[snapshot] Fix clearing compiled code from JSFunction

JSFunctions with an attached InterpreterEntryTrampoline should also be
reset to CompileLazy, but this was recently broken by
https://crrev.com/c/2345966.

This CL introduces a new JSFunction::CanDiscardCompiled helper to
mirror SFI::CanDiscardCompiled, and uses it during serialization.

Bug: v8:10869
Change-Id: I176b77278d2d40d34db671638232faec4dda1d9c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2390145Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69689}

src/objects/js-function.cc

@@ -147,6 +147,17 @@ CodeKind JSFunction::NextTier() const {
              : CodeKind::OPTIMIZED_FUNCTION;
 }
 
+bool JSFunction::CanDiscardCompiled() const {
+  // Essentially, what we are asking here is, has this function been compiled
+  // from JS code? We can currently tell only indirectly, by looking at
+  // available code kinds. If any JS code kind exists, we can discard.
+  //
+  // Note that when the function has not yet been compiled we also return
+  // false; that's fine, since nothing must be discarded in that case.
+  CodeKinds result = GetAvailableCodeKinds();
+  return (result & kJSFunctionCodeKindsMask) != 0;
+}
+
 bool JSFunction::HasOptimizationMarker() {
   return has_feedback_vector() && feedback_vector().has_optimization_marker();
 }

src/objects/js-function.h

@@ -116,6 +116,11 @@ class JSFunction : public JSFunctionOrBoundFunction {
 
   CodeKind NextTier() const;
 
+  // Similar to SharedFunctionInfo::CanDiscardCompiled. Returns true, if the
+  // attached code can be recreated at a later point by replacing it with
+  // CompileLazy.
+  bool CanDiscardCompiled() const;
+
   // Tells whether or not this function checks its optimization marker in its
   // feedback vector.
   bool ChecksOptimizationMarker();

src/snapshot/snapshot.cc

@@ -251,8 +251,8 @@ void Snapshot::ClearReconstructableDataForSerialization(
       continue;  // Don't clear extensions, they cannot be recompiled.
     }
 
-    // Also, clear out feedback vectors and any optimized code.
-    if (CodeKindIsJSFunction(fun.code().kind())) {
+    // Also, clear out feedback vectors and recompilable code.
+    if (fun.CanDiscardCompiled()) {
       fun.set_code(*BUILTIN_CODE(isolate, CompileLazy));
     }
     if (!fun.raw_feedback_cell().value().IsUndefined()) {