warn-access: Prevent -Wuse-after-free on ARM [PR104213]

  Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
return, as mandated by the EABI.  To be entirely correct, it only
requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
like changing that now and possibly running into issues later on.

This patch uses suppress_warning on 'this' for certain cdtor_returns_this
cases in the C++ FE, and then warn_invalid_pointer makes use of this
information and doesn't warn.

In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
we build in build_delete_destructor_body, but the complication is that
the suppress_warning bits don't always survive gimplification; see e.g.
gimplify_modify_expr where we do

 6130       if (COMPARISON_CLASS_P (*from_p))
 6131         copy_warning (assign, *from_p);

but here we're not dealing with a comparison.  Removing that check
regresses uninit-pr74762.C.  Adding copy_warning (assign, *expr_p)
regresses c-c++-common/uninit-17.c.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	PR target/104213

gcc/cp/ChangeLog:

	* decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
	(finish_destructor_body): Likewise.
	* optimize.cc (build_delete_destructor_body): Likewise.

gcc/ChangeLog:

	* gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
	warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wuse-after-free2.C: New test.
---
 gcc/cp/decl.cc                               |  2 ++
 gcc/cp/optimize.cc                           |  1 +
 gcc/gimple-ssa-warn-access.cc                | 14 +++++++++++---
 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
 4 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C


base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
  

On 1/25/22 16:33, Marek Polacek via Gcc-patches wrote:
> Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> return, as mandated by the EABI.  To be entirely correct, it only
> requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> like changing that now and possibly running into issues later on.
> 
> This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> cases in the C++ FE, and then warn_invalid_pointer makes use of this
> information and doesn't warn.
> 
> In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
> we build in build_delete_destructor_body, but the complication is that
> the suppress_warning bits don't always survive gimplification; see e.g.
> gimplify_modify_expr where we do
> 
>   6130       if (COMPARISON_CLASS_P (*from_p))
>   6131         copy_warning (assign, *from_p);
> 
> but here we're not dealing with a comparison.  Removing that check
> regresses uninit-pr74762.C.  Adding copy_warning (assign, *expr_p)
> regresses c-c++-common/uninit-17.c.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

Thanks for picking this up!

My only concern with suppressing the warning for the pointer rather
than just for the return statement is that it not lead to false
negatives.  I played with the patch a little, trying to trigger one
but couldn't so it might be unfounded.  Still, I'd expect targeting
the statement to be a simpler change (the warning already checks
for the suppression bit on the statement).  Did you try it?

For reference, one of the test cases I tried is below.  It would
be good to  add it to the test suite to make sure the bug is caught
(there's a duplicate warning there that should at some point get
squashed).

struct A
{
   virtual ~A ();
   void f ();
};

A::~A ()
{
   operator delete (this);
   f ();
}

Martin

> 
> 	PR target/104213
> 
> gcc/cp/ChangeLog:
> 
> 	* decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
> 	(finish_destructor_body): Likewise.
> 	* optimize.cc (build_delete_destructor_body): Likewise.
> 
> gcc/ChangeLog:
> 
> 	* gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
> 	warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wuse-after-free2.C: New test.
> ---
>   gcc/cp/decl.cc                               |  2 ++
>   gcc/cp/optimize.cc                           |  1 +
>   gcc/gimple-ssa-warn-access.cc                | 14 +++++++++++---
>   gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
>   4 files changed, 24 insertions(+), 3 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> 
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 22d3dd1e2ad..6534a7fd320 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
>         add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
>   
>         val = DECL_ARGUMENTS (current_function_decl);
> +      suppress_warning (val, OPT_Wuse_after_free);
>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>   		    DECL_RESULT (current_function_decl), val);
>         /* Return the address of the object.  */
> @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
>         tree val;
>   
>         val = DECL_ARGUMENTS (current_function_decl);
> +      suppress_warning (val, OPT_Wuse_after_free);
>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>   		    DECL_RESULT (current_function_decl), val);
>         /* Return the address of the object.  */
> diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
> index 4ad3f1dc9aa..13ab8b7361e 100644
> --- a/gcc/cp/optimize.cc
> +++ b/gcc/cp/optimize.cc
> @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
>     if (targetm.cxx.cdtor_returns_this ())
>       {
>         tree val = DECL_ARGUMENTS (delete_dtor);
> +      suppress_warning (val, OPT_Wuse_after_free);
>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>                       DECL_RESULT (delete_dtor), val);
>         add_stmt (build_stmt (0, RETURN_EXPR, val));
> diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> index 8bc33eeb6fa..484bcd34c25 100644
> --- a/gcc/gimple-ssa-warn-access.cc
> +++ b/gcc/gimple-ssa-warn-access.cc
> @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
>   				    bool maybe, bool equality /* = false */)
>   {
>     /* Avoid printing the unhelpful "<unknown>" in the diagnostics.  */
> -  if (ref && TREE_CODE (ref) == SSA_NAME
> -      && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
> -    ref = NULL_TREE;
> +  if (ref && TREE_CODE (ref) == SSA_NAME)
> +    {
> +      tree var = SSA_NAME_VAR (ref);
> +      if (!var)
> +	ref = NULL_TREE;
> +      /* Don't warn for cases like when a cdtor returns 'this' on ARM.  */
> +      else if (warning_suppressed_p (var, OPT_Wuse_after_free))
> +	return;
> +      else if (DECL_ARTIFICIAL (var))
> +	ref = NULL_TREE;
> +    }
>   
>     location_t use_loc = gimple_location (use_stmt);
>     if (use_loc == UNKNOWN_LOCATION)
> diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> new file mode 100644
> index 00000000000..6d5f2bf01b5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> @@ -0,0 +1,10 @@
> +// PR target/104213
> +// { dg-do compile }
> +// { dg-options "-Wuse-after-free" }
> +
> +class C
> +{
> +    virtual ~C();
> +};
> +
> +C::~C() {} // { dg-bogus "used after" }
> 
> base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
  

