Proper way to deal with this would be to move every CPU kernel into a namespace. That would ensure linker never re-uses "wrong" microarchitecture implementation.

Confirming it's caused by above mentioned commit. @Campbell Barton (campbellbarton): feel free to assign to me and I'll try my luck :)

afaict, this is also fixed by rBfb3528d08870, thx @Campbell Barton (campbellbarton)!

afaict, this is also fixed by rBfb3528d08870, thx @Campbell Barton (campbellbarton) !

Can confirm this, issue in undo. This can probably be merged into T54578, T54553?

Similar to T54553 (py API doesnt set TextUndoBuf), similar thing as D3139 will fix the crash here, too:

In T54464#491074, @LazyDodo (LazyDodo) wrote:

seems like you have forgotten to attach the file.

seems like you have forgotten to attach the file.

Discussed with other developers about ways to process here.

I'm aware of this, it's an intentional trade-off we are making. With Russian roulette you get more noise in simple cases, but it helps in more complex cases like transparent hair. The two are difficult to distinguish for the renderer and it's generally not helpful to do so in real world scenes where you have a mix of these.

Fabien, you need to recompile blender - best build blender-v2.79a-release, this will be the official stable release soon.

Thanks for your help
How can I apply the fix? Can I simply copy and paste fixed files?

Found the cause, looking into a fix.

there might be better ways to do this, but how about D3013: possible fix for T53843?

caused by rBf4fb329808a7

Can confirm this [this worked in 2.79], having a look if I can find the issue...

caused by rB04800ed43434d053359cb3035eb082902fe80e4b

So maybe disabling the render layer in properties panel should mute the renderlayer node too? If I mute the renderlayer node and leave the renderlayer enabled it still renders the renderlayer, so in 2.79.1 I had to disable in properties panel and mute in nodes to turn the layer off?

In Master, blender respect what user asks ; it saves an Image for a renderlayer that have not been rendered.
It is the set-up shown, here. A disabled renderlayer but a renderlayer node that is not mute.
If the set-up was a disabled renderlayer and a renderlayer node that is mute. Master still respects that and doesn't save a blank image.
Mute property can be animated. But it is not exposed in UI of properties of the node.

It is an exactly design issue. And any decision here is kind of arbitrary.

Tested it with some blur nodes between Renderlayer and Composite - in this case 2.79 also starts to save empty images. So maybe its more a design decision: should disabled Renderlayers be skipped in compositing or behave like empty/white/transparent image.

I made two Screenshots for better explanation ...

Well, didn't notice this worked before. But then still, what if you've got other nodes in between...

Thanks for tracking down the commit. This is quite an edge case - while the vector is normalized it's so close to zero to begin with, a second call is needed to make it really normalized (which fixes the bug).

caused by rB16fbb47c8860b61694b2e08270d198f8d173b32a

@Brecht Van Lommel (brecht) I don't have commit rights, could you commit it please?

here is the fix

@Mai Lavelle (maiself), think that one is for you? Thanks. :)