[C++ Patch] PR 67216 ("false is still a null pointer constant")

[Paolo Carlini]

Hi,

the bug is very clear: in C++11 we reject the testcase because 
null_ptr_cst_p returns 'true' for 'false', whereas [conv.ptr] is 
carefully worded in terms of integer literals not boolean literals. The 
obvious fix, using == INTEGER_TYPE instead of CP_INTEGRAL_TYPE_P, 
appears to work well.

Tested x86_64-linux.

Thanks,
Paolo.

///////////////////////

/cp
2015-08-17  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/67216
        * call.c (null_ptr_cst_p): In C++11 return 'false' for 'false'.

/testsuite
2015-08-17  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/67216
        * g++.dg/cpp0x/nullptr34.C: New.
        * g++.dg/warn/Wconversion2.C: Adjust.
        * g++.dg/warn/Wnull-conversion-1.C: Likewise.
Index: cp/call.c
===================================================================
--- cp/call.c   (revision 226939)
+++ cp/call.c   (working copy)
@@ -524,22 +524,34 @@ struct z_candidate {
 bool
 null_ptr_cst_p (tree t)
 {
+  tree type = TREE_TYPE (t);
+
   /* [conv.ptr]
 
      A null pointer constant is an integral constant expression
      (_expr.const_) rvalue of integer type that evaluates to zero or
      an rvalue of type std::nullptr_t. */
-  if (NULLPTR_TYPE_P (TREE_TYPE (t)))
+  if (NULLPTR_TYPE_P (type))
     return true;
-  if (CP_INTEGRAL_TYPE_P (TREE_TYPE (t)))
+
+  if (cxx_dialect >= cxx11)
     {
       /* Core issue 903 says only literal 0 is a null pointer constant.  */
-      if (cxx_dialect < cxx11)
-       t = fold_non_dependent_expr (t);
+      if (TREE_CODE (type) == INTEGER_TYPE)
+       {
+         STRIP_NOPS (t);
+         if (integer_zerop (t) && !TREE_OVERFLOW (t))
+           return true;
+       }
+    }
+  else if (CP_INTEGRAL_TYPE_P (type))
+    {
+      t = fold_non_dependent_expr (t);
       STRIP_NOPS (t);
       if (integer_zerop (t) && !TREE_OVERFLOW (t))
        return true;
     }
+
   return false;
 }
 
Index: testsuite/g++.dg/cpp0x/nullptr34.C
===================================================================
--- testsuite/g++.dg/cpp0x/nullptr34.C  (revision 0)
+++ testsuite/g++.dg/cpp0x/nullptr34.C  (working copy)
@@ -0,0 +1,17 @@
+// PR c++/67216
+// { dg-do compile { target c++11 } }
+
+struct s {
+    s( long ) {}
+};
+
+struct t {
+    t( void * ) {}
+};
+
+void foo(s) {}
+void foo(t) {}
+
+int main() {
+    foo(false);
+}
Index: testsuite/g++.dg/warn/Wconversion2.C
===================================================================
--- testsuite/g++.dg/warn/Wconversion2.C        (revision 226939)
+++ testsuite/g++.dg/warn/Wconversion2.C        (working copy)
@@ -1,3 +1,4 @@
 // { dg-options "-Wconversion-null" }
 void foo(const char *); 
-void bar() { foo(false); } // { dg-warning "pointer type for argument" }
+void bar() { foo(false); } // { dg-warning "pointer type for argument" "" { 
target { ! c++11 } } }
+// { dg-error "cannot convert" "" { target c++11 } 3 }
Index: testsuite/g++.dg/warn/Wnull-conversion-1.C
===================================================================
--- testsuite/g++.dg/warn/Wnull-conversion-1.C  (revision 226939)
+++ testsuite/g++.dg/warn/Wnull-conversion-1.C  (working copy)
@@ -6,10 +6,13 @@
 void func1(int* ptr);
 
 void func2() {
-  int* t = false;             // { dg-warning "converting 'false' to pointer" }
+  int* t = false;             // { dg-warning "converting 'false' to pointer" 
"" { target { ! c++11 } } }
+// { dg-error "cannot convert" "" { target c++11 } 9 }
   int* p;
-  p = false;                  // { dg-warning "converting 'false' to pointer" }
+  p = false;                  // { dg-warning "converting 'false' to pointer" 
"" { target { ! c++11 } } }
+// { dg-error "cannot convert" "" { target c++11 } 12 }
   int* r = sizeof(char) / 2;  // { dg-error "invalid conversion from" "" { 
target c++11 } }
-  func1(false);               // { dg-warning "converting 'false' to pointer" }
+  func1(false);               // { dg-warning "converting 'false' to pointer" 
"" { target { ! c++11 } } }
+// { dg-error "cannot convert" "" { target c++11 } 15 }
   int i = NULL;               // { dg-warning "converting to non-pointer" }
 }
Index: testsuite/g++.old-deja/g++.other/null3.C
===================================================================
--- testsuite/g++.old-deja/g++.other/null3.C    (revision 226939)
+++ testsuite/g++.old-deja/g++.other/null3.C    (working copy)
@@ -2,5 +2,6 @@
 
 void x()
 {
- int* p = 1==0;        // { dg-warning "converting 'false' to pointer" }
+ int* p = 1==0;        // { dg-warning "converting 'false' to pointer" "" { 
target { ! c++11 } } }
+// { dg-error "cannot convert" "" { target c++11 } 5 } 
 }