Add support for delegate GDV and method-based vtable GDV (dotnet#68703)

Add support for instrumenting delegate calls and vtable calls into method handle histograms. Use these histograms to do GDV for delegate calls and also support method-based GDV for vtable calls.

For instrumentation we now support class probes at interface call sites, method probes at delegate call sites and both class probes and method probes at vtable call sites. For vtable calls, when turned on, instrumentation produces both histograms as PGO data so that the JIT can later make the choice about what is the best form of guard to use at that site.

For guarding, there are some things to take into account. Delegate calls currently (practically) always point to precode, so this PR is just guarding on getFunctionFixedEntryPoint which returns the precode address, and this is generally quite cheap (same cost as class-based GDV). That's the case for delegates pointing to instance methods anyway, this PR does not support static methods yet -- those will be more expensive.

For vtable calls the runtime will backpatch the slots when tiering, so the JIT guards the address retrieved from the vtable against an indirection of the slot, which is slightly more expensive than a class-based guard.

Currently the instrumentation is enabled conditionally with COMPlus_JitDelegateProfiling=1 (for delegates) and COMPlus_JitVTableProfiling=1 (for vtable calls). Currently delegate profiling is turned on by default while vtable profiling is off by default.

eng/pipelines/common/templates/runtimes/run-test-job.yml

@@ -227,13 +227,13 @@ jobs:
         timeoutInMinutes: 300
       ${{ else }}:
         timeoutInMinutes: 200
-    ${{ if in(parameters.testGroup, 'outerloop', 'jit-experimental', 'pgo', 'jit-cfg') }}:
+    ${{ if in(parameters.testGroup, 'outerloop', 'jit-experimental', 'jit-cfg') }}:
       timeoutInMinutes: 270
     ${{ if in(parameters.testGroup, 'gc-longrunning', 'gc-simulator') }}:
       timeoutInMinutes: 480
     ${{ if in(parameters.testGroup, 'jitstress', 'jitstress-isas-arm', 'jitstressregs-x86', 'jitstressregs', 'jitstress2-jitstressregs', 'gcstress0x3-gcstress0xc', 'ilasm') }}:
       timeoutInMinutes: 390
-    ${{ if in(parameters.testGroup, 'gcstress-extra', 'r2r-extra', 'clrinterpreter') }}:
+    ${{ if in(parameters.testGroup, 'gcstress-extra', 'r2r-extra', 'clrinterpreter', 'pgo') }}:
       timeoutInMinutes: 510
     ${{ if eq(parameters.testGroup, 'jitstress-isas-x86') }}:
       timeoutInMinutes: 960
@@ -397,7 +397,7 @@ jobs:
           ${{ if eq(parameters.runtimeFlavor, 'mono') }}:
             # tiered compilation isn't done on mono yet
             scenarios:
-            - normal 
+            - normal
           ${{ elseif eq(variables['Build.Reason'], 'PullRequest') }}:
             scenarios:
             - no_tiered_compilation
@@ -545,7 +545,9 @@ jobs:
           - defaultpgo
           - dynamicpgo
           - fullpgo
+          - fullpgo_methodprofiling
           - fullpgo_random_gdv
+          - fullpgo_random_gdv_methodprofiling_only
           - fullpgo_random_edge
           - fullpgo_random_gdv_edge
         ${{ if in(parameters.testGroup, 'gc-longrunning') }}:
@@ -568,7 +570,6 @@ jobs:
           - jitelthookenabled_tiered
         ${{ if in(parameters.testGroup, 'jit-experimental') }}:
           scenarios:
-          - jitosr
           - jitosr_stress
           - jitosr_pgo
           - jitosr_stress_random

eng/pipelines/coreclr/libraries-pgo.yml

@@ -47,7 +47,7 @@ jobs:
     helixQueueGroup: libraries
     helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
     jobParameters:
-      timeoutInMinutes: 150
+      timeoutInMinutes: 600
       testScope: innerloop
       liveRuntimeBuildConfig: checked
       dependsOnTestBuildConfiguration: Release

eng/pipelines/libraries/run-test-job.yml

@@ -173,10 +173,11 @@ jobs:
               - defaultpgo
               - dynamicpgo
               - fullpgo
+              - fullpgo_methodprofiling
               - fullpgo_random_gdv
+              - fullpgo_random_gdv_methodprofiling_only
               - fullpgo_random_edge
               - fullpgo_random_gdv_edge
-              - jitosr
               - jitosr_stress
               - jitosr_stress_random
               - jitosr_pgo

src/coreclr/inc/corinfo.h

@@ -640,9 +640,14 @@ enum CorInfoHelpFunc
     CORINFO_HELP_STACK_PROBE,               // Probes each page of the allocated stack frame
 
