Re: [PATCH] Handle PHI nodes w/o a argument (PR ipa/80205).

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Mar 27, 2017 at 4:14 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Mon, Mar 27, 2017 at 2:47 PM, Martin Liška <mliska@suse.cz> wrote:
>> Hello.
>>
>> As described in the PR, we can create a PHI node in einline that has no argument.
>> That can cause ICE in devirtualization and should be thus handled.
>>
>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>
>> Ready to be installed?
>
> We shouldn't ever have a PHI w/o argument.

;;   basic block 14, loop depth 0
;;    pred:
  # SR.2_19 = PHI <>
<L4> [0.00%]:
  a::~a (&g);
  resx 12
;;    succ:       17

the CFG has not been cleaned up here (this block is unreachable).

Hmm, I see we are called from fold_stmt.  I suppose we process
statements_to_fold before removing unreachable blocks to not
walk over dead stmts...  chicken-and-egg...

Still not creating that PHI should be possible.

Index: gcc/tree-inline.c
===================================================================
--- gcc/tree-inline.c   (revision 246500)
+++ gcc/tree-inline.c   (working copy)
@@ -2344,6 +2344,13 @@ copy_phis_for_bb (basic_block bb, copy_b
       if (!virtual_operand_p (res))
        {
          walk_tree (&new_res, copy_tree_body_r, id, NULL);
+         if (EDGE_COUNT (new_bb->preds) == 0)
+           {
+             /* Technically we'd want a SSA_DEFAULT_DEF here... */
+             SSA_NAME_DEF_STMT (new_res) = gimple_build_nop ();
+           }
+         else
+           {
          new_phi = create_phi_node (new_res, new_bb);
          FOR_EACH_EDGE (new_edge, ei, new_bb->preds)
            {
@@ -2389,6 +2396,7 @@ copy_phis_for_bb (basic_block bb, copy_b

              add_phi_arg (new_phi, new_arg, new_edge, locus);
            }
+           }
        }
     }



>> Martin