[RFC] PR34389 -Wconversion produces wrong warning

[Richard Guenther]

On Feb 16, 2008 5:52 PM, Manuel López-Ibáñez <lopezibanez@gmail.com> wrote:
> The following patch  fixes PR 34389 in a ugly way, in my own opinion,
> but I am not able to come up with any other way to fix this.
>
> A more detailed analysis is in the PR. In summary the problem here is
> that fold_unary converts (T)(x & c) into (T)x & (T)c which in this
> case is (int) (x & 0x7fff) into ((int)x & 0x7fff). By using
> get_unwidened, we could handle the first form. However, get_unwidened
> won't handle the latter. Thus, when Wconversion sees that this
> expression is assigned to a short, it concludes that there may be a
> loss of precision.
>
> Bootstrapped and regression tested in x86_64-unknown-linux-gnu. This
> patch only affects Wconversion, which is new in 4.3.

The correct fix is to not fold expressions in the C frontend before doing
these kinds of warnings.

Richard.