Jit: fix a few issues with single def local tracking

src/jit/gentree.cpp

@@ -16379,6 +16379,14 @@ CORINFO_CLASS_HANDLE Compiler::gtGetClassHandle(GenTreePtr tree, bool* isExact,
     *isExact                      = false;
     CORINFO_CLASS_HANDLE objClass = nullptr;
 
+    // Bail out if we're just importing and not generating code, since
+    // the jit uses TYP_REF for CORINFO_TYPE_VAR locals and args, but
+    // these may not be ref types.
+    if (compIsForImportOnly())
+    {
+        return objClass;
+    }
+
     // Bail out if the tree is not a ref type.
     var_types treeType = tree->TypeGet();
     if (treeType != TYP_REF)

src/jit/importer.cpp

@@ -18515,6 +18515,18 @@ void Compiler::impDevirtualizeCall(GenTreeCall*            call,
     CORINFO_CLASS_HANDLE baseClass        = info.compCompHnd->getMethodClass(baseMethod);
     const DWORD          baseClassAttribs = info.compCompHnd->getClassAttribs(baseClass);
 
+#if !defined(FEATURE_CORECLR)
+    // If base class is not beforefieldinit then devirtualizing may
+    // cause us to miss a base class init trigger. Spec says we don't
+    // need a trigger for ref class callvirts but desktop seems to
+    // have one anyways. So defer.
+    if ((baseClassAttribs & CORINFO_FLG_BEFOREFIELDINIT) == 0)
+    {
+        JITDUMP("\nimpDevirtualizeCall: base class has precise initialization, sorry\n");
+        return;
+    }
+#endif // FEATURE_CORECLR
+
     // Is the call an interface call?
     const bool isInterface = (baseClassAttribs & CORINFO_FLG_INTERFACE) != 0;
 

src/jit/lclvars.cpp

@@ -2312,6 +2312,15 @@ void Compiler::lvaSetStruct(unsigned varNum, CORINFO_CLASS_HANDLE typeHnd, bool
 void Compiler::lvaSetClass(unsigned varNum, CORINFO_CLASS_HANDLE clsHnd, bool isExact)
 {
     noway_assert(varNum < lvaCount);
+
+    // If we are just importing, we cannot reliably track local ref types,
+    // since the jit maps CORINFO_TYPE_VAR to TYP_REF.
+    if (compIsForImportOnly())
+    {
+        return;
+    }
+
+    // Else we should have a type handle.
     assert(clsHnd != nullptr);
 
     LclVarDsc* varDsc = &lvaTable[varNum];
@@ -2384,6 +2393,15 @@ void Compiler::lvaSetClass(unsigned varNum, GenTreePtr tree, CORINFO_CLASS_HANDL
 void Compiler::lvaUpdateClass(unsigned varNum, CORINFO_CLASS_HANDLE clsHnd, bool isExact)
 {
     noway_assert(varNum < lvaCount);
+
+    // If we are just importing, we cannot reliably track local ref types,
+    // since the jit maps CORINFO_TYPE_VAR to TYP_REF.
+    if (compIsForImportOnly())
+    {
+        return;
+    }
+
+    // Else we should have a class handle to consider
     assert(clsHnd != nullptr);
 
     LclVarDsc* varDsc = &lvaTable[varNum];
@@ -2392,12 +2410,22 @@ void Compiler::lvaUpdateClass(unsigned varNum, CORINFO_CLASS_HANDLE clsHnd, bool
     // We should already have a class
     assert(varDsc->lvClassHnd != nullptr);
 
-    // This should be the first and only update for this var
-    assert(!varDsc->lvClassInfoUpdated);
-
 #if defined(DEBUG)
+
+    // In general we only expect one update per local var. However if
+    // a block is re-imported and that block has the only STLOC for
+    // the var, we may see multiple updates. All subsequent updates
+    // should agree on the type, since reimportation is triggered by
+    // type mismatches for things other than ref types.
+    if (varDsc->lvClassInfoUpdated)
+    {
+        assert(varDsc->lvClassHnd == clsHnd);
+        assert(varDsc->lvClassIsExact == isExact);
+    }
+
     // This counts as an update, even if nothing changes.
     varDsc->lvClassInfoUpdated = true;
+
 #endif // defined(DEBUG)
 
     // If previous type was exact, there is nothing to update.  Would