[Bug c++/95221] g++.dg/ubsan/vptr-12.C fails with -fstrong-eval-order=all

["mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95221

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
It is caused by this code:

 853       if (flag_strong_eval_order == 2
 854           && CALL_EXPR_FN (*expr_p)
 855           && cp_get_callee_fndecl_nofold (*expr_p) == NULL_TREE)
 856         {
 857           tree fnptrtype = TREE_TYPE (CALL_EXPR_FN (*expr_p));
 858           enum gimplify_status t
 859             = gimplify_to_rvalue (&CALL_EXPR_FN (*expr_p), pre_p, NULL,
 860                                   is_gimple_call_addr);
 861           if (t == GS_ERROR)
 862             ret = GS_ERROR;
 863           /* GIMPLE considers most pointer conversion useless, but for
 864              calls we actually care about the exact function pointer type.
 */
 865           else if (TREE_TYPE (CALL_EXPR_FN (*expr_p)) != fnptrtype)
 866             CALL_EXPR_FN (*expr_p)
 867               = build1 (NOP_EXPR, fnptrtype, CALL_EXPR_FN (*expr_p));
 868         }

and causes this difference:

--- 1g  2020-05-19 11:42:32.123168379 -0400
+++ 2g  2020-05-19 11:42:41.254133594 -0400
@@ -18,21 +18,21 @@
         operator delete (D.2725, 8);
       }
     c = D.2725;
+    _1 = c->_vptr.MyClass;
+    _2 = *_1;
     c.0 = c;
-    _1 = c.0->_vptr.MyClass;
-    _2 = (long unsigned int) _1;
-    .UBSAN_VPTR (c.0, _2, 2968783897514143607, &_ZTI7MyClass, 4B);
-    _3 = c->_vptr.MyClass;
-    _4 = *_3;
-    OBJ_TYPE_REF(_4;(struct MyClass)c->0) (c.0);
+    _3 = c.0->_vptr.MyClass;
+    _4 = (long unsigned int) _3;
+    .UBSAN_VPTR (c.0, _4, 2968783897514143607, &_ZTI7MyClass, 4B);
+    OBJ_TYPE_REF(_2;(struct MyClass)c->0) (c.0);
+    _5 = c->_vptr.MyClass;
+    _6 = _5 + 16;
+    _7 = *_6;
     c.1 = c;
-    _5 = c.1->_vptr.MyClass;
-    _6 = (long unsigned int) _5;
-    .UBSAN_VPTR (c.1, _6, 2968783897514143607, &_ZTI7MyClass, 4B);
-    _7 = c->_vptr.MyClass;
-    _8 = _7 + 16;
-    _9 = *_8;
-    OBJ_TYPE_REF(_9;(struct MyClass)c->2) (c.1);
+    _8 = c.1->_vptr.MyClass;
+    _9 = (long unsigned int) _8;
+    .UBSAN_VPTR (c.1, _9, 2968783897514143607, &_ZTI7MyClass, 4B);
+    OBJ_TYPE_REF(_7;(struct MyClass)c->2) (c.1);
     D.2751 = 0;
     return D.2751;
   }