isl 0.26 C++17 issues when bootstrapping with GCC

isl 0.26 C++17 issues when bootstrapping with GCC

[Ben Boeckel]

Hi,

I tried adding isl 0.26 to a 13.2 GCC build using Iain's macOS aarch64
patches:

    https://github.com/iains/gcc-13-branch

It seems that the bootstrap's `CXX='g++ -std=c++11'` confuses isl's
build where C++17 is expected to work by disabling C++17 behind its
back. Should GCC not add this flag for its dependencies but only its own
build perhaps?

isl bug report thread (with isl configure logs and the like):

    https://groups.google.com/g/isl-development/c/ShnQcW_35ZQ

Thanks,

--Ben

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Richard Biener]

> Am 29.08.2023 um 16:30 schrieb Ben Boeckel via Gcc <gcc@gcc.gnu.org>:
> 
> Hi,
> 
> I tried adding isl 0.26 to a 13.2 GCC build using Iain's macOS aarch64
> patches:
> 
>    https://github.com/iains/gcc-13-branch
> 
> It seems that the bootstrap's `CXX='g++ -std=c++11'` confuses isl's
> build where C++17 is expected to work by disabling C++17 behind its
> back. Should GCC not add this flag for its dependencies but only its own
> build perhaps?

I suppose for bootstrapping we could disable ISL during stage1 since it enables an optional feature only.  Other than that GCC only requires a C++11 compiler for building, so ISL breaks that constraint with requiring C++17.

Richard 

> isl bug report thread (with isl configure logs and the like):
> 
>    https://groups.google.com/g/isl-development/c/ShnQcW_35ZQ
> 
> Thanks,
> 
> --Ben

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Ben Boeckel]

On Tue, Aug 29, 2023 at 18:57:37 +0200, Richard Biener wrote:
> I suppose for bootstrapping we could disable ISL during stage1 since
> it enables an optional feature only.  Other than that GCC only
> requires a C++11 compiler for building, so ISL breaks that constraint
> with requiring C++17.

Note that it doesn't *require* it per sé; the tests that try it are
compiled if C++17 support was detected at all. The headers seem to just
have optional header-only `std::any`-using APIs if C++17 is around.
`isl` supporting a flag to disable the tests would also work, but that
doesn't fix 0.26. It also doesn't mean it won't start requiring C++17 at
some point in the future.

In light of that, I feel that skipping it for bootstrap is probably the
right solution here. Alas, my skill with autotools is closer to the
caveman-with-club level rather than that of a surgeon.

--Ben

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Iain Sandoe]

This 

> On 30 Aug 2023, at 00:32, Ben Boeckel via Gcc <gcc@gcc.gnu.org> wrote:
> 
> On Tue, Aug 29, 2023 at 18:57:37 +0200, Richard Biener wrote:
>> I suppose for bootstrapping we could disable ISL during stage1 since
>> it enables an optional feature only.  Other than that GCC only
>> requires a C++11 compiler for building, so ISL breaks that constraint
>> with requiring C++17.
> 
> Note that it doesn't *require* it per sé; the tests that try it are
> compiled if C++17 support was detected at all. The headers seem to just
> have optional header-only `std::any`-using APIs if C++17 is around.
> `isl` supporting a flag to disable the tests would also work, but that
> doesn't fix 0.26. It also doesn't mean it won't start requiring C++17 at
> some point in the future.

Perhaps, in the short-term (i.e. before it requires C++ > 11) we can
solve this by ensuring that we pass -std=c++11 to the configure stages
as well as to the build.  ISTM that configure is finding C++17-capability
(because we do not, I think, force C++11 for the configure) and then 
the build takes it away by forcing -std=c++11.

[ will try this out ]

> In light of that, I feel that skipping it for bootstrap is probably the
> right solution here. Alas, my skill with autotools is closer to the
> caveman-with-club level rather than that of a surgeon.

I am not sure we have an easy way to exclude a host module from
stage1 only (but ICBW).

