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From: Joseph Myers <joseph@codesourcery.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org>,
	liuhongt <hongtao.liu@intel.com>, <crazylht@gmail.com>,
	<hjl.tools@gmail.com>, <richard.sandiford@arm.com>
Subject: Re: [PATCH] [vect]Use intermiediate integer type for float_expr/fix_trunc_expr when direct optab is not existed.
Date: Wed, 21 Jun 2023 20:39:20 +0000	[thread overview]
Message-ID: <31edd667-fec7-7b0-a9af-5063d73922f@codesourcery.com> (raw)
In-Reply-To: <CAFiYyc0axUY7PiDG-teCDqbkR4bbW1-NhyxOPuZM50r0BwgLTw@mail.gmail.com>

On Wed, 21 Jun 2023, Richard Biener via Gcc-patches wrote:

> > > int32_t x = (int32_t)0x1.0p32;
> > > int32_t y = (int32_t)(int64_t)0x1.0p32;
> > >
> > > sets x to 2147483647 and y to 0.
> 
> Hmm, good question.  GENERIC has a direct truncation to unsigned char
> for example, the C standard generally says if the integral part cannot
> be represented then the behavior is undefined.  So I think we should be
> safe here (0x1.0p32 doesn't fit an int).

We should be following Annex F (unspecified value plus "invalid" exception 
for out-of-range floating-to-integer conversions rather than undefined 
behavior).  But we don't achieve that very well at present (see bug 93806 
comments 27-29 for examples of how such conversions produce wobbly 
values).

-- 
Joseph S. Myers
joseph@codesourcery.com

  parent reply	other threads:[~2023-06-21 20:39 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-02  1:00 liuhongt
2023-06-20  8:38 ` Richard Biener
2023-06-20  9:09   ` Hongtao Liu
2023-06-20  9:22     ` Richard Biener
2023-06-20 16:11       ` liuhongt
2023-06-21  7:49         ` Uros Bizjak
2023-06-21  8:19           ` Richard Biener
2023-06-21 14:37             ` Uros Bizjak
2023-06-22 20:36         ` Thiago Jung Bauermann
2023-06-21  9:10   ` Richard Sandiford
2023-06-21  9:32     ` Richard Sandiford
2023-06-21 11:04       ` Richard Biener
2023-06-21 11:20         ` Richard Sandiford
2023-06-21 20:39         ` Joseph Myers [this message]
2023-06-22  7:32           ` Richard Biener
2023-07-12  9:19             ` Robin Dapp

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