On Tue, Jan 25, 2022 at 05:35:20PM -0700, Martin Sebor wrote:
> On 1/25/22 16:33, Marek Polacek via Gcc-patches wrote:
> > Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> > return, as mandated by the EABI.  To be entirely correct, it only
> > requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> > like changing that now and possibly running into issues later on.
> > 
> > This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> > cases in the C++ FE, and then warn_invalid_pointer makes use of this
> > information and doesn't warn.
> > 
> > In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
> > we build in build_delete_destructor_body, but the complication is that
> > the suppress_warning bits don't always survive gimplification; see e.g.
> > gimplify_modify_expr where we do
> > 
> >   6130       if (COMPARISON_CLASS_P (*from_p))
> >   6131         copy_warning (assign, *from_p);
> > 
> > but here we're not dealing with a comparison.  Removing that check
> > regresses uninit-pr74762.C.  Adding copy_warning (assign, *expr_p)
> > regresses c-c++-common/uninit-17.c.
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> Thanks for picking this up!
> 
> My only concern with suppressing the warning for the pointer rather
> than just for the return statement is that it not lead to false
> negatives.  I played with the patch a little, trying to trigger one
> but couldn't so it might be unfounded.  Still, I'd expect targeting
> the statement to be a simpler change (the warning already checks
> for the suppression bit on the statement).  Did you try it?
 
I did -- that is the "In my first attempt..." paragraph in my patch
(we don't use copy_warning to propagate the suppress_warning bits).
Maybe it'd be a more correct way to approach this, that is, somehow
tweak gimplify_modify_expr to copy_warning for this special case.

> For reference, one of the test cases I tried is below.  It would
> be good to  add it to the test suite to make sure the bug is caught
> (there's a duplicate warning there that should at some point get
> squashed).
> 
> struct A
> {
>   virtual ~A ();
>   void f ();
> };
> 
> A::~A ()
> {
>   operator delete (this);
>   f ();
> }

Sure, happy to add it.

