c++/7614: Warning when function returning reference to volatile called in void context

c++/7614: Warning when function returning reference to volatile called in void context

[timb]

>Number:         7614
>Category:       c++
>Synopsis:       Warning when function returning reference to volatile called in void context
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Aug 16 10:16:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     timb@bluearc.com
>Release:        3.2
>Organization:
>Environment:
Debian GNU/Linux x86 unstable
>Description:
Was rather surprised to be deluged with warnings of the form "object of type `volatile X&' will not be accessed in statement" for practically every use of a volatile assignment operator. After much head-scratching, I found that it seems to be generated whenever a function returning a reference to volatile is called in a void context. It doesn't seem to be possible to disable this warning.

>From the long comment above convert_to_void() in gcc/cp/cvt.c, it appears that this behaviour is intentional. However, if the intention is indeed to reduce confusion, then IMHO it actually has the reverse effect. It also seems inconsistent to generate the warning for a reference but not a pointer.
>How-To-Repeat:
Here's a simple snippet that demonstrates the problem:-

volatile int& wibble(volatile int& x)
{
    x = 0;
    return x;
}

volatile int v;

void foo()
{
    wibble(v);
}
>Fix:

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

Re: c++/7614: Warning when function returning reference to volatile called in void context

[nathan]

Synopsis: Warning when function returning reference to volatile called in void context

State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Fri Sep 13 15:54:31 2002
State-Changed-Why:
    not a bug. references to volatile objects are evil. For instance, your wibble function contains
    'return x', which looks like a read of x - but it isn't.
    
    pointers are different, you have to put a * infront
    to dereference them 

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7614