void Expression::traverseTree( BTreeNode *root, bool conditionalRoot )
{
Traverser t(root);
t.start();
// special case: if we are starting at the root node then
// we are dealing with something of the form variable = 6
// or variable = portb
///TODO reimplement assignments as two branched trees?
if ( t.current() == root &&
!root->hasChildren() &&
t.current()->childOp() != pin &&
t.current()->childOp() != notpin &&
t.current()->childOp() != function &&
t.current()->childOp() != read_keypad )
{
switch(root->type())
{
case number: m_pic->assignNum(root->value()); break;
case variable: m_pic->assignVar(root->value()); break;
default: break; // Should never get here
}
// no need to traverse the tree as there is none.
return;
}
t.setCurrent(root);
if(t.current()->hasChildren())
{
// Here we work out what needs evaulating, and in which order.
// To minimize register usage, if only one branch needs traversing,
// then that branch should be done first.
bool evaluateLeft = t.current()->left()->needsEvaluating();
BTreeNode *evaluateFirst;
BTreeNode *evaluateSecond;
// If both need doing, then it really doesn't matter which we do
// first (unless we are looking to do really complex optimizations...
// Cases:
// - Both need evaluating,
// - or left needs doing first,
// in both cases we evaluate left, then right.
if( evaluateLeft )
{
evaluateFirst = t.current()->left();
evaluateSecond = t.current()->right();
}
// Otherwise it is best to evaluate right first for reasons given above.
else
{
evaluateFirst = t.current()->right();
evaluateSecond = t.current()->left();
}
QString dest1 = mb->dest();
mb->incDest();
QString dest2 = mb->dest();
mb->decDest();
bool evaluated = false;
if( evaluateFirst->hasChildren() )
{
traverseTree(evaluateFirst);
evaluated = true;
}
else if( isUnaryOp(evaluateFirst->childOp()) )
{
doUnaryOp( evaluateFirst->childOp(), evaluateFirst );
evaluated = true;
}
if ( evaluated )
{
// We need to save the result if we are going tro traverse the other
// branch, or if we are performing a subtraction in which case the
// value wanted in working is not the current value.
// But as the optimizer will deal with unnecessary variables anyway,
// always save to a register
evaluateFirst->setReg( dest1 );
evaluateFirst->setType( variable );
m_pic->saveToReg( dest1 );
}
evaluated = false;
if( evaluateSecond->hasChildren() )
{
mb->incDest();
mb->incDest();
traverseTree(evaluateSecond);
evaluated = true;
mb->decDest();
mb->decDest();
}
else if( isUnaryOp(evaluateSecond->childOp()) )
{
doUnaryOp( evaluateSecond->childOp(), evaluateSecond );
evaluated = true;
}
if ( evaluated )
{
evaluateSecond->setReg( dest2 );
evaluateSecond->setType( variable );
m_pic->saveToReg( dest2 );
}
}
if(t.current()->childOp()==divbyzero)
{
mistake( Microbe::DivisionByZero );
}
// If we are at the top level of something like 'if a == 3 then', then we are ready to put
// in the if code, else the expression just evaluates to 0 or 1
if(conditionalRoot && t.current() == root)
m_pic->setConditionalCode(m_ifCode, m_elseCode);
// Handle operations
// (functions are not actually supported)
if(isUnaryOp(t.current()->childOp()))
doUnaryOp( t.current()->childOp(), t.current() );
else
doOp( t.current()->childOp(), t.current()->left(), t.current()->right() );
}
