///<summary>
/// Returns a list of assembly instructions that evaluate a given expression,
/// returning the result in a specified <c>dest</c>ination <see>Variable</see>.
///</summary>
private List <string> EvaluateExpression(Expression expression,
Variable dest,
ref Dictionary <Variable, int> stackMap,
int stackClobber)
{
/*//TODO: Refactor `stackClobber`
* We need a better way of handling ad-hoc expands and reductions of the current
* stack frame. Currently, I use the `stackClobber` variable inconsistently in order
* to signify that there's a manually applied change from the `stackMap`, and to let
* this method know that when reading or writing to stack addresses that aren't a part
* of this evaluation, we need to offset by the `stackClobber`. However, this is dirty
* and hacky and inconsistent.
*
* //* A much better approach would be to maintain the `stackMap` as an absolute invariant,
* extending its `.Add()` and `.Remove()` methods to update the stack positions of all the
* other variables. This would eliminate a lot of inconsistencies, hacky patch jobs, and
* allow for much easier further expansion to more complicated operations involving the stack.
*/
List <string> result = new List <string>();
result.Add(" # [EvaluateExpression " + expression.ToString() + "]");
if (stackMap.ContainsKey(dest))
{
// Destination is already on the stack.
int destOffset = stackMap[dest];
// Need to back up $r1, set $r1 to the value, then
// sw $r1 --> stack[offset], then restore $r1
result.Add(" addi $r6, $r6, -1"); // Expand the stack
result.Add(" sw $r1, 0($r6)"); // Backup $r1 to stack
result.Add(" xor $r1, $r1, $r1"); // Zero out $r1
if (expression is LiteralConstant)
{
int newVal = (expression as LiteralConstant).value;
while (newVal > 31)
{
result.Add(
" addi $r1, $r1, 31"
);
newVal -= 31;
}
result.Add(
" addi $r1, $r1, "
+ newVal.ToString() // Set $r1 = literal value
);
}
else if (expression is Variable)
{
// This is a simple one. Simply get the variable's value and put it in $r1
int sourceOffset = stackMap[(expression as Variable)];
result.Add(" lw $r1, " + (sourceOffset + stackClobber + 1) + "($r6)");
}
else if (expression is SingleParamOperation)
{
//TODO: Single parameter operators.
throw new NotImplementedException("Single param operators are not yet supported.");
}
else if (expression is TwoParamOperation)
{
// Get an ID
string unique = UniqueIdentifier.NextStr();
// Evaluate the operands
Variable leftOperand = new Variable()
{
name = "__temp_leftop_" + unique,
type = Variable.VarType.Int
};
Variable rightOperand = new Variable()
{
name = "__temp_rightop_" + unique,
type = Variable.VarType.Int
};
result.Add(" addi $r6, $r6, -2");
stackMap.Add(leftOperand, 0);
stackMap.Add(rightOperand, 1);
result.AddRange(EvaluateExpression(
(expression as TwoParamOperation).operands[0],
leftOperand,
ref stackMap,
stackClobber + 2
));
result.AddRange(EvaluateExpression(
(expression as TwoParamOperation).operands[1],
rightOperand,
ref stackMap,
stackClobber + 2
));
result.Add(" # " + (expression as TwoParamOperation).ToString());
switch ((expression as TwoParamOperation).operationType)
{
case Operation.OperationType.TestEq: {
// Load both evaluated operands into registers
result.Add(" lw $r2, " + (stackMap[leftOperand]) + "($r6)");
result.Add(" lw $r3, " + (stackMap[rightOperand]) + "($r6)");
// Get a unique ID
string ifUnique = UniqueIdentifier.NextStr();
// Assume they're equal
result.Add(" addi $r1, $r0, 1");
// If they are, done!
result.Add(" beq $r2, $r3, __beq_" + ifUnique);
// Otherwise, $r1 <- 0
result.Add(" addi $r1, $r0, 0");
// Done
result.Add(" __beq_" + ifUnique + ":");
} break;
//TODO: Other comparisons
// case Operation.OperationType.TestGt: {
// } break;
// case Operation.OperationType.TestLt: {
// } break;
// case Operation.OperationType.TestGeq: {
// } break;
// case Operation.OperationType.TestLeq: {
// } break;
case Operation.OperationType.Addition: {
// Load both evaluated operands into registers
result.Add(" lw $r2, " + (stackMap[leftOperand]) + "($r6)");
result.Add(" lw $r3, " + (stackMap[rightOperand]) + "($r6)");
// Add them into another register
result.Add(" add $r1, $r2, $r3");
} break;
case Operation.OperationType.Subtraction: {
// Load both evaluated operands into registers
result.Add(" lw $r2, " + (stackMap[leftOperand]) + "($r6)");
result.Add(" lw $r3, " + (stackMap[rightOperand]) + "($r6)");
// Subtract them into another register
result.Add(" sub $r1, $r2, $r3");
} break;
case Operation.OperationType.Xor: {
// Load both evaluated operands into registers
result.Add(" lw $r2, " + (stackMap[leftOperand]) + "($r6)");
result.Add(" lw $r3, " + (stackMap[rightOperand]) + "($r6)");
// XOR them into another register
result.Add(" xor $r1, $r2, $r3");
} break;
//TODO: Shift operators
// case Operation.OperationType.ShiftLeft: {
// } break;
// case Operation.OperationType.ShiftRight: {
// } break;
default: {
throw new InvalidOperationException(
"Invalid operation: "
+ (expression as TwoParamOperation).operationType.ToString()
);
}
}
// Reset the stack
stackMap.Remove(leftOperand);
stackMap.Remove(rightOperand);
result.Add(" addi $r6, $r6, 2");
}
else
{
throw new NotImplementedException("Only supports evaluation of literal constants.");
}
result.Add(
" sw $r1, " + (destOffset + stackClobber).ToString() // Write to stack[dest]
+ "($r6)" // Offset of destOffset + 1 because we backed up $r1 to stack
);
result.Add(" lw $r1, 0($r6)"); // Restore $r1 from stack
result.Add(" addi $r6, $r6, 1"); // Restore the stack
return(result);
}
else
{
// Destination doesn't exist on the stack.
