On 9 May 2017 at 23:34, Martin Sebor <mse...@gmail.com> wrote:
> On 05/09/2017 07:24 AM, Prathamesh Kulkarni wrote:
>>
>> ping https://gcc.gnu.org/ml/gcc-patches/2017-05/msg00161.html
>>
>> Thanks,
>> Prathamesh
>>
>> On 3 May 2017 at 11:30, Prathamesh Kulkarni
>> <prathamesh.kulka...@linaro.org> wrote:
>>>
>>> On 3 May 2017 at 03:28, Martin Sebor <mse...@gmail.com> wrote:
>>>>
>>>> On 05/02/2017 11:11 AM, Prathamesh Kulkarni wrote:
>>>>>
>>>>>
>>>>> Hi,
>>>>> The attached patch attempts to add option -Wenum-conversion for C and
>>>>> objective-C similar to clang, which warns when an enum value of a type
>>>>> is implicitly converted to enum value of another type and is enabled
>>>>> by Wall.
>>>>
>>>>
>>>>
>>>> It seems quite useful. My only high-level concern is with
>>>> the growing number of specialized warnings and options for each
>>>> and their interaction.
>>>>
>>>> I've been working on -Wenum-assign patch that complains about
>>>> assigning to an enum variables an integer constants that doesn't
>>>> match any of the enumerators of the type. Testing revealed that
>>>> the -Wenum-assign duplicated a subset of warnings already issued
>>>> by -Wconversion enabled with -Wpedantic. I'm debating whether
>>>> to suppress that part of -Wenum-assign altogether or only when
>>>> -Wconversion and -Wpedantic are enabled.
>>>>
>>>> My point is that these dependencies tend to be hard to discover
>>>> and understand, and the interactions tricky to get right (e.g.,
>>>> avoid duplicate warnings for similar but distinct problems).
>>>>
>>>> This is not meant to be a negative comment on your patch, but
>>>> rather a comment about a general problem that might be worth
>>>> starting to think about.
>>>>
>>>> One comment on the patch itself:
>>>>
>>>> + warning_at_rich_loc (&loc, 0, "implicit conversion from"
>>>> + " enum type of %qT to %qT", checktype,
>>>> type);
>>>>
>>>> Unlike C++, the C front end formats an enumerated type E using
>>>> %qT as 'enum E' so the warning prints 'enum type of 'enum E'),
>>>> duplicating the "enum" part.
>>>>
>>>> I would suggest to simplify that to:
>>>>
>>>> warning_at_rich_loc (&loc, 0, "implicit conversion from "
>>>> "%qT to %qT", checktype, ...
>>>>
>>> Thanks for the suggestions. I have updated the patch accordingly.
>>> Hmm the issue you pointed out of warnings interaction is indeed of
>>> concern.
>>> I was wondering then if we should merge this warning with -Wconversion
>>> instead of having a separate option -Wenum-conversion ? Although that
>>> will not
>>> really help with your example below.
>>>>
>>>> Martin
>>>>
>>>> PS As an example to illustrate my concern above, consider this:
>>>>
>>>> enum __attribute__ ((packed)) E { e1 = 1 };
>>>> enum F { f256 = 256 };
>>>>
>>>> enum E e = f256;
>>>>
>>>> It triggers -Woverflow:
>>>>
>>>> warning: large integer implicitly truncated to unsigned type
>>>> [-Woverflow]
>>>> enum E e = f256;
>>>> ^~~~
>>>>
>>>> also my -Wenum-assign:
>>>>
>>>> warning: integer constant ‘256’ converted to ‘0’ due to limited range
>>>> [0,
>>>> 255] of type ‘‘enum E’’ [-Wassign-enum]
>>>> enum E e = f256;
>>>> ^~~~
>>>>
>>>> and (IIUC) will trigger your new -Wenum-conversion.
>>>
>>> Yep, on my branch it triggered -Woverflow and -Wenum-conversion.
>>> Running the example on clang shows a single warning, which they call
>>> as -Wconstant-conversion, which
>>> I suppose is similar to your -Wassign-enum.
>
>
> -Wassign-enum is a Clang warning too, it just isn't included in
> either -Wall or -Wextra. It warns when a constant is assigned
> to a variable of an enumerated type and is not representable in
> it. I enhanced it for GCC to also warn when the constant doesn't
> correspond to an enumerator in the type, but I'm starting to think
> that rather than adding yet another option to GCC it might be better
> to extend your -Wenum-conversion once it's committed to cover those
> cases (and also to avoid issuing multiple warnings for essentially
> the same problem). Let me ponder that some more.
>
> I can't approve patches but it looks good to me for the most part.
> There is one minor issue that needs to be corrected:
>
> + gcc_rich_location loc (location);
> + warning_at_rich_loc (&loc, 0, "implicit conversion from"
> + " %qT to %qT", checktype, type);
>
> Here the zero should be replaced with OPT_Wenum_conversion,
> otherwise the warning option won't be included in the message.
Oops, sorry about that, updated in the attached patch.