> Martin
> 
> > 
> > 	PR target/104213
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
> > 	(finish_destructor_body): Likewise.
> > 	* optimize.cc (build_delete_destructor_body): Likewise.
> > 
> > gcc/ChangeLog:
> > 
> > 	* gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
> > 	warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/warn/Wuse-after-free2.C: New test.
> > ---
> >   gcc/cp/decl.cc                               |  2 ++
> >   gcc/cp/optimize.cc                           |  1 +
> >   gcc/gimple-ssa-warn-access.cc                | 14 +++++++++++---
> >   gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
> >   4 files changed, 24 insertions(+), 3 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> > 
> > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > index 22d3dd1e2ad..6534a7fd320 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
> >         add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
> >         val = DECL_ARGUMENTS (current_function_decl);
> > +      suppress_warning (val, OPT_Wuse_after_free);
> >         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> >   		    DECL_RESULT (current_function_decl), val);
> >         /* Return the address of the object.  */
> > @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
> >         tree val;
> >         val = DECL_ARGUMENTS (current_function_decl);
> > +      suppress_warning (val, OPT_Wuse_after_free);
> >         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> >   		    DECL_RESULT (current_function_decl), val);
> >         /* Return the address of the object.  */
> > diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
> > index 4ad3f1dc9aa..13ab8b7361e 100644
> > --- a/gcc/cp/optimize.cc
> > +++ b/gcc/cp/optimize.cc
> > @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
> >     if (targetm.cxx.cdtor_returns_this ())
> >       {
> >         tree val = DECL_ARGUMENTS (delete_dtor);
> > +      suppress_warning (val, OPT_Wuse_after_free);
> >         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
> >                       DECL_RESULT (delete_dtor), val);
> >         add_stmt (build_stmt (0, RETURN_EXPR, val));
> > diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> > index 8bc33eeb6fa..484bcd34c25 100644
> > --- a/gcc/gimple-ssa-warn-access.cc
> > +++ b/gcc/gimple-ssa-warn-access.cc
> > @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
> >   				    bool maybe, bool equality /* = false */)
> >   {
> >     /* Avoid printing the unhelpful "<unknown>" in the diagnostics.  */
> > -  if (ref && TREE_CODE (ref) == SSA_NAME
> > -      && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
> > -    ref = NULL_TREE;
> > +  if (ref && TREE_CODE (ref) == SSA_NAME)
> > +    {
> > +      tree var = SSA_NAME_VAR (ref);
> > +      if (!var)
> > +	ref = NULL_TREE;
> > +      /* Don't warn for cases like when a cdtor returns 'this' on ARM.  */
> > +      else if (warning_suppressed_p (var, OPT_Wuse_after_free))
> > +	return;
> > +      else if (DECL_ARTIFICIAL (var))
> > +	ref = NULL_TREE;
> > +    }
> >     location_t use_loc = gimple_location (use_stmt);
> >     if (use_loc == UNKNOWN_LOCATION)
> > diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> > new file mode 100644
> > index 00000000000..6d5f2bf01b5
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> > @@ -0,0 +1,10 @@
> > +// PR target/104213
> > +// { dg-do compile }
> > +// { dg-options "-Wuse-after-free" }
> > +
> > +class C
> > +{
> > +    virtual ~C();
> > +};
> > +
> > +C::~C() {} // { dg-bogus "used after" }
> > 
> > base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
> 

Marek
  

On 1/25/22 18:33, Marek Polacek wrote:
> Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
> return, as mandated by the EABI.  To be entirely correct, it only
> requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
> like changing that now and possibly running into issues later on.
> 
> This patch uses suppress_warning on 'this' for certain cdtor_returns_this
> cases in the C++ FE, and then warn_invalid_pointer makes use of this
> information and doesn't warn.
> 
> In my first attempt I tried suppress_warning the MODIFY_EXPR or RETURN_EXPR
> we build in build_delete_destructor_body, but the complication is that
> the suppress_warning bits don't always survive gimplification; see e.g.
> gimplify_modify_expr where we do
> 
>   6130       if (COMPARISON_CLASS_P (*from_p))
>   6131         copy_warning (assign, *from_p);
> 
> but here we're not dealing with a comparison.  Removing that check
> regresses uninit-pr74762.C.  Adding copy_warning (assign, *expr_p)
> regresses c-c++-common/uninit-17.c.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK if Martin doesn't have any suggestions.

