Function getreg

1. If Y is in register (that holds no other values) and Y is not live and has no next use after

X = Y op Z

then return register of Y for L.

2. Failing (1) return an empty register

3. Failing (2) if X has a next use in the block or op requires register then get a register R, store its content into M (by Mov R, M) and use it.

4. else select memory location X as L

The function getreg returns the location L to hold the value of x for the assignment x := y op z.

1. If the name y is in a register that holds the value of no other names (recall that copy instructions such as x := y could cause a register to hold the value of two or more variables simultaneously), and y is not live and has no next use after execution of x := y op z, then return the register of y for L. Update the address descriptor of y to indicate that y is no longer in L.

2. Failing (1), return an empty register for L if there is one.

3. Failing (2), if x has a next use in the block, or op is an operator such as indexing, that requires a register, find an occupied register R. Store the value of R into memory location (by MOV R, M) if it is not already in the proper memory location M, update the address descriptor M, and return R. If R holds the value of several variables, a MOV instruction must be generated for each variable that needs to be stored. A suitable occupied register might be one whose datum is referenced furthest in the future, or one whose value is also in memory.

4. If x is not used in the block, or no suitable occupied register can be found, select the memory location of x as L.