     CORINFO_HELP_PATCHPOINT,                // Notify runtime that code has reached a patchpoint
+    CORINFO_HELP_PARTIAL_COMPILATION_PATCHPOINT,  // Notify runtime that code has reached a part of the method that wasn't originally jitted.
+
     CORINFO_HELP_CLASSPROFILE32,            // Update 32-bit class profile for a call site
     CORINFO_HELP_CLASSPROFILE64,            // Update 64-bit class profile for a call site
-    CORINFO_HELP_PARTIAL_COMPILATION_PATCHPOINT,  // Notify runtime that code has reached a part of the method that wasn't originally jitted.
+    CORINFO_HELP_DELEGATEPROFILE32,         // Update 32-bit method profile for a delegate call site
+    CORINFO_HELP_DELEGATEPROFILE64,         // Update 64-bit method profile for a delegate call site
+    CORINFO_HELP_VTABLEPROFILE32,           // Update 32-bit method profile for a vtable call site
+    CORINFO_HELP_VTABLEPROFILE64,           // Update 64-bit method profile for a vtable call site
 
     CORINFO_HELP_VALIDATE_INDIRECT_CALL,    // CFG: Validate function pointer
     CORINFO_HELP_DISPATCH_INDIRECT_CALL,    // CFG: Validate and dispatch to pointer

src/coreclr/inc/corjit.h

@@ -330,34 +330,36 @@ class ICorJitInfo : public ICorDynamicInfo
 
     // Data structure for a single class probe using 32-bit count.
     //
-    // CLASS_FLAG and INTERFACE_FLAG are placed into the Other field in the schema
+    // CLASS_FLAG, INTERFACE_FLAG and DELEGATE_FLAG are placed into the Other field in the schema.
+    // If CLASS_FLAG is set the handle table consists of type handles, and otherwise method handles.
     //
     // Count is the number of times a call was made at that call site.
     //
     // SIZE is the number of entries in the table.
     //
     // SAMPLE_INTERVAL must be >= SIZE. SAMPLE_INTERVAL / SIZE
     // gives the average number of calls between table updates.
-    //
-    struct ClassProfile32
+    // 
+    struct HandleHistogram32
     {
         enum
         {
             SIZE = 8,
             SAMPLE_INTERVAL = 32,
             CLASS_FLAG     = 0x80000000,
             INTERFACE_FLAG = 0x40000000,
-            OFFSET_MASK    = 0x3FFFFFFF
+            DELEGATE_FLAG  = 0x20000000,
+            OFFSET_MASK    = 0x0FFFFFFF
         };
 
         uint32_t Count;
-        CORINFO_CLASS_HANDLE ClassTable[SIZE];
+        void* HandleTable[SIZE];
     };
 
-    struct ClassProfile64
+    struct HandleHistogram64
     {
         uint64_t Count;
-        CORINFO_CLASS_HANDLE ClassTable[ClassProfile32::SIZE];
+        void* HandleTable[HandleHistogram32::SIZE];
     };
 
