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Date: Wed, 21 Jun 2023 20:39:20 +0000
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.
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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