char* CompiledLoop::findUpperBound() {
// find upper bound and loop variable
int condBCI = findStartOfSend(_endOfCond->bci() - InterpretedIC::size);
if (condBCI == IllegalBCI) return "loop condition: no send found";
// first find comparison in loop condition
Expr* loopCond = _scope->exprStackElems()->at(condBCI);
if (loopCond == NULL) return "loop condition: no expr (possible compiler bug)";
if (loopCond->isMergeExpr()) {
MergeExpr* cond = (MergeExpr*)loopCond;
if (cond->isSplittable()) {
Node* first = cond->exprs->first()->node();
if (first->nPredecessors() == 1) {
Node* prev = first->firstPrev();
if (prev->isBranchNode()) _loopBranch = (BranchNode*)prev;
}
}
}
if (!_loopBranch) return "loop condition: conditional branch not found";
NonTrivialNode* n = (NonTrivialNode*)_loopBranch->firstPrev();
PReg* operand;
if (n->isTArithNode()) {
operand = ((TArithRRNode*)n)->operand();
} else if (n->isArithNode()) {
operand = ((ArithRRNode*)n)->operand();
} else {
return "loop condition: comparison not found";
}
BranchOpCode op = _loopBranch->op();
// Now see if it's a simple comparison involving the loop variable
// and make an initial guess about the loop variable.
// NB: code generator inverts loop condition, i.e., branch leaves loop
if (op == LTBranchOp || op == LEBranchOp) {
// upperBound > loopVar
_loopVar = operand;
_upperBound = n->src();
} else if (op == GTBranchOp || op == GEBranchOp) {
// loopVar < upperBound
_loopVar = n->src();
_upperBound = operand;
} else {
return "loop condition: not oneof(<, <=, >, >=)";
}
// The above code assumes a loop counting up; check the loopVar now and switch
// directions if it doesn't work.
if (checkLoopVar()) {
// the reverse guess may be wrong too, but it doesn't hurt to try
PReg* temp = _loopVar; _loopVar = _upperBound; _upperBound = temp;
}
return NULL;
}
int InterpretedIC::findStartOfSend(methodOop m, int bci) {
u_char* p = findStartOfSend(m->codes(bci));
return (p == NULL) ? IllegalBCI : p - m->codes() + 1;
}