Bug 1445423

+++ This bug was initially created as a clone of Bug #1438891 +++
--- Additional comment from Ray Strode [halfline] on 2017-04-10 09:20 EDT ---

So I did a scratch build with the reversion mentioned in freedesktop.org 100613 and it helped quite a bit (no more black screen!), but still produced some misrendering. see above screenshot.

--- Additional comment from Adam Jackson on 2017-04-11 14:36:30 EDT ---

(In reply to Ray Strode [halfline] from comment #19)
> Created attachment 1270490 [details]
> better, but not adequate
> 
> So I did a scratch build with the reversion mentioned in freedesktop.org
> 100613 and it helped quite a bit (no more black screen!), but still produced
> some misrendering. see above screenshot.

This looks like channel swizzling confusion, since for 32-bit argb data if you're byte-swapped in the wrong place A and B get interchanged.

--- Additional comment from Ray Strode [halfline] on 2017-04-14 09:41:02 EDT ---

so i did some more investigation (bisecting) on this the last few days.  It seems like comment 19 is an llvm regression caused by this commit:

https://github.com/llvm-mirror/llvm/commit/76b12c4bf0bbc5c70def7b5d083a8a70547ea4e3

--- Additional comment from Ray Strode [halfline] on 2017-04-14 17:19:30 EDT ---

so worse comes to worse if we need a "right now" solution we can just ship the two reverts.  I've tested that and it works okay.

I'll let tstellar chime in on a potentially more right fix for llvm and Ben chime in on a potentially more right fix for mesa, but regardless we obviously can't ship 7.4 like this and we have potential path forward so devack+

--- Additional comment from Tom Stellard on 2017-04-20 09:51:26 EDT ---

Can you post the assembly/llvm IR output generated by the last good commit and also the commit that introduced the bug.  The environment variable GALLIVM_DEBUG=ir,asm will dump this output for you.

You will need to make sure these environment variables are set before you start gnome-shell.

--- Additional comment from Tom Stellard on 2017-04-24 05:35:41 EDT ---

Ben, are you able to reproduce the problem with newer versions of LLVM?

--- Additional comment from Ben Crocker on 2017-04-24 10:31:18 EDT ---

Tom, please clarify....
Ray says the problem was introduced somewhere between 3.8 & 3.9,
and reminds me that he identified the specific commit;
which newer version(s) are you asking about?  Was there a 3.9.x after
3.9?

I know there is a 4.0; is there anything more recent?  (LLVM site
says 4.0.0 is the latest release, so I guess I'm asking about 
whatever the next release is going to be.)

--- Additional comment from Steve Almy on 2017-04-24 10:48:52 EDT ---

changing from alpha to beta blocker, based on email feedback from EPM.

--- Additional comment from Ray Strode [halfline] on 2017-04-24 16:07:47 EDT ---

we may want to clone this bug into two issues.

To be clear there's the mesa problem in comment 0 and the llvm problem in comment 19.

--- Additional comment from Tom Stellard on 2017-04-24 20:57:32 EDT ---

(In reply to Ben Crocker from comment #30)
> Tom, please clarify....
> Ray says the problem was introduced somewhere between 3.8 & 3.9,
> and reminds me that he identified the specific commit;
> which newer version(s) are you asking about?  Was there a 3.9.x after
> 3.9?
> 
> I know there is a 4.0; is there anything more recent?  (LLVM site
> says 4.0.0 is the latest release, so I guess I'm asking about 
> whatever the next release is going to be.)

I meant testing with 4.0 or LLVM trunk, to see if this has been fixed upstream already.