protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
bool evaluateForSideEffectsOnly = false;
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
evaluateForSideEffectsOnly = true;
break;
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
break;
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
var what = Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.AddressOrNode);
if (what == null)
{
// it is a temporary (and lvalue), so must be an address
if (evaluateForSideEffectsOnly)
{
// value not needed for other expression
// stack has: address
context.GenerateInstruction("IDEC");
// stack has: ...
}
else
{
// stack has: address
context.GenerateInstruction("DUP"); // copy the address
// stack has: address, address
context.GenerateInstruction("Indirection");
// stack has: address, value
context.GenerateInstruction("SWAP");
// stack has: value, address
context.GenerateInstruction("IDEC");
// stack has: value
}
}
else if (what is VariableTreeNode variable)
{
context.GenerateInstruction("PUSH", variable.Value.ToString( ));
if (!evaluateForSideEffectsOnly)
{
context.GenerateInstruction("DUP"); // copy original value to leave on the stack
}
context.GenerateInstruction("DEC");
context.GenerateInstruction("POP", variable.Value.ToString( ));
}
else
{
throw new AssertionFailedException("unexpected target" + what.ToString());
}
return(null);
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
// NB: a C string's value is its address.
// (There is no notion of a string's address as that would be an address of an address.)
switch (purpose)
{
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
// might be a case of *(p+i), which can be done as p[i];
if (Arg is AddressOfTreeNode addrOf1)
{
// 3404
// 3401: collapse *&(expr) on RHS and just generate code for the underlying expr
context.SetPrettyPrintProlog("<skipped> ");
context.PrettyPrint(Arg);
return(addrOf1.Arg.GenerateCodeForValueWithPrettyPrint(context, purpose));
}
else
{
if (Arg is AdditionTreeNode addition)
{
context.SetPrettyPrintProlog("<skipped> ");
context.PrettyPrint(Arg);
addition.Left.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
addition.Right.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
context.GenerateInstruction("Subscript");
}
else
{
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
context.GenerateInstruction("Indirection");
}
}
break;
case EvaluationIntention.SideEffectsOnly:
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
break;
case EvaluationIntention.AddressOrNode:
if (Arg is AddressOfTreeNode addrOf2)
{
// 3401: collapse *&(expr) on LHS and just generate code for the underlying expr
context.SetPrettyPrintProlog("<skipped> ");
context.PrettyPrint(Arg);
return(addrOf2.Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.AddressOrNode));
}
else
{
// NB: if we did ValueOrNode here, we'd have to handle Node results specially
// as we cannot allow a Node from ValueOrNode unmodified as AddressOrNode
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
}
break;
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
return(null);
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
bool so = false;
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
so = true;
break;
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
break;
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
var secondChoice = context.CreateLabel();
Pre.GenerateCodeForConditionalBranchWithPrettyPrint(context, secondChoice, false);
Mid.GenerateCodeForValueWithPrettyPrint(context, so ? EvaluationIntention.SideEffectsOnly : EvaluationIntention.Value);
var joinPoint = context.CreateLabel();
context.GenerateUnconditionalBranch(joinPoint);
context.PlaceLabelHere(secondChoice);
Post.GenerateCodeForValueWithPrettyPrint(context, so ? EvaluationIntention.SideEffectsOnly : EvaluationIntention.Value);
context.PlaceLabelHere(joinPoint);
return(null);
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
// NB: a C string's value is its address. (There is no notion of a string's address.)
switch (purpose)
{
case EvaluationIntention.Value:
context.GenerateInstruction("PUSH", string.Format("\"{0}\"", Value));
break;
case EvaluationIntention.SideEffectsOnly:
break;
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
return(null);
}
// NB: Short Circut Evaluation (Left || Right): if "Left" evaluates to true we must not evaluate "Right"
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
// We have something like an expression statement:
// a || b;
// or perhaps a parameter as in
// f(a||b);
// This requires differentiated evaluation for left/first and right/second as follows:
// a's truth value determines whether b is executed or skipped (short-circuted).
// if a is false, then b is executed; otherwise if a is true, b is skipped.
