compilers-cw2/task3/CodegenImpl.java

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public class CodegenImpl implements Codegen {
private int labelCounter = 0;
public CodegenImpl() {}
public String codegen(Program p) throws CodegenException {
StringBuilder builder = new StringBuilder();
Declaration main = null;
for (Declaration d : p.decls) {
if (main == null) {
main = d;
}
builder.append(compileDeclaration(d));
}
return "call " + String.format("%s_%d\n", main.id, main.numOfArgs)
+ "li a7,93\n"
+ "ecall\n"
+ builder.toString();
}
private String generateLabel() {
return String.format("branch_%d", labelCounter++);
}
public String compileDeclaration(Declaration d) throws CodegenException {
return String.format("%s_%d:\n", d.id, d.numOfArgs)
+ compileExp(d.body)
+ "ret\n";
}
public String compileExp(Exp e) throws CodegenException {
if (e instanceof IntLiteral) {
return String.format("li a0,%d\n", ((IntLiteral) e).n);
} else if (e instanceof If) {
If eIf = (If) e;
String thenLabel = generateLabel();
String elseLabel = generateLabel();
String finalizeLabel = generateLabel();
return compileFullComp(eIf.l, eIf.r, eIf.comp, thenLabel, elseLabel)
+ thenLabel + ": " + compileExp(eIf.thenBody)
+ "j " + finalizeLabel + "\n"
+ elseLabel + ": " + compileExp(eIf.elseBody)
+ finalizeLabel + ": " + "lw s1,(sp)\n"
+ "addi sp,sp,4\n";
} else if (e instanceof Binexp) {
Binexp b = (Binexp) e;
return compileExp(b.l)
+ "sw s1,-4(sp)\n"
+ "addi sp,sp,-4\n"
+ "mv s1,a0\n"
+ compileExp(b.r)
+ "mv t1,a0\n"
+ compileExpBinop(b.binop)
+ "lw s1,(sp)\n"
+ "addi sp,sp,4\n";
} else if (e instanceof Variable) {
int offset = ((Variable) e).x - 1;
return String.format("lw a0,%d(s0)\n", offset * 4);
} else if (e instanceof Invoke) {
return compileCall((Invoke) e, false);
} else if (e instanceof Seq) {
String result = "";
Seq statements = (Seq) e;
if (statements.r instanceof Invoke) {
// tail call
result = compileCall((Invoke) statements.r, true);
} else {
result = compileExp(statements.r);
}
return compileExp(statements.l) + result;
} else if (e instanceof While) {
While eWhile = (While) e;
String startLabel = generateLabel();
String bodyLabel = generateLabel();
String exitLabel = generateLabel();
return "sw s2,-4(sp)\n"
+ "sw s3,-8(sp)\n"
+ "addi sp,sp,-8\n"
+ "la s2," + startLabel + "\n"
+ "la s3," + exitLabel + "\n"
+ startLabel + ": " + compileFullComp(eWhile.l, eWhile.r, eWhile.comp, bodyLabel, exitLabel)
+ bodyLabel + ": " + compileExp(eWhile.body)
+ "lw s1,(sp)\n"
+ "addi sp,sp,4\n"
+ "j " + startLabel + "\n"
+ exitLabel + ": lw s1,(sp)\n"
+ "lw s3,4(sp)\n"
+ "lw s2,8(sp)\n"
+ "addi sp,sp,12\n";
} else if (e instanceof RepeatUntil) {
RepeatUntil eUntil = (RepeatUntil) e;
String compLabel = generateLabel();
String bodyLabel = generateLabel();
String exitLabel = generateLabel();
String contLabel = generateLabel();
String breakLabel = generateLabel();
return "sw s2,-8(sp)\n"
+ "sw s3,-4(sp)\n"
+ "addi sp,sp,-8\n"
+ "la s2," + contLabel + "\n"
+ "la s3," + breakLabel + "\n"
+ bodyLabel + ": " + compileExp(eUntil.body)
+ contLabel + ": sw s4,-4(sp)\n"
+ "addi sp,sp,-4\n"
+ "mv s4,a0\n"
+ compileFullComp(eUntil.l, eUntil.r, eUntil.comp, exitLabel, compLabel)
