From 5ad3cc1ecc3c7c61d5e319f74cb7287fb80944fd Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Tue, 18 Oct 2022 09:38:03 +0200
Subject: [PATCH] tree-optimization/107301 - check if we can duplicate block
 before doing so

Path isolation failed to do that.

	PR tree-optimization/107301
	* gimple-ssa-isolate-paths.cc (handle_return_addr_local_phi_arg):
	Check whether we can duplicate the block.
	(find_implicit_erroneous_behavior): Likewise.

	* gcc.dg/torture/pr107301.c: New testcase.
---
 gcc/gimple-ssa-isolate-paths.cc         |  6 ++++--
 gcc/testsuite/gcc.dg/torture/pr107301.c | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr107301.c

diff --git a/gcc/gimple-ssa-isolate-paths.cc b/gcc/gimple-ssa-isolate-paths.cc
index 87ecd19ef4a..e4a4e08f549 100644
--- a/gcc/gimple-ssa-isolate-paths.cc
+++ b/gcc/gimple-ssa-isolate-paths.cc
@@ -647,7 +647,8 @@ handle_return_addr_local_phi_arg (basic_block bb, basic_block duplicate,
       if (!maybe
 	  && (flag_isolate_erroneous_paths_dereference
 	      || flag_isolate_erroneous_paths_attribute)
-	  && gimple_bb (use_stmt) == bb)
+	  && gimple_bb (use_stmt) == bb
+	  && (duplicate || can_duplicate_block_p (bb)))
 	{
 	  duplicate = isolate_path (bb, duplicate, e,
 				    use_stmt, lhs, true);
@@ -765,7 +766,8 @@ find_implicit_erroneous_behavior (void)
 		    ? gimple_location (use_stmt)
 		    : phi_arg_loc;
 
-		  if (stmt_uses_name_in_undefined_way (use_stmt, lhs, loc))
+		  if (stmt_uses_name_in_undefined_way (use_stmt, lhs, loc)
+		      && (duplicate || can_duplicate_block_p (bb)))
 		    {
 		      duplicate = isolate_path (bb, duplicate, e,
 						use_stmt, lhs, false);
diff --git a/gcc/testsuite/gcc.dg/torture/pr107301.c b/gcc/testsuite/gcc.dg/torture/pr107301.c
new file mode 100644
index 00000000000..5f0afcc0d10
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr107301.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+__attribute__ ((pure, returns_twice)) int
+foo (int x)
+{
+  int a;
+
+  a = x ? 3 : 0;
+  x /= a;
+  a = foo (x);
+  if (x == a)
+    __builtin_unreachable ();
+
+  return 0;
+}