From: Jakub Jelinek <jakub@redhat.com>
Date: Fri, 28 Jan 2022 18:02:26 +0000 (+0100)
Subject: store-merging: Fix up a -fcompare-debug bug in get_status_for_store_merging [PR104263]
X-Git-Tag: releases/gcc-10.4.0~200
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7bb29feb789dfa05297998e1c241d438307cc3d2;p=thirdparty%2Fgcc.git

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.c (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.

(cherry picked from commit a591c71b41e18e4ff86852a974592af4962aef57)
---

diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c
index 0623e6ec80b5..4093ccaaafc4 100644
--- a/gcc/gimple-ssa-store-merging.c
+++ b/gcc/gimple-ssa-store-merging.c
@@ -4963,6 +4963,7 @@ get_status_for_store_merging (basic_block bb)
   unsigned int num_statements = 0;
   gimple_stmt_iterator gsi;
   edge e;
+  gimple *last_stmt = NULL;
 
   for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); gsi_next (&gsi))
     {
@@ -4971,6 +4972,8 @@ 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;
     }
@@ -4979,7 +4982,7 @@ 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
index 000000000000..79b548c629ce
--- /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;
+}