This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: C++ PATCH to fix bogus maybe-uninitialized warning (PR c++/80119)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jason Merrill <jason at redhat dot com>
- Cc: Marek Polacek <polacek at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 21 Mar 2017 20:41:01 +0100
- Subject: Re: C++ PATCH to fix bogus maybe-uninitialized warning (PR c++/80119)
- Authentication-results: sourceware.org; auth=none
- Authentication-results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com
- Authentication-results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jakub at redhat dot com
- Dkim-filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 7E8A781233
- Dmarc-filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 7E8A781233
- References: <20170321153819.GM3172@redhat.com> <CADzB+2k5bWySc_7Z27mSxxa5UBuZyKZ1iJBaYmXJtZ3ggmCSKg@mail.gmail.com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Tue, Mar 21, 2017 at 03:27:02PM -0400, Jason Merrill wrote:
> OK.
>
> On Tue, Mar 21, 2017 at 11:38 AM, Marek Polacek <polacek@redhat.com> wrote:
> > This patch fixes a bogus maybe-uninitialized warning reported in the PR.
> > The issue is that we're not able to fold away useless CLEANUP_POINT_EXPRs,
> > as e.g. in
> > if (<<cleanup_point 0>>)
> > // bogus warning
> > Here, the cleanup_point was built as <<cleanup_point 0 && (i = 4) != 0>>,
> > which cp_fold_r reduces to <<cleanup_point 0>>, but leaves it as that and
> > passes it to the gimplifier.
> >
> > Jakub suggested handling this in cp_fold. fold_build_cleanup_point_expr says
> > that "if the expression does not have side effects then we don't have to wrap
> > it with a cleanup point expression", so I think the following should be safe.
> >
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> >
> > 2017-03-21 Marek Polacek <polacek@redhat.com>
> >
> > PR c++/80119
> > * cp-gimplify.c (cp_fold): Strip CLEANUP_POINT_EXPR if the expression
> > doesn't have side effects.
> >
> > * g++.dg/warn/Wuninitialized-9.C: New test.
> >
> > diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
> > index ebb5da9..b4319ca 100644
> > --- gcc/cp/cp-gimplify.c
> > +++ gcc/cp/cp-gimplify.c
> > @@ -2056,6 +2056,14 @@ cp_fold (tree x)
> > code = TREE_CODE (x);
> > switch (code)
> > {
> > + case CLEANUP_POINT_EXPR:
> > + /* Strip CLEANUP_POINT_EXPR if the expression doesn't have side
> > + effects. */
> > + r = cp_fold (TREE_OPERAND (x, 0));
Can CLEANUP_POINT_EXPR be an lvalue? If not, maybe cp_fold_rvalue instead?
> > + if (!TREE_SIDE_EFFECTS (r))
> > + x = r;
> > + break;
> > +
Jakub