Frontend

See files in compiler/ with nx in their name.

Backend

VINSNs

VINSN means Virtual Instruction.

Those likely belong to the same category of SBCL's Virtual Operations (VOPs).

<-    copy register
@     label
@=    label (aligned)
->    jump to label
^     branch
?     register (unwired)
$     register (wired)

(from compiler/X86/x862.lisp)

LAP

LAP means Lisp Assembly Parser (probably). It's a DSL that compiles into opcodes.

Operand syntax

(% x)    register
($ x)    immediate
(@ x)    memory operand; x ~ ([seg] [disp] [base] [index] [scale])
x        labelref
(:rcontext x)   memory operand, using segment register or gpr; see @ for syntax of x.
(:self fn)      self-reference

(from compiler/X86/x86-lap.lisp)