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

["Willgerodt, Felix" <felix.willgerodt@intel.com>]

> -----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?

In that case, I would open an issue with LLVM/clang and drop that part from
this patch for now. Clang 15.0.0 isn't released yet.

Regards,
Felix
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