into-ssa: Fix emitting debug stmts after asm goto [PR108095]

into-ssa: Fix emitting debug stmts after asm goto [PR108095]

The following testcase ICEs, because ccp1 replaced
  s.0_1 = &s;
  __asm__ goto("" : "=r" MEM[(T *)s.0_1] :  :  : "lab" lab);
with
  __asm__ goto("" : "=r" s :  :  : "lab" lab);
and because s is no longer addressable, we are rewriting it into
ssa and want
  __asm__ goto("" : "=r" s_7 :  :  : "lab" lab);
plus debug stmt
  # DEBUG s => s_7
The code assumes that there is at most one non-EH edge in that
case, but with the addition of outputs to asm goto that is no longer the
case, we can have many outgoing edges.

The patch keeps the checking assertion that there is at most one such
edge for everything but asm goto, but moves the addition of the debug
stmt into the loop, so that it can be added on all edges where it is
possible, not just one of them.

Furthermore, looking at gsi_insert_on_edge_immediate
-> gimple_find_edge_insert_loc, the conditions to insert stmt there
to the destination block are
  if (single_pred_p (dest)
      && gimple_seq_empty_p (phi_nodes (dest))
      && dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
(plus there is code to insert it in the previous block but that is
never true when the pred is known to be stmt_ends_bb_p), while
mayube_register_def was just checking
                 if (ef && single_pred_p (ef->dest)
                     && ef->dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
so if for whatever reason ef->dest had any PHIs, we'd split the
edge for -g and not for -g0, something we must avoid for -fcompare-debug
stability.  So, I've added the no phi_nodes check too.

2022-12-15  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108095
	* tree-into-ssa.cc (maybe_register_def): Insert debug stmt
	on all non-EH edges from asm goto if they have a single
	predecessor rather than asserting there is at most one such edge.
	Test whether there are no PHI nodes next to the single predecessor
	test.

	* gcc.dg/pr108095.c: New test.