[PATCH] c++: for contracts, cdtors never return this

[PATCH] c++: for contracts, cdtors never return this

[Alexandre Oliva]

When targetm.cxx.cdtor_return_this() holds, cdtors have a
non-VOID_TYPE_P result, but IMHO this ABI implementation detail
shouldn't leak to the abstract language conceptual framework, in which
cdtors don't have return values.  For contracts, specifically those
that establish postconditions on results, such a leakage is present,
and the present patch puts an end to it: with it, cdtors get an error
for result postconditions regardless of the ABI.  This fixes
g++.dg/contracts/contracts-ctor-dtor2.C on arm-eabi.

Regstrapped on x86_64-linux-gnu, also tested on arm-eabi with default
cpu on trunk, and with tms570 on gcc-13.  Ok to install?


for  gcc/cp/ChangeLog

	* contracts.cc (check_postcondition_result): Cope with
	cdtor_return_this.
---
 gcc/cp/contracts.cc |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/contracts.cc b/gcc/cp/contracts.cc
index 66d2298a9bfac..035ca4827e758 100644
--- a/gcc/cp/contracts.cc
+++ b/gcc/cp/contracts.cc
@@ -636,7 +636,11 @@ make_postcondition_variable (cp_expr id)
 bool
 check_postcondition_result (tree decl, tree type, location_t loc)
 {
-  if (VOID_TYPE_P (type))
+  /* Do not be confused by targetm.cxx.cdtor_return_this ();
+     conceptually, cdtors have no return value.  */
+  if (VOID_TYPE_P (type)
+      || DECL_CONSTRUCTOR_P (decl)
+      || DECL_DESTRUCTOR_P (decl))
     {
       error_at (loc,
 		DECL_CONSTRUCTOR_P (decl)


-- 
Alexandre Oliva, happy hacker            https://FSFLA.org/blogs/lxo/
   Free Software Activist                   GNU Toolchain Engineer
More tolerance and less prejudice are key for inclusion and diversity
Excluding neuro-others for not behaving ""normal"" is *not* inclusive

Re: [PATCH] c++: for contracts, cdtors never return this

[Jason Merrill]

On 11/19/23 02:28, Alexandre Oliva wrote:
> 
> When targetm.cxx.cdtor_return_this() holds, cdtors have a
> non-VOID_TYPE_P result, but IMHO this ABI implementation detail
> shouldn't leak to the abstract language conceptual framework, in which
> cdtors don't have return values.  For contracts, specifically those
> that establish postconditions on results, such a leakage is present,
> and the present patch puts an end to it: with it, cdtors get an error
> for result postconditions regardless of the ABI.  This fixes
> g++.dg/contracts/contracts-ctor-dtor2.C on arm-eabi.
> 
> Regstrapped on x86_64-linux-gnu, also tested on arm-eabi with default
> cpu on trunk, and with tms570 on gcc-13.  Ok to install?

OK.

> 
> for  gcc/cp/ChangeLog
> 
> 	* contracts.cc (check_postcondition_result): Cope with
> 	cdtor_return_this.
> ---
>   gcc/cp/contracts.cc |    6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/cp/contracts.cc b/gcc/cp/contracts.cc
> index 66d2298a9bfac..035ca4827e758 100644
> --- a/gcc/cp/contracts.cc
> +++ b/gcc/cp/contracts.cc
> @@ -636,7 +636,11 @@ make_postcondition_variable (cp_expr id)
>   bool
>   check_postcondition_result (tree decl, tree type, location_t loc)
>   {
> -  if (VOID_TYPE_P (type))
> +  /* Do not be confused by targetm.cxx.cdtor_return_this ();
> +     conceptually, cdtors have no return value.  */
> +  if (VOID_TYPE_P (type)
> +      || DECL_CONSTRUCTOR_P (decl)
> +      || DECL_DESTRUCTOR_P (decl))
>       {
>         error_at (loc,
>   		DECL_CONSTRUCTOR_P (decl)
> 
> 

Re: [PATCH] c++: for contracts, cdtors never return this

[Torbjorn SVENSSON]

Hi,

Is it okay to backport 71804526d3a71a8c0f189a89ce3aa615784bfd8b to 
releases/gcc-13?

