org.jruby.ir.representations.CFG Maven / Gradle / Ivy
package org.jruby.ir.representations;
import org.jruby.dirgra.DirectedGraph;
import org.jruby.dirgra.Edge;
import org.jruby.ir.IRManager;
import org.jruby.ir.IRScope;
import org.jruby.ir.Operation;
import org.jruby.ir.instructions.*;
import org.jruby.ir.operands.Label;
import org.jruby.ir.operands.Operand;
import org.jruby.ir.operands.Variable;
import org.jruby.ir.operands.WrappedIRClosure;
import org.jruby.ir.transformations.inlining.CloneInfo;
import org.jruby.util.log.Logger;
import org.jruby.util.log.LoggerFactory;
import java.util.*;
/**
* Represents the base build of a CFG. All information here is accessed via
* delegation from the CFG itself so this is meant as an internal
* organizational structure for a build.
*/
public class CFG {
public enum EdgeType {
REGULAR, // Any non-special edge. Not really used.
EXCEPTION, // Edge to exception handling basic blocks
FALL_THROUGH, // Edge which is the natural fall through choice on a branch
EXIT // Edge to dummy exit BB
}
private static final Logger LOG = LoggerFactory.getLogger(CFG.class);
private IRScope scope;
private Map bbMap;
// Map of bb -> first bb of the rescue block that initiates exception handling for all exceptions thrown within this bb
private Map rescuerMap;
/** Entry BB */
private BasicBlock entryBB;
/** Exit BB */
private BasicBlock exitBB;
/** BB that traps all exception-edges out of the cfg where we could add any cleanup/ensure code (ex: pop frames, etc.) */
private BasicBlock globalEnsureBB;
/** The graph itself */
private DirectedGraph graph;
private int nextBBId; // Next available basic block id
LinkedList postOrderList; // Post order traversal list of the cfg
public CFG(IRScope scope) {
this.scope = scope;
this.graph = new DirectedGraph<>();
this.bbMap = new HashMap<>();
this.rescuerMap = new HashMap<>();
this.nextBBId = 0;
this.entryBB = this.exitBB = null;
this.globalEnsureBB = null;
this.postOrderList = null;
}
public int getNextBBID() {
nextBBId++;
return nextBBId;
}
public IRManager getManager() {
return scope.getManager();
}
public int getMaxNodeID() {
return nextBBId;
}
public boolean bbIsProtected(BasicBlock b) {
return getRescuerBBFor(b) != null;
}
public BasicBlock getBBForLabel(Label label) {
return bbMap.get(label);
}
public BasicBlock getEntryBB() {
return entryBB;
}
public BasicBlock getExitBB() {
return exitBB;
}
public BasicBlock getGlobalEnsureBB() {
return globalEnsureBB;
}
public LinkedList postOrderList() {
// SSS FIXME: This caching is fragile -- requires invalidation
// on change of CFG state. We need a better setup than this.
if (postOrderList == null) postOrderList = buildPostOrderList();
return postOrderList;
}
public Iterator getPostOrderTraverser() {
return postOrderList().iterator();
}
public Iterator getReversePostOrderTraverser() {
return postOrderList().descendingIterator();
}
public void resetState() {
// SSS FIXME: anything else?
postOrderList = null;
}
public IRScope getScope() {
return scope;
}
/**
* How many BasicBlocks are there in this CFG?
