Yvo Smellenbergh <E-mail: yvo(DOT)s(AT)gmx.net> wrote:
> ...
> The slowdown is related to the new compiler version (Xcode 9), somehow
> the compiler isn't optimizing the code for this project.

That would certainly be a problem, but I think there's more going on.  Some of
my models are a lot slower with 3.8.0, and I just noticed a big difference.  It
also appears in the benchmark model

3.7.0 (the "r9" Mac build) shows this:

Render Statistics
Image Resolution 512 x 512
----------------------------------------------------------------------------
Pixels:           294912   Samples:          776043   Smpls/Pxl: 2.63
Rays:            2454702   Saved:             10620   Max Level: 12/12

3.8.0 has this:

Render Statistics
Image Resolution 512 x 512
----------------------------------------------------------------------------
Pixels:           294912   Samples:          779220   Smpls/Pxl: 2.64
Rays:            8101498   Saved:             66232   Max Level: 12/12

The samples/pixel value is slightly different -- I wonder why.  But the Rays
value is VERY different, much larger for 3.8.0.  I see that also in my models
where 3.8.0 is slower, though the factor isn't quite as large.  The details
below that summary (the intersection numbers) are correspondingly larger for
3.8.0 also.

Tracing 4x the rays would certainly slow things down even without "help" from
the compiler.

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