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From: =?UTF-8?B?4piCSm9zaCBDaGlhICjorJ3ku7vkuK0p?= <joshchia@gmail.com>
Date: Thu, 28 Oct 2021 18:54:33 +0800
Message-ID: <CALxtSbSbEL3PazoqMzoG0n4GWuC9A-69wFi0TcA0CnyVXCfksQ@mail.gmail.com>
Subject: Re: Generated assembly code for returning std::optional<uint32_t>
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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Yes, it is. Thanks.

On Thu, Oct 28, 2021 at 5:55 PM Jonathan Wakely <jwakely.gcc@gmail.com>
wrote:

> On Thu, 28 Oct 2021 at 08:11, =E2=98=82Josh Chia (=E8=AC=9D=E4=BB=BB=E4=
=B8=AD) via Gcc-help
> <gcc-help@gcc.gnu.org> wrote:
> >
> > Under -O3 -std=3Dc++17, the assembly code generated by gcc 11.2 for som=
e
> > std::optional C++ code seems less optimal than I expect; it is writing
> the
> > content of optional<uint64_t> return values to both the stack and to th=
e
> > RAX register. What am I missing? I was under the impression that return
> > values are put in RAX if they can fit. Why does gcc have to write the
> > return value to both the stack and RAX instead of just one of them? Can
> the
> > writing to the stack be avoided?
>
> Is this https://gcc.gnu.org/PR101326 ?
>