store-merging: Fix up a -fcompare-debug bug in get_status_for_store_merging [PR104263]

As mentioned in the PRthe following testcase fails, because the last
stmt of a bb with -g is a debug stmt and get_status_for_store_merging
uses gimple_seq_last_stmt (bb_seq (bb)) when testing if it is valid
for store merging.  The debug stmt isn't valid, while a stmt at that
position with -g0 is valid and so the divergence.

As we walk the whole bb already, this patch just remembers the last
non-debug stmt, so that we don't need to skip backwards debug stmts at the
end of the bb to find last real stmt.

2022-01-28  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/104263
	* gimple-ssa-store-merging.cc (get_status_for_store_merging): For
	cfun->can_throw_non_call_exceptions && cfun->eh test whether
	last non-debug stmt in the bb is store_valid_for_store_merging_p
	rather than last stmt.

	* gcc.dg/pr104263.c: New test.

diff --git a/gcc/gimple-ssa-store-merging.cc b/gcc/gimple-ssa-store-merging.cc
index eb70d90..e2e2157 100644 (file)
--- a/gcc/gimple-ssa-store-merging.cc
+++ b/gcc/gimple-ssa-store-merging.cc
@@ -5364,6 +5364,7 @@ get_status_for_store_merging (basic_block bb)
   unsigned int num_constructors = 0;
   gimple_stmt_iterator gsi;
   edge e;
+  gimple *last_stmt = NULL;
 
   for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); gsi_next (&gsi))
     {
@@ -5372,6 +5373,8 @@ get_status_for_store_merging (basic_block bb)
       if (is_gimple_debug (stmt))
        continue;
 
+      last_stmt = stmt;
+
       if (store_valid_for_store_merging_p (stmt) && ++num_statements >= 2)
        break;
 
@@ -5398,7 +5401,7 @@ get_status_for_store_merging (basic_block bb)
     return BB_INVALID;
 
   if (cfun->can_throw_non_call_exceptions && cfun->eh
-      && store_valid_for_store_merging_p (gimple_seq_last_stmt (bb_seq (bb)))
+      && store_valid_for_store_merging_p (last_stmt)
       && (e = find_fallthru_edge (bb->succs))
       && e->dest == bb->next_bb)
     return BB_EXTENDED_VALID;

diff --git a/gcc/testsuite/gcc.dg/pr104263.c b/gcc/testsuite/gcc.dg/pr104263.c
new file mode 100644 (file)
index 0000000..79b548c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104263.c
@@ -0,0 +1,25 @@
+/* PR tree-optimization/104263 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcompare-debug -fnon-call-exceptions -fno-inline-small-functions" } */
+
+int n;
+
+int
+bar (void)
+{
+  int a;
+
+  n = 0;
+  a = 0;
+
+  return n;
+}
+
+__attribute__ ((pure, returns_twice)) int
+foo (void)
+{
+  n = bar () + 1;
+  foo ();
+
+  return 0;
+}