Broken enum arithmetic in C

[Peter Osterlund]

Consider this C code:

	enum { v = 1 };
	signed char f()
	{
	    return -v;
	}

On i686-pc-linux-gnu, compiling this code with recent snapshots
generats a bogus warning:

	bug.c: In function `f':
	bug.c:4: warning: overflow in implicit constant conversion

For this source code, correct assembly code is generated in spite of
the warning, but I think the bug in message
http://gcc.gnu.org/ml/gcc-bugs/2000-02/msg00523.html is also caused by
this problem, and in that case incorrect assembly code is generated
for valid source code. That bug report was probably a bit misleading,
because the root of the problem doesn't seem to be related to
optimization.

If I explicitly cast the enum to int before negating the value,
ie. writing "return -(int)v", the warning goes away. The warning also
goes away if I compile the code as C++.

(This problem is also the reason why the chess program crafty is
miscompiled with recent gcc snapshots.)

-- 
Peter Österlund          Email:     peter.osterlund@mailbox.swipnet.se
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