[Bug middle-end/95464] [10/11 Regression] Miscompilation of mesa on x86_64-linux since r10-6426

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95464

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I wonder where we'd simplify things like

(insn 67 66 68 3 (parallel [
            (set (strict_low_part (subreg:QI (reg/v:SI 94 [ a ]) 0))
                (ior:QI (subreg:QI (reg/v:SI 94 [ a ]) 0)
                    (const_int 5 [0x5])))
            (clobber (reg:CC 17 flags))
        ]) "gallivm2.c":51:3 492 {*iorqi_1_slp}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))

I guess simplify_rtx would just see the SET_SRC?  The above might appear
quite frequently from bit fiddling RTL expansion I guess.