[Bug target/105135] [11/12/13 Regression] Optimization regression for handrolled branchless assignment since r11-4717-g3e190757fa332d32

[amonakov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105135

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |amonakov at gcc dot gnu.org

--- Comment #5 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
Regarding Clang's code, the key part is not use of 8-bit operations, but setbe
(2 uops) vs. setb (1 uop):

        cmpb    $25, %cl
        setbe   %al

vs

        cmpb    $26, %al
        setb    %al

(note comparison against 25 or 26).

---

Regarding cmov being a lottery, unless you mean Pentium4, then not really, it's
just 1 or 2 uops, each latency 1 or 2. uops.info has very nice summaries:

https://uops.info/html-instr/CMOVB_R32_R32.html
https://uops.info/html-instr/CMOVBE_R32_R32.html