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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/99520] Failure to detect bswap pattern
Date: Wed, 10 Mar 2021 16:19:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99520

--- Comment #4 from ktkachov at gcc dot gnu.org ---
(In reply to Jakub Jelinek from comment #3)
> Consider e.g.
> unsigned foo (unsigned x)
> {
>   return (x<<24) + ((x<<8)&0xff0000) + ((x>>8)&0xff00) + (x>>24) +
> (((x&0xff00)<<16)>>8);
> }
> as example that should not be optimized into __builtin_bswap32 (but should
> be with | instead of +).

interesting. That said, clang does do a better job than GCC on that too:
foo(unsigned int):                                // @foo(unsigned int)
        lsl     w9, w0, #8
        rev     w8, w0
        and     w9, w9, #0xff0000
        add     w0, w9, w8
        ret=