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Date: Thu, 4 Nov 2021 18:32:51 +0000
From: Joseph Myers <joseph@codesourcery.com>
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To: liuhongt <hongtao.liu@intel.com>
CC: <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH 1/2] [Middle-end] Simplify (trunc)copysign((extend)a,
 (extend)b) to .COPYSIGN (a, b).
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On Thu, 4 Nov 2021, liuhongt via Gcc-patches wrote:

> a and b are same type as the truncation type and has less precision
> than extend type.

Note that this is not safe with -fsignaling-nans, so needs to be disabled 
for that option (if there isn't already logic somewhere with that effect), 
because the extend will convert a signaling NaN to quiet (raising 
"invalid"), but copysign won't, so this transformation could result in a 
signaling NaN being wrongly returned when the original code would never 
have returned a signaling NaN.

-- 
Joseph S. Myers
joseph@codesourcery.com