[C++ PATCH] Fix -Wnonnull-compare warning from dynamic_cast <...> (this) (PR c++/69850)

[Jakub Jelinek]

Hi!

And here is a fix for the dynamic_cast issue I've mentioned recently.
Alternatively, ifnonnull could build instead NE_EXPR with swapped last
two arguments on the COND_EXPR, and then I believe the cp_fold change would
not be needed.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Or do you prefer the NE_EXPR variant?

2016-02-18  Jakub Jelinek  <ja...@redhat.com>

        PR c++/69850
        * rtti.c (ifnonnull): Set TREE_NO_WARNING on the EQ_EXPR
        condition.
        * cp-gimplify.c (cp_fold) <case COND_EXPR>: Preserve
        TREE_NO_WARNING on comparison if folding swaps arguments.

        * g++.dg/warn/Wnonnull-compare-4.C: New test.

--- gcc/cp/rtti.c.jj    2016-02-11 10:50:58.000000000 +0100
+++ gcc/cp/rtti.c       2016-02-18 18:04:24.611297291 +0100
@@ -507,10 +507,12 @@ get_typeid (tree type, tsubst_flags_t co
 static tree
 ifnonnull (tree test, tree result, tsubst_flags_t complain)
 {
-  return build3 (COND_EXPR, TREE_TYPE (result),
-                build2 (EQ_EXPR, boolean_type_node, test,
-                        cp_convert (TREE_TYPE (test), nullptr_node,
-                                    complain)),
+  tree cond = build2 (EQ_EXPR, boolean_type_node, test,
+                     cp_convert (TREE_TYPE (test), nullptr_node, complain));
+  /* This is a compiler generated comparison, don't emit
+     e.g. -Wnonnull-compare warning for it.  */
+  TREE_NO_WARNING (cond) = 1;
+  return build3 (COND_EXPR, TREE_TYPE (result), cond,
                 cp_convert (TREE_TYPE (result), nullptr_node, complain),
                 result);
 }
--- gcc/cp/cp-gimplify.c.jj     2016-02-18 11:20:08.000000000 +0100
+++ gcc/cp/cp-gimplify.c        2016-02-18 18:14:26.213996843 +0100
@@ -2101,6 +2101,11 @@ cp_fold (tree x)
       else
        x = fold (x);
 
+      if (COMPARISON_CLASS_P (TREE_OPERAND (org_x, 0))
+         && TREE_NO_WARNING (TREE_OPERAND (org_x, 0))
+         && TREE_CODE (x) == TREE_CODE (org_x)
+         && COMPARISON_CLASS_P (TREE_OPERAND (x, 0)))
+       TREE_NO_WARNING (TREE_OPERAND (x, 0)) = 1;
       break;
 
     case CALL_EXPR:
--- gcc/testsuite/g++.dg/warn/Wnonnull-compare-4.C.jj   2016-02-18 
18:03:04.777398778 +0100
+++ gcc/testsuite/g++.dg/warn/Wnonnull-compare-4.C      2016-02-18 
18:02:46.414652133 +0100
@@ -0,0 +1,14 @@
+// PR c++/69850
+// { dg-do compile }
+// { dg-options "-Wnonnull-compare" }
+
+struct A { virtual ~A (); int foo (); };
+struct B { virtual ~B () { } };
+struct C : B, A { };
+
+int
+A::foo ()
+{
+  C *c = dynamic_cast<C *> (this);     // { dg-bogus "nonnull argument" }
+  return !c;
+}

        Jakub