←back to thread

The ITTAGE indirect branch predictor

(blog.nelhage.com)
49 points Bogdanp | 1 comments | 04 Jul 25 23:57 UTC | HN request time: 0s | source
Show context
nynx ◴[05 Jul 25 00:40 UTC] No.44469206[source]▶
I must be missing something here. How would this help predict interpreter dispatch? Those won’t be a function of previous branch history or pc, which may very well be independent of the next opcode. They’d be a function of state in memory or registers.
replies(4): >>44469293 #>>44469360 #>>44469495 #>>44469524 #
1. saagarjha ◴[05 Jul 25 01:48 UTC] No.44469495[source]▶
Interpreters are just like normal programs, but splatted out a bit. In particular, they have branches and loops just like normal programs. The challenge for processors is that these high level constructs are far apart and dispatched through an interpreter loop, which obfuscates them. Being able to reach further back in history lets you recover this kind of information "through" the intervening bits.