[Bug tree-optimization/126946] [14/15/16/17 Regression] Phiopt lengthening dependency chain in loop for MIN/MAX operations

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126946

--- Comment #2 from ktkachov at gcc dot gnu.org ---
(In reply to Richard Biener from comment #1)
> So why does RTL if-conversion not produce the fcsel?  (and why do we have
> such strange BB order)
> 
> The COND_EXPR allows the x86 cmov expander to pattern-match its FP MIN/MAX
> operations which match IEEE semantics of m < a ? a : m
> 
> On trunk I do see fcsel being used on aarch64 just fine for your testcase,
> so what "fixed" it there?
> 
> .L3:
>         ldr     s31, [x1, x2, lsl 2]
>         add     x2, x2, 1
>         fabs    s31, s31
>         fcmpe   s31, s0
>         fcsel   s0, s31, s0, gt
>         cmp     x0, x2
>         bne     .L3
>         ret
> 
> We expand from
> 
>   _4 = MEM[(const float *)x_9(D) + _20 * 4];
>   a_10 = ABS_EXPR <_4>;
>   _12 = a_10 > m_16;
>   _11 = _12 ? a_10 : m_16;

In this case we do not want fcsel. GCC 13 kept the well-predicted branch
whereas GCC 14 starting using fcsel unconditionally because COND_EXPR expansion
goes through the movcc optabs