JIT: devirtualization support for EqualityComparer<T>.Default

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.

src/ToolBox/superpmi/superpmi-shared/icorjitinfoimpl.h

@@ -119,15 +119,23 @@ 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);
 
 // 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.

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)

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)

src/ToolBox/superpmi/superpmi-shared/methodcontext.h

@@ -872,6 +872,11 @@ class MethodContext
                                                   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 @@ class MethodContext
 };
 
 // ********************* 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,

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)

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)

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)

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)

src/inc/corinfo.h

@@ -213,11 +213,11 @@ TODO: Talk about initializing strutures before use
     #define SELECTANY extern __declspec(selectany)
 #endif
 
-SELECTANY const GUID JITEEVersionIdentifier = { /* 7f70c266-eada-427b-be8a-be1260e34b1b */
-    0x7f70c266,
-    0xeada,
-    0x427b,
-    {0xbe, 0x8a, 0xbe, 0x12, 0x60, 0xe3, 0x4b, 0x1b}
+SELECTANY const GUID JITEEVersionIdentifier = { /* 76a743cd-8a07-471e-9ac4-cd5806a8ffac */
+    0x76a743cd,
+    0x8a07,
+    0x471e,
+    {0x9a, 0xc4, 0xcd, 0x58, 0x06, 0xa8, 0xff, 0xac}
 };
 
 //////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -2085,6 +2085,12 @@ class ICorStaticInfo
             CORINFO_CONTEXT_HANDLE      ownerType = NULL        /* IN */
             ) = 0;
 
+    // Given T, return the type of the default EqualityComparer<T>.
+    // Returns null if the type can't be determined exactly.
+    virtual CORINFO_CLASS_HANDLE getDefaultEqualityComparerClass(
+            CORINFO_CLASS_HANDLE elemType
+            ) = 0;
+
     // 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 

src/jit/ICorJitInfo_API_names.h

@@ -168,5 +168,6 @@ DEF_CLR_API(getModuleNativeEntryPointRange)
 DEF_CLR_API(getExpectedTargetArchitecture)
 DEF_CLR_API(resolveVirtualMethod)
 DEF_CLR_API(expandRawHandleIntrinsic)
+DEF_CLR_API(getDefaultEqualityComparerClass)
 
 #undef DEF_CLR_API

src/jit/ICorJitInfo_API_wrapper.hpp

@@ -1620,6 +1620,16 @@ CORINFO_METHOD_HANDLE WrapICorJitInfo::resolveVirtualMethod(
     return result;
 }
 
+CORINFO_CLASS_HANDLE WrapICorJitInfo::getDefaultEqualityComparerClass(
+    CORINFO_CLASS_HANDLE elemType)
+{
+    API_ENTER(getDefaultEqualityComparerClass);
+    CORINFO_CLASS_HANDLE result = wrapHnd->getDefaultEqualityComparerClass(elemType);
+    API_LEAVE(getDefaultEqualityComparerClass);
+    return result;
+}
+
+
 void WrapICorJitInfo::expandRawHandleIntrinsic(
     CORINFO_RESOLVED_TOKEN *        pResolvedToken,
     CORINFO_GENERICHANDLE_RESULT *  pResult)

src/jit/compiler.h

@@ -2966,12 +2966,13 @@ class Compiler
                             IL_OFFSET          rawILOffset);
 
     void impDevirtualizeCall(GenTreeCall*            call,
-                             GenTreePtr              thisObj,
                              CORINFO_METHOD_HANDLE*  method,
                              unsigned*               methodFlags,
                              CORINFO_CONTEXT_HANDLE* contextHandle,
                              CORINFO_CONTEXT_HANDLE* exactContextHandle);
 
+    CORINFO_CLASS_HANDLE impGetSpecialIntrinsicExactReturnType(CORINFO_METHOD_HANDLE specialIntrinsicHandle);
+
     bool impMethodInfo_hasRetBuffArg(CORINFO_METHOD_INFO* methInfo);
 
     GenTreePtr impFixupCallStructReturn(GenTreeCall* call, CORINFO_CLASS_HANDLE retClsHnd);

src/jit/flowgraph.cpp

@@ -7056,6 +7056,19 @@ GenTreeCall* Compiler::fgGetStaticsCCtorHelper(CORINFO_CLASS_HANDLE cls, CorInfo
     GenTreeCall* result = gtNewHelperCallNode(helper, type, argList);
     result->gtFlags |= callFlags;
 
