Merge pull request #3198 from gacholio/hash

Add option to limit identity hash code to positive values
eclipse-openj9 · Oct 10, 2018 · 1870fe5 · 1870fe5
2 parents f3607dd + 44faec9
commit 1870fe5
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Showing 5 changed files with 19 additions and 2 deletions.
diff --git a/debugtools/DDR_VM/src/com/ibm/j9ddr/vm29/j9/ObjectHash.java b/debugtools/DDR_VM/src/com/ibm/j9ddr/vm29/j9/ObjectHash.java
@@ -23,9 +23,11 @@
 
 import com.ibm.j9ddr.CorruptDataException;
 import com.ibm.j9ddr.vm29.pointer.generated.J9BuildFlags;
+import com.ibm.j9ddr.vm29.structure.J9Consts;
 import com.ibm.j9ddr.vm29.pointer.generated.J9IdentityHashDataPointer;
 import com.ibm.j9ddr.vm29.pointer.generated.J9JavaVMPointer;
 import com.ibm.j9ddr.vm29.pointer.generated.J9ObjectPointer;
+import com.ibm.j9ddr.vm29.pointer.helper.J9JavaVMHelper;
 import com.ibm.j9ddr.vm29.structure.J9IdentityHashData;
 import com.ibm.j9ddr.vm29.types.I32;
 import com.ibm.j9ddr.vm29.types.U32;
@@ -134,6 +136,10 @@ private static I32 inlineConvertValueToHash(J9JavaVMPointer vm, UDATA objectPoin
 		hashValue = hashValue.mult(MUL2);
 		hashValue = hashValue.bitXor(hashValue.rightShift(16));
 
+		/* If forcing positive hash codes, AND out the sign bit */
+		if (J9JavaVMHelper.extendedRuntimeFlagIsSet(vm, J9Consts.J9_EXTENDED_RUNTIME_POSITIVE_HASHCODE)) {
+			hashValue = hashValue.bitAnd(0x7FFFFFFF);
+		}
 
 		return new I32(hashValue);
 	}

diff --git a/runtime/oti/ObjectHash.hpp b/runtime/oti/ObjectHash.hpp
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 1991, 2017 IBM Corp. and others
+ * Copyright (c) 1991, 2018 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -174,6 +174,11 @@ class VM_ObjectHash
 		hashValue *= MUL2;
 		hashValue ^= hashValue >> 16;
 
+		/* If forcing positive hash codes, AND out the sign bit */
+		if (J9_ARE_ANY_BITS_SET(vm->extendedRuntimeFlags, J9_EXTENDED_RUNTIME_POSITIVE_HASHCODE)) {
+			hashValue &= (U_32)0x7FFFFFFF;
+		}
+
 		return (I_32) hashValue;
 	}
 

diff --git a/runtime/oti/j9consts.h b/runtime/oti/j9consts.h
@@ -360,7 +360,7 @@ extern "C" {
 #define J9_EXTENDED_RUNTIME_METHOD_TRACE_ENABLED 0x100000
 #define J9_EXTENDED_RUNTIME_FOUND_JAVA_ASSERT_OPTION 0x200000
 #define J9_EXTENDED_RUNTIME_ALLOW_NON_VIRTUAL_CALLS 0x400000
-#define J9_EXTENDED_RUNTIME_UNUSED_0x800000 0x800000
+#define J9_EXTENDED_RUNTIME_POSITIVE_HASHCODE 0x800000
 #define J9_EXTENDED_RUNTIME_CLASS_OBJECT_ASSIGNED 0x1000000
 #define J9_EXTENDED_RUNTIME_FORCE_CLASSFILE_AS_INTERMEDIATE_DATA 0x2000000
 #define J9_EXTENDED_RUNTIME_RECREATE_CLASSFILE_ONLOAD 0x4000000

diff --git a/runtime/oti/jvminit.h b/runtime/oti/jvminit.h
@@ -366,6 +366,8 @@ enum INIT_STAGE {
 #define VMOPT_XXDISABLEJITWATCH "-XX:-JITInlineWatches"
 #define VMOPT_XXENABLEALWAYSSPLITBYTECODES "-XX:+AlwaysSplitBytecodes"
 #define VMOPT_XXDISABLEALWAYSSPLITBYTECODES "-XX:-AlwaysSplitBytecodes"
+#define VMOPT_XXENABLEPOSITIVEHASHCODE "-XX:+PositiveIdentityHash"
+#define VMOPT_XXDISABLEPOSITIVEHASHCODE "-XX:-PositiveIdentityHash"
 
 #define VMOPT_XX_NOSUBALLOC32BITMEM "-XXnosuballoc32bitmem"
 

diff --git a/runtime/vm/jvminit.c b/runtime/vm/jvminit.c
@@ -2956,6 +2956,10 @@ processVMArgsFromFirstToLast(J9JavaVM * vm)
 			vm->runtimeFlags |= J9_RUNTIME_ALWAYS_SPLIT_BYTECODES;
 		} else if (0 == strcmp(testString, VMOPT_XXDISABLEALWAYSSPLITBYTECODES)) {
 			vm->runtimeFlags &= ~(UDATA)J9_RUNTIME_ALWAYS_SPLIT_BYTECODES;
+		} else if (0 == strcmp(testString, VMOPT_XXENABLEPOSITIVEHASHCODE)) {
+			vm->extendedRuntimeFlags |= J9_EXTENDED_RUNTIME_POSITIVE_HASHCODE;
+		} else if (0 == strcmp(testString, VMOPT_XXDISABLEPOSITIVEHASHCODE)) {
+			vm->extendedRuntimeFlags &= ~(UDATA)J9_EXTENDED_RUNTIME_POSITIVE_HASHCODE;
 		}
 		/* -Xbootclasspath and -Xbootclasspath/p are not supported from Java 9 onwards */
 		if (J2SE_VERSION(vm) >= J2SE_19) {