     enum class PgoInstrumentationKind
@@ -387,7 +389,7 @@ class ICorJitInfo : public ICorDynamicInfo
         Done = None, // All instrumentation schemas must end with a record which is "Done"
         BasicBlockIntCount = (DescriptorMin * 1) | FourByte, // basic block counter using unsigned 4 byte int
         BasicBlockLongCount = (DescriptorMin * 1) | EightByte, // basic block counter using unsigned 8 byte int
-        HandleHistogramIntCount = (DescriptorMin * 2) | FourByte | AlignPointer, // 4 byte counter that is part of a type histogram. Aligned to match ClassProfile32's alignment.
+        HandleHistogramIntCount = (DescriptorMin * 2) | FourByte | AlignPointer, // 4 byte counter that is part of a type histogram. Aligned to match HandleHistogram32's alignment.
         HandleHistogramLongCount = (DescriptorMin * 2) | EightByte, // 8 byte counter that is part of a type histogram
         HandleHistogramTypes = (DescriptorMin * 3) | TypeHandle, // Histogram of type handles
         HandleHistogramMethods = (DescriptorMin * 3) | MethodHandle, // Histogram of method handles
@@ -396,6 +398,7 @@ class ICorJitInfo : public ICorDynamicInfo
         EdgeIntCount = (DescriptorMin * 6) | FourByte, // edge counter using unsigned 4 byte int
         EdgeLongCount = (DescriptorMin * 6) | EightByte, // edge counter using unsigned 8 byte int
         GetLikelyClass = (DescriptorMin * 7) | TypeHandle, // Compressed get likely class data
+        GetLikelyMethod = (DescriptorMin * 7) | MethodHandle, // Compressed get likely method data
     };
 
     struct PgoInstrumentationSchema
@@ -418,7 +421,7 @@ class ICorJitInfo : public ICorDynamicInfo
         Sampling= 6,    // PGO data derived from sampling
     };
 
-#define DEFAULT_UNKNOWN_TYPEHANDLE 1
+#define DEFAULT_UNKNOWN_HANDLE 1
 #define UNKNOWN_HANDLE_MIN 1
 #define UNKNOWN_HANDLE_MAX 33
 

src/coreclr/inc/jiteeversionguid.h

@@ -43,11 +43,11 @@ typedef const GUID *LPCGUID;
 #define GUID_DEFINED
 #endif // !GUID_DEFINED
 
-constexpr GUID JITEEVersionIdentifier = { /* af5b6632-6fbe-4a2e-82d6-24487a138e4a */
-    0xaf5b6632,
-    0x6fbe,
-    0x4a2e,
-    {0x82, 0xd6, 0x24, 0x48, 0x7a, 0x13, 0x8e, 0x4a}
+constexpr GUID JITEEVersionIdentifier = { /* f2faa5fc-a1ec-4244-aebb-5597bfd7153a */
+    0xf2faa5fc,
+    0xa1ec,
+    0x4244,
+    {0xae, 0xbb, 0x55, 0x97, 0xbf, 0xd7, 0x15, 0x3a}
   };
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////////

src/coreclr/inc/jithelpers.h

@@ -328,9 +328,14 @@
 #endif
 
     JITHELPER(CORINFO_HELP_PATCHPOINT, JIT_Patchpoint, CORINFO_HELP_SIG_REG_ONLY)
+    JITHELPER(CORINFO_HELP_PARTIAL_COMPILATION_PATCHPOINT, JIT_PartialCompilationPatchpoint, CORINFO_HELP_SIG_REG_ONLY)
+
     JITHELPER(CORINFO_HELP_CLASSPROFILE32, JIT_ClassProfile32, CORINFO_HELP_SIG_REG_ONLY)
     JITHELPER(CORINFO_HELP_CLASSPROFILE64, JIT_ClassProfile64, CORINFO_HELP_SIG_REG_ONLY)
-    JITHELPER(CORINFO_HELP_PARTIAL_COMPILATION_PATCHPOINT, JIT_PartialCompilationPatchpoint, CORINFO_HELP_SIG_REG_ONLY)
+    JITHELPER(CORINFO_HELP_DELEGATEPROFILE32, JIT_DelegateProfile32, CORINFO_HELP_SIG_REG_ONLY)
+    JITHELPER(CORINFO_HELP_DELEGATEPROFILE64, JIT_DelegateProfile64, CORINFO_HELP_SIG_REG_ONLY)
+    JITHELPER(CORINFO_HELP_VTABLEPROFILE32, JIT_VTableProfile32, CORINFO_HELP_SIG_4_STACK)
+    JITHELPER(CORINFO_HELP_VTABLEPROFILE64, JIT_VTableProfile64, CORINFO_HELP_SIG_4_STACK)
 
 #if defined(TARGET_AMD64) || defined(TARGET_ARM64)
     JITHELPER(CORINFO_HELP_VALIDATE_INDIRECT_CALL, JIT_ValidateIndirectCall, CORINFO_HELP_SIG_REG_ONLY)

src/coreclr/inc/readytorun.h

@@ -16,7 +16,7 @@
 
 // Keep these in sync with src/coreclr/tools/Common/Internal/Runtime/ModuleHeaders.cs
 #define READYTORUN_MAJOR_VERSION 0x0006
-#define READYTORUN_MINOR_VERSION 0x0001
+#define READYTORUN_MINOR_VERSION 0x0002
 