+    // If we're importing the special EqualityComparer<T>.Default
+    // intrinsic, flag the helper call. Later during inlining, we can
+    // remove the helper call if the associated field lookup is unused.
+    if ((info.compFlags & CORINFO_FLG_JIT_INTRINSIC) != 0)
+    {
+        NamedIntrinsic ni = lookupNamedIntrinsic(info.compMethodHnd);
+        if (ni == NI_System_Collections_Generic_EqualityComparer_get_Default)
+        {
+            JITDUMP("\nmarking helper call [06%u] as special dce...\n", result->gtTreeID);
+            result->gtCallMoreFlags |= GTF_CALL_M_HELPER_SPECIAL_DCE;
+        }
+    }
+
     return result;
 }
 
@@ -22233,7 +22246,7 @@ Compiler::fgWalkResult Compiler::fgUpdateInlineReturnExpressionPlaceHolder(GenTr
                 CORINFO_METHOD_HANDLE  method      = call->gtCallMethHnd;
                 unsigned               methodFlags = 0;
                 CORINFO_CONTEXT_HANDLE context     = nullptr;
-                comp->impDevirtualizeCall(call, tree, &method, &methodFlags, &context, nullptr);
+                comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr);
             }
         }
     }
@@ -22928,8 +22941,8 @@ GenTreePtr Compiler::fgInlinePrependStatements(InlineInfo* inlineInfo)
     GenTreeStmt* callStmt     = inlineInfo->iciStmt;
     IL_OFFSETX   callILOffset = callStmt->gtStmtILoffsx;
     GenTreeStmt* postStmt     = callStmt->gtNextStmt;
-    GenTreePtr   afterStmt    = callStmt; // afterStmt is the place where the new statements should be inserted after.
-    GenTreePtr   newStmt      = nullptr;
+    GenTree*     afterStmt    = callStmt; // afterStmt is the place where the new statements should be inserted after.
+    GenTree*     newStmt      = nullptr;
     GenTreeCall* call         = inlineInfo->iciCall->AsCall();
 
     noway_assert(call->gtOper == GT_CALL);
@@ -23074,6 +23087,8 @@ GenTreePtr Compiler::fgInlinePrependStatements(InlineInfo* inlineInfo)
                 if (argInfo.argHasSideEff)
                 {
                     noway_assert(argInfo.argIsUsed == false);
+                    newStmt     = nullptr;
+                    bool append = true;
 
