Re: [RFC] PR34389 -Wconversion produces wrong warning

["Manuel López-Ibáñez" <lopezibanez at gmail dot com>]

On 18/02/2008, Manuel López-Ibáñez <lopezibanez@gmail.com> wrote:
> On 18/02/2008, Joseph S. Myers <joseph@codesourcery.com> wrote:
> >
> > I agree with that in principle - but I also think it's useful to avoid
> > warning for such cases as short = (int & 0x7fff) when written directly by
> > the user (with any non-negative constant in the range of short there).  I
> > suppose there are other cases where it may be less likely that the user
> > will write the code created by the compiler, but anything affecting
> > expressions directly written by the user would still be of some use after
> > the front end no longer does the present folding.  (This means there
> > should be testcases where the problem expressions are written directly by
> > the user, not just the tests where they are compiler-generated.)

The following patch is a bit cleaner than the previous proposal.It
also handles a lot more of cases. In particular, it handles short =
(int & 0x7fff).

There is an XFAIL because common_types does completely different
things in C and C++. I think that is a latent bug exposed by my patch.

Let me know your opinions and suggestions.

Bootstrapped and regression tested in x86_64-unknown-linux-gnu.

Cheers,

Manuel.

2008-02-18  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

  PR 34389
  * c-typeck.c (build_binary_op): Encapsulate code into...
  * c-common.c (shorten_binary_op): ...this new function.
    (conversion_warning): Use the new function. Handle non-negative
constant in bitwise-and.
  * c-common.h (shorten_binary_op): Declare.
cp/
  * typeck.c (build_binary_op): Encapsulate code into the new function.
testsuite/
  * gcc.dg/Wconversion-pr34389.c: New.
  * g++.dg/warn/Wconversion-pr34389.C: New.

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