On Wed, 5 Sep 2018, Jakub Jelinek wrote:
> On Wed, Sep 05, 2018 at 12:55:55PM +0200, Richard Biener wrote:
> >
> > The following makes sure to call the default CTOR when emplacing a
> > vec<> in the avail hash-map. Certainly the intent was to zero-initialize
> > the m_vec member.
>
> Guess it would be nice to see what older versions of system g++ do with
> that.
> At least from what I remember last time, value-initialization vs.
> zero-initialization vs. no initialization in C++ is heavily dependent on
> compiler version and -std=c++NN version, there have been many bugs in the
> past and changes between standard versions.
It looks like g++ 4.8 puts extra zero-init with () but not without:
- (void) (struct vec *) operator new (8, (void *) TARGET_EXPR <D.107094,
(struct vec *) av>) >>>>>;
+ (void) (TARGET_EXPR <D.107096, (void *) TARGET_EXPR <D.107094, (struct
vec *) av>>;, TARGET_EXPR <D.107095, operator new (8, NON_LVALUE_EXPR
<D.107096>)>;;, (struct vec *) D.107095 != 0B ? *(struct vec *) D.107095 =
{.m_vec=0B};, (struct vec *) D.107095; : (struct vec *) D.107095;) >>>>>;
but yes, another option would be to explicitely do the following.
Cheaper av.m_vec = NULL doesn't work because m_vec is poisoned...
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 264123)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -5798,7 +5798,8 @@ rpo_elim::eliminate_push_avail (basic_bl
vec<std::pair<int, int> > &av = m_rpo_avail.get_or_insert (valnum,
&existed);
if (!existed)
{
- new (&av) vec<std::pair<int, int> >;
+ new (&av) vec<std::pair<int, int> >();
+ memset (&av, 0, sizeof (vec<std::pair<int, int> >));
av.reserve_exact (2);
}
av.safe_push (std::make_pair (bb->index, SSA_NAME_VERSION (leader)));
> > 2018-09-05 Richard Biener <rguent...@suse.de>
> >
> > PR bootstrap/87134
> > * tree-ssa-sccvn.c (rpo_elim::eliminate_push_avail): Make sure
> > to zero-init the emplaced vec.
> >
> > Index: gcc/tree-ssa-sccvn.c
> > ===================================================================
> > --- gcc/tree-ssa-sccvn.c (revision 264123)
> > +++ gcc/tree-ssa-sccvn.c (working copy)
> > @@ -5798,7 +5798,7 @@ rpo_elim::eliminate_push_avail (basic_bl
> > vec<std::pair<int, int> > &av = m_rpo_avail.get_or_insert (valnum,
> > &existed);
> > if (!existed)
> > {
> > - new (&av) vec<std::pair<int, int> >;
> > + new (&av) vec<std::pair<int, int> >();
> > av.reserve_exact (2);
> > }
> > av.safe_push (std::make_pair (bb->index, SSA_NAME_VERSION (leader)));
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
