Merge pull request #21804 from briansull/fix-unbox-opt

Fix issue with devirtualization and tailcalls

4 files changed, 34 insertions, 8 deletions

diff --git a/src/jit/compiler.h b/src/jit/compiler.h
index 21a426e3f1..6c93434dea 100644
--- a/src/jit/compiler.h
+++ b/src/jit/compiler.h
@@ -3329,7 +3329,8 @@ public:
                              unsigned*               methodFlags,
                              CORINFO_CONTEXT_HANDLE* contextHandle,
                              CORINFO_CONTEXT_HANDLE* exactContextHandle,
-                             bool                    isLateDevirtualization);
+                             bool                    isLateDevirtualization,
+                             bool                    isExplicitTailCall);
 
     //=========================================================================
     //                          PROTECTED
diff --git a/src/jit/flowgraph.cpp b/src/jit/flowgraph.cpp
index eedb1aa58f..86f18ca404 100644
--- a/src/jit/flowgraph.cpp
+++ b/src/jit/flowgraph.cpp
@@ -22552,7 +22552,9 @@ Compiler::fgWalkResult Compiler::fgLateDevirtualization(GenTree** pTree, fgWalkD
             unsigned               methodFlags            = 0;
             CORINFO_CONTEXT_HANDLE context                = nullptr;
             const bool             isLateDevirtualization = true;
-            comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr, isLateDevirtualization);
+            bool explicitTailCall = (call->gtCall.gtCallMoreFlags & GTF_CALL_M_EXPLICIT_TAILCALL) != 0;
+            comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr, isLateDevirtualization,
+                                      explicitTailCall);
         }
     }
     else if (tree->OperGet() == GT_ASG)
diff --git a/src/jit/importer.cpp b/src/jit/importer.cpp
index 47ed202e1b..27ea06abaf 100644
--- a/src/jit/importer.cpp
+++ b/src/jit/importer.cpp
@@ -5276,7 +5276,7 @@ BOOL Compiler::verIsSDArray(typeInfo ti)
 
 typeInfo Compiler::verGetArrayElemType(typeInfo arrayObjectType)
 {
-    assert(!arrayObjectType.IsNullObjRef()); // you need to check for null explictly since that is a success case
+    assert(!arrayObjectType.IsNullObjRef()); // you need to check for null explicitly since that is a success case
 
     if (!verIsSDArray(arrayObjectType))
     {
@@ -8590,9 +8590,11 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
             assert(obj->gtType == TYP_REF);
 
             // See if we can devirtualize.
+
+            bool       explicitTailCall       = (tailCall & PREFIX_TAILCALL_EXPLICIT) != 0;
             const bool isLateDevirtualization = false;
             impDevirtualizeCall(call->AsCall(), &callInfo->hMethod, &callInfo->methodFlags, &callInfo->contextHandle,
-                                &exactContextHnd, isLateDevirtualization);
+                                &exactContextHnd, isLateDevirtualization, explicitTailCall);
         }
 
         if (impIsThis(obj))
@@ -8742,7 +8744,6 @@ DONE:
 
             if (info.compCompHnd->canTailCall(info.compMethodHnd, methHnd, exactCalleeHnd, explicitTailCall))
             {
-                canTailCall = true;
                 if (explicitTailCall)
                 {
                     // In case of explicit tail calls, mark it so that it is not considered
@@ -20174,6 +20175,7 @@ bool Compiler::IsMathIntrinsic(GenTree* tree)
 //     contextHandle -- [IN/OUT] context handle for the call. Updated iff call devirtualized.
 //     exactContextHnd -- [OUT] updated context handle iff call devirtualized
 //     isLateDevirtualization -- if devirtualization is happening after importation
+//     isExplicitTailCalll -- [IN] true if we plan on using an explicit tail call
 //
 // Notes:
 //     Virtual calls in IL will always "invoke" the base class method.
@@ -20207,7 +20209,8 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
                                    unsigned*               methodFlags,
                                    CORINFO_CONTEXT_HANDLE* contextHandle,
                                    CORINFO_CONTEXT_HANDLE* exactContextHandle,
-                                   bool                    isLateDevirtualization)
+                                   bool                    isLateDevirtualization,
+                                   bool                    isExplicitTailCall)
 {
     assert(call != nullptr);
     assert(method != nullptr);
@@ -20558,6 +20561,12 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
     {
         JITDUMP("Now have direct call to boxed entry point, looking for unboxed entry point\n");
 
+        if (isExplicitTailCall)
+        {
+            JITDUMP("Call is an explicit tail call, we cannot perform an unbox\n");
+            return;
+        }
+
         // Note for some shared methods the unboxed entry point requires an extra parameter.
         bool                  requiresInstMethodTableArg = false;
         CORINFO_METHOD_HANDLE unboxedEntryMethod =
@@ -20640,6 +20649,18 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
                     call->gtCallMethHnd = unboxedEntryMethod;
                     call->gtCallMoreFlags |= GTF_CALL_M_UNBOXED;
                     derivedMethod = unboxedEntryMethod;
+
+#if FEATURE_TAILCALL_OPT
+                    if (call->IsImplicitTailCall())
+                    {
+                        JITDUMP("Clearing the implicit tail call flag\n");
+
+                        // If set, we clear the implicit tail call flag
+                        // as we just introduced a new address taken local variable
+                        //
+                        call->gtCallMoreFlags &= ~GTF_CALL_M_IMPLICIT_TAILCALL;
+                    }
+#endif // FEATURE_TAILCALL_OPT
                 }
                 else
                 {
diff --git a/src/jit/indirectcalltransformer.cpp b/src/jit/indirectcalltransformer.cpp
index 85d6d227cb..e0782b5b73 100644
--- a/src/jit/indirectcalltransformer.cpp
+++ b/src/jit/indirectcalltransformer.cpp
@@ -676,14 +676,16 @@ private:
 
             JITDUMP("Direct call [%06u] in block BB%02u\n", compiler->dspTreeID(call), thenBlock->bbNum);
 
-            // Then invoke impDevirtualizeCall do actually
+            // Then invoke impDevirtualizeCall to actually
             // transform the call for us. It should succeed.... as we have
             // now provided an exact typed this.
             CORINFO_METHOD_HANDLE  methodHnd              = inlineInfo->methInfo.ftn;
             unsigned               methodFlags            = inlineInfo->methAttr;
             CORINFO_CONTEXT_HANDLE context                = inlineInfo->exactContextHnd;
             const bool             isLateDevirtualization = true;
-            compiler->impDevirtualizeCall(call, &methodHnd, &methodFlags, &context, nullptr, isLateDevirtualization);
+            bool explicitTailCall = (call->gtCall.gtCallMoreFlags & GTF_CALL_M_EXPLICIT_TAILCALL) != 0;
+            compiler->impDevirtualizeCall(call, &methodHnd, &methodFlags, &context, nullptr, isLateDevirtualization,
+                                          explicitTailCall);
 
             // Presumably devirt might fail? If so we should try and avoid
             // making this a guarded devirt candidate instead of ending