TType *TCodeGenerator::EmitSimpleExpression(void)
{
TType *pOperandType; // ptr to operand's type
TType *pResultType; // ptr to result type
TTokenCode op; // operator
TTokenCode unaryOp = tcPlus; // unary operator
//--Unary + or -
if (TokenIn(token, tlUnaryOps)) {
unaryOp = token;
GetToken();
}
//--Emit code for the first term.
pResultType = EmitTerm();
//--If there was a unary operator, negate in integer value in ax
//--with the neg instruction, or negate a real value in dx:ax
//--by calling _FloatNegate.
if (unaryOp == tcMinus) {
if (pResultType->Base() == pIntegerType) Emit1(neg, Reg(ax))
else if (pResultType == pRealType) {
EmitPushOperand(pResultType);
Emit1(call, NameLit(FLOAT_NEGATE));
Emit2(add, Reg(sp), IntegerLit(4));
}
}
//--Loop to execute subsequent additive operators and terms.
while (TokenIn(token, tlAddOps)) {
op = token;
pResultType = pResultType->Base();
EmitPushOperand(pResultType);
GetToken();
pOperandType = EmitTerm()->Base();
//--Perform the operation, and push the resulting value
//--onto the stack.
if (op == tcOR) {
//--boolean OR boolean => boolean
//--ax = ax OR dx
Emit1(pop, Reg(dx));
Emit2(or, Reg(ax), Reg(dx));
pResultType = pBooleanType;
}
else if ((pResultType == pIntegerType) &&
(pOperandType == pIntegerType)) {
//--integer +|- integer => integer
Emit1(pop, Reg(dx));
if (op == tcPlus) Emit2(add, Reg(ax), Reg(dx))
else {
Emit2(sub, Reg(dx), Reg(ax));
Emit2(mov, Reg(ax), Reg(dx));
}
pResultType = pIntegerType;
}
else {
TType *TCodeGenerator::EmitExpression(void)
{
TType *pOperand1Type; // ptr to first operand's type
TType *pOperand2Type; // ptr to second operand's type
TType *pResultType; // ptr to result type
TTokenCode op; // operator
TInstruction jumpOpcode; // jump instruction opcode
int jumpLabelIndex; // assembly jump label index
//--Emit code for the first simple expression.
pResultType = EmitSimpleExpression();
//--If we now see a relational operator,
//--emit code for the second simple expression.
if (TokenIn(token, tlRelOps)) {
EmitPushOperand(pResultType);
op = token;
pOperand1Type = pResultType->Base();
GetToken();
pOperand2Type = EmitSimpleExpression()->Base();
//--Perform the operation, and push the resulting value
//--onto the stack.
if ( ((pOperand1Type == pIntegerType) &&
(pOperand2Type == pIntegerType))
|| ((pOperand1Type == pCharType) &&
(pOperand2Type == pCharType))
|| (pOperand1Type->form == fcEnum)) {
//--integer <op> integer
//--boolean <op> boolean
//--char <op> char
//--enum <op> enum
//--Compare dx (operand 1) to ax (operand 2).
Emit1(pop, Reg(dx));
Emit2(cmp, Reg(dx), Reg(ax));
}
else if ((pOperand1Type == pRealType) ||
(pOperand2Type == pRealType)) {
//--real <op> real
//--real <op> integer
//--integer <op> real
//--Convert the integer operand to real.
//--Call _FloatCompare to do the comparison, which
//--returns -1 (less), 0 (equal), or +1 (greater).
EmitPushOperand(pOperand2Type);
EmitPromoteToReal(pOperand1Type, pOperand2Type);
Emit1(call, NameLit(FLOAT_COMPARE));
Emit2(add, Reg(sp), IntegerLit(8));
Emit2(cmp, Reg(ax), IntegerLit(0));
}
else {
//--string <op> string
//--Compare the string pointed to by si (operand 1)
//--to the string pointed to by di (operand 2).
Emit1(pop, Reg(di));
Emit1(pop, Reg(si));
Emit2(mov, Reg(ax), Reg(ds));
Emit2(mov, Reg(es), Reg(ax));
Emit0(cld);
Emit2(mov, Reg(cx),
IntegerLit(pOperand1Type->array.elmtCount));
Emit0(repe_cmpsb);
}
Emit2(mov, Reg(ax), IntegerLit(1)); // default: load 1
switch (op) {
case tcLt: jumpOpcode = jl; break;
case tcLe: jumpOpcode = jle; break;
case tcEqual: jumpOpcode = je; break;
case tcNe: jumpOpcode = jne; break;
case tcGe: jumpOpcode = jge; break;
case tcGt: jumpOpcode = jg; break;
}
jumpLabelIndex = ++asmLabelIndex;
Emit1(jumpOpcode, Label(STMT_LABEL_PREFIX, jumpLabelIndex));
Emit2(sub, Reg(ax), Reg(ax)); // load 0 if false
EmitStatementLabel(jumpLabelIndex);
pResultType = pBooleanType;
}
return pResultType;
}
