JIT: devirtualization support for EqualityComparer<T>.Default (#14125)

Mark `EqualityComparer<T>.Default`'s getter as `[Intrinsic]` so
the jit knows there is something special about it. Extend the jit's
named intrinsic recognizer to recognize this method.

Add a new jit interface method to determine the exact type returned
by `EqualityComparer<T>.Default`, given `T`. Compute the return type by
mirroring the logic used in the actual implementation. Bail out when
`T` is not final as those cases won't simplify down much and lead to
code bloat.

Invoke this interface method when trying to devirtualize calls where
the 'this' object in the call comes from `EqualityComparer<T>.Default`.

The devirtualized methods can then be inlined. Since the specific comparer
`Equal` and `GetHashCode` methods look more complicated in IL than they
really are, mark them with AggressiveInlining attributes.

If devirtualization and inlining happen, it is quite likely that the value
of the comparer object itself is not used in the body of the comparer. This
value comes from a static field cache on the comparer helper.

When the comparer value is ignored, the jit removes the field access since it
is non-faulting. It also removes the the class init helper that is there to
ensure that the (no-longer accessed) field is properly initialized. This helper
has relatively high overhead even in the fast case where the class has been
initialized aready.

Add a perf test.

Closes #6688.

8 files changed, 69 insertions, 3 deletions

diff --git a/src/ToolBox/superpmi/superpmi-shared/icorjitinfoimpl.h b/src/ToolBox/superpmi/superpmi-shared/icorjitinfoimpl.h
index 4ce775d177..29baaa8a39 100644
--- a/src/ToolBox/superpmi/superpmi-shared/icorjitinfoimpl.h
+++ b/src/ToolBox/superpmi/superpmi-shared/icorjitinfoimpl.h
@@ -119,6 +119,15 @@ CORINFO_METHOD_HANDLE resolveVirtualMethod(CORINFO_METHOD_HANDLE  virtualMethod,
                                            CORINFO_CLASS_HANDLE   implementingClass,
                                            CORINFO_CONTEXT_HANDLE ownerType);
 
+// Given T, return the type of the default EqualityComparer<T>.
+// Returns null if the type can't be determined exactly.
+CORINFO_CLASS_HANDLE getDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE elemType);
+
+// Given resolved token that corresponds to an intrinsic classified as
+// a CORINFO_INTRINSIC_GetRawHandle intrinsic, fetch the handle associated
+// with the token. If this is not possible at compile-time (because the current method's 
+// code is shared and the token contains generic parameters) then indicate 
+// how the handle should be looked up at runtime.
 void expandRawHandleIntrinsic(
     CORINFO_RESOLVED_TOKEN *        pResolvedToken,
     CORINFO_GENERICHANDLE_RESULT *  pResult);
@@ -126,8 +135,7 @@ void expandRawHandleIntrinsic(
 // If a method's attributes have (getMethodAttribs) CORINFO_FLG_INTRINSIC set,
 // getIntrinsicID() returns the intrinsic ID.
 // *pMustExpand tells whether or not JIT must expand the intrinsic.
-CorInfoIntrinsics getIntrinsicID(CORINFO_METHOD_HANDLE method, bool* pMustExpand = NULL /* OUT */
-                                 );
+CorInfoIntrinsics getIntrinsicID(CORINFO_METHOD_HANDLE method, bool* pMustExpand = NULL /* OUT */);
 
 // Is the given module the System.Numerics.Vectors module?
 // This defaults to false.
diff --git a/src/ToolBox/superpmi/superpmi-shared/lwmlist.h b/src/ToolBox/superpmi/superpmi-shared/lwmlist.h
index 898641c790..21f7906510 100644
--- a/src/ToolBox/superpmi/superpmi-shared/lwmlist.h
+++ b/src/ToolBox/superpmi/superpmi-shared/lwmlist.h
@@ -69,6 +69,7 @@ LWM(GetClassName, DWORDLONG, DWORD)
 LWM(GetClassNumInstanceFields, DWORDLONG, DWORD)
 LWM(GetClassSize, DWORDLONG, DWORD)
 LWM(GetCookieForPInvokeCalliSig, GetCookieForPInvokeCalliSigValue, DLDL)
+LWM(GetDefaultEqualityComparerClass,  DWORDLONG, DWORDLONG)
 LWM(GetDelegateCtor, Agnostic_GetDelegateCtorIn, Agnostic_GetDelegateCtorOut)
 LWM(GetEEInfo, DWORD, Agnostic_CORINFO_EE_INFO)
 LWM(GetEHinfo, DLD, Agnostic_CORINFO_EH_CLAUSE)
diff --git a/src/ToolBox/superpmi/superpmi-shared/methodcontext.cpp b/src/ToolBox/superpmi/superpmi-shared/methodcontext.cpp
index 02a940d2b5..0bf288d196 100644
--- a/src/ToolBox/superpmi/superpmi-shared/methodcontext.cpp
+++ b/src/ToolBox/superpmi/superpmi-shared/methodcontext.cpp
@@ -3012,6 +3012,23 @@ CORINFO_METHOD_HANDLE MethodContext::repResolveVirtualMethod(CORINFO_METHOD_HAND
     return (CORINFO_METHOD_HANDLE)result;
 }
 