 #define MINIMUM_READYTORUN_MAJOR_VERSION 0x006
 

src/coreclr/jit/ClrJit.PAL.exports

@@ -1,4 +1,5 @@
 getJit
 jitStartup
 getLikelyClasses
+getLikelyMethods
 jitBuildString

src/coreclr/jit/ClrJit.exports

@@ -5,4 +5,5 @@ EXPORTS
     getJit
     jitStartup
     getLikelyClasses
+    getLikelyMethods
     jitBuildString

src/coreclr/jit/block.h

@@ -526,32 +526,32 @@ enum BasicBlockFlags : unsigned __int64
 
 #endif // defined(FEATURE_EH_FUNCLETS) && defined(TARGET_ARM)
 
-    BBF_BACKWARD_JUMP        = MAKE_BBFLAG(24), // BB is surrounded by a backward jump/switch arc
-    BBF_RETLESS_CALL         = MAKE_BBFLAG(25), // BBJ_CALLFINALLY that will never return (and therefore, won't need a paired
-                                                // BBJ_ALWAYS); see isBBCallAlwaysPair().
-    BBF_LOOP_PREHEADER       = MAKE_BBFLAG(26), // BB is a loop preheader block
-    BBF_COLD                 = MAKE_BBFLAG(27), // BB is cold
-
-    BBF_PROF_WEIGHT          = MAKE_BBFLAG(28), // BB weight is computed from profile data
-    BBF_IS_LIR               = MAKE_BBFLAG(29), // Set if the basic block contains LIR (as opposed to HIR)
-    BBF_KEEP_BBJ_ALWAYS      = MAKE_BBFLAG(30), // A special BBJ_ALWAYS block, used by EH code generation. Keep the jump kind
-                                                // as BBJ_ALWAYS. Used for the paired BBJ_ALWAYS block following the
-                                                // BBJ_CALLFINALLY block, as well as, on x86, the final step block out of a
-                                                // finally.
-    BBF_CLONED_FINALLY_BEGIN = MAKE_BBFLAG(31), // First block of a cloned finally region
-
-    BBF_CLONED_FINALLY_END   = MAKE_BBFLAG(32), // Last block of a cloned finally region
-    BBF_HAS_CALL             = MAKE_BBFLAG(33), // BB contains a call
+    BBF_BACKWARD_JUMP                  = MAKE_BBFLAG(24), // BB is surrounded by a backward jump/switch arc
+    BBF_RETLESS_CALL                   = MAKE_BBFLAG(25), // BBJ_CALLFINALLY that will never return (and therefore, won't need a paired
+                                                          // BBJ_ALWAYS); see isBBCallAlwaysPair().
+    BBF_LOOP_PREHEADER                 = MAKE_BBFLAG(26), // BB is a loop preheader block
+    BBF_COLD                           = MAKE_BBFLAG(27), // BB is cold
+
+    BBF_PROF_WEIGHT                    = MAKE_BBFLAG(28), // BB weight is computed from profile data
+    BBF_IS_LIR                         = MAKE_BBFLAG(29), // Set if the basic block contains LIR (as opposed to HIR)
+    BBF_KEEP_BBJ_ALWAYS                = MAKE_BBFLAG(30), // A special BBJ_ALWAYS block, used by EH code generation. Keep the jump kind
+                                                          // as BBJ_ALWAYS. Used for the paired BBJ_ALWAYS block following the
+                                                          // BBJ_CALLFINALLY block, as well as, on x86, the final step block out of a
+                                                          // finally.
+    BBF_CLONED_FINALLY_BEGIN           = MAKE_BBFLAG(31), // First block of a cloned finally region
+
+    BBF_CLONED_FINALLY_END             = MAKE_BBFLAG(32), // Last block of a cloned finally region
+    BBF_HAS_CALL                       = MAKE_BBFLAG(33), // BB contains a call
     BBF_DOMINATED_BY_EXCEPTIONAL_ENTRY = MAKE_BBFLAG(34), // Block is dominated by exceptional entry.
-    BBF_BACKWARD_JUMP_TARGET = MAKE_BBFLAG(35), // Block is a target of a backward jump
+    BBF_BACKWARD_JUMP_TARGET           = MAKE_BBFLAG(35), // Block is a target of a backward jump
 