> 	PR target/104213
> 
> gcc/cp/ChangeLog:
> 
> 	* decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
> 	(finish_destructor_body): Likewise.
> 	* optimize.cc (build_delete_destructor_body): Likewise.
> 
> gcc/ChangeLog:
> 
> 	* gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): Don't
> 	warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wuse-after-free2.C: New test.
> ---
>   gcc/cp/decl.cc                               |  2 ++
>   gcc/cp/optimize.cc                           |  1 +
>   gcc/gimple-ssa-warn-access.cc                | 14 +++++++++++---
>   gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
>   4 files changed, 24 insertions(+), 3 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> 
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 22d3dd1e2ad..6534a7fd320 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
>         add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
>   
>         val = DECL_ARGUMENTS (current_function_decl);
> +      suppress_warning (val, OPT_Wuse_after_free);
>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>   		    DECL_RESULT (current_function_decl), val);
>         /* Return the address of the object.  */
> @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
>         tree val;
>   
>         val = DECL_ARGUMENTS (current_function_decl);
> +      suppress_warning (val, OPT_Wuse_after_free);
>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>   		    DECL_RESULT (current_function_decl), val);
>         /* Return the address of the object.  */
> diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
> index 4ad3f1dc9aa..13ab8b7361e 100644
> --- a/gcc/cp/optimize.cc
> +++ b/gcc/cp/optimize.cc
> @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, tree complete_dtor)
>     if (targetm.cxx.cdtor_returns_this ())
>       {
>         tree val = DECL_ARGUMENTS (delete_dtor);
> +      suppress_warning (val, OPT_Wuse_after_free);
>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>                       DECL_RESULT (delete_dtor), val);
>         add_stmt (build_stmt (0, RETURN_EXPR, val));
> diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> index 8bc33eeb6fa..484bcd34c25 100644
> --- a/gcc/gimple-ssa-warn-access.cc
> +++ b/gcc/gimple-ssa-warn-access.cc
> @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, gimple *use_stmt,
>   				    bool maybe, bool equality /* = false */)
>   {
>     /* Avoid printing the unhelpful "<unknown>" in the diagnostics.  */
> -  if (ref && TREE_CODE (ref) == SSA_NAME
> -      && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
> -    ref = NULL_TREE;
> +  if (ref && TREE_CODE (ref) == SSA_NAME)
> +    {
> +      tree var = SSA_NAME_VAR (ref);
> +      if (!var)
> +	ref = NULL_TREE;
> +      /* Don't warn for cases like when a cdtor returns 'this' on ARM.  */
> +      else if (warning_suppressed_p (var, OPT_Wuse_after_free))
> +	return;
> +      else if (DECL_ARTIFICIAL (var))
> +	ref = NULL_TREE;
> +    }
>   
>     location_t use_loc = gimple_location (use_stmt);
>     if (use_loc == UNKNOWN_LOCATION)
> diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> new file mode 100644
> index 00000000000..6d5f2bf01b5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
> @@ -0,0 +1,10 @@
> +// PR target/104213
> +// { dg-do compile }
> +// { dg-options "-Wuse-after-free" }
> +
> +class C
> +{
> +    virtual ~C();
> +};
> +
> +C::~C() {} // { dg-bogus "used after" }
> 
> base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
  

On 1/26/22 08:24, Jason Merrill via Gcc-patches wrote:
> On 1/25/22 18:33, Marek Polacek wrote:
>> Here, -Wuse-after-free warns about using 'this' which, on ARM, cdtors
>> return, as mandated by the EABI.  To be entirely correct, it only
>> requires it for C1 and C2 ctors and D2 and D1 dtors, but I don't feel
>> like changing that now and possibly running into issues later on.
>>
>> This patch uses suppress_warning on 'this' for certain cdtor_returns_this
>> cases in the C++ FE, and then warn_invalid_pointer makes use of this
>> information and doesn't warn.
>>
>> In my first attempt I tried suppress_warning the MODIFY_EXPR or 
>> RETURN_EXPR
>> we build in build_delete_destructor_body, but the complication is that
>> the suppress_warning bits don't always survive gimplification; see e.g.
>> gimplify_modify_expr where we do
>>
>>   6130       if (COMPARISON_CLASS_P (*from_p))
>>   6131         copy_warning (assign, *from_p);
>>
>> but here we're not dealing with a comparison.  Removing that check
>> regresses uninit-pr74762.C.  Adding copy_warning (assign, *expr_p)
>> regresses c-c++-common/uninit-17.c.
>>
>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> OK if Martin doesn't have any suggestions.

Nothing further from me.

