Rely on PGO for isinst/castclass

src/coreclr/jit/compiler.h

@@ -4597,7 +4597,7 @@ class Compiler
                                            CORINFO_LOOKUP_KIND*    pGenericLookupKind = nullptr);
 
     bool impIsCastHelperEligibleForClassProbe(GenTree* tree);
-    bool impIsCastHelperMayHaveProfileData(GenTree* tree);
+    bool impIsCastHelperMayHaveProfileData(CorInfoHelpFunc helper);
 
     GenTree* impCastClassOrIsInstToTree(
         GenTree* op1, GenTree* op2, CORINFO_RESOLVED_TOKEN* pResolvedToken, bool isCastClass, IL_OFFSET ilOffset);

src/coreclr/jit/importer.cpp

@@ -2141,21 +2141,17 @@ bool Compiler::impIsCastHelperEligibleForClassProbe(GenTree* tree)
 // Returns:
 //    true if the tree is a cast helper with potential profile data
 //
-bool Compiler::impIsCastHelperMayHaveProfileData(GenTree* tree)
+bool Compiler::impIsCastHelperMayHaveProfileData(CorInfoHelpFunc helper)
 {
-    if (!opts.jitFlags->IsSet(JitFlags::JIT_FLAG_BBOPT) || (JitConfig.JitCastProfiling() != 1))
+    if (!opts.jitFlags->IsSet(JitFlags::JIT_FLAG_BBOPT))
     {
         return false;
     }
 
-    if (tree->IsCall() && tree->AsCall()->gtCallType == CT_HELPER)
+    if ((helper == CORINFO_HELP_ISINSTANCEOFINTERFACE) || (helper == CORINFO_HELP_ISINSTANCEOFCLASS) ||
+        (helper == CORINFO_HELP_CHKCASTCLASS) || (helper == CORINFO_HELP_CHKCASTINTERFACE))
     {
-        const CorInfoHelpFunc helper = eeGetHelperNum(tree->AsCall()->gtCallMethHnd);
-        if ((helper == CORINFO_HELP_ISINSTANCEOFINTERFACE) || (helper == CORINFO_HELP_ISINSTANCEOFCLASS) ||
-            (helper == CORINFO_HELP_CHKCASTCLASS) || (helper == CORINFO_HELP_CHKCASTINTERFACE))
-        {
-            return true;
-        }
+        return true;
     }
     return false;
 }
@@ -11561,8 +11557,11 @@ GenTree* Compiler::impCastClassOrIsInstToTree(
 
     // Pessimistically assume the jit cannot expand this as an inline test
     bool                  canExpandInline = false;
+    bool                  partialExpand   = false;
     const CorInfoHelpFunc helper          = info.compCompHnd->getCastingHelper(pResolvedToken, isCastClass);
 
+    GenTree* exactCls = nullptr;
+
     // Legality check.
     //
     // Not all classclass/isinst operations can be inline expanded.
@@ -11582,6 +11581,34 @@ GenTree* Compiler::impCastClassOrIsInstToTree(
                 canExpandInline = impIsClassExact(pResolvedToken->hClass);
             }
         }
+
+        // Check if this cast helper have some profile data
+        if (impIsCastHelperMayHaveProfileData(helper))
+        {
+            LikelyClassRecord likelyClass[1]; // multiple guesses aren't yet supported
+            if (getLikelyClasses(likelyClass, 1, fgPgoSchema, fgPgoSchemaCount, fgPgoData, ilOffset) > 0)
+            {
+                assert(likelyClass != nullptr);
+                CORINFO_CLASS_HANDLE likelyCls = likelyClass->clsHandle;
+
+                if ((likelyCls != NO_CLASS_HANDLE) &&
+                    (likelyClass->likelihood > (UINT32)JitConfig.JitGuardedDevirtualizationChainLikelihood()))
+                {
+                    if ((info.compCompHnd->compareTypesForCast(likelyCls, pResolvedToken->hClass) ==
+                         TypeCompareState::Must))
+                    {
+                        assert((info.compCompHnd->getClassAttribs(likelyCls) &
+                                (CORINFO_FLG_INTERFACE | CORINFO_FLG_ABSTRACT)) == 0);
+                        JITDUMP("Adding \"is %s (%X)\" check as a fast path for %s using PGO data.\n",
+                                eeGetClassName(likelyCls), likelyCls, isCastClass ? "castclass" : "isinst");
+
+                        canExpandInline = true;
+                        partialExpand   = true;
+                        exactCls        = gtNewIconEmbClsHndNode(likelyCls);
+                    }
+                }
+            }
+        }
     }
 
     const bool expandInline = canExpandInline && shouldExpandInline;
@@ -11633,13 +11660,13 @@ GenTree* Compiler::impCastClassOrIsInstToTree(
     //
 
     GenTree* op2Var = op2;
-    if (isCastClass)
+    if (isCastClass && !partialExpand)
     {
         op2Var                                                  = fgInsertCommaFormTemp(&op2);
         lvaTable[op2Var->AsLclVarCommon()->GetLclNum()].lvIsCSE = true;
     }
     temp   = gtNewMethodTableLookup(temp);
-    condMT = gtNewOperNode(GT_NE, TYP_INT, temp, op2);
+    condMT = gtNewOperNode(GT_NE, TYP_INT, temp, exactCls != nullptr ? exactCls : op2);
 
     GenTree* condNull;
     //
@@ -11664,7 +11691,12 @@ GenTree* Compiler::impCastClassOrIsInstToTree(
         //
         const CorInfoHelpFunc specialHelper = CORINFO_HELP_CHKCASTCLASS_SPECIAL;
 
-        condTrue = gtNewHelperCallNode(specialHelper, TYP_REF, gtNewCallArgs(op2Var, gtClone(op1)));
+        condTrue =
+            gtNewHelperCallNode(specialHelper, TYP_REF, gtNewCallArgs(partialExpand ? op2 : op2Var, gtClone(op1)));
+    }
+    else if (partialExpand)
+    {
+        condTrue = gtNewHelperCallNode(helper, TYP_REF, gtNewCallArgs(op2, gtClone(op1)));
     }
     else
     {

src/coreclr/jit/jitconfigvalues.h

@@ -486,7 +486,7 @@ CONFIG_STRING(JitEnablePatchpointRange, W("JitEnablePatchpointRange"))
 // Profile instrumentation options
 CONFIG_INTEGER(JitMinimalJitProfiling, W("JitMinimalJitProfiling"), 1)
 CONFIG_INTEGER(JitMinimalPrejitProfiling, W("JitMinimalPrejitProfiling"), 0)
-CONFIG_INTEGER(JitCastProfiling, W("JitCastProfiling"), 0)           // Profile castclass and isinst
+CONFIG_INTEGER(JitCastProfiling, W("JitCastProfiling"), 1)           // CI test, will disable it back
 CONFIG_INTEGER(JitClassProfiling, W("JitClassProfiling"), 1)         // Profile virtual and interface calls
 CONFIG_INTEGER(JitEdgeProfiling, W("JitEdgeProfiling"), 1)           // Profile edges instead of blocks
 CONFIG_INTEGER(JitCollect64BitCounts, W("JitCollect64BitCounts"), 0) // Collect counts as 64-bit values.