[LispM-Hackers] BR-*-LIKELY

[Raymond Wiker]

James A. Crippen writes:
 > The BR-NULL-LIKELY and BR-NOT-NULL-LIKELY insns just came to my
 > attention.  These are described in defop-lisp-function-p.lisp:
 > 
 > ;;; 174-177 are special BRANCH-LIKELY instructions
 > ;;; Hummingbird hardware will follow these branches in the macro-pipeline
 > 
 > Anyone care to explain this obscurity?

	I would guess that these are branch instructions with a hint
that the branch is *most likely* going to be taken. The effect on the
pipeline would be that the next instruction to enter the decoding
pipeline would be the branch target, and not the next (sequential)
address. 

	Some processors have a heuristic that says that branch
instructions that target a lower address will most likely be taken (as
this would mostly be used in implementing loops).

	//Raymond.

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