*/
public int size() {
return graph.size();
}
public Collection getBasicBlocks() {
return graph.allData();
}
public Collection getSortedBasicBlocks() {
return graph.getInorderData();
}
public void addEdge(BasicBlock source, BasicBlock destination, Object type) {
graph.findOrCreateVertexFor(source).addEdgeTo(destination, type);
}
public int inDegree(BasicBlock b) {
return graph.findVertexFor(b).inDegree();
}
public int outDegree(BasicBlock b) {
return graph.findVertexFor(b).outDegree();
}
public Iterable getIncomingSources(BasicBlock block) {
return graph.findVertexFor(block).getIncomingSourcesData();
}
public Iterable> getIncomingEdges(BasicBlock block) {
return graph.findVertexFor(block).getIncomingEdges();
}
public BasicBlock getIncomingSourceOfType(BasicBlock block, Object type) {
return graph.findVertexFor(block).getIncomingSourceDataOfType(type);
}
public BasicBlock getOutgoingDestinationOfType(BasicBlock block, Object type) {
return graph.findVertexFor(block).getOutgoingDestinationDataOfType(type);
}
public Iterable getOutgoingDestinations(BasicBlock block) {
return graph.findVertexFor(block).getOutgoingDestinationsData();
}
public Iterable getOutgoingDestinationsOfType(BasicBlock block, Object type) {
return graph.findVertexFor(block).getOutgoingDestinationsDataOfType(type);
}
public Iterable getOutgoingDestinationsNotOfType(BasicBlock block, Object type) {
return graph.findVertexFor(block).getOutgoingDestinationsDataNotOfType(type);
}
public Collection> getOutgoingEdges(BasicBlock block) {
return graph.findVertexFor(block).getOutgoingEdges();
}
public BasicBlock getRescuerBBFor(BasicBlock block) {
return rescuerMap.get(block);
}
/* Add 'b' as a global ensure block that protects all unprotected blocks in this scope */
public void addGlobalEnsureBB(BasicBlock geb) {
assert globalEnsureBB == null: "CFG for scope " + getScope() + " already has a global ensure block.";
addBasicBlock(geb);
addEdge(geb, getExitBB(), EdgeType.EXIT);
for (BasicBlock b: getBasicBlocks()) {
if (b != geb && !bbIsProtected(b) && b != getEntryBB()) {
addEdge(b, geb, EdgeType.EXCEPTION);
setRescuerBB(b, geb);
}
}
globalEnsureBB = geb;
}
public void setRescuerBB(BasicBlock block, BasicBlock rescuerBlock) {
rescuerMap.put(block, rescuerBlock);
}
/**
* Build the Control Flow Graph
*/
public DirectedGraph build(Instr[] instrs) {
// Map of label & basic blocks which are waiting for a bb with that label
Map> forwardRefs = new HashMap<>();
// List of bbs that have a 'return' instruction
List returnBBs = new ArrayList<>();
// List of bbs that have a 'throw' instruction
List exceptionBBs = new ArrayList<>();
// Stack of nested rescue regions
Stack nestedExceptionRegions = new Stack<>();
// List of all rescued regions
List allExceptionRegions = new ArrayList<>();
// Dummy entry basic block (see note at end to see why)
entryBB = createBB(nestedExceptionRegions);
// First real bb
BasicBlock firstBB = createBB(nestedExceptionRegions);
// Build the rest!
BasicBlock currBB = firstBB;
BasicBlock newBB;
boolean bbEnded = false;
boolean nextBBIsFallThrough = true;
for (Instr i: instrs) {
// System.out.println("Processing: " + i);
Operation iop = i.getOperation();
if (iop == Operation.LABEL) {
Label l = ((LabelInstr) i).getLabel();
newBB = createBB(l, nestedExceptionRegions);
// Jump instruction bbs dont add an edge to the succeeding bb by default
if (nextBBIsFallThrough) graph.addEdge(currBB, newBB, EdgeType.FALL_THROUGH);
currBB = newBB;
bbEnded = false;
nextBBIsFallThrough = true;
// Add forward reference edges
List frefs = forwardRefs.get(l);
if (frefs != null) {
for (BasicBlock b : frefs) {
graph.addEdge(b, newBB, EdgeType.REGULAR);
}
}
} else if (bbEnded && iop != Operation.EXC_REGION_END) {
newBB = createBB(nestedExceptionRegions);
// Jump instruction bbs dont add an edge to the succeeding bb by default
if (nextBBIsFallThrough) graph.addEdge(currBB, newBB, EdgeType.FALL_THROUGH); // currBB cannot be null!
currBB = newBB;
bbEnded = false;
nextBBIsFallThrough = true;
}
if (i instanceof ExceptionRegionStartMarkerInstr) {
// We dont need the instruction anymore -- so it is not added to the CFG.