Without this backport, I see these failures on arm-none-eabi:

FAIL: g++.dg/contracts/contracts-ctor-dtor2.C    (test for errors, line 23)
FAIL: g++.dg/contracts/contracts-ctor-dtor2.C    (test for errors, line 27

Kind regards,
Torbjörn

On 2023-11-20 16:40, Jason Merrill wrote:
> On 11/19/23 02:28, Alexandre Oliva wrote:
>>
>> When targetm.cxx.cdtor_return_this() holds, cdtors have a
>> non-VOID_TYPE_P result, but IMHO this ABI implementation detail
>> shouldn't leak to the abstract language conceptual framework, in which
>> cdtors don't have return values.  For contracts, specifically those
>> that establish postconditions on results, such a leakage is present,
>> and the present patch puts an end to it: with it, cdtors get an error
>> for result postconditions regardless of the ABI.  This fixes
>> g++.dg/contracts/contracts-ctor-dtor2.C on arm-eabi.
>>
>> Regstrapped on x86_64-linux-gnu, also tested on arm-eabi with default
>> cpu on trunk, and with tms570 on gcc-13.  Ok to install?
> 
> OK.
> 
>>
>> for  gcc/cp/ChangeLog
>>
>>     * contracts.cc (check_postcondition_result): Cope with
>>     cdtor_return_this.
>> ---
>>   gcc/cp/contracts.cc |    6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/gcc/cp/contracts.cc b/gcc/cp/contracts.cc
>> index 66d2298a9bfac..035ca4827e758 100644
>> --- a/gcc/cp/contracts.cc
>> +++ b/gcc/cp/contracts.cc
>> @@ -636,7 +636,11 @@ make_postcondition_variable (cp_expr id)
>>   bool
>>   check_postcondition_result (tree decl, tree type, location_t loc)
>>   {
>> -  if (VOID_TYPE_P (type))
>> +  /* Do not be confused by targetm.cxx.cdtor_return_this ();
>> +     conceptually, cdtors have no return value.  */
>> +  if (VOID_TYPE_P (type)
>> +      || DECL_CONSTRUCTOR_P (decl)
>> +      || DECL_DESTRUCTOR_P (decl))
>>       {
>>         error_at (loc,
>>           DECL_CONSTRUCTOR_P (decl)
>>
>>
> 

Re: [PATCH] c++: for contracts, cdtors never return this

[Jason Merrill]

On 2/7/24 11:22, Torbjorn SVENSSON wrote:
> Hi,
> 
> Is it okay to backport 71804526d3a71a8c0f189a89ce3aa615784bfd8b to 
> releases/gcc-13?

OK.

> Without this backport, I see these failures on arm-none-eabi:
> 
> FAIL: g++.dg/contracts/contracts-ctor-dtor2.C    (test for errors, line 23)
> FAIL: g++.dg/contracts/contracts-ctor-dtor2.C    (test for errors, line 27
> 
> Kind regards,
> Torbjörn
> 
> On 2023-11-20 16:40, Jason Merrill wrote:
>> On 11/19/23 02:28, Alexandre Oliva wrote:
>>>
>>> When targetm.cxx.cdtor_return_this() holds, cdtors have a
>>> non-VOID_TYPE_P result, but IMHO this ABI implementation detail
>>> shouldn't leak to the abstract language conceptual framework, in which
>>> cdtors don't have return values.  For contracts, specifically those
>>> that establish postconditions on results, such a leakage is present,
>>> and the present patch puts an end to it: with it, cdtors get an error
>>> for result postconditions regardless of the ABI.  This fixes
>>> g++.dg/contracts/contracts-ctor-dtor2.C on arm-eabi.
>>>
>>> Regstrapped on x86_64-linux-gnu, also tested on arm-eabi with default
>>> cpu on trunk, and with tms570 on gcc-13.  Ok to install?
>>
>> OK.
>>
>>>
>>> for  gcc/cp/ChangeLog
>>>
>>>     * contracts.cc (check_postcondition_result): Cope with
>>>     cdtor_return_this.
>>> ---
>>>   gcc/cp/contracts.cc |    6 +++++-
>>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/gcc/cp/contracts.cc b/gcc/cp/contracts.cc
>>> index 66d2298a9bfac..035ca4827e758 100644
>>> --- a/gcc/cp/contracts.cc
>>> +++ b/gcc/cp/contracts.cc
>>> @@ -636,7 +636,11 @@ make_postcondition_variable (cp_expr id)
>>>   bool
>>>   check_postcondition_result (tree decl, tree type, location_t loc)
>>>   {
>>> -  if (VOID_TYPE_P (type))
>>> +  /* Do not be confused by targetm.cxx.cdtor_return_this ();
>>> +     conceptually, cdtors have no return value.  */
>>> +  if (VOID_TYPE_P (type)
>>> +      || DECL_CONSTRUCTOR_P (decl)
>>> +      || DECL_DESTRUCTOR_P (decl))
>>>       {
>>>         error_at (loc,
>>>           DECL_CONSTRUCTOR_P (decl)
>>>
>>>
>>
> 

Re: [PATCH] c++: for contracts, cdtors never return this

[Torbjorn SVENSSON]

On 2024-02-07 20:46, Jason Merrill wrote:
> On 2/7/24 11:22, Torbjorn SVENSSON wrote:
>> Hi,
>>
>> Is it okay to backport 71804526d3a71a8c0f189a89ce3aa615784bfd8b to 
>> releases/gcc-13?
> 
> OK.

Pushed as eae51472f68d9f922aa3a1a636f81467bfdae87a.