[Bug libstdc++/106871] New: std::function should not check func ptr on each call

[Bug libstdc++/106871] New: std::function should not check func ptr on each call

[rockeet at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106871

            Bug ID: 106871
           Summary: std::function should not check func ptr on each call
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rockeet at gmail dot com
  Target Milestone: ---

std::function should not check func ptr on each call, an optimization should
be:

define a 'default throw' function which just throws a std::bad_function_call.

in std::function constructor, set the function ptr to this 'default throw'
function. (assign nullptr also set this 'default throw' to std::function).

in this way, it is not needed to check the function ptr in each std::function
call. and the nullptr check can use any other 2 ptr-width fields of
std::function.

[Bug libstdc++/106871] std::function should not check func ptr on each call

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106871

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I've looked into this and I don't think it can be done without an ABI break.
Objects constructed in old code compiled by an older GCC would still have a
null pointer, so code compiled by a new GCC can't assume that the pointer is
never null.

We have another PR on the same subject anyway.

*** This bug has been marked as a duplicate of bug 56551 ***