JIT: avoid creating unnecessary temp for indirect virtual stub calls

We don't need to spill the stub address if it's already a local.

Peeled off from dotnet#116771.

Author: AndyAyersMS

src/coreclr/jit/importercalls.cpp

@@ -310,14 +310,17 @@ var_types Compiler::impImportCall(OPCODE                  opcode,
                     // complex expression. As it is evaluated after the args,
                     // it may cause registered args to be spilled. Simply spill it.
                     //
-                    unsigned const lclNum = lvaGrabTemp(true DEBUGARG("VirtualCall with runtime lookup"));
-                    if (compDonotInline())
+                    if (!stubAddr->OperIs(GT_LCL_VAR))
                     {
-                        return TYP_UNDEF;
-                    }
+                        unsigned const lclNum = lvaGrabTemp(true DEBUGARG("VirtualCall with runtime lookup"));
+                        if (compDonotInline())
+                        {
+                            return TYP_UNDEF;
+                        }
 
-                    impStoreToTemp(lclNum, stubAddr, CHECK_SPILL_NONE);
-                    stubAddr = gtNewLclvNode(lclNum, TYP_I_IMPL);
+                        impStoreToTemp(lclNum, stubAddr, CHECK_SPILL_NONE);
+                        stubAddr = gtNewLclvNode(lclNum, TYP_I_IMPL);
+                    }
 
                     // Create the actual call node