[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

Paolo Carlini  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |FIXED
   Target Milestone|--- |8.0

--- Comment #10 from Paolo Carlini  ---
Fixed in trunk.

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #9 from paolo at gcc dot gnu.org  ---
Author: paolo
Date: Mon Oct  2 12:40:26 2017
New Revision: 253350

URL: https://gcc.gnu.org/viewcvs?rev=253350=gcc=rev
Log:
2017-10-02  Paolo Carlini  

PR c++/79180
* g++.dg/cpp0x/lambda/lambda-nested8.C: New.
* g++.dg/torture/pr79180.C: Likewise.

PR c++/71386
* g++.dg/cpp1y/lambda-generic-nested1.C: New.

Added:
trunk/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested8.C
trunk/gcc/testsuite/g++.dg/cpp1y/lambda-generic-nested1.C
trunk/gcc/testsuite/g++.dg/torture/pr79180.C
Modified:
trunk/gcc/testsuite/ChangeLog

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #7 from Richard Biener  ---
ISTR a similar bug in C++ lambda support related how we map them to nested
functions.  PR69756.

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #6 from Marc Glisse  ---
Slightly simpler

template
auto List(XS...xs)
{
  return [=](auto processList){return processList(xs...);};
};

auto l1 = List(42);

auto foo = [](auto... xs1)
  {
return [=]()
{ 
  return l1([=](auto)
  {
return __builtin_printf("%d",xs1...);
  });  
};
  };

int main()
{
  auto concat = l1(foo);
  concat();
  __builtin_printf("\n");
}


If I make xs1 non-variadic (just erase '...' in 2 places), things work. The
main difference seems to be in  [with auto:2 = {int}] (we
write to some place in the stack then re-read the value from another place) but
it isn't clear what is going wrong there.

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #5 from Marc Glisse  ---
(In reply to Anton Mitrokhin from comment #3)
> I see those warnings with -O3, but not with -O0. Why is that?

As the documentation says, this warning depends on optimizations. A bogus
optimization that breaks the code may thus also cause this warning.

> I also do not see what is wrong with the code.

If you manage to reduce the example a little more, with fewer lambdas, that
might help with the debugging.

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

Andrew Pinski  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2016-06-26
 Ever confirmed|0   |1

--- Comment #4 from Andrew Pinski  ---
Confirmed,  looks like GCC is getting confused somewhere but I can't figure it
out easily.

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[anton.mitrokhin at phystech dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #3 from Anton Mitrokhin  ---
I see those warnings with -O3, but not with -O0. Why is that?
I also do not see what is wrong with the code.

Note, that clang with all warnings enabled (and ub sanitizer!) will also not
produce any warnings and will generate correct code.

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #2 from Andrew Pinski  ---
With -Wall -W I get the following warnings from gcc:

t9.cc: In function ‘int main()’:
t9.cc:37:44: warning: ‘xs1#0’ is used uninitialized in this function
[-Wuninitialized]
 auto print_func = [](int x){printf("%d ",x);return x;};
^
t9.cc:9:30: note: ‘xs1#0’ was declared here
   return [=](auto processList){return processList(xs...);};
  ^
t9.cc:37:44: warning: ‘xs1#1’ is used uninitialized in this function
[-Wuninitialized]
 auto print_func = [](int x){printf("%d ",x);return x;};
^
t9.cc:9:30: note: ‘xs1#1’ was declared here
   return [=](auto processList){return processList(xs...);};
  ^
t9.cc:37:44: warning: ‘xs1#2’ is used uninitialized in this function
[-Wuninitialized]
 auto print_func = [](int x){printf("%d ",x);return x;};
^
t9.cc:9:30: note: ‘xs1#2’ was declared here
   return [=](auto processList){return processList(xs...);};
  ^

[Bug c++/71386] Wrong code on c++14 (GCC trunk)

[anton.mitrokhin at phystech dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71386

--- Comment #1 from Anton Mitrokhin  ---
Could anyone please take a look?