I think the title is pretty true based on the diffs though. In one example, the only difference was adding "true;" in the middle of the code somewhere -- essentially adding a no-op instruction causes vastly different benchmarks? definitely fraud.
I wouldn't be surprised if microsoft added code like "if (isSunspiderTest) {loadHandOptimizedAssembly()}"
Adding seemingly trivial things to code can sometimes throw off performance entirely, by disaligning cache tables and such. It's not always cheating.
That said, if this is a pure bug, it seems pretty pathetic. For one, it proves that the engine is not robust. For another, it probably means that someone spent hours upon hours tweaking the code with only the sunspider benchmark as test - analogous to over-fitting the training data. It's really tempting to do this, but it's also a common enough amateur mistake that Microsoft should have best practices to avoid it.
All this is speculative for now. Let's see what they say.
Noooooo! I can already imagine the pain writing HTML5 in 2014: "Well, IE9 is too slow to do common thing X reliably, so let's trigger the SunspiderTest optimizations using this hack..."
It's like finding out that IE9 only performs well on the subset of JS needed when you are drawing a fishtank..
The second example is even more of a smoking gun -- adding a "return;" to the end of a function shouldn't affect optimization within an earlier loop. Especially not that much!
I wouldn't be surprised if microsoft added code like "if (isSunspiderTest) {loadHandOptimizedAssembly()}"