                     if (argNode->gtOper == GT_OBJ || argNode->gtOper == GT_MKREFANY)
                     {
@@ -23084,16 +23099,92 @@ GenTreePtr Compiler::fgInlinePrependStatements(InlineInfo* inlineInfo)
                     }
                     else
                     {
-                        newStmt = gtNewStmt(gtUnusedValNode(argNode), callILOffset);
+                        // In some special cases, unused args with side effects can
+                        // trigger further changes.
+                        //
+                        // (1) If the arg is a static field access and the field access
+                        // was produced by a call to EqualityComparer<T>.get_Default, the
+                        // helper call to ensure the field has a value can be suppressed.
+                        // This helper call is marked as a "Special DCE" helper during
+                        // importation, over in fgGetStaticsCCtorHelper.
+                        //
+                        // (2) NYI. If, after tunneling through GT_RET_VALs, we find that
+                        // the actual arg expression has no side effects, we can skip
+                        // appending all together. This will help jit TP a bit.
+                        //
+                        // Chase through any GT_RET_EXPRs to find the actual argument
+                        // expression.
+                        GenTree* actualArgNode = argNode;
+                        while (actualArgNode->gtOper == GT_RET_EXPR)
+                        {
+                            actualArgNode = actualArgNode->gtRetExpr.gtInlineCandidate;
+                        }
+
+                        // For case (1)
+                        //
+                        // Look for the following tree shapes
+                        // prejit: (IND (ADD (CONST, CALL(special dce helper...))))
+                        // jit   : (COMMA (CALL(special dce helper...), (FIELD ...)))
+                        if (actualArgNode->gtOper == GT_COMMA)
+                        {
+                            // Look for (COMMA (CALL(special dce helper...), (FIELD ...)))
+                            GenTree* op1 = actualArgNode->gtOp.gtOp1;
+                            GenTree* op2 = actualArgNode->gtOp.gtOp2;
+                            if (op1->IsCall() && ((op1->gtCall.gtCallMoreFlags & GTF_CALL_M_HELPER_SPECIAL_DCE) != 0) &&
+                                (op2->gtOper == GT_FIELD) && ((op2->gtFlags & GTF_EXCEPT) == 0))
+                            {
+                                JITDUMP("\nPerforming special dce on unused arg [%06u]:"
+                                        " actual arg [%06u] helper call [%06u]\n",
+                                        argNode->gtTreeID, actualArgNode->gtTreeID, op1->gtTreeID);
+                                // Drop the whole tree
+                                append = false;
+                            }
+                        }
+                        else if (actualArgNode->gtOper == GT_IND)
+                        {
+                            // Look for (IND (ADD (CONST, CALL(special dce helper...))))
+                            GenTree* addr = actualArgNode->gtOp.gtOp1;
+
+                            if (addr->gtOper == GT_ADD)
+                            {
+                                GenTree* op1 = addr->gtOp.gtOp1;
+                                GenTree* op2 = addr->gtOp.gtOp2;
+                                if (op1->IsCall() &&
+                                    ((op1->gtCall.gtCallMoreFlags & GTF_CALL_M_HELPER_SPECIAL_DCE) != 0) &&
+                                    op2->IsCnsIntOrI())
+                                {
+                                    // Drop the whole tree
+                                    JITDUMP("\nPerforming special dce on unused arg [%06u]:"
+                                            " actual arg [%06u] helper call [%06u]\n",
+                                            argNode->gtTreeID, actualArgNode->gtTreeID, op1->gtTreeID);
+                                    append = false;
+                                }
+                            }
+                        }
                     }
-                    afterStmt = fgInsertStmtAfter(block, afterStmt, newStmt);
 
-#ifdef DEBUG
-                    if (verbose)
+                    if (!append)
                     {
-                        gtDispTree(afterStmt);
+                        assert(newStmt == nullptr);
+                        JITDUMP("Arg tree side effects were discardable, not appending anything for arg\n");
                     }
+                    else
+                    {
+                        // If we don't have something custom to append,
+                        // just append the arg node as an unused value.
+                        if (newStmt == nullptr)
+                        {
+                            newStmt = gtNewStmt(gtUnusedValNode(argNode), callILOffset);
+                        }
+
+                        afterStmt = fgInsertStmtAfter(block, afterStmt, newStmt);
+#ifdef DEBUG
+                        if (verbose)
+                        {
+                            gtDispTree(afterStmt);
+                        }
 #endif // DEBUG
+                    }
                 }
                 else if (argNode->IsBoxedValue())
                 {

src/jit/gentree.cpp

@@ -6415,6 +6415,7 @@ GenTreeLclFld* Compiler::gtNewLclFldNode(unsigned lnum, var_types type, unsigned
 }
 
 GenTreePtr Compiler::gtNewInlineCandidateReturnExpr(GenTreePtr inlineCandidate, var_types type)
+
 {
     assert(GenTree::s_gtNodeSizes[GT_RET_EXPR] == TREE_NODE_SZ_LARGE);
 

src/jit/gentree.h

@@ -3654,6 +3654,8 @@ struct GenTreeCall final : public GenTree
                                                     // to restore real function address and load hidden argument
                                                     // as the first argument for calli. It is CoreRT replacement for instantiating
                                                     // stubs, because executable code cannot be generated at runtime.
+#define GTF_CALL_M_HELPER_SPECIAL_DCE    0x00020000 // GT_CALL -- this helper call can be removed if it is part of a comma and
+                                                    // the comma result is unused.
 
     // clang-format on
 
@@ -4997,7 +4999,7 @@ struct GenTreeStoreInd : public GenTreeIndir
 
 struct GenTreeRetExpr : public GenTree
 {
-    GenTreePtr gtInlineCandidate;
+    GenTree* gtInlineCandidate;
 
     CORINFO_CLASS_HANDLE gtRetClsHnd;