Re: C/C++ PATCH to implement -Wpointer-compare warning (PR c++/64767)

[Marek Polacek <polacek@redhat.com>]

On Fri, Sep 30, 2016 at 05:48:03PM -0400, Jason Merrill wrote:
> On Fri, Sep 30, 2016 at 12:43 PM, Marek Polacek <polacek@redhat.com> wrote:
> > On Fri, Sep 23, 2016 at 10:31:33AM -0400, Jason Merrill wrote:
> >> On Fri, Sep 23, 2016 at 9:15 AM, Marek Polacek <polacek@redhat.com> wrote:
> >> > On Wed, Sep 21, 2016 at 03:52:09PM -0400, Jason Merrill wrote:
> >> >> On Mon, Sep 19, 2016 at 2:49 PM, Jason Merrill <jason@redhat.com> wrote:
> >> >> > I suppose that an INTEGER_CST of character type is necessarily a
> >> >> > character constant, so adding a check for !char_type_p ought to do the
> >> >> > trick.
> >> >>
> >> >> Indeed it does.  I'm checking this in:
> >> >
> >> > Nice, thanks.  What about the original patch?  We still need to warn
> >> > (or error for C++11) for pointer comparisons.
> >>
> >> If we still accept pointer comparisons in C++, that's another bug with
> >> treating \0 as a null pointer constant.  This seems to be because
> >> ocp_convert of \0 to int produces an INTEGER_CST indistinguishable
> >> from literal 0.
> >
> > I was trying to fix this in ocp_convert, by using NOP_EXPRs, but that wasn't
> > successful.  But since we're interested in ==/!=, I think this can be fixed
> > easily in cp_build_binary_op.  Actually, all that seems to be needed is using
> > orig_op as the argument to null_ptr_cst_p, but that wouldn't give the correct
> > diagnostics, so I did this.  By checking orig_op we can see if the operands are
> > character literals or not, because orig_op is an operand before the default
> > conversions.
> 
> What is wrong about the diagnostic from just using orig_op?  "ISO C++
> forbids comparison between pointer and integer" seems fine to me, and
> will help the user to realize that they need to index off the pointer.
> 
> I see that some of the calls to null_ptr_cst_p in cp_build_binary_op
> have already been changed to check orig_op*, but not all.  Let's
> update the remaining calls, that should do the trick without adding a
> new error.

Here you go:

Bootstrapped/regtested on x86_64-linux and ppc64-linux, ok for trunk?

2016-10-01  Marek Polacek  <polacek@redhat.com>

	Core 903
	* typeck.c (cp_build_binary_op): Pass original operands to
	null_ptr_cst_p, not those after the default conversions.

	* g++.dg/cpp0x/nullptr37.C: New test.

diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 617ca55..8b780be 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -4573,7 +4573,7 @@ cp_build_binary_op (location_t location,
 	      || code1 == COMPLEX_TYPE || code1 == ENUMERAL_TYPE))
 	short_compare = 1;
       else if (((code0 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type0))
-		&& null_ptr_cst_p (op1))
+		&& null_ptr_cst_p (orig_op1))
 	       /* Handle, eg, (void*)0 (c++/43906), and more.  */
 	       || (code0 == POINTER_TYPE
 		   && TYPE_PTR_P (type1) && integer_zerop (op1)))
@@ -4587,7 +4587,7 @@ cp_build_binary_op (location_t location,
 	  warn_for_null_address (location, op0, complain);
 	}
       else if (((code1 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type1))
-		&& null_ptr_cst_p (op0))
+		&& null_ptr_cst_p (orig_op0))
 	       /* Handle, eg, (void*)0 (c++/43906), and more.  */
 	       || (code1 == POINTER_TYPE
 		   && TYPE_PTR_P (type0) && integer_zerop (op0)))
@@ -4604,7 +4604,7 @@ cp_build_binary_op (location_t location,
 	       || (TYPE_PTRDATAMEM_P (type0) && TYPE_PTRDATAMEM_P (type1)))
 	result_type = composite_pointer_type (type0, type1, op0, op1,
 					      CPO_COMPARISON, complain);
-      else if (null_ptr_cst_p (op0) && null_ptr_cst_p (op1))
+      else if (null_ptr_cst_p (orig_op0) && null_ptr_cst_p (orig_op1))
 	/* One of the operands must be of nullptr_t type.  */
         result_type = TREE_TYPE (nullptr_node);
       else if (code0 == POINTER_TYPE && code1 == INTEGER_TYPE)
@@ -4623,7 +4623,7 @@ cp_build_binary_op (location_t location,
           else
             return error_mark_node;
 	}
-      else if (TYPE_PTRMEMFUNC_P (type0) && null_ptr_cst_p (op1))
+      else if (TYPE_PTRMEMFUNC_P (type0) && null_ptr_cst_p (orig_op1))
 	{
 	  if (TARGET_PTRMEMFUNC_VBIT_LOCATION
 	      == ptrmemfunc_vbit_in_delta)
@@ -4664,7 +4664,7 @@ cp_build_binary_op (location_t location,
 	    }
 	  result_type = TREE_TYPE (op0);
 	}
-      else if (TYPE_PTRMEMFUNC_P (type1) && null_ptr_cst_p (op0))
+      else if (TYPE_PTRMEMFUNC_P (type1) && null_ptr_cst_p (orig_op0))
 	return cp_build_binary_op (location, code, op1, op0, complain);
       else if (TYPE_PTRMEMFUNC_P (type0) && TYPE_PTRMEMFUNC_P (type1))
 	{
@@ -4877,21 +4877,21 @@ cp_build_binary_op (location_t location,
       else if (code0 == POINTER_TYPE && code1 == POINTER_TYPE)
 	result_type = composite_pointer_type (type0, type1, op0, op1,
 					      CPO_COMPARISON, complain);
-      else if (code0 == POINTER_TYPE && null_ptr_cst_p (op1))
+      else if (code0 == POINTER_TYPE && null_ptr_cst_p (orig_op1))
 	{
 	  result_type = type0;
 	  if (extra_warnings && (complain & tf_warning))
 	    warning (OPT_Wextra,
 		     "ordered comparison of pointer with integer zero");
 	}
-      else if (code1 == POINTER_TYPE && null_ptr_cst_p (op0))
+      else if (code1 == POINTER_TYPE && null_ptr_cst_p (orig_op0))
 	{
 	  result_type = type1;
 	  if (extra_warnings && (complain & tf_warning))
 	    warning (OPT_Wextra,
 		     "ordered comparison of pointer with integer zero");
 	}
-      else if (null_ptr_cst_p (op0) && null_ptr_cst_p (op1))
+      else if (null_ptr_cst_p (orig_op0) && null_ptr_cst_p (orig_op1))
 	/* One of the operands must be of nullptr_t type.  */
         result_type = TREE_TYPE (nullptr_node);
       else if (code0 == POINTER_TYPE && code1 == INTEGER_TYPE)
diff --git gcc/testsuite/g++.dg/cpp0x/nullptr37.C gcc/testsuite/g++.dg/cpp0x/nullptr37.C
index e69de29..e746a28 100644
--- gcc/testsuite/g++.dg/cpp0x/nullptr37.C
+++ gcc/testsuite/g++.dg/cpp0x/nullptr37.C
@@ -0,0 +1,78 @@
+/* PR c++/64767 */
+// { dg-do compile { target c++11 } }
+
+int
+f1 (int *p, int **q)
+{
+  int r = 0;
+
+  r += p == '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p == L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p == u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p == U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p != '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p != L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p != u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p != U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+
+  r += '\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += L'\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += u'\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += U'\0' == p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += '\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += L'\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += u'\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += U'\0' != p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+
+  r += q == '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q == L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q == u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q == U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q != '\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q != L'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q != u'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += q != U'\0'; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+
+  r += '\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += L'\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += u'\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += U'\0' == q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += '\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += L'\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += u'\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += U'\0' != q; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+
+  return r;
+}
+
+int
+f2 (int *p)
+{
+  int r = 0;
+
+  r += p == (void *) 0;
+  r += p != (void *) 0;
+  r += (void *) 0 == p;
+  r += (void *) 0 != p;
+
+  r += p == 0;
+  r += p != 0;
+  r += 0 == p;
+  r += 0 != p;
+
+  return r;
+}
+
+int
+f3 (int *p)
+{
+  int r = 0;
+
+  r += p == (char) 0; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += p != (char) 0; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+
+  r += (char) 0 == p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+  r += (char) 0 != p; // { dg-error "ISO C\\+\\+ forbids comparison between pointer and integer" }
+
+  return r;
+}

	Marek