[Bug c++/60095] New: Dubious diagnostics for attempted surrogate call function

[Bug c++/60095] New: Dubious diagnostics for attempted surrogate call function

[lucdanton at free dot fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60095

            Bug ID: 60095
           Summary: Dubious diagnostics for attempted surrogate call
                    function
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lucdanton at free dot fr

Using ‘gcc version 4.9.0 20140123 (experimental) (GCC)’ with the following
snippet:

//--------

struct foo {
    typedef void(*ptr)(int&);
    operator ptr() const;
};

int main()
{
    foo f;
    void* p = 0;
    f(p);
}

//--------

$ g++-trunk -std=c++03 main.cpp 
main.cpp: In function 'int main()':
main.cpp:10:8: error: no match for call to '(foo) (void*&)'
     f(p);
        ^
main.cpp:1:8: note: candidate is:
 struct foo {
        ^
main.cpp:10:8: note: foo::ptr {aka void (*)(int&)} <conversion>
     f(p);
        ^
main.cpp:10:8: note:   candidate expects 2 arguments, 2 provided

Same output for all -std=c++{03,11,1y} modes. If e.g. foo has a call operator
instead, then the appropriate ‘no known conversion for argument 1 from 'void*'
to 'int&'’ is produced.
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From: "bernd.edlinger at hotmail dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ada/60078] acats c761007 fails on ARM
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`078

--- Comment #8 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Eric Botcazou from comment #7)
> > could it be that the Finalize procedure is missing some sort of spin lock?
>
> There are already explicit delays in the test, so very likely not.

I added the line "delay 0.01; -- <= additional delay here"

and the result was the test fails on X86_64.

If I rewrite both Finalize methods to use protected data like this
the test starts to pass again with the delays.

$ cat c761007_0.ads

with Ada.Finalization;
package C761007_0 is

  type Internal is new Ada.Finalization.Controlled
    with record
      Effect : Character;
    end record;

  procedure Finalize( I: in out Internal );

  protected Data is
    procedure Add( Effect : Character );
  private
    Side_Effect : String(1..80);  -- way bigger than needed
    Side_Effect_Finger : Natural := 0;
  end Data;

end C761007_0;


$ cat c761007_0.adb:

with TCTouch;
package body C761007_0 is

  procedure Finalize( I : in out Internal ) is
  begin
    Data.Add(I.Effect);
  end Finalize;

  protected body Data is
    procedure Add( Effect : Character ) is
      Previous_Side_Effect : Boolean := False;
    begin
      -- look to see if this character has been finalized yet
      for SEI in 1..Side_Effect_Finger loop
        Previous_Side_Effect := Previous_Side_Effect
                                or Side_Effect(Side_Effect_Finger) = Effect;
      end loop;

      delay 0.01; -- <= additional delay here

      -- if not, then tack it on to the string, and touch the character
      if not Previous_Side_Effect then
        Side_Effect_Finger := Side_Effect_Finger +1;
        Side_Effect(Side_Effect_Finger) := Effect;
        TCTouch.Touch(Effect);
      end if;

    end Add;
  end Data;

end C761007_0;