From 8d699cd65dc276a3058e7f961b4af51d0d107a7c Mon Sep 17 00:00:00 2001
From: EgorBo <egorbo@gmail.com>
Date: Fri, 26 Jan 2024 23:40:43 +0100
Subject: [PATCH] remove morphing

---
 src/coreclr/jit/helperexpansion.cpp | 18 +++++-------------
 src/coreclr/jit/importer.cpp        |  3 +++
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/src/coreclr/jit/helperexpansion.cpp b/src/coreclr/jit/helperexpansion.cpp
index e98f37ad2c5d64..59a580a5f88eb8 100644
--- a/src/coreclr/jit/helperexpansion.cpp
+++ b/src/coreclr/jit/helperexpansion.cpp
@@ -2279,18 +2279,13 @@ bool Compiler::fgLateCastExpansionForCall(BasicBlock** pBlock, Statement* stmt,
     }
     else
     {
-        GenTreeCall* helperCall = call;
         if (typeCheckFailedAction == TypeCheckFailedAction::CallHelper_Specialized)
         {
-            // Re-create the call with a specialized helper
-            // For JIT we probably can just change the gtCallMethHnd in the existing call, but let's unify with AOT
-            helperCall = gtNewHelperCallNode(CORINFO_HELP_CHKCASTCLASS_SPECIAL, call->TypeGet(),
-                                             helperCall->gtArgs.GetUserArgByIndex(0)->GetNode(),
-                                             helperCall->gtArgs.GetUserArgByIndex(1)->GetNode());
-            fgMorphCall(helperCall);
-            gtSetEvalOrder(helperCall);
+            // A slightly faster fallback which assumes that we've already checked
+            // for null and for castToCls itself.
+            call->gtCallMethHnd = eeFindHelper(CORINFO_HELP_CHKCASTCLASS_SPECIAL);
         }
-        GenTree* fallbackTree = gtNewTempStore(tmpNum, helperCall);
+        GenTree* fallbackTree = gtNewTempStore(tmpNum, call);
         fallbackBb            = fgNewBBFromTreeAfter(BBJ_ALWAYS, typeCheckBb, fallbackTree, debugInfo, lastBb, true);
     }
 
@@ -2337,10 +2332,7 @@ bool Compiler::fgLateCastExpansionForCall(BasicBlock** pBlock, Statement* stmt,
     //
     nullcheckBb->inheritWeight(firstBb);
     typeCheckBb->inheritWeightPercentage(nullcheckBb, 50);
-    fallbackBb->inheritWeightPercentage(typeCheckBb,
-                                        (typeCheckFailedAction == TypeCheckFailedAction::CallHelper_AlwaysThrows)
-                                            ? 0
-                                            : 100 - likelihood);
+    fallbackBb->inheritWeightPercentage(typeCheckBb, fallbackBb->KindIs(BBJ_THROW) ? 0 : 100 - likelihood);
     typeCheckSucceedBb->inheritWeightPercentage(typeCheckBb, likelihood);
     lastBb->inheritWeight(firstBb);
 
diff --git a/src/coreclr/jit/importer.cpp b/src/coreclr/jit/importer.cpp
index 205fca7a584a33..955b75af71faae 100644
--- a/src/coreclr/jit/importer.cpp
+++ b/src/coreclr/jit/importer.cpp
@@ -5460,6 +5460,9 @@ GenTree* Compiler::impCastClassOrIsInstToTree(
         shouldExpandInline = isCastClass && isClassExact;
     }
 
+    // CI test
+    shouldExpandInline = false;
+
     // Pessimistically assume the jit cannot expand this as an inline test
     bool                  canExpandInline = false;
     bool                  reversedMTCheck = false;