Hi,
On 08/05/2014 03:58 AM, Jason Merrill wrote:
On 08/04/2014 07:01 PM, Paolo Carlini wrote:
In fact I wondered about that a few minutes after sending my message...
And this is what I figured out: normally we have hard errors from
composite_pointer_type (eg, try scalar types, class types), even for
null values. The only exception I have been able to find earlier today
is that of pointer to the same function type, eg:
extern void z();
typedef void (*ptr)();
void i() { if ( z != (ptr)0 ); }
but in this case the C front-end too doesn't warn.
I don't see why we wouldn't want to warn in this case; it's still the
case thet the comparison will always be false.
In general, I agree of course. I was trying to understand if keeping the
issue as minimally one of consistency with the C front-end simplified it.
We can also see this situation for non-function pointers:
void f()
{
int i;
if (&i != (int*)0);
}
Sure. Then, however, we must be careful about the actual pointer types,
otherwise we change hard errors to warnings. And void* is an exception
to the general rule. I tried using ptr_reasonably_similar to avoid the
explicit call of comptypes + separate VOID_TYPE_P, but unfortunately it
appears too loose about at least pointers to function types.
Thanks!
Paolo.
//////////////////////////
Index: cp/typeck.c
===================================================================
--- cp/typeck.c (revision 213631)
+++ cp/typeck.c (working copy)
@@ -4353,12 +4353,14 @@ cp_build_binary_op (location_t location,
&& (code1 == INTEGER_TYPE || code1 == REAL_TYPE
|| code1 == COMPLEX_TYPE || code1 == ENUMERAL_TYPE))
short_compare = 1;
- else if ((code0 == POINTER_TYPE && code1 == POINTER_TYPE)
- || (TYPE_PTRDATAMEM_P (type0) && TYPE_PTRDATAMEM_P (type1)))
- result_type = composite_pointer_type (type0, type1, op0, op1,
- CPO_COMPARISON, complain);
else if ((code0 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type0))
- && null_ptr_cst_p (op1))
+ && (null_ptr_cst_p (op1)
+ /* Handle, eg, (void*)0 (c++/43906), and more. */
+ || (TYPE_PTR_P (type1) && integer_zerop (op1)
+ && (VOID_TYPE_P (TREE_TYPE (type1))
+ || comptypes (TYPE_MAIN_VARIANT (TREE_TYPE (type0)),
+ TYPE_MAIN_VARIANT (TREE_TYPE (type1)),
+ COMPARE_BASE | COMPARE_DERIVED)))))
{
if (TREE_CODE (op0) == ADDR_EXPR
&& decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)))
@@ -4371,7 +4373,13 @@ cp_build_binary_op (location_t location,
result_type = type0;
}
else if ((code1 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type1))
- && null_ptr_cst_p (op0))
+ && (null_ptr_cst_p (op0)
+ /* Handle, eg, (void*)0 (c++/43906), and more. */
+ || (TYPE_PTR_P (type0) && integer_zerop (op0)
+ && (VOID_TYPE_P (TREE_TYPE (type0))
+ || comptypes (TYPE_MAIN_VARIANT (TREE_TYPE (type0)),
+ TYPE_MAIN_VARIANT (TREE_TYPE (type1)),
+ COMPARE_BASE | COMPARE_DERIVED)))))
{
if (TREE_CODE (op1) == ADDR_EXPR
&& decl_with_nonnull_addr_p (TREE_OPERAND (op1, 0)))
@@ -4383,6 +4391,10 @@ cp_build_binary_op (location_t location,
}
result_type = type1;
}
+ else if ((code0 == POINTER_TYPE && code1 == POINTER_TYPE)
+ || (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))
/* One of the operands must be of nullptr_t type. */
result_type = TREE_TYPE (nullptr_node);
Index: testsuite/g++.dg/warn/Waddress-1.C
===================================================================
--- testsuite/g++.dg/warn/Waddress-1.C (revision 0)
+++ testsuite/g++.dg/warn/Waddress-1.C (working copy)
@@ -0,0 +1,42 @@
+// PR c++/43906
+// { dg-options "-Waddress" }
+
+extern void z();
+typedef void (*ptrf) ();
+typedef int (*ptrfn) (int);
+int n;
+const int m = 1;
+struct S { };
+struct T : S { };
+struct U;
+S s;
+T t;
+double d;
+
+void f() { if (z) z(); } // { dg-warning "address" }
+
+void gl() { if (z != 0) z(); } // { dg-warning "address" }
+void hl() { if (z != (ptrf)0) z(); } // { dg-warning "address" }
+void il() { if (z != (void*)0) z(); } // { dg-warning "address" }
+void jl() { if (&n != (int*)0) z(); } // { dg-warning "address" }
+void kl() { if (&m != (int*)0) z(); } // { dg-warning "address" }
+void ll() { if (&s != (T*)0) z(); } // { dg-warning "address" }
+void ml() { if (&t != (S*)0) z(); } // { dg-warning "address" }
+
+void nl() { if (z != (S*)0) z(); } // { dg-error "comparison" }
+void pl() { if (z != (ptrfn)0) z(); } // { dg-error "comparison" }
+void ql() { if (&d != (int*)0) z(); } // { dg-error "comparison" }
+void rl() { if (&s != (U*)0) z(); } // { dg-error "comparison" }
+
+void gr() { if (0 != z) z(); } // { dg-warning "address" }
+void hr() { if ((ptrf)0 != z) z(); } // { dg-warning "address" }
+void ir() { if ((void*)0 != z) z(); } // { dg-warning "address" }
+void jr() { if ((int*)0 != &n) z(); } // { dg-warning "address" }
+void kr() { if ((int*)0 != &m) z(); } // { dg-warning "address" }
+void lr() { if ((T*)0 != &s) z(); } // { dg-warning "address" }
+void mr() { if ((S*)0 != &t) z(); } // { dg-warning "address" }
+
+void nr() { if ((S*)0 != z) z(); } // { dg-error "comparison" }
+void pr() { if ((ptrfn)0 != z) z(); } // { dg-error "comparison" }
+void qr() { if ((int*)0 != &d) z(); } // { dg-error "comparison" }
+void rr() { if ((U*)0 != &s) z(); } // { dg-error "comparison" }
