The optimizer was allowed, but not obligated, to transform that into: x = a
However, in this case, b was sometimes 0. And if so, the unoptimized version computed: x = a / 0 * 0 = Inf * 0 = NaN
So badness ensued if the that particular path didn't get optimized, which could happen under various circumstances. We had to add some code to ensure that transformation always happened on that game.
- deciding to inform the game developer & wait for reply vs not waiting for reply vs just fixing it yourself without informing the developer; and
- if informed: developer actually fixing it vs only saying they would fix it vs no reply whatsoever (not counting automated "thank you for your inquiry" replies, in cases where you don't already have more direct channels to the dev than email)
I've always kind of wondered this because in a way, it's kind of weird that it's fixed for them, at least for new releases / games actively being developed.
(Full disclosure: I'm a game developer myself, with a very high interest in engine plumbing & dev [including graphics], though finding a job for the latter is easier said than done.)