RE: [PATCH 1/1] gdb, testsuite: Adapt gdb.base/callfuncs.exp for new clang warnings.

[Andrew Burgess <aburgess@redhat.com>]

"Willgerodt, Felix via Gdb-patches" <gdb-patches@sourceware.org> writes:

>> -----Original Message-----
>> From: Andrew Burgess <aburgess@redhat.com>
>> Sent: Montag, 18. Juli 2022 15:37
>> To: Willgerodt, Felix <felix.willgerodt@intel.com>; Bruno Larsen
>> <blarsen@redhat.com>; gdb-patches@sourceware.org
>> Subject: RE: [PATCH 1/1] gdb, testsuite: Adapt gdb.base/callfuncs.exp for
>> new clang warnings.
>> 
>> "Willgerodt, Felix via Gdb-patches" <gdb-patches@sourceware.org> writes:
>> 
>> >> -----Original Message-----
>> >> From: Bruno Larsen <blarsen@redhat.com>
>> >> Sent: Mittwoch, 8. Juni 2022 14:59
>> >> To: Willgerodt, Felix <felix.willgerodt@intel.com>; gdb-
>> >> patches@sourceware.org
>> >> Subject: Re: [PATCH 1/1] gdb, testsuite: Adapt gdb.base/callfuncs.exp for
>> >> new clang warnings.
>> >>
>> >>
>> >> On 6/8/22 04:17, Felix Willgerodt via Gdb-patches wrote:
>> >> > This patch fixes two issues with callfuncs.exp, which are both related
>> >> > to new Clang warnings:
>> >>
>> >> Hi Felix!
>> >>
>> >> Thanks for this!
>> >>
>> >> >
>> >> > 1) Clang 15.0.0 added a new warning for deprecated non-prototype
>> >> functions:
>> >> > https://reviews.llvm.org/D122895
>> >> > Callfuncs.exp is impacted and won't run due to new warnings:
>> >> >
>> >> > callfuncs.c:339:5: warning: a function declaration without a prototype is
>> >> > deprecated in all versions of C and is not supported in C2x
>> >> > [-Wdeprecated-non-prototype]
>> >> > int t_float_values (float_arg1, float_arg2)
>> >> >
>> >> > This patch disables those warnings with -Wno-deprecated-non-
>> prototype.
>> >> > Removing the test for deprecated syntax would also be an option. But I
>> will
>> >> > leave that for others to decide.
>> >>
>> >> I like your solution with -Wno-deprecated-non-prototype.
>> >>
>> >> I think it is important (at least for now) to keep this test, since we have to
>> >> support very old setups.
>> >>
>> >> >
>> >> > 2) The other new warnings are about comparing a define with floats and
>> >> doubles:
>> >> >
>> >> > callfuncs.c:518:1: warning: floating-point comparison is always true;
>> >> constant
>> >> > cannot be represented exactly in type 'float' [-Wliteral-range]
>> >> > DEF_FUNC_VALUES_3(fc, float, crealf, cimagf)
>> >> >
>> >> > This can be fixed by making the define a float.
>> >>
>> >> Genuine question, would this not cause a problem for the times where
>> the
>> >> parameters are doubles and DELTA is a float? If it isn't a problem, I'm fine
>> >> with this.
>> >>
>> >
>> > I was wondering about that as well, but it still passes with GCC, clang and
>> Intel
>> > compilers and there are no compiler warnings about it.
>> > I couldn't really figure it out if it would actually a problem somewhere. I
>> could only
>> > test on linux x86 though. My best guess was, as it is the "smaller precision"
>> the
>> > compiler will do the right thing.
>> 
>> Indeed, my understanding of type promotion is that the compiler will
>> promote the float argument to double or long double as needed.
>> 
>> But then, prior to this patch, when DELTA was just (0.001), and would be
>> considered a double, I would have expected, in any comparison between a
>> float and DELTA, for the float to be converted to double, so I don't
>> really understand that part of the original patch.
>> 
>> Thanks,
>> Andrew
>
> Thanks for your input.
> What I didn't quite realize when writing the patch, is that float literals without
> suffix are of type double. I double checked the ISO C11 draft and it is mentioned
> there as well.
>
> So to me this is likely a compiler bug. Or did I miss anything?

I did wonder the same, but I don't claim to be an expert on language
details.  I don't have immediate access to clang 15, but it might be
interesting to try and reduce the test program down to just that
error/warning case, and see if the code makes sense.

Thanks,
Andrew