[wasm] Delete hand-written R2R-to-interpreter thunks; use crossgen2's

src/coreclr/build-runtime.cmd

@@ -281,6 +281,9 @@ if "%__TargetOS%"=="android" (
 if "%__TargetOS%"=="browser" (
     set __CrossTarget=1
 )
+if "%__TargetOS%"=="wasi" (
+    set __CrossTarget=1
+)
 
 if %__CrossTarget% EQU 0 (
     call "%__RepoRootDir%\eng\native\version\copy_version_files.cmd"

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs

@@ -862,14 +862,22 @@ public void CompileMethod(MethodWithGCInfo methodCodeNodeNeedingCode, Logger log
                     }
                 }
 
-                // For managed methods on Wasm, add an interpreter-to-R2R thunk so the
-                // interpreter can call into this R2R-compiled function.
+                // For managed methods on Wasm, add both interpreter transition thunks for this
+                // method's signature. The interpreter-to-R2R thunk lets the interpreter call into
+                // this R2R function. The R2R-to-interpreter thunk is keyed by signature, not method:
+                // a method of the same shape that runs interpreted must be enterable from R2R (via a
+                // function pointer, delegate, virtual slot, or the interpreter's own
+                // GetMultiCallableAddrOfCode path), and its thunk is not otherwise rooted unless an
+                // R2R call site happens to share the signature.
                 if (_compilation.NodeFactory.Target.IsWasm && !MethodBeingCompiled.IsUnmanagedCallersOnly)
                 {
                     WasmSignature wasmSig = WasmLowering.GetSignature(MethodBeingCompiled);
                     AddAdditionalDependency(
                         _compilation.NodeFactory.WasmInterpreterToR2RThunk(wasmSig),
                         "Interpreter-to-R2R thunk for compiled method");
+                    AddAdditionalDependency(
+                        _compilation.NodeFactory.WasmR2RToInterpreterThunk(wasmSig),
+                        "R2R-to-interpreter thunk for compiled method signature");
                 }
 
                 var compilationResult = CompileMethodInternal(methodCodeNodeNeedingCode, methodIL);