// thus, we need to evaluate "a" for conditional branch, and to branch around "b"!
// however, b does not affect anything further (and we don't need a final value for (a||b) either).
// Thus, b is evaluated for side effects only.
var joinPoint1 = context.CreateLabel();
Left.GenerateCodeForConditionalBranchWithPrettyPrint(context, joinPoint1, true);
Right.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
context.PlaceLabelHere(joinPoint1);
return(null);
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
// we have an expression like (a || b) + 3 so we treat that like: ((a || b) ? 1 : 0) + 3;
var zero = context.CreateLabel();
context.EvalEither(Left, Right, zero, false);
// get temp, so easy on stack machine
context.GenerateInstruction("PUSH", "#1");
var joinPoint2 = context.CreateLabel();
context.GenerateUnconditionalBranch(joinPoint2);
context.PlaceLabelHere(zero);
context.GenerateInstruction("PUSH", "#0");
context.PlaceLabelHere(joinPoint2);
return(null);
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
}
// This on is to be invoked; it performs pretty printing, and then invokes the protected (real/overridden) one.
public AbstractSyntaxTree GenerateCodeForValueWithPrettyPrint(CodeGenContext context, EvaluationIntention purpose)
{
context.PrettyPrint(this);
return(GenerateCodeForValue(context, purpose));
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
switch (purpose)
{
case EvaluationIntention.Value:
context.GenerateInstruction("PUSH", Value.ToString());
break;
case EvaluationIntention.ValueOrNode:
return(this);
case EvaluationIntention.SideEffectsOnly:
break;
case EvaluationIntention.AddressOrNode:
return(this);
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
return(null);
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
return(null);
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
if (Op != Operators.Operator.FixPoint)
{
context.GenerateInstruction(Op.ToString());
}
return(null);
// case EvaluationIntention.AddressOrNode:
// Arg.GenerateCodeForValueWithPrettyPrint ( context, EvaluationIntention.Value );
// return null;
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
}
/// <summary> /// Generates code for the given tree node. /// </summary> /// <param name="context"> /// where the generated code is output to, and some helper functions /// </param> /// <param name="purpose"> /// A tree can be evalutated for code generation: /// for side effects only: /// used to evaluate statements that discard results /// expect null for return value /// for the value produced by the expression (unconditionally): /// used to evaluate most operators in an expression context /// expect null for return value meaning the result is in the "temporary" location /// for the value produced by the expression when complex, or the node when a simple variable /// used to evaluate function expressions /// expect null meaning the result is in the "temporary" location, or, /// a variable if the expression evaluates to a simple variable /// for the address of the expression when complex, or the node when a simple variable /// used to evaluate left-hand-side of assignment operators /// expect null when the result is in the "temporary" location, or, /// variable if the result is the address of a variable /// Note: a tree can also be evalutated for conditional branch, but that is done with GenerateCodeForConditionalBranch, below. /// See EvaluationIntention for more details. /// </param> /// <returns> /// The return value takes on meaning in the context of the intended purpose of evaluation. /// It is a tree node that captures the mode of the loaded value: /// null -- indicating the expression result is a "temporary", or is nothing /// variable -- if the temporary result is a variable or address /// </returns> /// This is meant to be overridden by subclasses, but not called; hence protected! protected abstract AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose);
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
Arg.GenerateCodeForValueWithPrettyPrint(context, purpose);
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
return(null);
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
context.GenerateInstruction("NEG");
return(null);
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
// To take the address of a child expression, we capitalize on having an evaluation intention mode that matches this.
// We have this mode to support assignment and address of operations.
// Note that we must have a notion of evaluating an expression for its location rather than for its value, as
// we could not evaluate the left hand side of an assignment for value, and then take its address -- that doesn't work!
// By using the address evaluation intention for the child, there is then sometimes no code to generate for this operator.
// When it does need to generate code, the case of &a, for example, the it uses the PEA instruction
// Also note that this approach automatically detects and optimizes a sequence like &*
//
// Contrast this above with the Indirection operator
// The other operator, Indirection, needs to special case *& to collapse these two.
