[Bug middle-end/104958] New: missing -Wdangling-pointer leaking local address through struct member

[Bug middle-end/104958] New: missing -Wdangling-pointer leaking local address through struct member

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104958

            Bug ID: 104958
           Summary: missing -Wdangling-pointer leaking local address
                    through struct member
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

As discussed in
https://gcc.gnu.org/pipermail/gcc-patches/2022-February/590230.html both
functions in the following test case leak the address of the local variable to
their caller and should trigger a -Wdangling pointer but only one of them does.
 The patch submitted to implement this missing functionality was deferred until
GCC 13:

https://gcc.gnu.org/pipermail/gcc-patches/attachments/20220210/2641dce0/attachment-0003.bin

$ cat x.c && gcc -S -Wall x.c
struct S { void *p; };

void f (struct S *p)
{
  int j;
  p->p = &j;             // -Wdangling-pointer
}

struct S g (void)
{
  int i;
  struct S s = { &i };   // missing -Wdangling-pointer
  return s;
}

x.c: In function ‘f’:
x.c:6:8: warning: storing the address of local variable ‘j’ in ‘*p.p’
[-Wdangling-pointer=]
    6 |   p->p = &j;             // -Wdangling-pointer
      |   ~~~~~^~~~
x.c:5:7: note: ‘j’ declared here
    5 |   int j;
      |       ^
x.c:5:7: note: ‘p’ declared here

[Bug middle-end/104958] missing -Wdangling-pointer leaking local address through struct member

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104958

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-03-16
           Keywords|                            |diagnostic
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
             Blocks|                            |104077


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104077
[Bug 104077] bogus/missing -Wdangling-pointer

[Bug middle-end/104958] missing -Wdangling-pointer leaking local address through struct member

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104958

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ozixtheorange at gmail dot com

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 106508 has been marked as a duplicate of this bug. ***

[Bug middle-end/104958] missing -Wdangling-pointer leaking local address through struct member

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104958

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
A C++ example with lamdbas which shows the same issue here (the IR is basically
the same):

int outer;
auto fn1(int val = 0){
  return [&]{
    outer = val; // invalid
  };
}