public override IAstNode VisitForExpression([NotNull] ForExpressionContext context)
{
var initializer = ( LocalVariableDeclaration )context.Initializer.Accept(this);
ForInExpression retVal;
using (NamedValues.EnterScope( ))
{
Push(initializer);
var step = ( IExpression )context.StepExpression?.Accept(this) ?? new ConstantExpression(default, 1.0);
/*
* // Output for-loop as:
* // ...
* // start = startexpr
* // goto loop
* // loop:
* // variable = phi [start, loopheader], [nextvariable, loopend]
* // ...
* // bodyexpr
* // ...
* // loopend:
* // step = stepexpr
* // nextvariable = variable + step
* // endcond = endexpr
* // br endcond, loop, endloop
* // outloop:
*/
public override Value VisitForExpression([NotNull] ForExpressionContext context)
{
var function = InstructionBuilder.InsertBlock.ContainingFunction;
string varName = context.Initializer.Name;
var allocaVar = CreateEntryBlockAlloca(function, varName);
// Emit the start code first, without 'variable' in scope.
Value startVal = null;
if (context.Initializer.Value != null)
{
startVal = context.Initializer.Value.Accept(this);
if (startVal == null)
{
return(null);
}
}
else
{
startVal = Context.CreateConstant(0.0);
}
// store the value into allocated location
InstructionBuilder.Store(startVal, allocaVar);
// Make the new basic block for the loop header, inserting after current
// block.
var preHeaderBlock = InstructionBuilder.InsertBlock;
var loopBlock = Context.CreateBasicBlock("loop", function);
// Insert an explicit fall through from the current block to the loopBlock.
InstructionBuilder.Branch(loopBlock);
// Start insertion in loopBlock.
InstructionBuilder.PositionAtEnd(loopBlock);
// Start the PHI node with an entry for Start.
var variable = InstructionBuilder.PhiNode(Context.DoubleType)
.RegisterName(varName);
variable.AddIncoming(startVal, preHeaderBlock);
// Within the loop, the variable is defined equal to the PHI node. If it
// shadows an existing variable, we have to restore it, so save it now.
NamedValues.TryGetValue(varName, out Alloca oldValue);
NamedValues[varName] = allocaVar;
// Emit the body of the loop. This, like any other expr, can change the
// current BB. Note that we ignore the value computed by the body, but don't
// allow an error.
if (context.BodyExpression.Accept(this) == null)
{
return(null);
}
Value stepValue = Context.CreateConstant(1.0);
// DEBUG: How does ANTLR represent optional context (Null or IsEmpty == true)
if (context.StepExpression != null)
{
stepValue = context.StepExpression.Accept(this);
if (stepValue == null)
{
return(null);
}
}
// Compute the end condition.
Value endCondition = context.EndExpression.Accept(this);
if (endCondition == null)
{
return(null);
}
var curVar = InstructionBuilder.Load(allocaVar)
.RegisterName(varName);
var nextVar = InstructionBuilder.FAdd(curVar, stepValue)
.RegisterName("nextvar");
InstructionBuilder.Store(nextVar, allocaVar);
// Convert condition to a bool by comparing non-equal to 0.0.
endCondition = InstructionBuilder.Compare(RealPredicate.OrderedAndNotEqual, endCondition, Context.CreateConstant(1.0))
.RegisterName("loopcond");
// Create the "after loop" block and insert it.
var loopEndBlock = InstructionBuilder.InsertBlock;
var afterBlock = Context.CreateBasicBlock("afterloop", function);
// Insert the conditional branch into the end of LoopEndBB.
InstructionBuilder.Branch(endCondition, loopBlock, afterBlock);
InstructionBuilder.PositionAtEnd(afterBlock);
// Add a new entry to the PHI node for the backedge.
variable.AddIncoming(nextVar, loopEndBlock);
// Restore the unshadowed variable.
if (oldValue != null)
{
NamedValues[varName] = oldValue;
}
else
{
NamedValues.Remove(varName);
}
// for expr always returns 0.0 for consistency, there is no 'void'
return(Context.DoubleType.GetNullValue( ));
}
