[EXT] [PATCH 6/7] powerpc: Remove modf optimization

[Peter Bergner]

On 5/28/25 7:59 AM, Adhemerval Zanella wrote:
> The generic implementation is slight more optimized than the powerpc
> one, where it has a more optimized inf/nan check (by not using FP
> unit checks, along with branch prediction hints), and removed one
> branch by issuing trunc instead of a combination of floor/ceil (which
> also generated less code).
> 
> On power10 with gcc 14.2.1:
> 
> reciprocal-throughput        master         patch        difference
> workload-0_1                 1.1351        0.9067            20.12%
> workload-1_maxint            1.4230        0.9040            36.47%
> workload-maxint_maxfloat     1.5038        0.9076            39.65%
> workload-integral            1.1280        0.9111            19.23%
> 
> latency                      master         patch        difference
> workload-0_1                 1.1440        2.7117          -137.03%
> workload-1_maxint            4.0556        2.7070            33.25%
> workload-maxint_maxfloat     3.2122        2.7164            15.43%
> workload-integral            3.2381        2.7281            15.75%

I like the idea of using an optimized generic routine over an arch
specific routine, but I'm confused by your data.  For the data above,
it looks like the throughput is less with the patch (ie, smaller number)
and the latency is longer with the patch (ie, bigger number).  ...and not
just on Power, but x86 as well.  Is that just my confusion?  If so, what
are these data values actually specifying?

Peter