Iain

> 
> --Ben

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Iain Sandoe]

> On 13 May 2024, at 16:05, Iain Sandoe via Gcc <gcc@gcc.gnu.org> wrote:
>> On 30 Aug 2023, at 00:32, Ben Boeckel via Gcc <gcc@gcc.gnu.org> wrote:
>> 
>> On Tue, Aug 29, 2023 at 18:57:37 +0200, Richard Biener wrote:
>>> I suppose for bootstrapping we could disable ISL during stage1 since
>>> it enables an optional feature only.  Other than that GCC only
>>> requires a C++11 compiler for building, so ISL breaks that constraint
>>> with requiring C++17.
>> 
>> Note that it doesn't *require* it per sé; the tests that try it are
>> compiled if C++17 support was detected at all. The headers seem to just
>> have optional header-only `std::any`-using APIs if C++17 is around.
>> `isl` supporting a flag to disable the tests would also work, but that
>> doesn't fix 0.26. It also doesn't mean it won't start requiring C++17 at
>> some point in the future.
> 
> Perhaps, in the short-term (i.e. before it requires C++ > 11) we can
> solve this by ensuring that we pass -std=c++11 to the configure stages
> as well as to the build.  ISTM that configure is finding C++17-capability
> (because we do not, I think, force C++11 for the configure) and then 
> the build takes it away by forcing -std=c++11.

That was not right.
We add std=c++11 to the compiler command.

However,as noted (earlier in this thread) the isl configure has the idiom
 - does the compiler do c++17 with no options?
 - does the compiler do c++17 if we add -std=c++17?

where the second one overrides our setting of std=c++11 in the compiler
comand.

(I think that this is a reasonably often used idiom in configures)

However the isl configure _does_ still append CXXFLAGS, and so that if
we add -std=c++11 to those, it re-asserts our intent.

Maybe we should just add the -std=c++11 to CXXFLAGS instead of the
compiler command?

Iain

>> In light of that, I feel that skipping it for bootstrap is probably the
>> right solution here. Alas, my skill with autotools is closer to the
>> caveman-with-club level rather than that of a surgeon.
> 
> I am not sure we have an easy way to exclude a host module from
> stage1 only (but ICBW).
> 
> Iain
> 
>> 
>> --Ben

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Richard Biener]

On Mon, May 13, 2024 at 6:00 PM Iain Sandoe <iain@sandoe.co.uk> wrote:
>
>
>
> > On 13 May 2024, at 16:05, Iain Sandoe via Gcc <gcc@gcc.gnu.org> wrote:
> >> On 30 Aug 2023, at 00:32, Ben Boeckel via Gcc <gcc@gcc.gnu.org> wrote:
> >>
> >> On Tue, Aug 29, 2023 at 18:57:37 +0200, Richard Biener wrote:
> >>> I suppose for bootstrapping we could disable ISL during stage1 since
> >>> it enables an optional feature only.  Other than that GCC only
> >>> requires a C++11 compiler for building, so ISL breaks that constraint
> >>> with requiring C++17.
> >>
> >> Note that it doesn't *require* it per sé; the tests that try it are
> >> compiled if C++17 support was detected at all. The headers seem to just
> >> have optional header-only `std::any`-using APIs if C++17 is around.
> >> `isl` supporting a flag to disable the tests would also work, but that
> >> doesn't fix 0.26. It also doesn't mean it won't start requiring C++17 at
> >> some point in the future.
> >
> > Perhaps, in the short-term (i.e. before it requires C++ > 11) we can
> > solve this by ensuring that we pass -std=c++11 to the configure stages
> > as well as to the build.  ISTM that configure is finding C++17-capability
> > (because we do not, I think, force C++11 for the configure) and then
> > the build takes it away by forcing -std=c++11.
>
> That was not right.
> We add std=c++11 to the compiler command.
>
> However,as noted (earlier in this thread) the isl configure has the idiom
>  - does the compiler do c++17 with no options?
>  - does the compiler do c++17 if we add -std=c++17?
>
> where the second one overrides our setting of std=c++11 in the compiler
> comand.
>
> (I think that this is a reasonably often used idiom in configures)
>
> However the isl configure _does_ still append CXXFLAGS, and so that if
> we add -std=c++11 to those, it re-asserts our intent.
>
> Maybe we should just add the -std=c++11 to CXXFLAGS instead of the
> compiler command?

