On Wed, 13 Jul 2016, Jan Hubicka wrote:
> >
> > I'd rather not expose/change need_fake_edge_p as that has a very
> > specific purpose.
> >
> > Why don't you simply add a call to is_ctrl_altering_stmt on the
> > last stmt of the block in loop_only_exit_p? It's a waste of
> > time doing stuff on every stmt that can only make a difference
> > on the last one of a BB.
>
> I am not sure I understand your suggestion. is_ctrl_altering_stmt checks
> whether stmt terminates BB (i.e. it does control flow we represent
> explicitly).
> Here we look for cases where BB execution can terminate in the middle of BB
> in ways not explicitly represented in CFG.
>
> For example:
>
> ...stmt...
> *ptr=0
> ...stmt...
>
> the control flow can terminate by the memory access that may throw non-call
> exception.
>
> or
>
> ...stmt...
> volatile asm statement eventually leading to longjmp
> ...stmt...
>
> I worte RTL version of need_fake_edge_p many years ago to check particularly
> these cases. This is what loop code checks - it wants to know that the loop
> will eventually terminate by the exit edge on hand, not by other ways.
Ah, ok. I dove into the code and that indeed seems to be the case.
Why is that function ignoring volatiles but not volatile asms or
old-style asms? I think the only control-flow transfer asms are
allowed to make are asm gotos?
Anyway, that's a pre-existing issue so the patch is ok.
Thanks,
Richard.
> Honza
> >
> > Richard.
> >
> > > Honza
> > >
> > > * gimple.h (stmt_can_terminate_bb_p): New function.
> > > * tree-cfg.c (need_fake_edge_p): Rename to ...
> > > (stmt_can_terminate_bb_p): ... this; return true if stmt can
> > > throw external; handle const and pure calls.
> > > * tree-ssa-loop-niter.c (loop_only_exit_p): Use it.
> > > Index: gimple.h
> > > ===================================================================
> > > --- gimple.h (revision 238191)
> > > +++ gimple.h (working copy)
> > > @@ -1526,6 +1526,7 @@ extern void gimple_seq_set_location (gim
> > > extern void gimple_seq_discard (gimple_seq);
> > > extern void maybe_remove_unused_call_args (struct function *, gimple *);
> > > extern bool gimple_inexpensive_call_p (gcall *);
> > > +extern bool stmt_can_terminate_bb_p (gimple *);
> > >
> > > /* Formal (expression) temporary table handling: multiple occurrences of
> > > the same scalar expression are evaluated into the same temporary. */
> > > Index: tree-cfg.c
> > > ===================================================================
> > > --- tree-cfg.c (revision 238191)
> > > +++ tree-cfg.c (working copy)
> > > @@ -7919,15 +7919,20 @@ gimple_block_ends_with_condjump_p (const
> > > }
> > >
> > >
> > > -/* Return true if we need to add fake edge to exit at statement T.
> > > - Helper function for gimple_flow_call_edges_add. */
> > > +/* Return true if statement T may terminate execution of BB in ways not
> > > + explicitly represtented in the CFG. */
> > >
> > > -static bool
> > > -need_fake_edge_p (gimple *t)
> > > +bool
> > > +stmt_can_terminate_bb_p (gimple *t)
> > > {
> > > tree fndecl = NULL_TREE;
> > > int call_flags = 0;
> > >
> > > + /* Eh exception not handled internally terminates execution of the
> > > whole
> > > + function. */
> > > + if (stmt_can_throw_external (t))
> > > + return true;
> > > +
> > > /* NORETURN and LONGJMP calls already have an edge to exit.
> > > CONST and PURE calls do not need one.
> > > We don't currently check for CONST and PURE here, although
> > > @@ -7960,6 +7965,13 @@ need_fake_edge_p (gimple *t)
> > > edge e;
> > > basic_block bb;
> > >
> > > + if (call_flags & (ECF_PURE | ECF_CONST)
> > > + && !(call_flags & ECF_LOOPING_CONST_OR_PURE))
> > > + return false;
> > > +
> > > + /* Function call may do longjmp, terminate program or do other
> > > things.
> > > + Special case noreturn that have non-abnormal edges out as in this case
> > > + the fact is sufficiently represented by lack of edges out of T. */
> > > if (!(call_flags & ECF_NORETURN))
> > > return true;
> > >
> > > @@ -8024,7 +8036,7 @@ gimple_flow_call_edges_add (sbitmap bloc
> > > if (!gsi_end_p (gsi))
> > > t = gsi_stmt (gsi);
> > >
> > > - if (t && need_fake_edge_p (t))
> > > + if (t && stmt_can_terminate_bb_p (t))
> > > {
> > > edge e;
> > >
> > > @@ -8059,7 +8071,7 @@ gimple_flow_call_edges_add (sbitmap bloc
> > > do
> > > {
> > > stmt = gsi_stmt (gsi);
> > > - if (need_fake_edge_p (stmt))
> > > + if (stmt_can_terminate_bb_p (stmt))
> > > {
> > > edge e;
> > >
> > > Index: tree-ssa-loop-niter.c
> > > ===================================================================
> > > --- tree-ssa-loop-niter.c (revision 238191)
> > > +++ tree-ssa-loop-niter.c (working copy)
> > > @@ -2159,7 +2159,6 @@ loop_only_exit_p (const struct loop *loo
> > > basic_block *body;
> > > gimple_stmt_iterator bsi;
> > > unsigned i;
> > > - gimple *call;
> > >
> > > if (exit != single_exit (loop))
> > > return false;
> > > @@ -2168,17 +2167,8 @@ loop_only_exit_p (const struct loop *loo
> > > for (i = 0; i < loop->num_nodes; i++)
> > > {
> > > for (bsi = gsi_start_bb (body[i]); !gsi_end_p (bsi); gsi_next
> > > (&bsi))
> > > - {
> > > - call = gsi_stmt (bsi);
> > > - if (gimple_code (call) != GIMPLE_CALL)
> > > - continue;
> > > -
> > > - if (gimple_has_side_effects (call))
> > > - {
> > > - free (body);
> > > - return false;
> > > - }
> > > - }
> > > + if (stmt_can_terminate_bb_p (gsi_stmt (bsi)))
> > > + return true;
> > > }
> > >
> > > free (body);
> > > if (EDGE_COUNT (bb->succs) > 1)
> > >
> > >
> >
> > --
> > Richard Biener <rguent...@suse.de>
> > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
> > 21284 (AG Nuernberg)
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
