14 Regression] bogus -Wdangling-pointer on non-pointer values

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110091

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jamborm at gcc dot gnu.org
           Keywords|needs-bisection             |

--- Comment #3 from Martin Jambor <jamborm at gcc dot gnu.org> ---
The warning started appearing from its very introduction to gcc in
r12-6606-g9d6a0f388eb048 (Martin Sebor: Add -Wdangling-pointer [PR63272]).

[Bug tree-optimization/110091] [12/13/14 Regression] bogus -Wdangling-pointer on non-pointer values

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110091

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Honza?  Why do we consider to split before anotherfunc(5)?  It's an odd
place since we'll always arrive there from the point we insert the call?
The only other sensible point would have been before if (out), thus
BB4?