5.18 Y-variable scoreboarding

The idea of Y-variable scoreboarding is to safe memory bandwidth by remembering which Y-variable was already loaded into an X-register. Every time a Y-variable is `touched', the corresponding X-register is saved as a pair (Y-variable X-register) on an assoc-list named y-x-usage-list, which is a global variable meaning that the Y-variable can also be found in an X-register.

The following functions are dealing with Y-variable scoreboarding:

• (is-y-in-x y-vari y-x-usage-list)
  This function associates the Y-variable with its X-argument position. If the Y-variable is not in an X-register, the result is nil.
• (add-y-x-list y-vari x-reg y-x-usage-list)
  This function adds a (Y-variable X-register) pair to the scoreboard.
• (d_yreg_assoc yreg y-x-usage-list)
  This is used to eliminate a pair specified by its Y-variable.
• (d_xreg_assoc xreg y-x-usage-list)
  This is used to eliminate a pair specified by its X-variable.