-    BBF_PATCHPOINT           = MAKE_BBFLAG(36), // Block is a patchpoint
-    BBF_HAS_CLASS_PROFILE    = MAKE_BBFLAG(37), // BB contains a call needing a class profile
-    BBF_PARTIAL_COMPILATION_PATCHPOINT  = MAKE_BBFLAG(38), // Block is a partial compilation patchpoint
-    BBF_HAS_ALIGN            = MAKE_BBFLAG(39), // BB ends with 'align' instruction
-    BBF_TAILCALL_SUCCESSOR   = MAKE_BBFLAG(40), // BB has pred that has potential tail call
+    BBF_PATCHPOINT                     = MAKE_BBFLAG(36), // Block is a patchpoint
+    BBF_HAS_HISTOGRAM_PROFILE          = MAKE_BBFLAG(37), // BB contains a call needing a histogram profile
+    BBF_PARTIAL_COMPILATION_PATCHPOINT = MAKE_BBFLAG(38), // Block is a partial compilation patchpoint
+    BBF_HAS_ALIGN                      = MAKE_BBFLAG(39), // BB ends with 'align' instruction
+    BBF_TAILCALL_SUCCESSOR             = MAKE_BBFLAG(40), // BB has pred that has potential tail call
 
-    BBF_BACKWARD_JUMP_SOURCE = MAKE_BBFLAG(41), // Block is a source of a backward jump
+    BBF_BACKWARD_JUMP_SOURCE           = MAKE_BBFLAG(41), // Block is a source of a backward jump
 
     // The following are sets of flags.
 
@@ -582,7 +582,7 @@ enum BasicBlockFlags : unsigned __int64
     // TODO: Should BBF_RUN_RARELY be added to BBF_SPLIT_GAINED ?
 
     BBF_SPLIT_GAINED = BBF_DONT_REMOVE | BBF_HAS_JMP | BBF_BACKWARD_JUMP | BBF_HAS_IDX_LEN | BBF_HAS_NEWARRAY | BBF_PROF_WEIGHT | \
-                       BBF_HAS_NEWOBJ | BBF_KEEP_BBJ_ALWAYS | BBF_CLONED_FINALLY_END | BBF_HAS_NULLCHECK | BBF_HAS_CLASS_PROFILE,
+                       BBF_HAS_NEWOBJ | BBF_KEEP_BBJ_ALWAYS | BBF_CLONED_FINALLY_END | BBF_HAS_NULLCHECK | BBF_HAS_HISTOGRAM_PROFILE,
 };
 
 inline constexpr BasicBlockFlags operator ~(BasicBlockFlags a)
@@ -918,8 +918,8 @@ struct BasicBlock : private LIR::Range
     };
 
     union {
-        unsigned bbStkTempsOut;      // base# for output stack temps
-        int      bbClassSchemaIndex; // schema index for class instrumentation
+        unsigned bbStkTempsOut;          // base# for output stack temps
+        int      bbHistogramSchemaIndex; // schema index for histogram instrumentation
     };
 
 #define MAX_XCPTN_INDEX (USHRT_MAX - 1)

src/coreclr/jit/compiler.cpp

@@ -6384,10 +6384,10 @@ int Compiler::compCompileHelper(CORINFO_MODULE_HANDLE classPtr,
     compHndBBtabCount      = 0;
     compHndBBtabAllocCount = 0;
 
-    info.compNativeCodeSize    = 0;
-    info.compTotalHotCodeSize  = 0;
-    info.compTotalColdCodeSize = 0;
-    info.compClassProbeCount   = 0;
+    info.compNativeCodeSize            = 0;
+    info.compTotalHotCodeSize          = 0;
+    info.compTotalColdCodeSize         = 0;
+    info.compHandleHistogramProbeCount = 0;
 
     compHasBackwardJump          = false;
     compHasBackwardJumpInHandler = false;

src/coreclr/jit/compiler.h

@@ -1821,6 +1821,7 @@ class Compiler
     friend class MorphInitBlockHelper;
     friend class MorphCopyBlockHelper;
     friend class CallArgs;
+    friend class IndirectCallTransformer;
 