+void MethodContext::recGetDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls, CORINFO_CLASS_HANDLE result)
+{
+    if (GetDefaultEqualityComparerClass == nullptr)
+        GetDefaultEqualityComparerClass = new LightWeightMap<DWORDLONG, DWORDLONG>();
+
+    GetDefaultEqualityComparerClass->Add((DWORDLONG)cls, (DWORDLONG)result);
+}
+void MethodContext::dmpGetDefaultEqualityComparerClass(DWORDLONG key, DWORDLONG value)
+{
+    printf("GetDefaultEqualityComparerClass key cls-%016llX, value cls-%016llX", key, value);
+}
+CORINFO_CLASS_HANDLE MethodContext::repGetDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls)
+{
+    CORINFO_CLASS_HANDLE result = (CORINFO_CLASS_HANDLE)GetDefaultEqualityComparerClass->Get((DWORDLONG)cls);
+    return result;
+}
+
 void MethodContext::recGetTokenTypeAsHandle(CORINFO_RESOLVED_TOKEN* pResolvedToken, CORINFO_CLASS_HANDLE result)
 {
     if (GetTokenTypeAsHandle == nullptr)
diff --git a/src/ToolBox/superpmi/superpmi-shared/methodcontext.h b/src/ToolBox/superpmi/superpmi-shared/methodcontext.h
index 7f79b2b9f6..52515733d3 100644
--- a/src/ToolBox/superpmi/superpmi-shared/methodcontext.h
+++ b/src/ToolBox/superpmi/superpmi-shared/methodcontext.h
@@ -872,6 +872,11 @@ public:
                                                   CORINFO_CLASS_HANDLE   implClass,
                                                   CORINFO_CONTEXT_HANDLE ownerType);
 
+    void recGetDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls, CORINFO_CLASS_HANDLE result);
+    void dmpGetDefaultEqualityComparerClass(DWORDLONG key, DWORDLONG value);
+    CORINFO_CLASS_HANDLE repGetDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls);
+
+
     void recGetTokenTypeAsHandle(CORINFO_RESOLVED_TOKEN* pResolvedToken, CORINFO_CLASS_HANDLE result);
     void dmpGetTokenTypeAsHandle(const GetTokenTypeAsHandleValue& key, DWORDLONG value);
     CORINFO_CLASS_HANDLE repGetTokenTypeAsHandle(CORINFO_RESOLVED_TOKEN* pResolvedToken);
@@ -1252,7 +1257,7 @@ private:
 };
 
 // ********************* Please keep this up-to-date to ease adding more ***************
-// Highest packet number: 161
+// Highest packet number: 162
 // *************************************************************************************
 enum mcPackets
 {
@@ -1319,6 +1324,7 @@ enum mcPackets
     Packet_GetIntConfigValue                             = 151, // Added 2/12/2015
     Packet_GetStringConfigValue                          = 152, // Added 2/12/2015
     Packet_GetCookieForPInvokeCalliSig                   = 48,
+    Packet_GetDefaultEqualityComparerClass               = 162, // Added 9/24/2017
     Packet_GetDelegateCtor                               = 49,
     Packet_GetEEInfo                                     = 50,
     Packet_GetEHinfo                                     = 51,
diff --git a/src/ToolBox/superpmi/superpmi-shim-collector/icorjitinfo.cpp b/src/ToolBox/superpmi/superpmi-shim-collector/icorjitinfo.cpp
index 2a477a07e3..6051de8840 100644
--- a/src/ToolBox/superpmi/superpmi-shim-collector/icorjitinfo.cpp
+++ b/src/ToolBox/superpmi/superpmi-shim-collector/icorjitinfo.cpp
@@ -236,6 +236,16 @@ CORINFO_METHOD_HANDLE interceptor_ICJI::resolveVirtualMethod(CORINFO_METHOD_HAND
     return result;
 }
 