In the patch, I have left the warning in Wall, however I was wondering
whether it should be
in Wextra instead ?
The warning triggered for icv.c in libgomp for following assignment:
icv->run_sched_var = kind;
because icv->run_sched_var was of type enum gomp_schedule_type and
'kind' was of type enum omp_sched_t.
However although these enums have different names, they are
structurally identical (same values),
so the warning in this case, although not a false positive, seems a
bit artificial ?
Thanks,
Prathamesh
>
> Martin
>
>
>>>
>>> test-eg.c:3:12: warning: implicit conversion from 'int' to 'enum E'
>>> changes value from 256 to 0 [-Wconstant-conversion]
>>> enum E e = f256;
>>> ~ ^~~~
>>>
>>> Thanks,
>>> Prathamesh
>>>>
>>>>
>>>> Martin
>
>
2017-05-10 Prathamesh Kulkarni <prathamesh.kulka...@linaro.org>
* doc/invoke.text: Document Wenum-conversion.
* c-family/c.opt (Wenum-conversion): New option.
* c/c-typeck.c (convert_for_assignment): Handle Wenum-conversion.
testsuite/
* gcc.dg/Wenum-conversion.c: New test-case.
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 9ad2f6e1fcc..e04312ec253 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -492,6 +492,10 @@ Wenum-compare
C ObjC C++ ObjC++ Var(warn_enum_compare) Init(-1) Warning LangEnabledBy(C
ObjC,Wall || Wc++-compat)
Warn about comparison of different enum types.
+Wenum-conversion
+C ObjC Var(warn_enum_conversion) Init(0) Warning LangEnabledBy(C Objc,Wall)
+Warn about implicit conversion of enum types.
+
Werror
C ObjC C++ ObjC++
; Documented in common.opt
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 6f9909c6396..d7570835c61 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -6309,6 +6309,20 @@ convert_for_assignment (location_t location, location_t
expr_loc, tree type,
}
}
+ if (warn_enum_conversion)
+ {
+ tree checktype = origtype != NULL_TREE ? origtype : rhstype;
+ if (checktype != error_mark_node
+ && TREE_CODE (checktype) == ENUMERAL_TYPE
+ && TREE_CODE (type) == ENUMERAL_TYPE
+ && TYPE_MAIN_VARIANT (checktype) != TYPE_MAIN_VARIANT (type))
+ {
+ gcc_rich_location loc (location);
+ warning_at_rich_loc (&loc, OPT_Wenum_conversion, "implicit conversion
from"
+ " %qT to %qT", checktype, type);
+ }
+ }
+
if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (rhstype))
return rhs;
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 0eeea7b3b87..79b1e175374 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -273,7 +273,7 @@ Objective-C and Objective-C++ Dialects}.
-Wdisabled-optimization @gol
-Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
-Wno-div-by-zero -Wdouble-promotion -Wduplicated-cond @gol
--Wempty-body -Wenum-compare -Wno-endif-labels -Wexpansion-to-defined @gol
+-Wempty-body -Wenum-compare -Wenum-conversion -Wno-endif-labels
-Wexpansion-to-defined @gol
-Werror -Werror=* -Wextra-semi -Wfatal-errors @gol
-Wfloat-equal -Wformat -Wformat=2 @gol
-Wno-format-contains-nul -Wno-format-extra-args @gol
@@ -3754,6 +3754,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect
Options}.
-Wcomment @gol
-Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol
-Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
+-Wenum-conversion @r{in C/ObjC;} @gol
-Wformat @gol
-Wint-in-bool-context @gol
-Wimplicit @r{(C and Objective-C only)} @gol
@@ -5961,6 +5962,12 @@ In C++ enumerated type mismatches in conditional
expressions are also
diagnosed and the warning is enabled by default. In C this warning is
enabled by @option{-Wall}.
+@item -Wenum-conversion @r{(C, Objective-C only)}
+@opindex Wenum-conversion
+@opindex Wno-enum-conversion
+Warn when an enum value of a type is implicitly converted to an enum of
+another type. This warning is enabled by @option{-Wall}.
+
@item -Wextra-semi @r{(C++, Objective-C++ only)}
@opindex Wextra-semi
@opindex Wno-extra-semi
diff --git a/gcc/testsuite/gcc.dg/Wenum-conversion.c
b/gcc/testsuite/gcc.dg/Wenum-conversion.c
new file mode 100644
index 00000000000..86033399b7d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wenum-conversion.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-Wenum-conversion" } */
+
+enum X { x1, x2 };
+enum Y { y1, y2 };
+
+enum X obj = y1; /* { dg-warning "implicit conversion from .enum Y. to .enum
X." } */
+enum Y obj2 = y1;
+
+enum X obj3;
+void foo()
+{
+ obj3 = y2; /* { dg-warning "implicit conversion from .enum Y. to .enum X." }
*/
+}
+
+void bar(enum X);
+void f(void)
+{
+ bar (y1); /* { dg-warning "implicit conversion from .enum Y. to .enum X." }
*/
+}
