linux-kernel - Re: x86/include/asm/arch_hweight.h:49:15: error: invalid input size for constraint 'D'

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Message-ID: <Y+J/4kGuIqb8qeob@zn.tnic>
Date:   Tue, 7 Feb 2023 17:44:18 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>, llvm@...ts.linux.dev,
        open list <linux-kernel@...r.kernel.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: x86/include/asm/arch_hweight.h:49:15: error: invalid input size
 for constraint 'D'

On Tue, Feb 07, 2023 at 09:37:37AM -0700, Nathan Chancellor wrote:
> Clang does its semantic analysis before optimization, so it cannot dead
> code eliminate that chunk before it checks the validity of the asm
> constraints, that is just how the pipeline is structured as far as I
> understand it. That is one of the biggest and longest standing
> differences between clang and GCC that we know about, the upstream link
> in the issue below has some more info.
> 
> https://github.com/ClangBuiltLinux/linux/issues/3
> 
> I am not super familiar with the internal details of LLVM and clang as
> other folks are though so I could be wrong or missing something :)

Thanks and wow, that's issue #3. Like wow that's old. And reading Nick's
text, it sure does sound like that's the one.

Fun.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette