[C++ PATCH] Do not warn about zero-as-null when NULL is used.

[Ville Voutilainen]

I smacked my head against conversion_null_warnings for a while,
and then I realized that we could just stop convert_like_real from
changing the node type for null_node.

Tested manually on Linux-x64, running full suite on Linux-PPC64,
ok for trunk?

2018-05-25  Ville Voutilainen  <ville.voutilai...@gmail.com>

    gcc/cp/

    Do not warn about zero-as-null when NULL is used.
    * call.c (convert_like_real): Don't turn a null_node into integer_cst.
    * cvt.c (cp_convert_to_pointer): Don't warn about null_nodes.

    testsuite/

    Do not warn about zero-as-null when NULL is used.
    * g++.dg/warn/Wzero-as-null-pointer-constant-7.C: New.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 7aadd64..cb07bb7 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -6799,12 +6799,6 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 
       if (type_unknown_p (expr))
 	expr = instantiate_type (totype, expr, complain);
-      if (expr == null_node
-	  && INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (totype))
-	/* If __null has been converted to an integer type, we do not want to
-	   continue to warn about uses of EXPR as an integer, rather than as a
-	   pointer.  */
-	expr = build_int_cst (totype, 0);
       return expr;
     case ck_ambig:
       /* We leave bad_p off ck_ambig because overload resolution considers
diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index f29dacd..36529f9 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -208,8 +208,8 @@ cp_convert_to_pointer (tree type, tree expr, bool dofold,
 	return build_ptrmemfunc (TYPE_PTRMEMFUNC_FN_TYPE (type), expr, 0,
 				 /*c_cast_p=*/false, complain);
 
-      if (complain & tf_warning)
-	maybe_warn_zero_as_null_pointer_constant (expr, loc);
+      if (!null_node_p (expr) && (complain & tf_warning))
+       maybe_warn_zero_as_null_pointer_constant (expr, loc);
 
       /* A NULL pointer-to-data-member is represented by -1, not by
 	 zero.  */
diff --git a/gcc/testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-7.C b/gcc/testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-7.C
new file mode 100644
index 0000000..0d06dbf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-7.C
@@ -0,0 +1,13 @@
+// { dg-options "-Wzero-as-null-pointer-constant" }
+// { dg-do compile { target c++11 } }
+
+#include <cstddef>
+
+void test01()
+{
+  char* x(NULL);
+  char* x2{NULL};
+  char* x3 = NULL;
+  char* x4(0); // { dg-warning "zero as null pointer" }
+  char* x5 = 0; // { dg-warning "zero as null pointer" }
+}