Hi,
as requested by Jakub, this patch makes devirtualization code to turn off
transformations based on assumption that cxa_pure_virtual will never be called
by a virtual call when -fsanitize=undefined is used.

Bootstrapped/regtested x86_64-linux, will commit it shortly.

        PR ipa/66223
        * ipa-devirt.c (maybe_record_node): Do not optimize cxa_pure_virtual
        calls when sanitizing.
        (possible_polymorphic_call_target_p)" FIx formating.

        * g++.dg/ipa/devirt-51.C: New testcase.
Index: ipa-devirt.c
===================================================================
--- ipa-devirt.c        (revision 234715)
+++ ipa-devirt.c        (working copy)
@@ -2438,10 +2438,14 @@ maybe_record_node (vec <cgraph_node *> &
     {
       gcc_assert (!target_node->global.inlined_to);
       gcc_assert (target_node->real_symbol_p ());
+      /* When sanitizing, do not asume that cxa_pure_virutal is not called
+        by valid program.  */
+      if (flag_sanitize & SANITIZE_UNDEFINED)
+       ;
       /* Only add pure virtual if it is the only possible target.  This way
         we will preserve the diagnostics about pure virtual called in many
         cases without disabling optimization in other.  */
-      if (pure_virtual)
+      else if (pure_virtual)
        {
          if (nodes.length ())
            return;
@@ -3374,8 +3378,7 @@ possible_polymorphic_call_target_p (tree
   bool final;
 
   if (TREE_CODE (TREE_TYPE (n->decl)) == FUNCTION_TYPE
-      && ((fcode = DECL_FUNCTION_CODE (n->decl))
-         == BUILT_IN_UNREACHABLE
+      && ((fcode = DECL_FUNCTION_CODE (n->decl)) == BUILT_IN_UNREACHABLE
           || fcode == BUILT_IN_TRAP))
     return true;
 
Index: testsuite/g++.dg/ipa/devirt-51.C
===================================================================
--- testsuite/g++.dg/ipa/devirt-51.C    (revision 0)
+++ testsuite/g++.dg/ipa/devirt-51.C    (working copy)
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fsanitize=undefined -fdump-tree-optimized"  } */
+namespace {
+  struct B {
+        B* self;
+        B() : self( this ) { self->f(); }
+       void E(void);
+        virtual void f() = 0;
+    };
+
+    struct D : B
+    {
+        void f() {}
+    };
+}
+
+struct D e;
+
+__attribute__ ((used))
+void B::E(void)
+  {
+    this->f();
+}
+
+    int main()
+    {
+        D d;
+    }
+/* { dg-final { scan-tree-dump "cxa_pure_virtual" "optimized"  } } */

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