Degenerate virtual PHIs can break DSEs fragile heuristic as to what
defs it can handle for further processing. The following enhances
it to look through degenerate PHIs by means of a worklist, processing
the degenerate PHI defs uses to the defs array. The rewrite of
virtuals into loop-closed SSA caused this to issue appear more often.
The patch itself is mostly re-indenting the new loop body.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/106293
* tree-ssa-dse.cc (dse_classify_store): Use a worklist to
process degenerate PHI defs.
* gcc.dg/tree-ssa/ssa-dse-46.c: New testcase.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-46.c | 23 +++
gcc/tree-ssa-dse.cc | 181 +++++++++++----------
2 files changed, 121 insertions(+), 83 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-46.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-46.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-46.c
new file mode 100644
index 00000000000..68b36433ffc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-46.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-dse1" } */
+
+int a;
+static long b = 4073709551612, d;
+short c;
+void foo();
+char e(int **f) {
+ **f = 0;
+ if (a) {
+ unsigned long *g = &b;
+ unsigned long **h = &g;
+ for (; d;) {
+ foo();
+ for (; c;) {
+ unsigned long ***i = &h;
+ }
+ }
+ }
+ return 1;
+}
+
+/* { dg-final { scan-tree-dump-not "&b" "dse1" } } */
diff --git a/gcc/tree-ssa-dse.cc b/gcc/tree-ssa-dse.cc
index 89e2fa2c3f5..46ab57d5754 100644
--- a/gcc/tree-ssa-dse.cc
+++ b/gcc/tree-ssa-dse.cc
@@ -984,108 +984,123 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
else
defvar = gimple_vdef (temp);
- /* If we're instructed to stop walking at region boundary, do so. */
- if (defvar == stop_at_vuse)
- return DSE_STORE_LIVE;
-
auto_vec<gimple *, 10> defs;
gphi *first_phi_def = NULL;
gphi *last_phi_def = NULL;
- FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
+
+ auto_vec<tree, 10> worklist;
+ worklist.quick_push (defvar);
+
+ do
{
- /* Limit stmt walking. */
- if (++cnt > param_dse_max_alias_queries_per_store)
- {
- fail = true;
- break;
- }
+ defvar = worklist.pop ();
+ /* If we're instructed to stop walking at region boundary, do so. */
+ if (defvar == stop_at_vuse)
+ return DSE_STORE_LIVE;
- /* In simple cases we can look through PHI nodes, but we
- have to be careful with loops and with memory references
- containing operands that are also operands of PHI nodes.
- See gcc.c-torture/execute/20051110-*.c. */
- if (gimple_code (use_stmt) == GIMPLE_PHI)
+ FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
{
- /* If we already visited this PHI ignore it for further
- processing. */
- if (!bitmap_bit_p (visited,
- SSA_NAME_VERSION (PHI_RESULT (use_stmt))))
+ /* Limit stmt walking. */
+ if (++cnt > param_dse_max_alias_queries_per_store)
{
- /* If we visit this PHI by following a backedge then we have
- to make sure ref->ref only refers to SSA names that are
- invariant with respect to the loop represented by this
- PHI node. */
- if (dominated_by_p (CDI_DOMINATORS, gimple_bb (stmt),
- gimple_bb (use_stmt))
- && !for_each_index (ref->ref ? &ref->ref : &ref->base,
- check_name, gimple_bb (use_stmt)))
- return DSE_STORE_LIVE;
- defs.safe_push (use_stmt);
- if (!first_phi_def)
- first_phi_def = as_a <gphi *> (use_stmt);
- last_phi_def = as_a <gphi *> (use_stmt);
+ fail = true;
+ break;
}
- }
- /* If the statement is a use the store is not dead. */
- else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
- {
- if (dse_stmt_to_dr_map
- && ref->ref
- && is_gimple_assign (use_stmt))
+
+ /* In simple cases we can look through PHI nodes, but we
+ have to be careful with loops and with memory references
+ containing operands that are also operands of PHI nodes.
