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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114363] inconsistent optimization of pow(x,2)+pow(y,2)
Date: Sat, 16 Mar 2024 11:26:43 +0000	[thread overview]
Message-ID: <bug-114363-4-reqziPThlo@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114363-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114363

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
                 CC|                            |xry111 at gcc dot gnu.org
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Harald van Dijk from comment #1)
> This is, I believe, correct. Before C++11, calling std::pow with float and
> int arguments, it returned a float. As of C++11, it returns a double.
> 
> If the result of pow(x,2) is immediately converted to float, then it is a
> valid optimisation to convert it to x*x: that is guaranteed to produce the
> exact same result. But if it isn't, then converting to x*x loses accuracy
> and alters the result.

Thus invalid.

> You can call std::powf instead of std::pow to avoid the promotion to double.

Or add -std=c++98.

  parent reply	other threads:[~2024-03-16 11:26 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-16  9:31 [Bug tree-optimization/114363] New: " vincenzo.innocente at cern dot ch
2024-03-16 10:37 ` [Bug tree-optimization/114363] " harald at gigawatt dot nl
2024-03-16 11:26 ` xry111 at gcc dot gnu.org [this message]
2024-03-16 12:58 ` jakub at gcc dot gnu.org
2024-03-16 15:06 ` vincenzo.innocente at cern dot ch

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