[C++ Patch/RFC] PR 67576 ("[4.9/5/6 Regression] expression of typeid( expression ) is evaluated twice")

[Paolo Carlini]

Hi,

submitter noticed that the fix for c++/25466:
    https://gcc.gnu.org/ml/gcc-patches/2013-04/msg00553.html

caused a double evaluation of the typeid, at least in some cases. I had 
a quick look and wondered if it could make sense to just use the new 
code when we are outside the straightforward INDIRECT_REF cases which we 
already handled correctly... The below passes testing, anyway.

Thanks,
Paolo.

//////////////////
Index: cp/rtti.c
===================================================================
--- cp/rtti.c   (revision 227849)
+++ cp/rtti.c   (working copy)
@@ -336,10 +336,25 @@ build_typeid (tree exp, tsubst_flags_t complain)
     {
       /* So we need to look into the vtable of the type of exp.
          Make sure it isn't a null lvalue.  */
-      exp = cp_build_addr_expr (exp, complain);
-      exp = stabilize_reference (exp);
-      cond = cp_convert (boolean_type_node, exp, complain);
-      exp = cp_build_indirect_ref (exp, RO_NULL, complain);
+      if (INDIRECT_REF_P (exp)
+         && TYPE_PTR_P (TREE_TYPE (TREE_OPERAND (exp, 0))))
+       {
+         exp = mark_lvalue_use (exp);
+         exp = stabilize_reference (exp);
+         cond = cp_convert (boolean_type_node, TREE_OPERAND (exp, 0),
+                            complain);
+       }
+      else
+       {
+         /* The standard is somewhat unclear here, but makes sense
+            to always check whether the address is null rather than
+            confine the check to when the immediate operand of typeid
+            is an INDIRECT_REF.  */
+         exp = cp_build_addr_expr (exp, complain);
+         exp = stabilize_reference (exp);
+         cond = cp_convert (boolean_type_node, exp, complain);
+         exp = cp_build_indirect_ref (exp, RO_NULL, complain);
+       }
     }
 
   exp = get_tinfo_decl_dynamic (exp, complain);
Index: testsuite/g++.dg/rtti/typeid11.C
===================================================================
--- testsuite/g++.dg/rtti/typeid11.C    (revision 0)
+++ testsuite/g++.dg/rtti/typeid11.C    (working copy)
@@ -0,0 +1,17 @@
+// PR c++/67576
+// { dg-do run }
+
+#include <typeinfo>
+
+struct Base { virtual void foo() {} };
+
+int main()
+{
+  Base b;
+  Base *ary[] = { &b, &b, &b };
+
+  int iter = 0;
+  typeid(*ary[iter++]);
+  if (iter != 1)
+    __builtin_abort();
+}