netdev - Re: [PATCH bpf] selftests/bpf: adjust strobemeta loop to satisfy latest clang

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Date:   Wed, 25 Sep 2019 22:33:01 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH bpf] selftests/bpf: adjust strobemeta loop to satisfy
 latest clang

On Wed, Sep 25, 2019 at 11:52:05AM -0700, Andrii Nakryiko wrote:
> Some recent changes in latest Clang started causing the following
> warning when unrolling strobemeta test case main loop:
> 
>   progs/strobemeta.h:416:2: warning: loop not unrolled: the optimizer was
>   unable to perform the requested transformation; the transformation might
>   be disabled or specified as part of an unsupported transformation
>   ordering [-Wpass-failed=transform-warning]
> 
> This patch simplifies loop's exit condition to depend only on constant
> max iteration number (STROBE_MAX_MAP_ENTRIES), while moving early
> termination logic inside the loop body. The changes are equivalent from
> program logic standpoint, but fixes the warning. It also appears to
> improve generated BPF code, as it fixes previously failing non-unrolled
> strobemeta test cases.
> 
> Cc: Alexei Starovoitov <ast@...com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Sounds like a clang regression? Was that from an official release?

Applied.