Re: [PATCH] fix typing error in compound assignment

[Al Viro <viro@ZenIV.linux.org.uk>]

On Wed, Dec 07, 2016 at 03:33:42PM +0100, Luc Van Oostenryck wrote:
> But what is really done currently is something like:
> 	x = x + (typeof(x)) a;
> In other words, the left-hand side is casted to the same type as the
> rhs and the operation is always done with this type, neglecting the
> usual conversions and thus forcing the operation to always be done
> with the rhs type, here 'int' instead of 'long'.

Addition is a bad example, actually - your variant (promotions + operaton +
cast down to the first argument due to assignment) will yield the same value.
It's division where the real trouble happens -
	unsigned n1 = 1, n2 = 1;
	long v = -1;
	n1 /= v;
	n2 /= (unsigned)v;

should yield n1 == ~0U, n2 == 0.  And yes, the current logics in sparse
does not distinguish between those.  So ACK on the fix, but you want
a better testcase.