[gcc r12-7467] Call mark_dfs_back_edges before testing EDGE_DFS_BACK [PR104761].

[Martin Sebor]

https://gcc.gnu.org/g:51149a05b8cc8e4fc5a77a65857894daa371de89

commit r12-7467-g51149a05b8cc8e4fc5a77a65857894daa371de89
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu Mar 3 13:58:00 2022 -0700

    Call mark_dfs_back_edges before testing EDGE_DFS_BACK [PR104761].
    
    Resolves:
    PR middle-end/104761 - bogus -Wdangling-pointer with cleanup and infinite loop
    
    gcc/ChangeLog:
    
            PR middle-end/104761
            * gimple-ssa-warn-access.cc (pass_waccess::execute): Call
            mark_dfs_back_edges.
    
    gcc/testsuite/ChangeLog:
    
            PR middle-end/104761
            * g++.dg/warn/Wdangling-pointer-4.C: New test.
            * gcc.dg/Wdangling-pointer-4.c: New test.

Diff:
---
 gcc/gimple-ssa-warn-access.cc                   |  5 ++++-
 gcc/testsuite/g++.dg/warn/Wdangling-pointer-4.C | 22 ++++++++++++++++++++++
 gcc/testsuite/gcc.dg/Wdangling-pointer-4.c      | 22 ++++++++++++++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index b7cdad517b3..b519712d76e 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -47,7 +47,7 @@
 #include "tree-object-size.h"
 #include "tree-ssa-strlen.h"
 #include "calls.h"
-#include "cfgloop.h"
+#include "cfganal.h"
 #include "intl.h"
 #include "gimple-range.h"
 #include "stringpool.h"
@@ -4710,6 +4710,9 @@ pass_waccess::execute (function *fun)
   calculate_dominance_info (CDI_DOMINATORS);
   calculate_dominance_info (CDI_POST_DOMINATORS);
 
+  /* Set or clear EDGE_DFS_BACK bits on back edges.  */
+  mark_dfs_back_edges (fun);
+
   /* Create a new ranger instance and associate it with FUN.  */
   m_ptr_qry.rvals = enable_ranger (fun);
   m_func = fun;
diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-pointer-4.C b/gcc/testsuite/g++.dg/warn/Wdangling-pointer-4.C
new file mode 100644
index 00000000000..7177a545970
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-pointer-4.C
@@ -0,0 +1,22 @@
+/* PR middle-end/104761 - bogus -Wdangling-pointer with cleanup and infinite loop
+   { dg-do compile }
+   { dg-options "-O -Wall -fno-exceptions" } */
+
+struct S { int i; };
+
+struct X { ~X (); };
+
+void g (int);
+
+void test (int i)
+{
+  S s = { 0 };
+
+  X x;
+
+  if (i)
+    {
+      g (s.i);                // { dg-bogus "-Wdangling-pointer" }
+      for ( ; ; );
+    }
+}
diff --git a/gcc/testsuite/gcc.dg/Wdangling-pointer-4.c b/gcc/testsuite/gcc.dg/Wdangling-pointer-4.c
new file mode 100644
index 00000000000..36c8da5113a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wdangling-pointer-4.c
@@ -0,0 +1,22 @@
+/* PR middle-end/104761 - bogus -Wdangling-pointer with cleanup and infinite loop
+   { dg-do compile }
+   { dg-options "-O -Wall" } */
+
+typedef struct { int i; } S;
+
+void f (S **);
+
+int g (int);
+
+void nowarn (int x)
+{
+  S s = { 0 };
+
+  __attribute__((__cleanup__ (f))) S *p = 0;
+
+  if (x)
+    {
+      g (s.i);                // { dg-bogus "-Wdangling-pointer" }
+      for ( ; ; );
+    }
+}