Optimize GDV checks for objects with known type (#84661)

Co-authored-by: Jan Kotas <jkotas@microsoft.com>
dotnet · Apr 22, 2023 · 7c61b98 · 7c61b98
1 parent a3e0d47
commit 7c61b98
Showing 1 changed file with 37 additions and 12 deletions.
diff --git a/src/coreclr/jit/valuenum.cpp b/src/coreclr/jit/valuenum.cpp
@@ -10638,23 +10638,48 @@ void Compiler::fgValueNumberTree(GenTree* tree)
             {
                 assert(!isVolatile); // We don't expect both volatile and invariant
 
-                // Are we dereferencing the method table slot of some newly allocated object?
-                //
-                bool wasNewobj = false;
-                if ((oper == GT_IND) && (addr->TypeGet() == TYP_REF) && (tree->TypeGet() == TYP_I_IMPL))
+                bool returnsTypeHandle = false;
+                if ((oper == GT_IND) && addr->TypeIs(TYP_REF) && tree->TypeIs(TYP_I_IMPL))
                 {
-                    VNFuncApp  funcApp;
-                    const bool addrIsVNFunc = vnStore->GetVNFunc(addrNvnp.GetLiberal(), &funcApp);
-
-                    if (addrIsVNFunc && (funcApp.m_func == VNF_JitNew) && addrNvnp.BothEqual())
+                    // We try to access GC object's type, let's see if we know the exact type already
+                    // First, we're trying to do that via gtGetClassHandle.
+                    //
+                    bool                 isExact   = false;
+                    bool                 isNonNull = false;
+                    CORINFO_CLASS_HANDLE handle    = gtGetClassHandle(addr, &isExact, &isNonNull);
+                    if (isExact && (handle != NO_CLASS_HANDLE))
                     {
-                        tree->gtVNPair =
-                            vnStore->VNPWithExc(ValueNumPair(funcApp.m_args[0], funcApp.m_args[0]), addrXvnp);
-                        wasNewobj = true;
+                        JITDUMP("IND(obj) is actually a class handle for %s\n", eeGetClassName(handle));
+                        // Filter out all shared generic instantiations
+                        if ((info.compCompHnd->getClassAttribs(handle) & CORINFO_FLG_SHAREDINST) == 0)
+                        {
+                            void* pEmbedClsHnd;
+                            void* embedClsHnd = (void*)info.compCompHnd->embedClassHandle(handle, &pEmbedClsHnd);
+                            if (pEmbedClsHnd == nullptr)
+                            {
+                                // Skip indirect handles for now since this path is mostly for PGO scenarios
+                                assert(embedClsHnd != nullptr);
+                                ValueNum handleVN = vnStore->VNForHandle((ssize_t)embedClsHnd, GTF_ICON_CLASS_HDL);
+                                tree->gtVNPair    = vnStore->VNPWithExc(ValueNumPair(handleVN, handleVN), addrXvnp);
+                                returnsTypeHandle = true;
+                            }
+                        }
+                    }
+                    else
+                    {
+                        // Then, let's see if we can find JitNew at least
+                        VNFuncApp  funcApp;
+                        const bool addrIsVNFunc = vnStore->GetVNFunc(addrNvnp.GetLiberal(), &funcApp);
+                        if (addrIsVNFunc && (funcApp.m_func == VNF_JitNew) && addrNvnp.BothEqual())
+                        {
+                            tree->gtVNPair =
+                                vnStore->VNPWithExc(ValueNumPair(funcApp.m_args[0], funcApp.m_args[0]), addrXvnp);
+                            returnsTypeHandle = true;
+                        }
                     }
                 }
 
-                if (!wasNewobj)
+                if (!returnsTypeHandle)
                 {
                     // Indirections off of addresses for boxed statics represent bases for
                     // the address of the static itself. Here we will use "nullptr" for the