Exercises for Section 8.3

8.3.1

Generate code for the following three-address statements assuming stack allocation where register SP points to the top of the stack.

call p
call q
return
call r
return
return

Answer

100:  LD SP, #stackStart
108： ADD SP, SP, #psize
116:  ST *SP, #132
124:  BR pStart
132:  SUB SP, SP, #psize
140:  ADD SP, SP, #qsize
148:  ST *SP, #164
156:  BR qStart
164:  SUB SP, SP, #qsize
172:  BR **SP

8.3.2

Generate code for the following three-address statements assuming stack allocation where register SP points to the top of the stack.

1. x = 1
2. x=a
3. x = a + 1
4. x = a+b
5. The two statements
   • x = b * c
   • y = a + x

8.3.3

Generate code for the following three-address statements again assuming stack allocation and assuming a and b are arrays whose elements are 4-byte values.

1. The four-statement sequence

    x = a[i]
    y = b[j]
    a[i] = y
    b[j] = x

2. The three-statement sequence

    x = a[i]
    y = b[i]
    z = x * y

3. The three-statement sequence

    x = a[i]
    y = b[x]
    a[i] = y

   ---

Note

1. 指令长度

120:  ST 364, #140
132:  BR 200
140:  ACTION2

图 8-4 部分代码

• 每行指令前面的标号代表了这行代码的起始位置（即偏移量），和下一行指令的标号差代表这行指令的长度。
• 第一行有 1 个指令和 2 个常量，所以指令长度是 12，同理第二行有 1 个指令和 1 个常量，所以长度为 8.

100:  LD, SP, #600
108:  ACTION1
128:  ADD SP, SP, #msize
136:  ST *SP, #152

图 8-6 部分代码

• 由于 SP 不占空间，所以上图中的几行指令长度均为 8。