I just want a portable version of __builtin_addcarry and __builtin_subborrow. 
Of course if we have things __builtin_rcl and __builtin_rcr would be even 
better.

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From: Paul Koning<mailto:paulkon...@comcast.net>
Sent: Wednesday, October 27, 2021 12:36
To: sotrdg sotrdg<mailto:euloa...@live.com>
Cc: GCC Development<mailto:gcc@gcc.gnu.org>; 
gcc-requ...@gcc.gnu.org<mailto:gcc-requ...@gcc.gnu.org>; 
gcc-h...@gcc.gnu.org<mailto:gcc-h...@gcc.gnu.org>
Subject: Re: __builtin_addc support??



> On Oct 27, 2021, at 12:12 PM, sotrdg sotrdg via Gcc <gcc@gcc.gnu.org> wrote:
>
> 79173 – add-with-carry and subtract-with-borrow support (x86_64 and others) 
> (gnu.org)<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79173>
>
> What I find quite interesting is things like this.
>
> Since llvm clang provides __builtin_addc __builtin_subc for all targets. Can 
> we provide something similar? Since currently no solutions we can access 
> carry flag besides x86

Certainly some other targets could do this.  The LLVM builtins explicitly 
expose carry, which isn't actually what you want (you'd want the carry flag in 
the condition code to be propagated).  Presumably optimization would eliminate 
those explicit arguments and reduce them to CC references.

        paul


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