[patch] fix PR65048: check that jump-thread paths are still valid

[Jeff Law]

On 02/13/15 16:50, Sebastian Pop wrote:
> Hi,
>
> the attached patch fixes PR65048 by checking before jump-threading that a path
> to be threaded is still valid: as the testcase shows, there may be paths that
> are not connected anymore because the cfg has changed in a previous jump-thread.
>
>          PR tree-optimization/65048
>          * tree-ssa-threadupdate.c (valid_jump_thread_path): New.
>          (thread_through_all_blocks): Call valid_jump_thread_path.
>          Remove invalid FSM jump-thread paths.
>
>          * gcc.dg/tree-ssa/ssa-dom-thread-9.c: New.
>
> The patch passed bootstrap and regression tests on x86_64-linux.
> Ok for trunk?
These kinds of situations are normally pruned out in mark_threaded_blocks.

The dumps for the FSM threads are a bit sparse -- they don't show the 
entire path.  That makes it much harder to see what's going on.

It also appears that FSM is  registering lots of duplicate paths.

grep Registering j*.dom1 | grep -v PHI | sort
   Registering FSM jump thread: (10, 12) incoming edge;  (15, 3) nocopy;
   Registering FSM jump thread: (11, 12) incoming edge;  (15, 16) nocopy;
   Registering FSM jump thread: (16, 3) incoming edge;  (15, 16) nocopy;
   Registering FSM jump thread: (5, 10) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (5, 10) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (5, 11) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (5, 11) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (6, 14) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (6, 14) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (6, 3) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (6, 3) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (7, 10) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (7, 10) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (7, 11) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (7, 11) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (8, 14) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (8, 14) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (8, 3) incoming edge;  (13, 14) nocopy;
   Registering FSM jump thread: (8, 3) incoming edge;  (13, 14) nocopy;


Something seems wrong there.


Anyway, so what node precisely is not connected?  Is that happening as a 
result of the duplicated jump threads or is it something else?

Jeff