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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 5 May 2020 12:57:39 -0700
Message-ID: <CAKwvOdnLze0e3Vwmb1Xdqwcwe9h6gnAwGnt3ksiNX7ENb_3Y9w@mail.gmail.com>
Subject: Re: [PATCH v4 14/18] static_call: Add static_cond_call()
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        x86 <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        bristot <bristot@redhat.com>, jbaron <jbaron@akamai.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, Nadav Amit <namit@vmware.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Tue, May 5, 2020 at 12:00 PM Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> ----- On May 5, 2020, at 2:48 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> [...]
> >
> > Your initial reaction that "you can't compile away the read and the
> > test of NULL" was correct, I think.
>
> I suspect this pattern of "if (func != NULL) func(...)" could be semantically
> changed to just invoking an empty function which effectively does nothing.
> This would remove the need to do a pointer check in the first place. But maybe
> I'm missing something subtle about why it has not been done in this context.

Good idea, this eliminates the check: https://godbolt.org/z/Xugo9w
but you still have an indirect tail call (I think a direct tail call
is the desired solution?)
-- 
Thanks,
~Nick Desaulniers