Apply trapping nullcheck to uncompressed object for compressed pointer.

Trapping nullcheck might generate two uncompress instructions for
the same compressed oop on AArch64. One is inserted by the backend
when it emits nullcheck. If the object is a compressed pointer, it
is uncompressed before the nullcheck is emitted. And another one is
generated by the uncompression node used for memory access. These
two instructions are duplicated with each other.

The generated codes on AArch64 like:

  ldr   w0, [x0,oracle#112]
  lsl   x2, x0, oracle#3      ; uncompressing (first)
  ldr   xzr, [x2]       ; implicit exception: deoptimizes
  ......                ; fixed operations
  lsl   x0, x0, oracle#3      ; uncompressing (second)
  str   w1, [x0,oracle#12]

A simple way to avoid this is to creat a new uncompression node for
the nullcheck, and let the value numbering remove the duplicated one
if possible. Since the address lowering of AMD64 can handle the
uncompressing computation for address, the created uncompression node
is wrapped to an address node and the nullcheck is finally applied on
the address.

With the modification, the codes above could be optimized to:

  ldr   w0, [x0,oracle#112]
  lsl   x0, x0, oracle#3      ; uncompressing
  ldr   xzr, [x0]       ; implicit exception: deoptimizes
  ......                ; fixed operations
  str   w1, [x0,oracle#12]

Change-Id: Iabfe47bbf984ed11c42555f84bdd0ccf2a5bdddb

Author: Xiaohong Gong

compiler/src/org.graalvm.compiler.core.common/src/org/graalvm/compiler/core/common/type/AbstractPointerStamp.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -161,4 +161,8 @@ public JavaConstant nullConstant() {
     public JavaKind getStackKind() {
         return JavaKind.Illegal;
     }
+
+    public boolean isCompressed() {
+        return false;
+    }
 }

compiler/src/org.graalvm.compiler.core/src/org/graalvm/compiler/core/phases/LowTier.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -70,10 +70,10 @@ public LowTier(OptionValues options) {
         appendPhase(new FixReadsPhase(true,
                         new SchedulePhase(GraalOptions.StressTestEarlyReads.getValue(options) ? SchedulingStrategy.EARLIEST : SchedulingStrategy.LATEST_OUT_OF_LOOPS_IMPLICIT_NULL_CHECKS)));
 
-        appendPhase(canonicalizerWithoutGVN);
-
         appendPhase(new UseTrappingNullChecksPhase());
 
+        appendPhase(canonicalizerWithoutGVN);
+
         appendPhase(new DeadCodeEliminationPhase(Required));
 
         appendPhase(new PropagateDeoptimizeProbabilityPhase());

compiler/src/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/meta/AddressLoweringHotSpotSuitesProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2020, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2017, Red Hat Inc. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -56,11 +56,13 @@ public Suites createSuites(OptionValues options) {
         Suites suites = super.createSuites(options);
 
         ListIterator<BasePhase<? super LowTierContext>> findPhase = suites.getLowTier().findPhase(UseTrappingNullChecksPhase.class);
-        if (findPhase == null) {
+        if (findPhase != null) {
+            findPhase.add(addressLowering);
+        } else {
             findPhase = suites.getLowTier().findPhase(SchedulePhase.class);
+            findPhase.previous();
+            findPhase.add(addressLowering);
         }
-        findPhase.previous();
-        findPhase.add(addressLowering);
 
         return suites;
     }

compiler/src/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/nodes/type/KlassPointerStamp.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -146,6 +146,7 @@ public LIRKind getLIRKind(LIRKindTool tool) {
         }
     }
 
+    @Override
     public boolean isCompressed() {
         return encoding != null;
     }

compiler/src/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/extended/NullCheckNode.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -28,11 +28,18 @@
 import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_2;
 import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_2;
 
+import org.graalvm.compiler.core.common.type.AbstractPointerStamp;
+import org.graalvm.compiler.core.common.type.Stamp;
 import org.graalvm.compiler.core.common.type.StampFactory;
+import org.graalvm.compiler.graph.Graph;
+import org.graalvm.compiler.graph.Node;
 import org.graalvm.compiler.graph.NodeClass;
 import org.graalvm.compiler.nodeinfo.NodeInfo;
+import org.graalvm.compiler.nodes.CompressionNode;
 import org.graalvm.compiler.nodes.DeoptimizingFixedWithNextNode;
+import org.graalvm.compiler.nodes.NodeView;
 import org.graalvm.compiler.nodes.ValueNode;
+import org.graalvm.compiler.nodes.memory.address.OffsetAddressNode;
 import org.graalvm.compiler.nodes.spi.LIRLowerable;
 import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;
 
@@ -47,6 +54,46 @@ public NullCheckNode(ValueNode object) {
         this.object = object;
     }
 