ExceptionRegionStartMarkerInstr ersmi = (ExceptionRegionStartMarkerInstr) i;
ExceptionRegion rr = new ExceptionRegion(ersmi.getFirstRescueBlockLabel(), currBB);
rr.addBB(currBB);
allExceptionRegions.add(rr);
if (!nestedExceptionRegions.empty()) {
nestedExceptionRegions.peek().addNestedRegion(rr);
}
nestedExceptionRegions.push(rr);
} else if (i instanceof ExceptionRegionEndMarkerInstr) {
// We dont need the instruction anymore -- so it is not added to the CFG.
nestedExceptionRegions.pop().setEndBB(currBB);
} else if (iop.endsBasicBlock()) {
bbEnded = true;
currBB.addInstr(i);
Label tgt = null;
nextBBIsFallThrough = false;
if (i instanceof BranchInstr) {
tgt = ((BranchInstr) i).getJumpTarget();
nextBBIsFallThrough = true;
} else if (i instanceof MultiBranchInstr) {
Label[] tgts = ((MultiBranchInstr) i).getJumpTargets();
for (Label l : tgts) addEdge(currBB, l, forwardRefs);
} else if (i instanceof JumpInstr) {
tgt = ((JumpInstr) i).getJumpTarget();
} else if (iop.isReturn()) { // BREAK, RETURN, CLOSURE_RETURN
tgt = null;
returnBBs.add(currBB);
} else if (i instanceof ThrowExceptionInstr) {
tgt = null;
exceptionBBs.add(currBB);
} else {
throw new RuntimeException("Unhandled case in CFG builder for basic block ending instr: " + i);
}
if (tgt != null) addEdge(currBB, tgt, forwardRefs);
} else if (iop != Operation.LABEL) {
currBB.addInstr(i);
}
}
// Process all rescued regions
for (ExceptionRegion rr: allExceptionRegions) {
// When this exception region represents an unrescued region
// from a copied ensure block, we have a dummy label
Label rescueLabel = rr.getFirstRescueBlockLabel();
if (!Label.UNRESCUED_REGION_LABEL.equals(rescueLabel)) {
BasicBlock firstRescueBB = bbMap.get(rescueLabel);
// Mark the BB as a rescue entry BB
firstRescueBB.markRescueEntryBB();
// Record a mapping from the region's exclusive basic blocks to the first bb that will start exception
// handling for all their exceptions. Add an exception edge from every exclusive bb of the region to
// firstRescueBB unless it is incapable of raising.
for (BasicBlock b: rr.getExclusiveBBs()) {
if (b.canRaiseExceptions()) {
setRescuerBB(b, firstRescueBB);
graph.addEdge(b, firstRescueBB, EdgeType.EXCEPTION);
}
}
}
}
buildExitBasicBlock(nestedExceptionRegions, firstBB, returnBBs, exceptionBBs, nextBBIsFallThrough, currBB, entryBB);
// System.out.println("-------------- CFG before optimizing --------------");
// System.out.println("\nGraph:\n" + toStringGraph());
// System.out.println("\nInstructions:\n" + toStringInstrs());
optimize(returnBBs); // remove useless cfg edges & orphaned bbs
return graph;
}
private void addEdge(BasicBlock src, Label targetLabel, Map> forwardRefs) {
BasicBlock target = bbMap.get(targetLabel);
if (target != null) {
graph.addEdge(src, target, EdgeType.REGULAR);
return;
}
// Add a forward reference from target -> source
List forwardReferences = forwardRefs.get(targetLabel);
if (forwardReferences == null) {
forwardReferences = new ArrayList<>();
forwardRefs.put(targetLabel, forwardReferences);
}
forwardReferences.add(src);
}
/**
* Create special empty exit BasicBlock that all BasicBlocks will eventually
* flow into. All Edges to this 'dummy' BasicBlock will get marked with
* an edge type of EXIT.
