But that's an optimisation. Which can be switched off to get the benefits from parallelism. This is a tradeoff that programmers would traditionally have to consider, but with functional programming the compiler can figure it out for us.
"It's not decidable" is not a guarantee that humans can do better than a compiler. It means any approach will sometimes be wrong, but a compiler might well (in principle) be wrong less often than a human.
This is separate from the "a human has a lot of additional context that's hard to express" argument, which is valid but has nothing to do with decidability.
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But that's an optimisation. Which can be switched off to get the benefits from parallelism. This is a tradeoff that programmers would traditionally have to consider, but with functional programming the compiler can figure it out for us.
That's assuming that "figuring it out for us" is decidable. Many of the things we wish the compiler could do for us are not.
"It's not decidable" is not a guarantee that humans can do better than a compiler. It means any approach will sometimes be wrong, but a compiler might well (in principle) be wrong less often than a human.
This is separate from the "a human has a lot of additional context that's hard to express" argument, which is valid but has nothing to do with decidability.