+// Given T, return the type of the default EqualityComparer<T>.
+// Returns null if the type can't be determined exactly.
+CORINFO_CLASS_HANDLE interceptor_ICJI::getDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls)
+{
+    mc->cr->AddCall("getDefaultEqualityComparerClass");
+    CORINFO_CLASS_HANDLE result = original_ICorJitInfo->getDefaultEqualityComparerClass(cls);
+    mc->recGetDefaultEqualityComparerClass(cls, result);
+    return result;
+}
+
 void interceptor_ICJI::expandRawHandleIntrinsic(
     CORINFO_RESOLVED_TOKEN *        pResolvedToken,
     CORINFO_GENERICHANDLE_RESULT *  pResult)
diff --git a/src/ToolBox/superpmi/superpmi-shim-counter/icorjitinfo.cpp b/src/ToolBox/superpmi/superpmi-shim-counter/icorjitinfo.cpp
index a54ead5661..17da100dac 100644
--- a/src/ToolBox/superpmi/superpmi-shim-counter/icorjitinfo.cpp
+++ b/src/ToolBox/superpmi/superpmi-shim-counter/icorjitinfo.cpp
@@ -163,6 +163,14 @@ CORINFO_METHOD_HANDLE interceptor_ICJI::resolveVirtualMethod(CORINFO_METHOD_HAND
     return original_ICorJitInfo->resolveVirtualMethod(virtualMethod, implementingClass, ownerType);
 }
 
+// Given T, return the type of the default EqualityComparer<T>.
+// Returns null if the type can't be determined exactly.
+CORINFO_CLASS_HANDLE interceptor_ICJI::getDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls)
+{
+    mcs->AddCall("getDefaultEqualityComparerClass");
+    return original_ICorJitInfo->getDefaultEqualityComparerClass(cls);
+}
+
 void interceptor_ICJI::expandRawHandleIntrinsic(
     CORINFO_RESOLVED_TOKEN *        pResolvedToken,
     CORINFO_GENERICHANDLE_RESULT *  pResult)
diff --git a/src/ToolBox/superpmi/superpmi-shim-simple/icorjitinfo.cpp b/src/ToolBox/superpmi/superpmi-shim-simple/icorjitinfo.cpp
index 7e0ded9f0f..df4cfcfbcd 100644
--- a/src/ToolBox/superpmi/superpmi-shim-simple/icorjitinfo.cpp
+++ b/src/ToolBox/superpmi/superpmi-shim-simple/icorjitinfo.cpp
@@ -150,6 +150,13 @@ CORINFO_METHOD_HANDLE interceptor_ICJI::resolveVirtualMethod(CORINFO_METHOD_HAND
     return original_ICorJitInfo->resolveVirtualMethod(virtualMethod, implementingClass, ownerType);
 }
 
+// Given T, return the type of the default EqualityComparer<T>.
+// Returns null if the type can't be determined exactly.
+CORINFO_CLASS_HANDLE interceptor_ICJI::getDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls)
+{
+    return original_ICorJitInfo->getDefaultEqualityComparerClass(cls);
+}
+
 void interceptor_ICJI::expandRawHandleIntrinsic(
     CORINFO_RESOLVED_TOKEN *        pResolvedToken,
     CORINFO_GENERICHANDLE_RESULT *  pResult)
diff --git a/src/ToolBox/superpmi/superpmi/icorjitinfo.cpp b/src/ToolBox/superpmi/superpmi/icorjitinfo.cpp
index 2e78113991..7c119b86dd 100644
--- a/src/ToolBox/superpmi/superpmi/icorjitinfo.cpp
+++ b/src/ToolBox/superpmi/superpmi/icorjitinfo.cpp
@@ -185,6 +185,15 @@ CORINFO_METHOD_HANDLE MyICJI::resolveVirtualMethod(CORINFO_METHOD_HANDLE  virtua
     return result;
 }
 
+// Given T, return the type of the default EqualityComparer<T>.
+// Returns null if the type can't be determined exactly.
+CORINFO_CLASS_HANDLE MyICJI::getDefaultEqualityComparerClass(CORINFO_CLASS_HANDLE cls)
+{
+    jitInstance->mc->cr->AddCall("getDefaultEqualityComparerClass");
+    CORINFO_CLASS_HANDLE result = jitInstance->mc->repGetDefaultEqualityComparerClass(cls);
+    return result;
+}
+
 void MyICJI::expandRawHandleIntrinsic(
     CORINFO_RESOLVED_TOKEN *        pResolvedToken,
     CORINFO_GENERICHANDLE_RESULT *  pResult)