I don't understand.  If we set CXX to g++ -std=c++11 and ISL checks
for -std=c++17 why does it then fail to add that to CXXFLAGS?

> Iain
>
> >> In light of that, I feel that skipping it for bootstrap is probably the
> >> right solution here. Alas, my skill with autotools is closer to the
> >> caveman-with-club level rather than that of a surgeon.
> >
> > I am not sure we have an easy way to exclude a host module from
> > stage1 only (but ICBW).
> >
> > Iain
> >
> >>
> >> --Ben
>

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Iain Sandoe]

> On 13 May 2024, at 18:46, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Mon, May 13, 2024 at 6:00 PM Iain Sandoe <iain@sandoe.co.uk> wrote:
>> 
>> 
>> 
>>> On 13 May 2024, at 16:05, Iain Sandoe via Gcc <gcc@gcc.gnu.org> wrote:
>>>> On 30 Aug 2023, at 00:32, Ben Boeckel via Gcc <gcc@gcc.gnu.org> wrote:
>>>> 
>>>> On Tue, Aug 29, 2023 at 18:57:37 +0200, Richard Biener wrote:
>>>>> I suppose for bootstrapping we could disable ISL during stage1 since
>>>>> it enables an optional feature only.  Other than that GCC only
>>>>> requires a C++11 compiler for building, so ISL breaks that constraint
>>>>> with requiring C++17.
>>>> 
>>>> Note that it doesn't *require* it per sé; the tests that try it are
>>>> compiled if C++17 support was detected at all. The headers seem to just
>>>> have optional header-only `std::any`-using APIs if C++17 is around.
>>>> `isl` supporting a flag to disable the tests would also work, but that
>>>> doesn't fix 0.26. It also doesn't mean it won't start requiring C++17 at
>>>> some point in the future.
>>> 
>>> Perhaps, in the short-term (i.e. before it requires C++ > 11) we can
>>> solve this by ensuring that we pass -std=c++11 to the configure stages
>>> as well as to the build.  ISTM that configure is finding C++17-capability
>>> (because we do not, I think, force C++11 for the configure) and then
>>> the build takes it away by forcing -std=c++11.
>> 
>> That was not right.
>> We add std=c++11 to the compiler command.
>> 
>> However,as noted (earlier in this thread) the isl configure has the idiom
>> - does the compiler do c++17 with no options?
>> - does the compiler do c++17 if we add -std=c++17?
>> 
>> where the second one overrides our setting of std=c++11 in the compiler
>> comand.
>> 
>> (I think that this is a reasonably often used idiom in configures)
>> 
>> However the isl configure _does_ still append CXXFLAGS, and so that if
>> we add -std=c++11 to those, it re-asserts our intent.
>> 
>> Maybe we should just add the -std=c++11 to CXXFLAGS instead of the
>> compiler command?
> 
> I don't understand.  If we set CXX to g++ -std=c++11 and ISL checks
> for -std=c++17 why does it then fail to add that to CXXFLAGS?

This appears to be the underlying bug.

— isl configure.ac does:

AX_CXX_COMPILE_STDCXX_17([], [optional])

….

AM_CONDITIONAL(HAVE_CXX17, test "x$HAVE_CXX17" = "x1”)

— and then Makefile.am adds the c++17-requirements:

if HAVE_CXX17
  noinst_PROGRAMS += isl_test_cpp17 isl_test_cpp17-checked
  TESTS += isl_test_cpp17 isl_test_cpp17-checked
endif

.. this mechanism does not seem to preserve the fact that an additional
-std=c++17 was needed to get the CXX17 (and there is no mention of
CXXFLAGS in Makefile.am) 

Not sure if it’s a bug in isl’s config - or a limitation of 
AX_CXX_COMPILE_STDCXX_17 itself.

— assuming we file a bug and it gets agreed and fixed, we’ll still need 
either to skip broken versions or work around it (I have no specific
preference - although I do build isl in-tree, so far 0.24 has been OK).