+ compLabel + ": lw s1,(sp)\n"
+ "lw s4,4(sp)\n"
+ "addi sp,sp,8\n"
+ "j " + bodyLabel + "\n"
+ breakLabel + ": sw s1,-8(sp)\n"
+ "sw s4,-4(sp)\n"
+ "addi sp,sp,-8\n"
+ "mv s4,a0\n"
+ exitLabel + ": lw s1,(sp)\n"
+ "mv a0,s4\n" // body result to accumulator
+ "lw s4,4(sp)\n" // restore previous s4
+ "lw s2,8(sp)\n"
+ "lw s3,12(sp)\n"
+ "addi sp,sp,16\n";
} else if (e instanceof Assign) {
Assign assign = (Assign) e;
return compileExp(assign.e)
+ String.format("sw a0,%d(s0)\n", (assign.x - 1) * 4);
} else if (e instanceof Continue) {
return "jr s2\n";
} else if (e instanceof Break) {
return "jr s3\n";
} else if (e instanceof Skip) {
return "nop\n";
}
throw new CodegenException("Unsupported expression!");
}
public String compileCall(Invoke call, boolean tailCall) throws CodegenException {
int argLen = call.args.size();
String methodLabel = String.format("%s_%d", call.name, argLen);
StringBuilder builder = new StringBuilder();
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// Store return address
builder.append("sw ra,-4(sp)\n");
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builder.append("mv t0,sp\n");
// shuffle stack pointer to start of arguments
builder.append(String.format("addi sp,sp,-%d\n", (argLen + 1) * 4));
builder.append("sw t0,-8(sp)\n"); // store old stack pointer (top of frame)
for (int i = argLen - 1; i >= 0; i--) {
Exp argExp = call.args.get(i);
builder.append(compileExp(argExp));
builder.append(
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String.format("sw a0,%d(sp)\n", i*4)
);
}
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// push old frame pointer
builder.append("sw s0,-4(sp)\n");
builder.append("addi sp,sp,-8\n");
builder.append(
// set frame pointer to start of arguments
"addi s0,sp,8\n"
+ "call " + methodLabel + "\n"
// restore old frame pointer & stack pointer
+ "lw s0,4(sp)\n"
+ "lw sp,(sp)\n"
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// restore return address of caller
+ "lw ra,-4(sp)\n"
);
return builder.toString();
}
public String compileFullComp(Exp left, Exp right, Comp c, String successLabel, String failLabel) throws CodegenException {
return compileExp(left)
+ "sw s1,-4(sp)\n"
+ "addi sp,sp,-4\n"
+ "mv s1,a0\n"
+ compileExp(right)
+ "mv t1,a0\n"
+ compileComp(c, successLabel, failLabel);
}
public String compileComp(Comp c, String thenLabel, String elseLabel) throws CodegenException {
String instruction = "";
if (c instanceof Equals) {
instruction = "beq";
} else if (c instanceof Less) {
instruction = "blt";
} else if (c instanceof LessEq) {
instruction = "ble";
} else if (c instanceof Greater) {
instruction = "bgt";
} else if (c instanceof GreaterEq) {
instruction = "bge";
} else {
throw new CodegenException("Unsupported comparison!");
}
return String.format("%s s1,t1,%s\nb %s\n", instruction, thenLabel, elseLabel);
}
public String compileExpBinop(Binop bin) throws CodegenException {
if (bin instanceof Plus) {
return "add a0,s1,t1\n";
} else if (bin instanceof Minus) {
return "sub a0,s1,t1\n";
} else if (bin instanceof Times) {
return "mul a0,s1,t1\n";
} else if (bin instanceof Div) {
return "div a0,s1,t1\n";
}
throw new CodegenException("Unsupported bin-op! " + bin);
}
}