+ See gcc.c-torture/execute/20051110-*.c. */
+ if (gimple_code (use_stmt) == GIMPLE_PHI)
{
- if (!dra)
- dra.reset (create_data_ref (NULL, NULL, ref->ref, stmt,
- false, false));
- bool existed_p;
- data_reference_p &drb
- = dse_stmt_to_dr_map->get_or_insert (use_stmt, &existed_p);
- if (!existed_p)
- drb = create_data_ref (NULL, NULL,
- gimple_assign_rhs1 (use_stmt),
- use_stmt, false, false);
- if (!dr_may_alias_p (dra.get (), drb, NULL))
+ /* Look through single-argument PHIs. */
+ if (gimple_phi_num_args (use_stmt) == 1)
+ worklist.safe_push (gimple_phi_result (use_stmt));
+
+ /* If we already visited this PHI ignore it for further
+ processing. */
+ else if (!bitmap_bit_p (visited,
+ SSA_NAME_VERSION
+ (PHI_RESULT (use_stmt))))
{
- if (gimple_vdef (use_stmt))
- defs.safe_push (use_stmt);
- continue;
+ /* If we visit this PHI by following a backedge then we
+ have to make sure ref->ref only refers to SSA names
+ that are invariant with respect to the loop
+ represented by this PHI node. */
+ if (dominated_by_p (CDI_DOMINATORS, gimple_bb (stmt),
+ gimple_bb (use_stmt))
+ && !for_each_index (ref->ref ? &ref->ref : &ref->base,
+ check_name, gimple_bb (use_stmt)))
+ return DSE_STORE_LIVE;
+ defs.safe_push (use_stmt);
+ if (!first_phi_def)
+ first_phi_def = as_a <gphi *> (use_stmt);
+ last_phi_def = as_a <gphi *> (use_stmt);
}
}
+ /* If the statement is a use the store is not dead. */
+ else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
+ {
+ if (dse_stmt_to_dr_map
+ && ref->ref
+ && is_gimple_assign (use_stmt))
+ {
+ if (!dra)
+ dra.reset (create_data_ref (NULL, NULL, ref->ref, stmt,
+ false, false));
+ bool existed_p;
+ data_reference_p &drb
+ = dse_stmt_to_dr_map->get_or_insert (use_stmt,
+ &existed_p);
+ if (!existed_p)
+ drb = create_data_ref (NULL, NULL,
+ gimple_assign_rhs1 (use_stmt),
+ use_stmt, false, false);
+ if (!dr_may_alias_p (dra.get (), drb, NULL))
+ {
+ if (gimple_vdef (use_stmt))
+ defs.safe_push (use_stmt);
+ continue;
+ }
+ }
- /* Handle common cases where we can easily build an ao_ref
- structure for USE_STMT and in doing so we find that the
- references hit non-live bytes and thus can be ignored.
+ /* Handle common cases where we can easily build an ao_ref
+ structure for USE_STMT and in doing so we find that the
+ references hit non-live bytes and thus can be ignored.
- TODO: We can also use modref summary to handle calls. */
- if (byte_tracking_enabled
- && is_gimple_assign (use_stmt))
- {
- ao_ref use_ref;
- ao_ref_init (&use_ref, gimple_assign_rhs1 (use_stmt));
- if (valid_ao_ref_for_dse (&use_ref)
- && operand_equal_p (use_ref.base, ref->base,
- OEP_ADDRESS_OF)
- && !live_bytes_read (&use_ref, ref, live_bytes))
+ TODO: We can also use modref summary to handle calls. */
+ if (byte_tracking_enabled
+ && is_gimple_assign (use_stmt))
{
- /* If this is a store, remember it as we possibly
- need to walk the defs uses. */
- if (gimple_vdef (use_stmt))
- defs.safe_push (use_stmt);
- continue;
+ ao_ref use_ref;
+ ao_ref_init (&use_ref, gimple_assign_rhs1 (use_stmt));
+ if (valid_ao_ref_for_dse (&use_ref)
+ && operand_equal_p (use_ref.base, ref->base,
+ OEP_ADDRESS_OF)
+ && !live_bytes_read (&use_ref, ref, live_bytes))
+ {
+ /* If this is a store, remember it as we possibly
+ need to walk the defs uses. */
+ if (gimple_vdef (use_stmt))
+ defs.safe_push (use_stmt);
+ continue;
+ }
}
- }
- fail = true;
- break;
+ fail = true;
+ break;
+ }
+ /* We have visited ourselves already so ignore STMT for the
+ purpose of chaining. */
+ else if (use_stmt == stmt)
+ ;
+ /* If this is a store, remember it as we possibly need to walk the
+ defs uses. */
+ else if (gimple_vdef (use_stmt))
+ defs.safe_push (use_stmt);
}
- /* We have visited ourselves already so ignore STMT for the
- purpose of chaining. */
- else if (use_stmt == stmt)
- ;
- /* If this is a store, remember it as we possibly need to walk the
- defs uses. */
- else if (gimple_vdef (use_stmt))
- defs.safe_push (use_stmt);
}
+ while (!fail && !worklist.is_empty ());
if (fail)
{
--
2.35.3
