Strengthen graphs with constants propagated through static analysis

Author: Christian Wimmer

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/flow/context/bytecode/ContextSensitiveSingleTypeState.java

@@ -36,6 +36,8 @@
 import com.oracle.graal.pointsto.typestate.SingleTypeState;
 import com.oracle.graal.pointsto.typestate.TypeState;
 
+import jdk.vm.ci.meta.JavaConstant;
+
 public class ContextSensitiveSingleTypeState extends SingleTypeState {
     /** The objects of this type state. */
     protected final AnalysisObject[] objects;
@@ -145,8 +147,16 @@ public boolean isAllocation() {
     }
 
     @Override
-    public boolean isConstant() {
-        return objects[0].isConstantContextSensitiveObject();
+    public JavaConstant asConstant() {
+        JavaConstant result = null;
+        for (AnalysisObject object : objects) {
+            JavaConstant objectConstant = object.asConstant();
+            if (objectConstant == null || (result != null && !result.equals(objectConstant))) {
+                return null;
+            }
+            result = objectConstant;
+        }
+        return result;
     }
 
     @Override

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/flow/context/object/AnalysisObject.java

@@ -179,12 +179,8 @@ public final boolean isAllocationContextSensitiveObject() {
         return this.kind == AnalysisObjectKind.AllocationContextSensitive;
     }
 
-    public final boolean isConstantContextSensitiveObject() {
-        return this.kind == AnalysisObjectKind.ConstantContextSensitive;
-    }
-
-    public final boolean isConstantObject() {
-        return this.kind == AnalysisObjectKind.ConstantObject;
+    public JavaConstant asConstant() {
+        return null;
     }
 
     public ArrayElementsTypeStore getArrayElementsTypeStore() {

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/flow/context/object/ConstantContextSensitiveObject.java

@@ -79,7 +79,8 @@ public ConstantContextSensitiveObject(PointsToAnalysis bb, AnalysisType type, Ja
         bb.profileConstantObject(type);
     }
 
-    public JavaConstant getConstant() {
+    @Override
+    public JavaConstant asConstant() {
         return constant;
     }
 
@@ -128,7 +129,7 @@ public boolean isEmptyObjectArrayConstant(PointsToAnalysis bb) {
             return false;
         }
 
-        return AnalysisObject.isEmptyObjectArrayConstant(bb, getConstant());
+        return AnalysisObject.isEmptyObjectArrayConstant(bb, asConstant());
     }
 
     @Override

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/results/StrengthenGraphs.java

@@ -83,6 +83,7 @@
 import com.oracle.graal.pointsto.flow.MethodFlowsGraph;
 import com.oracle.graal.pointsto.flow.MethodTypeFlow;
 import com.oracle.graal.pointsto.flow.TypeFlow;
+import com.oracle.graal.pointsto.heap.ImageHeapConstant;
 import com.oracle.graal.pointsto.infrastructure.Universe;
 import com.oracle.graal.pointsto.meta.AnalysisField;
 import com.oracle.graal.pointsto.meta.AnalysisMethod;
@@ -91,6 +92,7 @@
 import com.oracle.graal.pointsto.typestate.TypeState;
 import com.oracle.svm.util.ImageBuildStatistics;
 
+import jdk.vm.ci.meta.JavaConstant;
 import jdk.vm.ci.meta.JavaKind;
 import jdk.vm.ci.meta.JavaMethodProfile;
 import jdk.vm.ci.meta.JavaTypeProfile;
@@ -105,7 +107,7 @@
  * processing the graph.
  * 
  * From the single-method view that the compiler has when later compiling the graph, static analysis
- * results appear "out of thin air": At some some random point in the graph, we suddenly have a more
+ * results appear "out of thin air": At some random point in the graph, we suddenly have a more
  * precise type (= stamp) for a value. Since many nodes are floating, and even currently fixed nodes
  * might float later, we need to be careful that all information coming from the type flow graph
  * remains properly anchored to the point where the static analysis actually proved the information.
@@ -246,20 +248,26 @@ public void simplify(Node n, SimplifierTool tool) {
             if (n instanceof ParameterNode) {
                 ParameterNode node = (ParameterNode) n;
                 StartNode anchorPoint = graph.start();
-                Stamp newStamp = strengthenStampFromTypeFlow(node, parameterFlows[node.index()], anchorPoint, tool);
-                updateStampUsingPiNode(node, newStamp, anchorPoint, tool);
+                Object newStampOrConstant = strengthenStampFromTypeFlow(node, parameterFlows[node.index()], anchorPoint, tool);
+                updateStampUsingPiNode(node, newStampOrConstant, anchorPoint, tool);
 
             } else if (n instanceof LoadFieldNode || n instanceof LoadIndexedNode) {
                 FixedWithNextNode node = (FixedWithNextNode) n;
-                Stamp newStamp = strengthenStampFromTypeFlow(node, getNodeFlow(node), node, tool);
+                Object newStampOrConstant = strengthenStampFromTypeFlow(node, getNodeFlow(node), node, tool);
                 /*
                  * Even though the memory load will be a floating node later, we can update the
                  * stamp directly because the type information maintained by the static analysis
                  * about memory is not flow-sensitive and not context-sensitive. If we ever revive a
                  * context-sensitive analysis, we will need to change this. But for now, we are
                  * fine.
                  */
-                updateStampInPlace(node, newStamp, tool);
+                if (newStampOrConstant instanceof JavaConstant) {
+                    ConstantNode replacement = ConstantNode.forConstant((JavaConstant) newStampOrConstant, bb.getMetaAccess(), graph);
+                    graph.replaceFixedWithFloating(node, replacement);
+                    tool.addToWorkList(replacement);
+                } else {
+                    updateStampInPlace(node, (Stamp) newStampOrConstant, tool);
+                }
 
             } else if (n instanceof Invoke) {
                 Invoke invoke = (Invoke) n;
@@ -385,13 +393,13 @@ private void handleInvoke(Invoke invoke, SimplifierTool tool) {
             NodeInputList<ValueNode> arguments = callTarget.arguments();
             for (int i = 0; i < arguments.size(); i++) {
                 ValueNode argument = arguments.get(i);
-                Stamp newStamp = strengthenStampFromTypeFlow(argument, invokeFlow.getActualParameters()[i], beforeInvoke, tool);
+                Object newStampOrConstant = strengthenStampFromTypeFlow(argument, invokeFlow.getActualParameters()[i], beforeInvoke, tool);
                 if (node.isDeleted()) {
                     /* Parameter stamp was empty, so invoke is unreachable. */
                     return;
-                } else if (newStamp != null) {
-                    PiNode pi = insertPi(argument, newStamp, beforeInvoke);
-                    if (pi != null) {
+                } else if (newStampOrConstant != null) {
+                    ValueNode pi = insertPi(argument, newStampOrConstant, beforeInvoke);
+                    if (pi != null && pi != argument) {
                         callTarget.replaceAllInputs(argument, pi);
                     }
                 }
@@ -423,8 +431,8 @@ private void handleInvoke(Invoke invoke, SimplifierTool tool) {
             optimizeReturnedParameter(callees, arguments, node, tool);
 
             FixedWithNextNode anchorPointAfterInvoke = (FixedWithNextNode) (invoke instanceof InvokeWithExceptionNode ? invoke.next() : invoke);
-            Stamp newStamp = strengthenStampFromTypeFlow(node, invokeFlow.getResult(), anchorPointAfterInvoke, tool);
-            updateStampUsingPiNode(node, newStamp, anchorPointAfterInvoke, tool);
+            Object newStampOrConstant = strengthenStampFromTypeFlow(node, invokeFlow.getResult(), anchorPointAfterInvoke, tool);
+            updateStampUsingPiNode(node, newStampOrConstant, anchorPointAfterInvoke, tool);
         }
 
         /**
@@ -519,19 +527,22 @@ private void updateStampInPlace(ValueNode node, Stamp newStamp, SimplifierTool t
             }
         }
 
-        private void updateStampUsingPiNode(ValueNode node, Stamp newStamp, FixedWithNextNode anchorPoint, SimplifierTool tool) {
-            if (newStamp != null && node.hasUsages() && !createdPiNodes.isMarked(node)) {
-                PiNode pi = insertPi(node, newStamp, anchorPoint);
+        private void updateStampUsingPiNode(ValueNode node, Object newStampOrConstant, FixedWithNextNode anchorPoint, SimplifierTool tool) {
+            if (newStampOrConstant != null && node.hasUsages() && !createdPiNodes.isMarked(node)) {
+                ValueNode pi = insertPi(node, newStampOrConstant, anchorPoint);
                 if (pi != null) {
                     /*
                      * The Canonicalizer that drives all of our node processing is iterative. We
                      * only want to insert the PiNode the first time we handle a node.
                      */
                     createdPiNodes.mark(node);
 