 #ifdef FEATURE_HW_INTRINSICS
     friend struct HWIntrinsicInfo;
@@ -3539,6 +3540,18 @@ class Compiler
                              bool                    isExplicitTailCall,
                              IL_OFFSET               ilOffset = BAD_IL_OFFSET);
 
+    bool impConsiderCallProbe(GenTreeCall* call, IL_OFFSET ilOffset);
+
+    enum class GDVProbeType
+    {
+        None,
+        ClassProfile,
+        MethodProfile,
+        MethodAndClassProfile,
+    };
+
+    GDVProbeType compClassifyGDVProbeType(GenTreeCall* call);
+
     //=========================================================================
     //                          PROTECTED
     //=========================================================================
@@ -5427,19 +5440,21 @@ class Compiler
     bool fgGetProfileWeightForBasicBlock(IL_OFFSET offset, weight_t* weight);
 
     Instrumentor* fgCountInstrumentor;
-    Instrumentor* fgClassInstrumentor;
+    Instrumentor* fgHistogramInstrumentor;
 
     PhaseStatus fgPrepareToInstrumentMethod();
     PhaseStatus fgInstrumentMethod();
     PhaseStatus fgIncorporateProfileData();
     void        fgIncorporateBlockCounts();
     void        fgIncorporateEdgeCounts();
 
-    CORINFO_CLASS_HANDLE getRandomClass(ICorJitInfo::PgoInstrumentationSchema* schema,
-                                        UINT32                                 countSchemaItems,
-                                        BYTE*                                  pInstrumentationData,
-                                        int32_t                                ilOffset,
-                                        CLRRandom*                             random);
+    void getRandomGDV(ICorJitInfo::PgoInstrumentationSchema* schema,
+                      UINT32                                 countSchemaItems,
+                      BYTE*                                  pInstrumentationData,
+                      int32_t                                ilOffset,
+                      CLRRandom*                             random,
+                      CORINFO_CLASS_HANDLE*                  classGuess,
+                      CORINFO_METHOD_HANDLE*                 methodGuess);
 
 public:
     const char*                            fgPgoFailReason;
@@ -5679,6 +5694,7 @@ class Compiler
                                                      Statement*       paramAssignmentInsertionPoint);
     GenTree* fgMorphCall(GenTreeCall* call);
     GenTree* fgExpandVirtualVtableCallTarget(GenTreeCall* call);
+
     void fgMorphCallInline(GenTreeCall* call, InlineResult* result);
     void fgMorphCallInlineHelper(GenTreeCall* call, InlineResult* result, InlineContext** createdContext);
 #if DEBUG
@@ -6806,13 +6822,21 @@ class Compiler
         optMethodFlags |= OMF_HAS_GUARDEDDEVIRT;
     }
 
+    void pickGDV(GenTreeCall*           call,
+                 IL_OFFSET              ilOffset,
+                 bool                   isInterface,
+                 CORINFO_CLASS_HANDLE*  classGuess,
+                 CORINFO_METHOD_HANDLE* methodGuess,
+                 unsigned*              likelihood);
+
     void considerGuardedDevirtualization(GenTreeCall*            call,
                                          IL_OFFSET               ilOffset,
                                          bool                    isInterface,
                                          CORINFO_METHOD_HANDLE   baseMethod,
                                          CORINFO_CLASS_HANDLE    baseClass,
-                                         CORINFO_CONTEXT_HANDLE* pContextHandle DEBUGARG(CORINFO_CLASS_HANDLE objClass)
-                                             DEBUGARG(const char* objClassName));
+                                         CORINFO_CONTEXT_HANDLE* pContextHandle);
+
+    bool isCompatibleMethodGDV(GenTreeCall* call, CORINFO_METHOD_HANDLE gdvTarget);
 
     void addGuardedDevirtualizationCandidate(GenTreeCall*          call,
                                              CORINFO_METHOD_HANDLE methodHandle,
@@ -9548,7 +9572,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         unsigned genCPU; // What CPU are we running on
 
         // Number of class profile probes in this method
-        unsigned compClassProbeCount;
+        unsigned compHandleHistogramProbeCount;
 
     } info;