• Lynne's avatar
    x86: replace explicit REP_RETs with RETs · bbe95f73
    Lynne authored
    From x86inc:
    > On AMD cpus <=K10, an ordinary ret is slow if it immediately follows either
    > a branch or a branch target. So switch to a 2-byte form of ret in that case.
    > We can automatically detect "follows a branch", but not a branch target.
    > (SSSE3 is a sufficient condition to know that your cpu doesn't have this problem.)
    
    x86inc can automatically determine whether to use REP_RET rather than
    REP in most of these cases, so impact is minimal. Additionally, a few
    REP_RETs were used unnecessary, despite the return being nowhere near a
    branch.
    
    The only CPUs affected were AMD K10s, made between 2007 and 2011, 16
    years ago and 12 years ago, respectively.
    
    In the future, everyone involved with x86inc should consider dropping
    REP_RETs altogether.
    bbe95f73
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