Course notes

Question 4. Consider the following Java code segment: 1. int i = 1; 2. while (i } 0 2 The following is an example JVM code that a compiler could generate. Every variable area is a 1-dimensional array of memory cells indexed, i.e., addressed, by integers starting from 0. Every instruction is labeled by a relative integer address starting from 0. The top stack frame of the runtime stack contains data for the function call currently being executed. In the action description, "stack" and "variable area" refer to the operand stack and the variable area, respectively, in the top runtime stack frame. First, let's assume S is empty. iconst_o push int constant o onto stack 1 istore_o pop stack and store into address o in variable area (1-0); local variable i is allocated to address 0 of variable area 2 iload_o push value at address 0 in variable area onto stack 3 bipush 100 push int constant 100 onto stack 5 if_icmpge 14 pop top two values from stack; if stack[top-1] 2 stack[top], jump to the instruction at address 14, in this case "return" (test if i = 100 is false, no jump to "retum" instruction " 0 linc 01 } golo 2, iload o 1 iinc 01 goto 2, iload_0 I bipush 100 100 1 1 if_icmpge 14, 1 >= 100 is false, no jump to "return" instruction 1 Powered By Visual Paradigne Community Edition Eventually address 0 of the variable area will have 100. At this time 100 2 100 is true, so the execution jumps to the return instruction at address 14, causing the function call to return. For a non-empty S, we simply insert JVM code for S after the if_icmpge instruction and make necessary increments to instruction addresses. 0 iconst_0 istore_0 iload_0 bipush 100 if icmpge X+14 push int constant 0 onto stack pop stack and store into address 0 in variable area (i=0) push value at address 0 onto stack push int constant 100 onto stack pop top two values from stack; if stack[top-1] > stack[top] then go to X+14 (test if i