[C++ Patch / RFC] PR 48420

[Paolo Carlini]

Hi,

this issue seems pretty easy to deal with: submitter complains that we 
warn for

void foo(int* p);

void bar() {
  foo(false);
}

and we do *not* for:

void foo(int* p);

void bar() {
  const bool kDebugMode = false;
  foo(kDebugMode);
}

thus I tried using decl_constant_var_p / integral_constant_value and it 
worked fine, as expected. However - I may be wrong - but I'm not seeing 
*much* of this kind of idea around for diagnostic purposes, I'm afraid 
I'm missing something. It is actually Ok?

Anyway, testsuite passes on x86_64-linux (bootstrap pending, important 
because the W is on by default!)

Thanks,
Paolo.

//////////////////
/cp
2011-11-03  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/48420
        * call.c (conversion_null_warnings): For 'false' to NULL pointer,
        look also inside constant VAR_DECLs.

/testsuite
2011-11-03  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/48420
        * g++.dg/warn/Wconversion-null-3.C: New.
Index: testsuite/g++.dg/warn/Wconversion-null-3.C
===================================================================
--- testsuite/g++.dg/warn/Wconversion-null-3.C  (revision 0)
+++ testsuite/g++.dg/warn/Wconversion-null-3.C  (revision 0)
@@ -0,0 +1,8 @@
+// PR c++/48420
+
+void foo(int* p);
+
+void bar() {
+  const bool kDebugMode = false;
+  foo(kDebugMode);   // { dg-warning "converting 'false'" }
+}
Index: cp/call.c
===================================================================
--- cp/call.c   (revision 180806)
+++ cp/call.c   (working copy)
@@ -5542,17 +5542,22 @@ conversion_null_warnings (tree totype, tree expr,
        warning_at (input_location, OPT_Wconversion_null,
                    "converting to non-pointer type %qT from NULL", totype);
     }
+  else if (TYPE_PTR_P (totype))
+    {
+      if (decl_constant_var_p (expr))
+       expr = integral_constant_value (expr);
 
-  /* Issue warnings if "false" is converted to a NULL pointer */
-  else if (expr == boolean_false_node && TYPE_PTR_P (totype))
-    {
-      if (fn)
-       warning_at (input_location, OPT_Wconversion_null,
-                   "converting %<false%> to pointer type for argument %P "
-                   "of %qD", argnum, fn);
-      else
-       warning_at (input_location, OPT_Wconversion_null,
-                   "converting %<false%> to pointer type %qT", totype);
+      /* Issue warnings if "false" is converted to a NULL pointer */
+      if (expr == boolean_false_node)
+       {
+         if (fn)
+           warning_at (input_location, OPT_Wconversion_null,
+                       "converting %<false%> to pointer type for argument %P "
+                       "of %qD", argnum, fn);
+         else
+           warning_at (input_location, OPT_Wconversion_null,
+                       "converting %<false%> to pointer type %qT", totype);
+       }
     }
 }