Re: c++/3615: unneccessary temporary instance created during function call

Re: c++/3615: unneccessary temporary instance created during function call

[mmitchel]

Synopsis: unneccessary temporary instance created during function call

State-Changed-From-To: analyzed->closed
State-Changed-By: mmitchel
State-Changed-When: Tue Nov 20 01:06:21 2001
State-Changed-Why:
    Fixed.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=3615&database=gcc

Re: c++/3615: unneccessary temporary instance created during function call

[mmitchel]

The following reply was made to PR c++/3615; it has been noted by GNATS.

From: mmitchel@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  gdr@gcc.gnu.org, niemayer@isg.de
Cc:  
Subject: Re: c++/3615: unneccessary temporary instance created during function call
Date: 20 Nov 2001 09:06:22 -0000

 Synopsis: unneccessary temporary instance created during function call
 
 State-Changed-From-To: analyzed->closed
 State-Changed-By: mmitchel
 State-Changed-When: Tue Nov 20 01:06:21 2001
 State-Changed-Why:
     Fixed.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=3615&database=gcc

Re: c++/3615: unneccessary temporary instance created during function call

[gdr]

Synopsis: unneccessary temporary instance created during function call

Responsible-Changed-From-To: unassigned->gdr
Responsible-Changed-By: gdr
Responsible-Changed-When: Sun Aug 12 04:00:33 2001
Responsible-Changed-Why:
    See below.
State-Changed-From-To: open->analyzed
State-Changed-By: gdr
State-Changed-When: Sun Aug 12 04:00:33 2001
State-Changed-Why:
    Confirmed as an horrible bug.  A regression over gcc-2.95.2.
    See also PR #3471.
    
    -- Gaby

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=3615&database=gcc

c++/3615: unneccessary temporary instance created during function call

[niemayer]

>Number:         3615
>Category:       c++
>Synopsis:       unneccessary temporary instance created during function call
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 09 03:56:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Peter Niemayer
>Release:        gcc-3.0
>Organization:
>Environment:
i686-pc-linux-gnu
>Description:
When calling a function that takes a reference to a base
class "base" with an argument that is an instance of a
class that can be casted to a "class foo &" (where foo
is derived from "base"), gcc3 tries to create a temporary
"foo" instance without any reason and failing if copying
of "foo" isn't allowed.
>How-To-Repeat:
compiling the following small code example with gcc2 works
fine, with gcc-3.0 it results in the error:

bug.cxx: In function `void bug()':
bug.cxx:26: `foo::foo(const foo&)' is private
bug.cxx:47: within this context
bug.cxx:47:   initializing temporary from result of `Ptr<T>::operator T&() 
   [with T = foo]'
bug.cxx:38: in passing argument 1 of `void func2(base&)'
---------- code sample -----------

template <class T>
class Ptr {
protected:
	T * ptr;
	
public:
	
	Ptr(void) : ptr(0) { };
	Ptr(T * p) : ptr(p) { };

	~Ptr(void)	{ delete ptr; }

	operator T & () { return *ptr; }
};

class base {
public:	
	base(void) { }
	~base(void) { }
};


class foo : public base {
private:
	foo(const foo & rv); // does not exist - no copy allowed!
	
public:
	
	foo(void) { }
	~foo(void) { }
};

void func(foo & f) {
	// ...
}

void func2(base & b) {
	// ...
}

void bug(void) {
	
	Ptr<foo> f = new foo;
	
	func(f); // works as expected with gcc2 and gcc3
	func2(f); // works with gcc2, creates an unneccessary
	          // temporary instance with gcc-3.0
}

---------- code sample end ------------
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: