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Date:   Thu, 5 Apr 2018 09:20:17 +0200
From:   Peter Zijlstra <>
To:     Matthias Kaehlcke <>
Cc:     Linus Torvalds <>,
        Arnd Bergmann <>, Ingo Molnar <>,
        Linux Kernel Mailing List <>,
        Thomas Gleixner <>,
        Andrew Morton <>,
        James Y Knight <>,
        Chandler Carruth <>,
        Stephen Hines <>,
        Nick Desaulniers <>,
        Kees Cook <>,
        Guenter Roeck <>,
        Greg Hackmann <>,
        Greg Kroah-Hartman <>
Subject: Re: [GIT PULL] x86/build changes for v4.17

On Wed, Apr 04, 2018 at 04:31:11PM -0700, Matthias Kaehlcke wrote:

> From some experiments it looks like clang, in difference to gcc, does
> not treat constant values passed as parameters to inline function as
> constants.

Then you're also missing a heap of optimizations in code like
rb_erase_augmented() which is specifically constructed to take advantage
of constant propagation like that.

Other sites where we expect that to happen is __mutex_lock_common(),
__update_load_sum() and a bunch of others. There isn't strictly a bug
here, but not doing that constant propagation will still result in shit
code gen.

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