Patchwork [C++] PR 54170

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Submitter Paolo Carlini
Date Nov. 30, 2012, 9:05 p.m.
Message ID <50B91F80.3080100@oracle.com>
Download mbox | patch
Permalink /patch/203048/
State New
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Comments

Paolo Carlini - Nov. 30, 2012, 9:05 p.m.
Hi,

this wrong code PR is some sort of continuation of PR 52988, where we 
discard side-effects of expression of nullptr_t. Here too, in 
cp_convert_to_pointer and in build_ptrmemfunc, we don't check for 
side-effects and we replace the expression with a plain int_cst or 
nullptr_node. The testcase in the PR exercises only plain pointers but 
we have also to handle correctly pointers to members, thus I extended it 
and the patch became slightly more complex: for the case of pointer to 
data member in particular I have to call by hand build2 and build a 
COMPOUND_EXPR to host the side-effects (similarly to what I found used 
in cp_build_addr_expr_1).

Tested x86_64-linux.

Thanks,
Paolo.

/////////////////////////////
/cp
2012-11-30  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/54170
	* cvt.c (cp_convert_to_pointer): Don't discard side-effects from
	expressions of nullptr_t.
	* typeck.c (build_ptrmemfunc): Likewise.

/testsuite
2012-11-30  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/54170
	* g++.dg/cpp0x/lambda/lambda-nullptr.C: New.
Jason Merrill - Dec. 1, 2012, 6:13 a.m.
On 11/30/2012 04:05 PM, Paolo Carlini wrote:
> @@ -219,10 +219,15 @@ cp_convert_to_pointer (tree type, tree expr, tsubs
> -	expr = build_int_cst (type, 0);
> +	expr = (TREE_SIDE_EFFECTS (expr)
> +		? build_nop (type, expr)
> +		: build_int_cst (type, 0));

This seems to rely on a nop being sufficient to convert from any null 
pointer constant to the appropriate pointer type, which I don't think is 
safe if the integer is smaller than a pointer.

I'm also not sure if we want to rely on nullptr_t expressions actually 
having the value 0.

> -      pfn = build_c_cast (input_location, type, nullptr_node);
> +      pfn = (TREE_SIDE_EFFECTS (pfn)
> +	     ? build_nop (type, pfn)
> +	     : build_c_cast (input_location, type, nullptr_node));

Here we should be able to just convert pfn to the appropriate function 
pointer type so that we don't need to duplicate the logic.

Jason

Patch

Index: cp/cvt.c
===================================================================
--- cp/cvt.c	(revision 193995)
+++ cp/cvt.c	(working copy)
@@ -219,10 +219,15 @@  cp_convert_to_pointer (tree type, tree expr, tsubs
 	{
 	  /* A NULL pointer-to-member is represented by -1, not by
 	     zero.  */
-	  expr = build_int_cst_type (type, -1);
+	  expr = (TREE_SIDE_EFFECTS (expr)
+		  ? build2 (COMPOUND_EXPR, type, expr,
+			    build_int_cst_type (type, -1))
+		  : build_int_cst_type (type, -1));
 	}
       else
-	expr = build_int_cst (type, 0);
+	expr = (TREE_SIDE_EFFECTS (expr)
+		? build_nop (type, expr)
+		: build_int_cst (type, 0));
 
       return expr;
     }
Index: cp/typeck.c
===================================================================
--- cp/typeck.c	(revision 193995)
+++ cp/typeck.c	(working copy)
@@ -7567,7 +7567,9 @@  build_ptrmemfunc (tree type, tree pfn, int force,
   /* Handle null pointer to member function conversions.  */
   if (null_ptr_cst_p (pfn))
     {
-      pfn = build_c_cast (input_location, type, nullptr_node);
+      pfn = (TREE_SIDE_EFFECTS (pfn)
+	     ? build_nop (type, pfn)
+	     : build_c_cast (input_location, type, nullptr_node));
       return build_ptrmemfunc1 (to_type,
 				integer_zero_node,
 				pfn);
Index: testsuite/g++.dg/cpp0x/lambda/lambda-nullptr.C
===================================================================
--- testsuite/g++.dg/cpp0x/lambda/lambda-nullptr.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/lambda/lambda-nullptr.C	(working copy)
@@ -0,0 +1,47 @@ 
+// PR c++/54170
+// { dg-do run { target c++11 } }
+
+#include <cassert> 
+
+struct A;
+typedef A* ptr;
+typedef int (A::*pmf) (int);
+typedef int (A::*pdm);
+
+int total;
+
+void add(int n)
+{
+  total += n;
+}
+
+template <typename RType, typename Callable>
+RType Call(Callable native_func, int arg)
+{
+  return native_func(arg);
+}
+
+template <typename RType>
+RType do_test(int delta)
+{
+  return Call<RType>([=](int delta) { add(delta); return nullptr; }, delta);
+}
+
+template <typename RType>
+void test()
+{
+  total = 0;
+  assert (!do_test<RType>(5));
+  assert (total == 5);
+  assert (!do_test<RType>(20));
+  assert (total == 25);
+  assert (!do_test<RType>(-256));
+  assert (total == -231);
+}
+
+int main()
+{
+  test<ptr>();
+  test<pdm>();
+  test<pmf>();
+}