Re: Help diagnosing a GCC 10.2 problem : error: 'removed_return.213' may be used uninitialized in this function

[Martin Sebor <msebor@gmail.com>]

On 1/5/21 2:31 PM, Nick Savoiu via Gcc-help wrote:
> Hi all, I'm trying to upgrade a codebase from GCC 9.1 to GCC 10.2 and running into weird warning/error messages in the optimized build (-O2).
> 
>    error: 'removed_return.213' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> I thought that I can just downgrade the -Werror and go on but the code actually crashes on that statement.

Do you mean to say the compiler crashes or the program crashes at
runtime?  The former would be a bug in the compiler.  The latter
likely a bug in the program.

The removed_return.213 name refers to a variable GCC synthesizes
internally from one called removed_return in the code.  It just
means that GCC can't prove the variable is initialized when it's
used.  Initializing it on declaration should avoid the warning.

> 
> The problem code seems to be around a macro that looks like this:
> 
> extern bool IsDebugOn();
> #define debug IsDebugOn() && std::cout
> 
> and that's used like this:
> 
>    debug << "print something" << std::endl;
> 
> The error goes away if I use
> 
>     if (IsDebugOn())
>       debug << "print something" << endl;
> 
> so I guess the shortcircuited && somehow makes a difference. Unfortunately this happens way deep in the code and any attempts so far to extract the code such that it still exhibits the problem have failed.
> 
> I'd appreciate any pointers.

If you suspect a bug in GCC then, at a minimum, we need to see
the full GCC output (the warning/error, followed by any informational
notes and stack trace if GCC dies with an ICE).  Better yet would be
a translation unit (the result of preprocessing the file with -E) and
the full command line so we can reproduce the problem.  Since you
mentioned <iostream> it's probably going to be too big for the list
so opening a bug report and attaching the translation unit to it
would be preferable.

Martin