Our GCD program did not employ subroutines. Extend the grammar of Figure 15.6 to handle procedures without parameters (feel free to adopt any reasonable conventions on the structure of the syntax tree). Be sure to generate appropriate prologue and epilogue code for each subroutine, and to save and restore any needed temporary registers.

Figure 15.6:

Transcribed Image Text:

reg_names : array [0..k-1] of register.name := ["r1, "r2" .., "rk"] -- ordered set of temporaries program + stmt stmt.next.free_reg := 0 program.code := ["main:"] + stmt.code + ["goto exit"] while : stmt expr stmtz stmtz expr.next.free_reg := stmt2.next.free_reg := stmt3.next.free.reg := stmtj.next.free_reg L1:= new.label(); L2 := newJabel() stmtj.code := ["goto" L1] + [L2 ":"] + stmt2.code + [L1 ":"] + expr.code + ["if" expr.reg "goto" L2] + stmt3.code if : stmti expr stmt2 stmtz stmtą expr.next_free_reg := stmt2.next.free reg := stmt3.next.free_reg := stmt4.next.free_reg := stmtj.next.free-reg L1:= new.label); L2 := newJabel() stmtj.code := expr.code + ["if" expr.reg "goto" L1] + stmt3.code + ["goto" L2] + [L1 ":"] + stmt2.code + [L2 ":"] + stmtą.code assign : stmt - id expr stmtz expr.next.free_reg := stmt2.next.freereg := stmtj.next.free.reg stmtı.code := expr.code + [id.stp→name ":=" expr.reg] + stmt2.code read : stmt + id, idz stmt2 stmtj.code := ["a1 := &" id.stp→name] + ["call" if id2.stp>type = int then "readint" else ...] + [idz.stp→name ":= rv"] + stmt2.code %3D -- file write : stmt → id expr stmt2 expr.next_free_reg := stmt2.next.freereg := stmtj.next.free.reg stmtj.code := ["a1 := &" id.stp→name] + ["a2 :=" expr.reg] + ["call" if id.stp type = int then "writeint" else ..] + stmt2.code -- file -- value writeln : stmti + id stmtz stmtj.code := ["a1 := &" id.stpname] + ["call writeln"] + stmt2.code null : stmt €