Iain


> 
>> Iain
>> 
>>>> In light of that, I feel that skipping it for bootstrap is probably the
>>>> right solution here. Alas, my skill with autotools is closer to the
>>>> caveman-with-club level rather than that of a surgeon.
>>> 
>>> I am not sure we have an easy way to exclude a host module from
>>> stage1 only (but ICBW).
>>> 
>>> Iain
>>> 
>>>> 
>>>> --Ben

Re: isl 0.26 C++17 issues when bootstrapping with GCC

[Iain Sandoe]

> On 13 May 2024, at 19:43, Iain Sandoe <iain@sandoe.co.uk> wrote:
> 
> 
> 
>> On 13 May 2024, at 18:46, Richard Biener <richard.guenther@gmail.com> wrote:
>> 
>> On Mon, May 13, 2024 at 6:00 PM Iain Sandoe <iain@sandoe.co.uk> wrote:
>>> 
>>> 
>>> 
>>>> On 13 May 2024, at 16:05, Iain Sandoe via Gcc <gcc@gcc.gnu.org> wrote:
>>>>> On 30 Aug 2023, at 00:32, Ben Boeckel via Gcc <gcc@gcc.gnu.org> wrote:
>>>>> 
>>>>> On Tue, Aug 29, 2023 at 18:57:37 +0200, Richard Biener wrote:
>>>>>> I suppose for bootstrapping we could disable ISL during stage1 since
>>>>>> it enables an optional feature only.  Other than that GCC only
>>>>>> requires a C++11 compiler for building, so ISL breaks that constraint
>>>>>> with requiring C++17.
>>>>> 
>>>>> Note that it doesn't *require* it per sé; the tests that try it are
>>>>> compiled if C++17 support was detected at all. The headers seem to just
>>>>> have optional header-only `std::any`-using APIs if C++17 is around.
>>>>> `isl` supporting a flag to disable the tests would also work, but that
>>>>> doesn't fix 0.26. It also doesn't mean it won't start requiring C++17 at
>>>>> some point in the future.
>>>> 
>>>> Perhaps, in the short-term (i.e. before it requires C++ > 11) we can
>>>> solve this by ensuring that we pass -std=c++11 to the configure stages
>>>> as well as to the build.  ISTM that configure is finding C++17-capability
>>>> (because we do not, I think, force C++11 for the configure) and then
>>>> the build takes it away by forcing -std=c++11.
>>> 
>>> That was not right.
>>> We add std=c++11 to the compiler command.
>>> 
>>> However,as noted (earlier in this thread) the isl configure has the idiom
>>> - does the compiler do c++17 with no options?
>>> - does the compiler do c++17 if we add -std=c++17?
>>> 
>>> where the second one overrides our setting of std=c++11 in the compiler
>>> comand.
>>> 
>>> (I think that this is a reasonably often used idiom in configures)
>>> 
>>> However the isl configure _does_ still append CXXFLAGS, and so that if
>>> we add -std=c++11 to those, it re-asserts our intent.
>>> 
>>> Maybe we should just add the -std=c++11 to CXXFLAGS instead of the
>>> compiler command?
>> 
>> I don't understand.  If we set CXX to g++ -std=c++11 and ISL checks
>> for -std=c++17 why does it then fail to add that to CXXFLAGS?
> 
> This appears to be the underlying bug.
> 
> — isl configure.ac does:
> 
> AX_CXX_COMPILE_STDCXX_17([], [optional])
> 
> ….
> 
> AM_CONDITIONAL(HAVE_CXX17, test "x$HAVE_CXX17" = "x1”)
> 
> — and then Makefile.am adds the c++17-requirements:
> 
> if HAVE_CXX17
>  noinst_PROGRAMS += isl_test_cpp17 isl_test_cpp17-checked
>  TESTS += isl_test_cpp17 isl_test_cpp17-checked
> endif
> 
> .. this mechanism does not seem to preserve the fact that an additional
> -std=c++17 was needed to get the CXX17 (and there is no mention of
> CXXFLAGS in Makefile.am) 
> 
> Not sure if it’s a bug in isl’s config - or a limitation of 
> AX_CXX_COMPILE_STDCXX_17 itself.
> 
> — assuming we file a bug and it gets agreed and fixed, we’ll still need 
> either to skip broken versions or work around it (I have no specific
> preference - although I do build isl in-tree, so far 0.24 has been OK)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115077