*
* Special BasicBlocks worth noting:
* 1. Exceptions, Returns, Entry(why?) -> ExitBB
* 2. Returns -> ExitBB
*/
private BasicBlock buildExitBasicBlock(Stack nestedExceptionRegions, BasicBlock firstBB,
List returnBBs, List exceptionBBs, boolean nextIsFallThrough, BasicBlock currBB, BasicBlock entryBB) {
exitBB = createBB(nestedExceptionRegions);
graph.addEdge(entryBB, exitBB, EdgeType.EXIT);
graph.addEdge(entryBB, firstBB, EdgeType.FALL_THROUGH);
for (BasicBlock rb : returnBBs) {
graph.addEdge(rb, exitBB, EdgeType.EXIT);
}
for (BasicBlock rb : exceptionBBs) {
graph.addEdge(rb, exitBB, EdgeType.EXIT);
}
if (nextIsFallThrough) graph.addEdge(currBB, exitBB, EdgeType.EXIT);
return exitBB;
}
private BasicBlock createBB(Label label, Stack nestedExceptionRegions) {
BasicBlock basicBlock = new BasicBlock(this, label);
addBasicBlock(basicBlock);
if (label.isGlobalEnsureBlockLabel()) {
globalEnsureBB = basicBlock;
}
if (!nestedExceptionRegions.empty()) nestedExceptionRegions.peek().addBB(basicBlock);
return basicBlock;
}
private BasicBlock createBB(Stack nestedExceptionRegions) {
return createBB(scope.getNewLabel(), nestedExceptionRegions);
}
public void addBasicBlock(BasicBlock bb) {
graph.findOrCreateVertexFor(bb); // adds vertex to graph
bbMap.put(bb.getLabel(), bb);
// Reset so later dataflow analyses get all basic blocks
postOrderList = null;
}
public void removeAllOutgoingEdgesForBB(BasicBlock b) {
graph.findVertexFor(b).removeAllOutgoingEdges();
}
private void deleteOrphanedBlocks(DirectedGraph graph) {
// System.out.println("\nGraph:\n" + toStringGraph());
// System.out.println("\nInstructions:\n" + toStringInstrs());
Queue worklist = new LinkedList();
Set living = new HashSet();
worklist.add(entryBB);
living.add(entryBB);
while (!worklist.isEmpty()) {
BasicBlock current = worklist.remove();
for (BasicBlock bb: graph.findVertexFor(current).getOutgoingDestinationsData()) {
if (!living.contains(bb)) {
worklist.add(bb);
living.add(bb);
}
}
}
// Seems like Java should have simpler way of doing this.
// We canot just remove in this loop or we get concmodexc.
Set dead = new HashSet();
for (BasicBlock bb: graph.allData()) {
if (!living.contains(bb)) dead.add(bb);
}
for (BasicBlock bb: dead) {
removeBB(bb);
removeNestedScopesFromBB(bb);
}
}
private boolean mergeBBs(BasicBlock a, BasicBlock b) {
BasicBlock aR = getRescuerBBFor(a);
BasicBlock bR = getRescuerBBFor(b);
// We can merge 'a' and 'b' if one of the following is true:
// 1. 'a' and 'b' are both not empty
// They are protected by the same rescue block.
// NOTE: We need not check the ensure block map because all ensure blocks are already
// captured in the bb rescue block map. So, if aR == bR, it is guaranteed that the
// ensure blocks for the two are identical.
// 2. One of 'a' or 'b' is empty. We dont need to check for rescue block match because
// an empty basic block cannot raise an exception, can it?
if (aR == bR || a.isEmpty() || b.isEmpty()) {
// First, remove straight-line jump, if present
Instr lastInstr = a.getLastInstr();
if (lastInstr instanceof JumpInstr) a.removeInstr(lastInstr);
// Swallow b's instrs.
a.swallowBB(b);
// Fixup edges
removeEdge(a, b);
for (Edge e : getOutgoingEdges(b)) {
addEdge(a, e.getDestination().getData(), e.getType());
}
// Move all incoming edges of b to be incoming edges of a.
for (Edge e : getIncomingEdges(b)) {
BasicBlock fixupBB = e.getSource().getData();
removeEdge(fixupBB, b);
addEdge(fixupBB, a, e.getType());
// a -fall-through->b handled above. Any jumps to b must be pointed to a's label.
