| Message ID | 54F9671B.1040002@oracle.com |
|---|---|
| State | New |
| Headers | show |
On 03/06/2015 03:36 AM, Paolo Carlini wrote: > this is a regression about duplicate warnings with > -Wzero-as-null-pointer-constant. The regression is rather old, affects > 4_8-branch too, and started when check_default_argument got a > perform_implicit_conversion_flags call which warns a first time, then > maybe_warn_zero_as_null_pointer_constant as called by > check_default_argument itself warns a second time. The latter call is > even older, dates back to c++/52718, I think we can now safely remove it > and keep on returning nullptr_node to avoid warning later still at the > call sites (that was the point of c++/52718). Tested x86_64-linux. Do we need this special handling at all? When I remove that whole 'if' block I still only get one warning from the 52718 testcase. Jason
Hi, On 03/11/2015 09:26 PM, Jason Merrill wrote: > On 03/06/2015 03:36 AM, Paolo Carlini wrote: >> this is a regression about duplicate warnings with >> -Wzero-as-null-pointer-constant. The regression is rather old, affects >> 4_8-branch too, and started when check_default_argument got a >> perform_implicit_conversion_flags call which warns a first time, then >> maybe_warn_zero_as_null_pointer_constant as called by >> check_default_argument itself warns a second time. The latter call is >> even older, dates back to c++/52718, I think we can now safely remove it >> and keep on returning nullptr_node to avoid warning later still at the >> call sites (that was the point of c++/52718). Tested x86_64-linux. > > Do we need this special handling at all? When I remove that whole > 'if' block I still only get one warning from the 52718 testcase. I just tried again for this reduced version of 52718 (I added a 0 && to the 'if'): void* fun(void* a = 0); void* f2 = fun(); and I got (removed the irrelevant carets): 52718_red.C:1:22: warning: zero as null pointer constant [-Wzero-as-null-pointer-constant] void* fun(void* a = 0); 52718_red.C:2:16: warning: zero as null pointer constant [-Wzero-as-null-pointer-constant] void* f2 = fun(); That is, as far as I can see, the rationale that led to an early *return* for 52718 still stand: no matter what we do at the beginning of check_default_argument, whether we warn via perform_implicit_conversion_flags or immediately, we still want to early return to avoid warning again at the call site. Paolo.
On 03/12/2015 06:13 AM, Paolo Carlini wrote: > 52718_red.C:1:22: warning: zero as null pointer constant > [-Wzero-as-null-pointer-constant] > void* fun(void* a = 0); > > 52718_red.C:2:16: warning: zero as null pointer constant > [-Wzero-as-null-pointer-constant] > void* f2 = fun(); OK, then your second patch is OK. But please add a comment that the code is there to avoid a redundant warning at the call site. Jason
Index: decl.c =================================================================== --- decl.c (revision 221230) +++ decl.c (working copy) @@ -11227,11 +11227,9 @@ check_default_argument (tree decl, tree arg, tsubs LOOKUP_IMPLICIT); --cp_unevaluated_operand; - if (warn_zero_as_null_pointer_constant - && TYPE_PTR_OR_PTRMEM_P (decl_type) + if (TYPE_PTR_OR_PTRMEM_P (decl_type) && null_ptr_cst_p (arg) - && (complain & tf_warning) - && maybe_warn_zero_as_null_pointer_constant (arg, input_location)) + && !NULLPTR_TYPE_P (TREE_TYPE (arg))) return nullptr_node; /* [dcl.fct.default]