Compiler bug or gray area in C?

[Jeff Anton]

Dave ment to write:
	extern	double D, foo();
	
	bar( i )
	int i;
	{
		double	x;
		int	changes = 0;
		do {
	
			x = foo( i );
	
			if( x < D )
			{
				changed++;
				D = x;
			}
	
		} while( !changed );	
	}

The obvious compilation and recursion problems are clear
with the original code.  The issue is the legality
of compilers extending the precision of variable when
they are placed in registers.
				Jeff Anton