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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Joseph Myers <joseph@codesourcery.com>
Cc: "linux-snps-arc@lists.infradead.org"
	<linux-snps-arc@lists.infradead.org>,
	"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>
Subject: Re: ARC math test regressions (was Re: [PATCH v7 00/13] glibc port to ARC processors)
Date: Thu, 2 Jul 2020 17:45:47 +0000
Message-ID: <972989fe-916b-4012-530a-8aeeac758aa7@synopsys.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2007021618480.21468@digraph.polyomino.org.uk>

On 7/2/20 9:27 AM, Joseph Myers wrote:
> On Thu, 2 Jul 2020, Vineet Gupta via Libc-alpha wrote:
> 
>> Now acos can come from 2 places depending on LIBM_SVID_COMPAT
>>  - math/w_acos_template.c	<-- sets errno only
> 
> This wrapper, unlike the compat one, always calls __ieee754_acos 
> (appropriately suffixed), relying on it to raise appropriate exceptions.  
> The implementation in sysdeps/ieee754/dbl-64/e_asin.c raises the exception 
> by doing an Inf / Inf computation.
> 
>     u.i[HIGH_HALF]=0x7ff00000;
>     v.i[HIGH_HALF]=0x7ff00000;
>     u.i[LOW_HALF]=0;
>     v.i[LOW_HALF]=0;
>     return u.x/v.x;
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95115

Aha. I almost forgot that this was upstream gcc-10 for ARC too (and problem
doesn't happen with gcc-9). So my glibc updates didn't trigger this, phew !

> The right place to fix this is in GCC, to stop it constant-folding Inf / 
> Inf when flag_trapping_math.  That should be a straightforward fix.
> 
> It would also be reasonable to change the above code to just "return 0.0 / 
> 0.0;", as a simpler, more idiomatic way of returning a NaN with "invalid" 
> raised.  (Any code constructing infinities / NaNs via bit patterns likely 
> predates built-in functions that can be used to represent such values 
> directly.  Though the GCC bug means a literal replacement with "return 
> __builtin_inf () / __builtin_inf ();" wouldn't fix the present problem.)
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Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-15 20:14 [PATCH v7 00/13] glibc port to ARC processors Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 01/13] ARC: ABI Implementation Vineet Gupta
2020-07-01  0:06   ` [PATCH v7.1 " Vineet Gupta
     [not found]     ` <b6322150-240a-5f06-b700-83e3eb79deec@linaro.org>
2020-07-01 19:36       ` Vineet Gupta
2020-07-01 19:45         ` Adhemerval Zanella
2020-06-15 20:14 ` [PATCH v7 02/13] ARC: startup and dynamic linking code Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 03/13] ARC: Thread Local Storage support Vineet Gupta
2020-07-01  0:07   ` [PATCH v7.1 " Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 04/13] ARC: Atomics and Locking primitives Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 05/13] ARC: math soft float support Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 06/13] ARC: hardware floating point support Vineet Gupta
2020-07-01  0:08   ` [PATCH v7.1 " Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 07/13] ARC: Linux Syscall Interface Vineet Gupta
2020-07-01  0:08   ` [PATCH v7.1 " Vineet Gupta
     [not found]     ` <e9e2ae28-cd78-5924-c1fa-52b1499c245a@linaro.org>
2020-07-04  3:54       ` Vineet Gupta
2020-07-06 13:20         ` Adhemerval Zanella
2020-07-07  1:25           ` Vineet Gupta
2020-07-07 19:24             ` Adhemerval Zanella
2020-07-07 20:55               ` [PATCH v7.2 " Vineet Gupta
     [not found]                 ` <b64d0df1-4229-d619-0ab1-ded287323775@linaro.org>
2020-07-08 19:32                   ` Vineet Gupta
2020-07-09 16:03                     ` Adhemerval Zanella
2020-07-09 16:24                       ` Vineet Gupta
2020-07-09 16:25                         ` Adhemerval Zanella
2020-07-09 21:13                         ` Vineet Gupta
2020-07-09 21:36                           ` ARC testsuite regressions (was Re: [PATCH v7.2 07/13] ARC: Linux Syscall Interface) Vineet Gupta
2020-07-09 22:01                             ` Alistair Francis
2020-07-09 22:16                               ` Vineet Gupta
2020-07-10  9:28                               ` Florian Weimer
2020-07-10 15:53                                 ` Vineet Gupta
2020-07-10 17:02                                   ` Florian Weimer
2020-07-10 20:07                                     ` Vineet Gupta
2020-07-10 20:32                                       ` Florian Weimer
2020-07-10 19:12                                   ` Alistair Francis
2020-07-10 20:33                                     ` Florian Weimer
2020-07-10 20:56                                       ` Alistair Francis
2020-07-10 19:10                                 ` Alistair Francis
2020-07-07 21:07               ` [PATCH v7.1 07/13] ARC: Linux Syscall Interface Vineet Gupta
2020-07-07 21:32                 ` Joseph Myers
2020-07-07 23:16                   ` Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 08/13] ARC: Linux ABI Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 09/13] ARC: Linux Startup and Dynamic Loading Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 10/13] ARC: ABI lists Vineet Gupta
2020-07-01  0:09   ` [PATCH v7.1 " Vineet Gupta
2020-06-15 20:14 ` [PATCH v7 11/13] ARC: Build Infrastructure Vineet Gupta
2020-07-03 17:09   ` Adhemerval Zanella
2020-06-15 20:14 ` [PATCH v7 12/13] build-many-glibcs.py: Enable ARC builds Vineet Gupta
2020-07-03 17:37   ` Adhemerval Zanella
2020-06-15 20:14 ` [PATCH v7 13/13] Documentation for ARC port Vineet Gupta
2020-07-03 17:38   ` Adhemerval Zanella
2020-06-23 16:56 ` [PATCH v7 00/13] glibc port to ARC processors Vineet Gupta
2020-07-01  0:11   ` Vineet Gupta
2020-07-01  1:44     ` Adhemerval Zanella
2020-07-01 19:13       ` Vineet Gupta
2020-07-02  1:00         ` ARC math test regressions (was Re: [PATCH v7 00/13] glibc port to ARC processors) Vineet Gupta
2020-07-02  7:17           ` Andreas Schwab
2020-07-02 16:27           ` Joseph Myers
2020-07-02 17:45             ` Vineet Gupta [this message]
2020-07-02 21:27       ` [PATCH v7 00/13] glibc port to ARC processors Joseph Myers

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