throw new ArgumentOutOfRangeException("Destination: " + dest.ToString() + " not on stack.");
}
}
private void EmitActionCode(ref List <string> result,
Action action,
Function function,
ref Dictionary <Variable, int> stackMap,
ref int stackSize)
{
// Emit comment with action ToString header
result.Add("\n # " + action.ToString());
if (action is InlineAssembly)
{
// For an inline assembly command, we just need to output all of the lines
// directly to the .text section
foreach (string line in (action as InlineAssembly).code)
{
result.Add(" " + line);
}
}
else if (action is ReturnInstruction)
{
if (!((action as ReturnInstruction).returnValue is null))
{
// Need to evaluate the returnValue and place it in $r5
// $r5 isn't on the stack, so we have to define a new temp variable
Variable tempResult = new Variable()
{
name = "__temp_expr",
type = Variable.VarType.Int
};
result.Add(" addi $r6, $r6, -1");
stackMap.Add(tempResult, 0);
List <string> steps = EvaluateExpression(
(action as ReturnInstruction).returnValue,
tempResult,
ref stackMap,
1
);
result.AddRange(steps);
// Result is now in tempResult. Need to put it in $r5 and then jr $ra
result.Add(" xor $r5, $r5, $r5");
result.Add(" lw $r5, " + stackMap[tempResult] + "($r6)");
// Restore the dirty stack
stackMap.Remove(tempResult);
result.Add(" addi $r6, $r6, 1");
}
result.AddRange(GenerateReturn(stackSize));
}
else if (action is FunctionCall)
{
// First, we need to evaluate each argument onto the stack
// How many args?
int numArgs = (action as FunctionCall).arguments.Count;
if (numArgs > 4)
{
throw new ArgumentException(
"Can't have more than 4 arguments (" + (action as FunctionCall).function.name + ")"
);
}
// Evaluate all arguments -->
for (int argNum = 1; argNum <= numArgs; argNum++)
{
Variable tempResult = new Variable()
{
name = "__temp_expr_" + UniqueIdentifier.NextStr(),
type = Variable.VarType.Int
};
result.Add(" addi $r6, $r6, -1");
stackMap.Add(tempResult, 0);
List <string> steps = EvaluateExpression(
(action as FunctionCall).arguments[argNum - 1],
tempResult,
ref stackMap,
1
);
result.AddRange(steps);
// Result is now in tempResult. Need to put it in correct arg register
result.Add(
" lw $r" + argNum.ToString() + ", " + stackMap[tempResult] + "($r6)"
);
// Restore the dirty stack
stackMap.Remove(tempResult);
result.Add(" addi $r6, $r6, 1");
}
// Now, do the function call
string calleeName = (action as FunctionCall).function.name;
result.Add(" jal " + calleeName);
}
else if (action is LocalVarDeclaration)
{
// The variable already exists!
// Only need to do something if we are initializing it with a value.
Variable target = (action as LocalVarDeclaration).variable;
Expression newVal = (action as LocalVarDeclaration).initValue;
// Need to evaluate the new value and place it in the target
List <string> steps = EvaluateExpression(
newVal,
target,
ref stackMap,
1
);
result.AddRange(steps);
}
else if (action is VarAssignment)
{
// The variable already exists!
// Only need to do something if we are initializing it with a value.
Variable target = (action as VarAssignment).variable;
Expression newVal = (action as VarAssignment).newValue;
// Need to evaluate the new value and place it in the target
List <string> steps = EvaluateExpression(
newVal,
target,
ref stackMap,
0
);
result.AddRange(steps);
}
else if (action is If)
{
// First, need to evaluate the if condition
Expression ifCond = (action as If).condition;
Variable tempResult = new Variable()
{
name = "__temp_expr_" + UniqueIdentifier.NextStr(),
type = Variable.VarType.Int
};
result.Add(" addi $r6, $r6, -2");
stackMap.Add(tempResult, 0);
List <string> steps = EvaluateExpression(
ifCond,
tempResult,
ref stackMap,
2
);
result.AddRange(steps);
// Result is now in tempResult
//result.Add(" sw $r1, 1($r6)");
result.Add(" lw $r1, " + (stackMap[tempResult] + 1) + "($r6)");
// Result of condition is now in $r1
// Can be either 1 or 0. If it's 1 --> keep going, but if it's 0 --> skip body.
string skipLabel = "__if_skip_" + UniqueIdentifier.NextStr();
result.Add(" addi $r6, $r6, 1");
result.Add(" beq $r1, $r0, " + skipLabel); // If cond = 0 --> skip
//result.Add(" lw $r1, 1($r6)");
// Body of the IF block
foreach (Action ifAction in (action as If).ifActions)
{
EmitActionCode(ref result, ifAction, function, ref stackMap, ref stackSize);
}
result.Add(" " + skipLabel + ":");
// Restore the dirty stack
stackMap.Remove(tempResult);
result.Add(" addi $r6, $r6, 1");
}
}