Originally raised as part of bug 1687554, however on further investigation the issue is unrelated to, and long predates, the recent regression on the HTC 10.

Rendering is completely broken. Mozregression points to the commit which introduced optimized shaders. Setting gfx.webrender.use-optimized-shaders=false fixes rendering completely.

By reducing the shader by hand, I managed to establish that removing the uniform sampler2D sGpuCache declaration from the fragment shader is what breaks the rendering. Manually adding the declaration back to the optimized fragment shaders fixes it.

I have so far been unable to work out why this is the case. I plan to disable optimized shaders on Mali-T6xx in the meantime.

Webrender's pre-optimized shaders result in completely broken
rendering on a Huawei MediaPad M2 (Mali-T628). As a precaution,
disable optimized shaders on all Mali-T6xx devices.

Backed out changeset 5338c029ee7c (Bug 1689064) for causing GTest failures CLOSED TREE

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&group_state=expanded&collapsedPushes=842382&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&revision=5338c029ee7c7b2ed24aefe56dd69e75b1f0d216&selectedTaskRun=alIQWzeJSLORThzaVklatQ.0

Failure log: https://treeherder.mozilla.org/logviewer?job_id=329560064&repo=autoland&lineNumber=28275
https://treeherder.mozilla.org/logviewer?job_id=329560493&repo=autoland&lineNumber=28469
https://treeherder.mozilla.org/logviewer?job_id=329558936&repo=autoland&lineNumber=28255

Backout: https://hg.mozilla.org/integration/autoland/rev/6970f524758af309e3724c2bef6917d95049a596

Ah, the tests crash because the new feature doesn't get initialized by them. A clever way of ensuring new features get tested properly! I'll initialize the feature and add the relevant assertions to the tests.

Backed out changeset e602ff8fea83 (bug 1689064) for assertion failures in gfxFeature.cpp.
https://hg.mozilla.org/integration/autoland/rev/160b47b7163e1a80ac366e0ef9fc10b631c35c03

Push with failures:
https://treeherder.mozilla.org/jobs?repo=autoland&revision=e602ff8fea8362db48bafff91ac6a127a82b0836&selectedTaskRun=L8gQ-AnzQfyBJoOTass6lQ.0

Failure log:
https://treeherder.mozilla.org/logviewer?job_id=329607723&repo=autoland&lineNumber=1580

Sorry! It looks like I need to call ConfigureFromBlocklist() before ForceDisable() because webrender is disabled. Not sure why it only fails on windows and not linux where I tested..

This run looks greener so far: https://treeherder.mozilla.org/jobs?repo=try&revision=911750f05096b5f92384cd8855bcdcce7dc72352

https://hg.mozilla.org/mozilla-central/rev/312d863215bc