public static void killCFG(FixedNode node) {
assert node.isAlive();
if (node instanceof AbstractEndNode) {
// We reached a control flow end.
AbstractEndNode end = (AbstractEndNode) node;
killEnd(end);
} else {
// Normal control flow node.
/*
* We do not take a successor snapshot because this iterator supports concurrent
* modifications as long as they do not change the size of the successor list. Not
* taking a snapshot allows us to see modifications to other branches that may happen
* while processing one branch.
*/
for (Node successor : node.successors()) {
killCFG((FixedNode) successor);
}
}
propagateKill(node);
}
/**
* Precondition: This method assumes that either:
*
* <ul>
* <li>the state has already stabilized (ie no more pending iterations in the "iterative"
* dataflow algorithm); or
* <li>any rewritings made based on the state in its current form are conservative enough to be
* safe.
* </ul>
*
* <p>The overarching goal is to perform just enough rewriting to trigger other phases ( {@link
* com.oracle.graal.graph.spi.SimplifierTool SimplifierTool}, {@link
* com.oracle.graal.phases.common.DeadCodeEliminationPhase DeadCodeEliminationPhase}, etc) to
* perform the bulk of rewriting, thus lowering the maintenance burden.
*/
@Override
protected void node(FixedNode node) {
assert node.isAlive();
/*-------------------------------------------------------------------------------------
* Step 1: Unreachable paths are still visited (PostOrderNodeIterator requires all ends
* of a merge to have been visited), but time is saved by neither updating the state nor
* rewriting anything while on an an unreachable path.
*-------------------------------------------------------------------------------------
*/
if (state.isUnreachable) {
return;
}
/*-------------------------------------------------------------------------------------
* Step 2: For an AbstractBeginNode, determine whether this path is reachable, register
* any associated guards.
*-------------------------------------------------------------------------------------
*/
if (node instanceof BeginNode) {
BeginNode begin = (BeginNode) node;
Node pred = node.predecessor();
if (pred != null) {
registerControlSplit(pred, begin);
}
return;
}
/*-------------------------------------------------------------------------------------
* Step 3: Check whether EquationalReasoner caches should be cleared upon state updates.
*-------------------------------------------------------------------------------------
*/
reasoner.updateState(state);
/*-------------------------------------------------------------------------------------
* Step 4: Whatever special-case handling makes sense for the FixedNode at hand before
* its inputs are reduced.
*-------------------------------------------------------------------------------------
*/
if (node instanceof AbstractEndNode) {
visitAbstractEndNode((AbstractEndNode) node);
return;
} else if (node instanceof Invoke) {
visitInvoke((Invoke) node);
return;
} else if (node instanceof CheckCastNode) {
// it's important not to call deverbosification for visitCheckCastNode()
visitCheckCastNode((CheckCastNode) node);
return;
} else if (node instanceof GuardingPiNode) {
visitGuardingPiNode((GuardingPiNode) node);
return;
} else if (node instanceof NullCheckNode) {
visitNullCheckNode((NullCheckNode) node);
return;
} else if (node instanceof FixedGuardNode) {
visitFixedGuardNode((FixedGuardNode) node);
return;
} else if (node instanceof ConditionAnchorNode) {
// ConditionAnchorNode shouldn't occur during HighTier
return;
}
/*-------------------------------------------------------------------------------------
* Step 5: After special-case handling, we do our best for those FixedNode-s
* where the effort to reduce their inputs might pay off.
*
* Why is this useful? For example, by the time the BeginNode for an If-branch
* is visited (in general a ControlSplitNode), the If-condition will have gone already
* through simplification (and thus potentially have been reduced to a
* LogicConstantNode).
*-------------------------------------------------------------------------------------
*/
boolean paysOffToReduce = false;
if (node instanceof ControlSplitNode) {
// desire to simplify control flow
paysOffToReduce = true;
} else if (node instanceof ReturnNode) {
paysOffToReduce = true;
} else if (node instanceof AccessFieldNode || node instanceof AccessArrayNode) {
// desire to remove null-checks
paysOffToReduce = true;
}
// TODO comb remaining FixedWithNextNode subclasses, pick those with chances of paying-off
// TODO UnsafeLoadNode takes a condition
if (paysOffToReduce) {
deverbosifyInputsInPlace(node);
}
/*---------------------------------------------------------------------------------------
* Step 6: Any additional special-case handling, this time after having inputs reduced.
* For example, leverage anchors provided by the FixedNode, to add facts to the factbase.
*---------------------------------------------------------------------------------------
*/
// TODO some nodes are GuardingNodes (eg, FixedAccessNode) we could use them to track state
// TODO other nodes are guarded (eg JavaReadNode), thus *their* guards could be replaced.
}