[Bug debug/70935] [6/7 Regression] ICE: verify_ssa failed (error: definition in block 9 does not dominate use in block 12) w/ -O3 -g

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70935

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Yuri Rumyantsev from comment #3)
> Here is a simple fix - do not take into consideration edges destination of
> which is loop latch block, i.e. loop is endless:
> diff --git a/gcc/tree-ssa-loop-unswitch.c b/gcc/tree-ssa-loop-unswitch.c
> index dd6fd01..7de5fba 100644
> --- a/gcc/tree-ssa-loop-unswitch.c
> +++ b/gcc/tree-ssa-loop-unswitch.c
> @@ -532,6 +532,12 @@ find_loop_guard (struct loop *loop)
>                  guard_edge->src->index, guard_edge->dest->index);
>        return NULL;
>      }
> +  if (guard_edge->dest == loop->latch)
> +    {
> +      if (dump_file && (dump_flags & TDF_DETAILS))
> +       fprintf(dump_file,"Guard edge destination is loop latch!\n");

Formatting - missing space before (.

> +      return NULL;
> +    }
>  
>    if (dump_file && (dump_flags & TDF_DETAILS))
>      fprintf (dump_file,
> 
> Is it OK for you?

Richard knows this code much better than I do, so I'll defer to him.

That said, is there any guarantee that for non-endless loop we won't run into
the debug stmt issue?  For normal non-debug uses of something set inside of the
loop there would need to be a PHI on the exit block if it is reachable from
outside of the loop too, the question is if it is possible even in the
non-endless case that the exit block will be only reachable from within the
loop.  If yes, even normal SSA_NAME uses, not just in debug stmts, could be a
problem.