// This is because we don't have an evaluation intention mode for indirection,
// Instead we generate the indirection's value and the use an Indirection instruction to dereference it.
//
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
break;
case EvaluationIntention.Value:
var ans = Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.AddressOrNode);
if (ans != null)
{
if (ans is VariableTreeNode variable)
{
// PEA == Push Effective Address
context.GenerateInstruction("PEA", variable.Value.ToString());
}
else
{
throw new AssertionFailedException("unexpected result for &");
}
}
break;
case EvaluationIntention.ValueOrNode:
return(Arg.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.AddressOrNode));
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
return(null);
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
switch (purpose)
{
case EvaluationIntention.SideEffectsOnly:
Left.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
Right.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.SideEffectsOnly);
return(null);
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
Left.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
Right.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
context.GenerateInstruction(Op.ToString());
return(null);
case EvaluationIntention.AddressOrNode:
Left.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
Right.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
context.GenerateInstruction("AddIndex");
return(null);
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
var functionToCall = Left.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.ValueOrNode);
// NB: Function calls are binary operators in the sense that they have two arguments.
// The first argument is the function to call, and the second is:
// possibly null -- if no arguments are supplied, or,
// a single parameter -- if one argument is supplied, or,
// a tree of ArgumentSeparator, whose left is
// a single parameter, or,
// a tree of ArugmentSeparator ...
// and whose Right is a single parameter.
var argCount = context.EvaluateArgumentList(Right);
if (functionToCall == null)
{
context.GenerateInstruction("ICALL", string.Format("#{0}", argCount));
}
else if (functionToCall is VariableTreeNode variable)
{
context.GenerateInstruction("CALL", variable.Value.ToString(), string.Format("#{0}", argCount));
}
else
{
throw new AssertionFailedException("unknown function");
}
if (purpose == EvaluationIntention.SideEffectsOnly)
{
context.GenerateInstruction("POP");
}
return(null);
}
protected override AbstractSyntaxTree GenerateCodeForValue(CodeGenContext context, EvaluationIntention purpose)
{
// When we ask for AddressOrNode, we will get either an address
// e.g. for a[i] += ..., we'll get a+i on the stack, or,
// for i += ..., we'll get nothing on the stack, so we can pop directly into i
var target = Left.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.AddressOrNode);
var variable = target as VariableTreeNode;
if (Op != Assignment)
{
GenerateLHSValue(context, target, variable);
}
Right.GenerateCodeForValueWithPrettyPrint(context, EvaluationIntention.Value);
var keep = false;
switch (purpose)
{
case EvaluationIntention.Value:
case EvaluationIntention.ValueOrNode:
keep = true;
break;
case EvaluationIntention.SideEffectsOnly:
break;
default:
throw new AssertionFailedException("unexpected evaluation intention" + purpose);
}
if (Op != Assignment)
{
GenerateAssignmentComputation(context);
}
if (target == null)
{
// this case is that we generated an address onto the stack for the target
// so, we need to use indirection operators
if (keep)
{
// Stack has LeftY | RightTop <-- stack top
// This instruction does *LeftY = RightTop
// and pops only Left off the stack, leaving Right
context.GenerateInstruction("ISTORE");
}
else
{
// Stack has LeftY | RightTop <-- stack top
// This instruction does *LeftYT = RightTop
// and pops both Left and Right off the stack
context.GenerateInstruction("IPOP");
}
}
else
{
// this case is that we generated nothing onto the stack for the left hand side
// so, we'll pop or store directly into
if (keep)
{
// Stack has RightTop <-- stack top
// This instruction does var = RightTop
// and does not pop Right
// This form is used when the assignment is used
// as in f(a=b); in which b is assigned into a, and the value is passed to f
context.GenerateInstruction("STORE", variable.Value.ToString());
}
else
{
// Stack has RightTop <-- stack top
// This instruction does var = RightTop
// and does pop Right off the stack, because the value is not wanted.
context.GenerateInstruction("POP", variable.Value.ToString());
}
}
return(null);
}