-                    FrameState anchorState = node instanceof StateSplit ? ((StateSplit) node).stateAfter() : graph.start().stateAfter();
-                    node.replaceAtUsages(pi, usage -> usage != pi && usage != anchorState);
-
+                    if (pi.isConstant()) {
+                        node.replaceAtUsages(pi);
+                    } else {
+                        FrameState anchorState = node instanceof StateSplit ? ((StateSplit) node).stateAfter() : graph.start().stateAfter();
+                        node.replaceAtUsages(pi, usage -> usage != pi && usage != anchorState);
+                    }
                     tool.addToWorkList(pi.usages());
                 }
             }
@@ -540,7 +551,17 @@ private void updateStampUsingPiNode(ValueNode node, Stamp newStamp, FixedWithNex
         /*
          * See comment on {@link StrengthenGraphs} on why anchoring is necessary.
          */
-        private PiNode insertPi(ValueNode input, Stamp piStamp, FixedWithNextNode anchorPoint) {
+        private ValueNode insertPi(ValueNode input, Object newStampOrConstant, FixedWithNextNode anchorPoint) {
+            if (newStampOrConstant instanceof JavaConstant) {
+                JavaConstant constant = (JavaConstant) newStampOrConstant;
+                if (input.isConstant()) {
+                    assert input.asConstant().equals(constant);
+                    return null;
+                }
+                return ConstantNode.forConstant(constant, bb.getMetaAccess(), graph);
+            }
+
+            Stamp piStamp = (Stamp) newStampOrConstant;
             Stamp oldStamp = input.stamp(NodeView.DEFAULT);
             Stamp computedStamp = oldStamp.improveWith(piStamp);
             if (oldStamp.equals(computedStamp)) {
@@ -553,7 +574,7 @@ private PiNode insertPi(ValueNode input, Stamp piStamp, FixedWithNextNode anchor
             return graph.unique(new PiNode(input, piStamp, anchor));
         }
 
-        private Stamp strengthenStampFromTypeFlow(ValueNode node, TypeFlow<?> nodeFlow, FixedWithNextNode anchorPoint, SimplifierTool tool) {
+        private Object strengthenStampFromTypeFlow(ValueNode node, TypeFlow<?> nodeFlow, FixedWithNextNode anchorPoint, SimplifierTool tool) {
             PointsToAnalysis pta = getAnalysis();
             if (node.getStackKind() != JavaKind.Object) {
                 return null;
@@ -571,6 +592,23 @@ private Stamp strengthenStampFromTypeFlow(ValueNode node, TypeFlow<?> nodeFlow,
             }
 
             TypeState nodeTypeState = methodFlow.foldTypeFlow(pta, nodeFlow);
+
+            if (!nodeTypeState.canBeNull()) {
+                JavaConstant constantValue = nodeTypeState.asConstant();
+                if (constantValue instanceof ImageHeapConstant) {
+                    /*
+                     * GR-42996: until the AOT compilation can properly constant fold also
+                     * ImageHeapConstant, we unwrap the ImageHeapConstant to the hosted object. This
+                     * also means we do not constant fold yet when the constant does not wrap a
+                     * hosted object.
+                     */
+                    constantValue = ((ImageHeapConstant) constantValue).getHostedObject();
+                }
+                if (constantValue != null) {
+                    return constantValue;
+                }
+            }
+
             node.inferStamp();
             ObjectStamp oldStamp = (ObjectStamp) node.stamp(NodeView.DEFAULT);
             AnalysisType oldType = (AnalysisType) oldStamp.type();

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/typestate/ConstantTypeState.java

@@ -100,8 +100,8 @@ public void noteMerge(PointsToAnalysis bb) {
     }
 
     @Override
-    public boolean isConstant() {
-        return true;
+    public JavaConstant asConstant() {
+        return constant;
     }
 
     @Override

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/typestate/PointsToStats.java

@@ -632,7 +632,7 @@ public static String asString(TypeState s) {
             return "<Null>";
         }
 
-        String sKind = s.isAllocation() ? "Alloc" : s.isConstant() ? "Const" : s instanceof SingleTypeState ? "Single" : s instanceof MultiTypeState ? "Multi" : "";
+        String sKind = s.isAllocation() ? "Alloc" : s.asConstant() != null ? "Const" : s instanceof SingleTypeState ? "Single" : s instanceof MultiTypeState ? "Multi" : "";
         String sSizeOrType = s instanceof MultiTypeState ? s.typesCount() + "" : s.exactType().toJavaName(false);
         int objectsNumber = s.objectsCount();
         String canBeNull = s.canBeNull() ? "null" : "!null";

substratevm/src/com.oracle.graal.pointsto/src/com/oracle/graal/pointsto/typestate/TypeState.java

@@ -115,8 +115,16 @@ public boolean isAllocation() {
         return false;
     }
 
-    public boolean isConstant() {
-        return false;
+    /**
+     * Returns a non-null value when this type state represents a single constant value, or null if
+     * this type state is not a single constant.
+     *
+     * Note that the {@link #canBeNull()} flag still applies when a constant is returned. A type
+     * state that is a "constant or null" both returns a non-null result for {@link #asConstant()}}
+     * and true for {@link #canBeNull()}.
+     */
+    public JavaConstant asConstant() {
+        return null;
     }
 
     public boolean isEmpty() {