Open Bug 1484908 Opened Last year Updated Last year
Intermittent failure in/css/css-images/tiled-gradients
.html on Haswell
You don't see this on Mozilla CI because the Amazon instances are pre-Haswell. By manipulating CPUID I was able to show that the failures occur when FMA3 is enabled and disappear when FMA3 is disabled. There's noise along the diagonal of the gradient which varies between test and reference. Skia has some Haswell-specific code paths that are probably relevant.
This seems to only affect WebRender rendering.
I guess it's more likely to be the Gallium/LLVM JIT that's creating FMA-dependent code paths here.
Debugging: https://pernos.co/debug/_PKRP2-vC_AXVb9dTkFlfA/index.html This intermittent is very frequent >= Haswell.
Component: Graphics → Graphics: WebRender
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