Re: [PATCH] Fix PR89437

[Wilco Dijkstra <Wilco.Dijkstra@arm.com>]

Hi Richard,
  
>On Thu, Feb 21, 2019 at 6:09 PM Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>>
>> Hi Richard,
>>
>> >>Fix an issue with sinl (atanl (sqrtl (LDBL_MAX)) returning 0.0
>> >>instead of 1.0 by using x < sqrtl (LDBL_MAX) in match.pd.
>> >
>> > Wasn't that a intermediate problem with the mpfr exponent range limiting?
>> > Please check whether that's still needed.
>>
>> I tested it with trunk about an hour ago, and it included Jacub's patch.
>> Are there other fixes outstanding which haven't been committed yet?
>
> Not that I know of.  Did we root-cause the bogus folding to 0.0?  Because
> I don't really understand why using < can "fix" this...

Yes, the underlying issue is that build_sinatan_real returns the first value that does
overflow when squared. Maybe that wasn't intended, but using less-than on the first
value that does overflow works. With my patch (now committed) the test passes in
all rounding modes.

Like I mentioned, in the future this check could use a much smaller value based on
the size of the mantissa - that's safer since you're not close to infinity.

> Latest trunk also still gives an assertion failure in mpc with the gcc.dg/torture/builtin-math-5.c
> which started at the same time as the other mpc/mpfr releated issues:
>
> build/src/mpc/src/pow.c:631: MPC assertion failed: z_imag || mpfr_number_p (MPC_RE(u))
> build/src/gcc/gcc/testsuite/gcc.dg/torture/builtin-math-5.c:95:3: internal compiler error: Aborted
> 0x6725ab crash_signal
> build/src/gcc/gcc/toplev.c:326
>
> Ick.  Is there a PR about this?

This happens when using an old mpc (0.8.2). It's valid according to the configure check,
however it works with the 1.0.3 version that download-prerequisites uses. Maybe we should
increase the minimum mpc version in configure?

Wilco