Instr fixupLastInstr = fixupBB.getLastInstr();
if (fixupLastInstr instanceof JumpTargetInstr) {
((JumpTargetInstr) fixupLastInstr).setJumpTarget(a.getLabel());
}
}
// Delete bb
removeBB(b);
// Update rescue map
if (aR == null && bR != null) {
setRescuerBB(a, bR);
}
return true;
} else {
return false;
}
}
public void removeBB(BasicBlock b) {
if (b == globalEnsureBB) globalEnsureBB = null;
graph.removeVertexFor(b);
bbMap.remove(b.getLabel());
rescuerMap.remove(b);
}
/**
* Wrapped IRClosures in dead BB are lexically rooted to that dead BB so they can
* be removed from the parent scope if the BB they live in died.
*/
private void removeNestedScopesFromBB(BasicBlock bb) {
for (Instr instr: bb.getInstrs()) {
for (Operand oper: instr.getOperands()) {
if (oper instanceof WrappedIRClosure) {
scope.removeClosure(((WrappedIRClosure) oper).getClosure());
break; // Only one WrappedIRClosure possible per instr
}
}
}
}
public void collapseStraightLineBBs() {
// Collect cfgs in a list first since the cfg/graph API returns an iterator
// over live data. But, basic block merging modifies that live data.
//
// SSS FIXME: So, we need a cfg/graph API that returns an iterator over
// frozen data rather than live data.
List cfgBBs = new ArrayList<>();
for (BasicBlock b: getBasicBlocks()) cfgBBs.add(b);
Set mergedBBs = new HashSet<>();
for (BasicBlock b: cfgBBs) {
if (!mergedBBs.contains(b) && outDegree(b) == 1) {
for (Edge e : getOutgoingEdges(b)) {
BasicBlock outB = e.getDestination().getData();
// 1:1 BBs can just be one since there is only one place to go. An empty entering any BB can merge
// since the empty one does nothing (Note: mergeBBs uses empty as destination impl-wise but outcome
// is the same).
if (e.getType() != EdgeType.EXCEPTION && (inDegree(outB) == 1 || b.isEmpty()) && mergeBBs(b, outB)) {
mergedBBs.add(outB);
}
}
}
}
}
public void optimize(List returnBBs) {
// Propagate returns backwards where possible.
// If:
// - there is an edge from BB: x -> r, and
// - r has a single instr, the return, and
// - last instr of x is a copy, and
// - the copy feeds the return
// then:
// - replace the copy with a return that returns the copied value
// - remove the edge from x -> r
// - add an edge from x -> exit-bb
//
// If a jump intervenes in 'x', skip over it and if merge succeeds,
// delete the jump.
List> toRemove = new ArrayList<>();
for (BasicBlock retBB: returnBBs) {
List rbInstrs = retBB.getInstrs();
Instr first = rbInstrs.get(0);
if (first instanceof ReturnInstr) {
Operand rv = ((ReturnInstr)first).getReturnValue();
if (rv instanceof Variable) {
for (Edge e : getIncomingEdges(retBB)) {
BasicBlock srcBB = e.getSource().getData();
List srcInstrs = srcBB.getInstrs();
int n = srcInstrs.size();
// Skip over empty bbs
if (n == 0) continue;
Instr jump = null;
Instr last = srcInstrs.get(n-1);
// Skip over a jump
if (last instanceof JumpInstr && n > 2) {
jump = last;
last = srcInstrs.get(n-2);
}
// Merge
if (last instanceof CopyInstr && ((CopyInstr)last).getResult().equals(rv)) {
srcInstrs.set(n-1, new ReturnInstr(((CopyInstr)last).getSource()));
toRemove.add(e);
addEdge(srcBB, exitBB, EdgeType.EXIT);
// System.out.println("Merged " + last + " with " + ri + " in " + scope);
if (jump != null) {
srcInstrs.remove(jump);
// System.out.println("Deleting " + jump);
}
}
}
}
}
}
for (Edge edge: toRemove) {
graph.removeEdge(edge);
}
deleteOrphanedBlocks(graph);
collapseStraightLineBBs();
}
public String toStringGraph() {
return graph.toString();
}
public String toStringInstrs() {
StringBuilder buf = new StringBuilder();
