re PR ipa/83983 (FAIL: g++.dg/lto/pr83121 (test for LTO warnings, pr83121_0.C line 8))

	PR ipa/83983
	* ipa-devirt.c (odr_subtypes_equivalent_p): Get the ODR type of both
	arguments if they are comparable.

From-SVN: r258133

gcc/ChangeLog

+2018-03-02  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR ipa/83983
+	* ipa-devirt.c (odr_subtypes_equivalent_p): Get the ODR type of both
+	arguments if they are comparable.
+
 2018-03-02  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	PR tree-optimization/84634

gcc/ipa-devirt.c

@@ -684,9 +684,14 @@ odr_subtypes_equivalent_p (tree t1, tree t2,
     {
       if (!types_same_for_odr (t1, t2, true))
         return false;
-      /* Limit recursion: If subtypes are ODR types and we know
-         that they are same, be happy.  */
-      if (!odr_type_p (t1) || !get_odr_type (t1, true)->odr_violated)
+      /* Limit recursion: if subtypes are ODR types and we know that they are
+	 same, be happy.  We need to call get_odr_type on both subtypes since
+	 we don't know which among t1 and t2 defines the common ODR type and
+	 therefore which call will report the ODR violation, if any.  */
+	 if (!odr_type_p (t1)
+	     || !odr_type_p (t2)
+	     || (!get_odr_type (t1, true)->odr_violated
+		 && !get_odr_type (t2, true)->odr_violated))
         return true;
     }