Re: [PATCH 3/6] return auto_vec from get_loop_hot_path

[Trevor Saunders <tbsaunde@tbsaunde.org>]

On Thu, Jun 17, 2021 at 03:48:28PM +0200, Christophe Lyon wrote:
> On Tue, 15 Jun 2021 at 08:47, Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Tue, Jun 15, 2021 at 8:01 AM Trevor Saunders <tbsaunde@tbsaunde.org> wrote:
> > >
> > > This ensures callers take ownership of the returned vector.
> > >
> > > Signed-off-by: Trevor Saunders <tbsaunde@tbsaunde.org>
> > >
> > > bootstrapped and regtested on x86_64-linux-gnu, ok?
> >
> > OK.
> 
> Since this was committed, I've noticed build errors (for cross-compilers):
> /tmp/9562118_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgloopanal.c:
> In function 'auto_vec<basic_block_def*> get_loop_hot_path(const
> loop*)':
> /tmp/9562118_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgloopanal.c:528:10:
> error: could not convert 'path' from 'vec<basic_block_def*>' to
> 'auto_vec<basic_block_def*>'
>    return path;
>           ^
> /tmp/9562118_6.tmpdir/aci-gcc-fsf/sources/gcc-fsf/gccsrc/gcc/cfgloopanal.c:529:1:
> warning: control reaches end of non-void function [-Wreturn-type]
>  }
>  ^
> 
> I'm using gcc-4.8.5 as host compiler

Ah, interesting, I believe the following patch corrects the oversight
here.  Its interesting that newer compilers use the auto_vec(vec<T> &&)
constructor to fix this up but 4.8.5 refuses.

diff --git a/gcc/cfgloopanal.c b/gcc/cfgloopanal.c
index fdd8d3f43fe..2db46c81036 100644
--- a/gcc/cfgloopanal.c
+++ b/gcc/cfgloopanal.c
@@ -504,7 +504,7 @@ auto_vec<basic_block>
 get_loop_hot_path (const class loop *loop)
  {
     basic_block bb = loop->header;
     -  vec<basic_block> path = vNULL;
     +  auto_vec<basic_block> path;
        bitmap visited = BITMAP_ALLOC (NULL);

	   while (true)

	   Sorry about the trouble, will commit the above as obvious if
	   it bootstraps.

	   Trev

> 
> Christophe
> 
> >
> > > gcc/ChangeLog:
> > >
> > >         * cfgloop.h (get_loop_hot_path): Return auto_vec<basic_block>.
> > >         * cfgloopanal.c (get_loop_hot_path): Likewise.
> > >         * tree-ssa-loop-ivcanon.c (tree_estimate_loop_size): Likewise.
> > > ---
> > >  gcc/cfgloop.h               | 2 +-
> > >  gcc/cfgloopanal.c           | 2 +-
> > >  gcc/tree-ssa-loop-ivcanon.c | 5 ++---
> > >  3 files changed, 4 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/gcc/cfgloop.h b/gcc/cfgloop.h
> > > index 113241da130..5e699276c88 100644
> > > --- a/gcc/cfgloop.h
> > > +++ b/gcc/cfgloop.h
> > > @@ -840,7 +840,7 @@ enum
> > >
> > >  extern void doloop_optimize_loops (void);
> > >  extern void move_loop_invariants (void);
> > > -extern vec<basic_block> get_loop_hot_path (const class loop *loop);
> > > +extern auto_vec<basic_block> get_loop_hot_path (const class loop *loop);
> > >
> > >  /* Returns the outermost loop of the loop nest that contains LOOP.*/
> > >  static inline class loop *
> > > diff --git a/gcc/cfgloopanal.c b/gcc/cfgloopanal.c
> > > index d0eade3dd34..e7b7ae2163e 100644
> > > --- a/gcc/cfgloopanal.c
> > > +++ b/gcc/cfgloopanal.c
> > > @@ -500,7 +500,7 @@ single_likely_exit (class loop *loop, vec<edge> exits)
> > >     order against direction of edges from latch.  Specially, if
> > >     header != latch, latch is the 1-st block.  */
> > >
> > > -vec<basic_block>
> > > +auto_vec<basic_block>
> > >  get_loop_hot_path (const class loop *loop)
> > >  {
> > >    basic_block bb = loop->header;
> > > diff --git a/gcc/tree-ssa-loop-ivcanon.c b/gcc/tree-ssa-loop-ivcanon.c
> > > index 3f9e9d0869f..b1971f83544 100644
> > > --- a/gcc/tree-ssa-loop-ivcanon.c
> > > +++ b/gcc/tree-ssa-loop-ivcanon.c
> > > @@ -218,7 +218,7 @@ tree_estimate_loop_size (class loop *loop, edge exit, edge edge_to_cancel,
> > >    gimple_stmt_iterator gsi;
> > >    unsigned int i;
> > >    bool after_exit;
> > > -  vec<basic_block> path = get_loop_hot_path (loop);
> > > +  auto_vec<basic_block> path = get_loop_hot_path (loop);
> > >
> > >    size->overall = 0;
> > >    size->eliminated_by_peeling = 0;
> > > @@ -342,7 +342,6 @@ tree_estimate_loop_size (class loop *loop, edge exit, edge edge_to_cancel,
> > >               - size->last_iteration_eliminated_by_peeling) > upper_bound)
> > >             {
> > >                free (body);
> > > -             path.release ();
> > >               return true;
> > >             }
> > >         }
> > > @@ -379,7 +378,7 @@ tree_estimate_loop_size (class loop *loop, edge exit, edge edge_to_cancel,
> > >             size->num_branches_on_hot_path++;
> > >         }
> > >      }
> > > -  path.release ();
> > > +
> > >    if (dump_file && (dump_flags & TDF_DETAILS))
> > >      fprintf (dump_file, "size: %i-%i, last_iteration: %i-%i\n", size->overall,
> > >              size->eliminated_by_peeling, size->last_iteration,
> > > --
> > > 2.20.1
> > >