On Thu, 10 Jul 2014, Richard Biener wrote:
--- gcc/tree-into-ssa.c (revision 212109)
+++ gcc/tree-into-ssa.c (working copy)
@@ -1831,26 +1831,38 @@ maybe_register_def (def_operand_p def_p,
{
tree def = DEF_FROM_PTR (def_p);
tree sym = DECL_P (def) ? def : SSA_NAME_VAR (def);
/* If DEF is a naked symbol that needs renaming, create a new
name for it. */
if (marked_for_renaming (sym))
{
if (DECL_P (def))
{
- tree tracked_var;
-
- def = make_ssa_name (def, stmt);
+ if (gimple_clobber_p (stmt) && is_gimple_reg (sym))
sym should always be a gimple reg here (it's marked for renaming).
+ {
+ /* Replace clobber stmts with a default def. Create a new
+ variable so we don't later think we must coalesce, which
would
+ fail with some ada abnormal PHIs. Still, we try to keep a
+ similar name so error messages make sense. */
+ unlink_stmt_vdef (stmt);
I think that's redundant with gsi_replace (note that using gsi_replace
looks dangerous here as it calls update_stmt during SSA rewrite...
that might open a can of worms).
IIRC it was failing without unlink_stmt_vdef (maybe that was in a
different version of the patch not using gsi_replace, but I don't think
so). I was hoping that a clobber had little enough effects that
update_stmt was unlikely to break anything. Anyway it doesn't matter if I
use your suggestion below.
+ gsi_replace (&gsi, gimple_build_nop (), true);
+ tree id = DECL_NAME (sym);
+ const char* name = id ? IDENTIFIER_POINTER (id) : 0;
+ tree newvar = create_tmp_var (TREE_TYPE (sym), name);
+ def = get_or_create_ssa_default_def (cfun, newvar);
So - can't you simply do
gimple_assign_set_rhs_from_tree (&gsi,
get_or_create_dda_default_def (cfun, sym));
? Thus replace x = CLOBBER; with x_3 = x_2(D);
+ }
+ else
and of course still rewrite the DEF then. IMHO the copy-propagation
you do is premature optimization.
I'll try that. I was trying to remain as close as possible to what you
wrote in rewrite_stmt:
if (gimple_clobber_p (stmt)
&& is_gimple_reg (var))
{
/* If we rewrite a DECL into SSA form then drop its
clobber stmts and replace uses with a new default def. */
gcc_checking_assert (TREE_CODE (var) == VAR_DECL
&& !gimple_vdef (stmt));
gsi_replace (si, gimple_build_nop (), true);
register_new_def (get_or_create_ssa_default_def (cfun, var), var);
break;
}
I'll be away next week, but I'll re-read all the replies carefully when I
come back.
--
Marc Glisse
