>
> 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.
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)