Thanks
Martin

> 
>>     PR target/104213
>>
>> gcc/cp/ChangeLog:
>>
>>     * decl.cc (finish_constructor_body): Suppress -Wuse-after-free.
>>     (finish_destructor_body): Likewise.
>>     * optimize.cc (build_delete_destructor_body): Likewise.
>>
>> gcc/ChangeLog:
>>
>>     * gimple-ssa-warn-access.cc (pass_waccess::warn_invalid_pointer): 
>> Don't
>>     warn when the SSA_NAME_VAR of REF has supressed -Wuse-after-free.
>>
>> gcc/testsuite/ChangeLog:
>>
>>     * g++.dg/warn/Wuse-after-free2.C: New test.
>> ---
>>   gcc/cp/decl.cc                               |  2 ++
>>   gcc/cp/optimize.cc                           |  1 +
>>   gcc/gimple-ssa-warn-access.cc                | 14 +++++++++++---
>>   gcc/testsuite/g++.dg/warn/Wuse-after-free2.C | 10 ++++++++++
>>   4 files changed, 24 insertions(+), 3 deletions(-)
>>   create mode 100644 gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>>
>> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
>> index 22d3dd1e2ad..6534a7fd320 100644
>> --- a/gcc/cp/decl.cc
>> +++ b/gcc/cp/decl.cc
>> @@ -17315,6 +17315,7 @@ finish_constructor_body (void)
>>         add_stmt (build_stmt (input_location, LABEL_EXPR, cdtor_label));
>>         val = DECL_ARGUMENTS (current_function_decl);
>> +      suppress_warning (val, OPT_Wuse_after_free);
>>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>>               DECL_RESULT (current_function_decl), val);
>>         /* Return the address of the object.  */
>> @@ -17408,6 +17409,7 @@ finish_destructor_body (void)
>>         tree val;
>>         val = DECL_ARGUMENTS (current_function_decl);
>> +      suppress_warning (val, OPT_Wuse_after_free);
>>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>>               DECL_RESULT (current_function_decl), val);
>>         /* Return the address of the object.  */
>> diff --git a/gcc/cp/optimize.cc b/gcc/cp/optimize.cc
>> index 4ad3f1dc9aa..13ab8b7361e 100644
>> --- a/gcc/cp/optimize.cc
>> +++ b/gcc/cp/optimize.cc
>> @@ -166,6 +166,7 @@ build_delete_destructor_body (tree delete_dtor, 
>> tree complete_dtor)
>>     if (targetm.cxx.cdtor_returns_this ())
>>       {
>>         tree val = DECL_ARGUMENTS (delete_dtor);
>> +      suppress_warning (val, OPT_Wuse_after_free);
>>         val = build2 (MODIFY_EXPR, TREE_TYPE (val),
>>                       DECL_RESULT (delete_dtor), val);
>>         add_stmt (build_stmt (0, RETURN_EXPR, val));
>> diff --git a/gcc/gimple-ssa-warn-access.cc 
>> b/gcc/gimple-ssa-warn-access.cc
>> index 8bc33eeb6fa..484bcd34c25 100644
>> --- a/gcc/gimple-ssa-warn-access.cc
>> +++ b/gcc/gimple-ssa-warn-access.cc
>> @@ -3880,9 +3880,17 @@ pass_waccess::warn_invalid_pointer (tree ref, 
>> gimple *use_stmt,
>>                       bool maybe, bool equality /* = false */)
>>   {
>>     /* Avoid printing the unhelpful "<unknown>" in the diagnostics.  */
>> -  if (ref && TREE_CODE (ref) == SSA_NAME
>> -      && (!SSA_NAME_VAR (ref) || DECL_ARTIFICIAL (SSA_NAME_VAR (ref))))
>> -    ref = NULL_TREE;
>> +  if (ref && TREE_CODE (ref) == SSA_NAME)
>> +    {
>> +      tree var = SSA_NAME_VAR (ref);
>> +      if (!var)
>> +    ref = NULL_TREE;
>> +      /* Don't warn for cases like when a cdtor returns 'this' on 
>> ARM.  */
>> +      else if (warning_suppressed_p (var, OPT_Wuse_after_free))
>> +    return;
>> +      else if (DECL_ARTIFICIAL (var))
>> +    ref = NULL_TREE;
>> +    }
>>     location_t use_loc = gimple_location (use_stmt);
>>     if (use_loc == UNKNOWN_LOCATION)
>> diff --git a/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C 
>> b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>> new file mode 100644
>> index 00000000000..6d5f2bf01b5
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/warn/Wuse-after-free2.C
>> @@ -0,0 +1,10 @@
>> +// PR target/104213
>> +// { dg-do compile }
>> +// { dg-options "-Wuse-after-free" }
>> +
>> +class C
>> +{
>> +    virtual ~C();
>> +};
>> +
>> +C::~C() {} // { dg-bogus "used after" }
>>
>> base-commit: aeac414923aa1e87986c7fc6f9b921d89a9b86cf
>