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@ -11,11 +11,14 @@ const ACCUMULATOR2 int = 1
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var tmpOffset int = 0
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func CodeGen(tree *treeNode) {
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// 初始化
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emitRM("LD", MEMORY_POINTER, 0, ACCUMULATOR1)
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emitComment("Load maxaddress from location 0")
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emitRM("ST", ACCUMULATOR1, 0, ACCUMULATOR1)
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emitComment("Clear location 0")
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// 对根节点开始遍历，生成代码
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cGen(tree)
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// 结束
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emitRO("HALT", 0, 0, 0)
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}
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@ -36,54 +39,80 @@ func cGen(t *treeNode) {
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func genStmt(t *treeNode) {
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switch t.stmt {
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case ifStmt:
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// if <expr> then <stmt1> else <stmt2> end
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// 或 if <expr> then <stmt1> end
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emitComment("-> if")
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p1 := t.child[0]
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p2 := t.child[1]
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p3 := t.child[2]
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// 生成条件表达式的代码
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cGen(p1)
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// 空一个跳转 stmt1 末尾的位置
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savedLoc1 := emitSkip(1)
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emitComment("if: jump to else belongs here")
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// 生成 stmt1 的代码
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cGen(p2)
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// 空一个指令，供跳转到 stmt2 结束
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savedLoc2 := emitSkip(1)
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emitComment("if: jump to end belongs here")
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// 获得 stmt2 的开始位置
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currLoc := emitSkip(0)
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// 回到 expr 判断结束处，写入条件跳转语句
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emitBackup(savedLoc1)
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emitAbsRM("JEQ", ACCUMULATOR1, currLoc)
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emitComment("if: jmp to else")
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// 回到 stmt2 开始处
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emitRestore()
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// 生成 stmt2 语句的代码
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cGen(p3)
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// 获得 stmt2 结束后的位置
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currLoc = emitSkip(0)
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// 回到 stmt1 结束处，无条件跳转到 stmt2 结束处
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emitBackup(savedLoc2)
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emitAbsRM("LDA", PROGRAM_COUNTER, currLoc)
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emitComment("if: jmp to end")
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// 回到 stmt2 结束处
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emitRestore()
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emitComment("<- if")
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case repeatStmt:
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// repeat <stmt1> until <expr>
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emitComment("-> repeat")
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p1 := t.child[0]
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p2 := t.child[1]
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// 保存循环前的位置
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savedLoc1 := emitSkip(0)
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emitComment("repeat: jump after body comes back here")
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// 执行语句
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cGen(p1)
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// 判断条件
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cGen(p2)
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// 如果符合，跳转到 savedLoc1，即循环前
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emitAbsRM("JEQ", ACCUMULATOR1, savedLoc1)
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emitComment("<- repeat")
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case assignStmt:
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// <id> := <expr>
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emitComment("-> assign")
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// 计算表达式的值，存入 ACCUMULATOR1
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cGen(t.child[0])
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// 找到 id 的内存偏移
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loc, _ := lookupSymtab(t.attr)
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// 将表达式的值存入 id 的内存偏移
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emitRM("ST", ACCUMULATOR1, loc, GLOBAL_POINTER)
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emitComment("<- assign")
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case readStmt:
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// read <id>
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emitComment("-> read")
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// 读取输入，存入 ACCUMULATOR1
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emitRO("IN", ACCUMULATOR1, 0, 0)
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loc, _ := lookupSymtab(t.attr)
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// 将输入的值存入 id 的内存偏移
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emitRM("ST", ACCUMULATOR1, loc, GLOBAL_POINTER)
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emitComment("<- read")
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case writeStmt:
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emitComment("-> write")
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// 计算表达式的值，存入 ACCUMULATOR1
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cGen(t.child[0])
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// 将 ACCUMULATOR1 的值输出
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emitRO("OUT", ACCUMULATOR1, 0, 0)
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emitComment("<- write")
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}
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@ -93,47 +122,64 @@ func genExp(t *treeNode) {
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switch t.expr {
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case constExpr:
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emitComment("-> Const")
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// 将常量存入 ACCUMULATOR1
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emitRM("LDC", ACCUMULATOR1, t.val, 0)
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emitComment("load const")
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emitComment("<- Const")
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case idExpr:
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emitComment("-> Id")
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// 找到 id 的内存偏移
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loc, _ := lookupSymtab(t.attr)
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// 将该地址对应的值存入 ACCUMULATOR1
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emitRM("LD", ACCUMULATOR1, loc, GLOBAL_POINTER)
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emitComment("load id value")
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emitComment("<- Id")
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case opExpr:
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emitComment("-> Op")
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// 求左子表达式的值，存入 ACCUMULATOR1
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cGen(t.child[0])
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// 将 ACCUMULATOR1 的值存入内存偏移 tmpOffset
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emitRM("ST", ACCUMULATOR1, tmpOffset, MEMORY_POINTER)
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// 将 tmpOffset 加 1，即指向下一个内存偏移（当然后面存的不能重合了）
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tmpOffset--
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emitComment("op: push left")
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// 求右子表达式的值，存入 ACCUMULATOR1
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cGen(t.child[1])
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tmpOffset++
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// 将左子表达式的值存入 ACCUMULATOR2
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emitRM("LD", ACCUMULATOR2, tmpOffset, MEMORY_POINTER)
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emitComment("op: load left")
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switch t.op {
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case plusToken:
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// AC1 = AC2 + AC1
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emitRO("ADD", ACCUMULATOR1, ACCUMULATOR2, ACCUMULATOR1)
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emitComment("op +")
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case minusToken:
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// AC1 = AC2 - AC1
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emitRO("SUB", ACCUMULATOR1, ACCUMULATOR2, ACCUMULATOR1)
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emitComment("op -")
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case timesToken:
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// AC1 = AC2 * AC1
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emitRO("MUL", ACCUMULATOR1, ACCUMULATOR2, ACCUMULATOR1)
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emitComment("op *")
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case overToken:
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// AC1 = AC2 / AC1
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emitRO("DIV", ACCUMULATOR1, ACCUMULATOR2, ACCUMULATOR1)
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emitComment("op /")
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case ltToken:
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// AC1 = AC2 - AC1
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emitRO("SUB", ACCUMULATOR1, ACCUMULATOR2, ACCUMULATOR1)
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emitComment("op <")
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// 若 AC1<AC2（新 AC1<0），则往后跳两个指令
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emitRM("JLT", ACCUMULATOR1, 2, PROGRAM_COUNTER)
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emitComment("br if true")
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// 若 AC1>=AC2，则 AC1=0
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emitRM("LDC", ACCUMULATOR1, 0, ACCUMULATOR1)
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emitComment("false case")
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// 无条件跳一条指令
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emitRM("LDA", PROGRAM_COUNTER, 1, PROGRAM_COUNTER)
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emitComment("unconditional jmp")
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// 若 AC1<AC2，则 AC1=1
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emitRM("LDC", ACCUMULATOR1, 1, ACCUMULATOR1)
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emitComment("true case")
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case eqToken:
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