for (BasicBlock b : getSortedBasicBlocks()) {
buf.append(b.toStringInstrs());
}
buf.append("\n\n------ Rescue block map ------\n");
List e = new ArrayList<>(rescuerMap.keySet());
Collections.sort(e);
for (BasicBlock bb : e) {
buf.append("BB ").append(bb.getID()).append(" --> BB ").append(rescuerMap.get(bb).getID()).append("\n");
}
/*
Collection closures = scope.getClosures();
if (!closures.isEmpty()) {
buf.append("\n\n------ Closures encountered in this scope ------\n");
for (IRClosure c : closures) {
buf.append(c.toStringBody());
}
buf.append("------------------------------------------------\n");
}
*/
return buf.toString();
}
public void removeEdge(BasicBlock a, BasicBlock b) {
graph.removeEdge(a, b);
}
private LinkedList buildPostOrderList() {
BasicBlock root = getEntryBB();
LinkedList list = new LinkedList<>();
Stack stack = new Stack<>();
boolean[] visited = new boolean[1 + getMaxNodeID()];
stack.push(root);
visited[root.getID()] = true;
// Non-recursive post-order traversal (the added flag is required to handle cycles and common ancestors)
while (!stack.empty()) {
// Check if all children of the top of the stack have been added
BasicBlock b = stack.peek();
boolean allChildrenVisited = true;
for (BasicBlock dst: getOutgoingDestinations(b)) {
int dstID = dst.getID();
if (!visited[dstID]) {
allChildrenVisited = false;
// This ensures that no matter what order we visit children, we process exit nodes before anything.
// else. Alternatively, getOutgoingDestinations(..) would have to return nodes in a specific order
// that is dependent on basic block numbering -- which would be fragile.
if (graph.findVertexFor(dst).outDegree() == 0) {
list.add(dst);
} else {
stack.push(dst);
}
visited[dstID] = true;
}
}
// If all children have been added previously, we are ready with 'b' in this round!
if (allChildrenVisited) {
stack.pop();
list.add(b);
}
}
// Sanity check!
for (BasicBlock b : getBasicBlocks()) {
if (!visited[b.getID()]) {
printError("BB " + b.getID() + " missing from po list!");
break;
}
}
return list;
}
/**
* Clone this CFG and return a new one.
*
* @param info context object to perform the clone
* @param clonedScope already cloned IRScope which this new CFG will belong to
* @return a newly cloned CFG
*/
public CFG clone(CloneInfo info, IRScope clonedScope) {
CFG newCFG = new CFG(clonedScope);
Map cloneBBMap = new HashMap<>();
// Part 1: Clone all BBs and stuff in map so graph building in 2 will have all BBs available.
for (BasicBlock bb: getBasicBlocks()) { // clone bbs
BasicBlock newBB = bb.clone(info, newCFG);
newCFG.addBasicBlock(newBB);
cloneBBMap.put(bb, newBB);
}
// Part 2: Clone graph (build new edges from new BBs made in previous phase)
for (BasicBlock bb: getBasicBlocks()) {
BasicBlock newSource = cloneBBMap.get(bb);
for (Edge edge : getOutgoingEdges(bb)) {
BasicBlock newDestination = cloneBBMap.get(edge.getDestination().getData());
newCFG.addEdge(newSource, newDestination, edge.getType());
}
}
// Part 3: clone all non-derivable fields
for (BasicBlock bb: rescuerMap.keySet()) { // clone rescuer map
newCFG.setRescuerBB(cloneBBMap.get(bb), cloneBBMap.get(rescuerMap.get(bb)));
}
newCFG.entryBB = cloneBBMap.get(entryBB); // clone entry BB
newCFG.exitBB = cloneBBMap.get(exitBB); // clone exit BB
newCFG.globalEnsureBB = cloneBBMap.get(globalEnsureBB); // clone GEB
return newCFG;
}
private void printError(String message) {
LOG.error(message + "\nGraph:\n" + this + "\nInstructions:\n" + toStringInstrs());
}
}
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