+    public static NullCheckNode create(ValueNode object) {
+        // Try to uncompress a compressed object before applying null check.
+        NullCheckNode nullCheck = tryUseUncompressedNullCheck(object);
+        if (nullCheck != null) {
+            return nullCheck;
+        }
+        return new NullCheckNode(object);
+    }
+
+    private static NullCheckNode tryUseUncompressedNullCheck(ValueNode value) {
+        Stamp stamp = value.stamp(NodeView.DEFAULT);
+        // Do nothing if the value is not a compressed pointer.
+        if (!(stamp instanceof AbstractPointerStamp) || !((AbstractPointerStamp) stamp).isCompressed()) {
+            return null;
+        }
+
+        // Copy an uncompressing node from one of the existed uncompressing usages.
+        CompressionNode uncompressed = null;
+        for (Node usage : value.usages()) {
+            if (usage instanceof CompressionNode) {
+                if (((CompressionNode) usage).getOp() == CompressionNode.CompressionOp.Uncompress) {
+                    uncompressed = (CompressionNode) usage;
+                    break;
+                }
+            }
+        }
+        // Do nothing if there is not an uncompressing usage. The uncompressing operation will be
+        // handled at back-end.
+        if (uncompressed == null) {
+            return null;
+        }
+
+        assert uncompressed.getValue().equals(value);
+        Graph graph = value.graph();
+        CompressionNode compression = (CompressionNode) uncompressed.copyWithInputs(false);
+        compression = graph.addOrUniqueWithInputs(compression);
+        OffsetAddressNode address = graph.addOrUniqueWithInputs(OffsetAddressNode.create(compression));
+        return new NullCheckNode(address);
+    }
+
     public ValueNode getObject() {
         return object;
     }

compiler/src/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/memory/address/OffsetAddressNode.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -58,13 +58,18 @@ public OffsetAddressNode(ValueNode base, ValueNode offset) {
         super(TYPE);
         this.base = base;
         this.offset = offset;
-
         assert base != null && (base.stamp(NodeView.DEFAULT) instanceof AbstractPointerStamp || IntegerStamp.getBits(base.stamp(NodeView.DEFAULT)) == 64) &&
                         offset != null && IntegerStamp.getBits(offset.stamp(NodeView.DEFAULT)) == 64 : "both values must have 64 bits";
     }
 
     public static OffsetAddressNode create(ValueNode base) {
-        return new OffsetAddressNode(base, ConstantNode.forIntegerBits(PrimitiveStamp.getBits(base.stamp(NodeView.DEFAULT)), 0));
+        ValueNode offset;
+        if (base.stamp(NodeView.DEFAULT) instanceof AbstractPointerStamp) {
+            offset = ConstantNode.forIntegerBits(64, 0);
+        } else {
+            offset = ConstantNode.forIntegerBits(PrimitiveStamp.getBits(base.stamp(NodeView.DEFAULT)), 0);
+        }
+        return new OffsetAddressNode(base, offset);
     }
 
     @Override

compiler/src/org.graalvm.compiler.nodes/src/org/graalvm/compiler/nodes/type/NarrowOopStamp.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -115,4 +115,9 @@ public boolean equals(Object obj) {
 
     @Override
     public abstract boolean isCompatible(Constant other);
+
+    @Override
+    public boolean isCompressed() {
+        return true;
+    }
 }

compiler/src/org.graalvm.compiler.phases.common/src/org/graalvm/compiler/phases/common/UseTrappingNullChecksPhase.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -265,7 +265,7 @@ private static void replaceWithTrappingNullCheck(AbstractDeoptimizeNode deopt, I
 
         if (trappingNullCheck == null) {
             // Need to add a null check node.
-            trappingNullCheck = deopt.graph().add(new NullCheckNode(value));
+            trappingNullCheck = deopt.graph().add(NullCheckNode.create(value));
             deopt.graph().replaceSplit(ifNode, trappingNullCheck, nonTrappingContinuation);
             deopt.getDebug().log("Inserted NullCheckNode %s", trappingNullCheck);
         }

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/NativeImageGenerator.java

@@ -89,10 +89,10 @@
 import org.graalvm.compiler.phases.common.CanonicalizerPhase;
 import org.graalvm.compiler.phases.common.DeoptimizationGroupingPhase;
 import org.graalvm.compiler.phases.common.ExpandLogicPhase;
-import org.graalvm.compiler.phases.common.FixReadsPhase;
 import org.graalvm.compiler.phases.common.FrameStateAssignmentPhase;
 import org.graalvm.compiler.phases.common.LoopSafepointInsertionPhase;
 import org.graalvm.compiler.phases.common.LoweringPhase;
+import org.graalvm.compiler.phases.common.UseTrappingNullChecksPhase;
 import org.graalvm.compiler.phases.common.inlining.InliningPhase;
 import org.graalvm.compiler.phases.tiers.HighTierContext;
 import org.graalvm.compiler.phases.tiers.LowTierContext;
@@ -1300,7 +1300,7 @@ private static Suites modifySuites(SubstrateBackend backend, Suites suites, Feat
         if (firstTier) {
             lowTier.findPhase(ExpandLogicPhase.class).add(addressLoweringPhase);
         } else {
-            lowTier.findPhase(FixReadsPhase.class).add(addressLoweringPhase);
+            lowTier.findPhase(UseTrappingNullChecksPhase.class).add(addressLoweringPhase);
         }
 
         if (SubstrateOptions.MultiThreaded.getValue()) {