> I get the impression that CPU designers in the 80s and early 90s massively underestimated just how beneficial even a small predictor can be.
It's got a lot to do with how cpu clock speeds were getting way faster, but ram wasn't. That's what makes deeper pipelines attractive, and if you give a cpu a deeper pipeline, it's gonna want a good branch predictor.
I'm more thinking about how MIPS were quite late to branch predictors.
They were shipping the high-performance R4000 and R4400 with 8 stage pipelines and no branch predictors.
They could have really done with a branch predictor, each branch took three cycles (and the branch delay slot could fill only one instruction, often a useless NOP).
The Pentium only had a 5 stage pipeline and massively benefited from its branch predictor. IBM was slapping branch predictors on PowerPC designs with 4 stage integer pipelines. You simply don't need a long pipeline to justify the benefits of a branch predictor.