[interpreter] Iterate dispatch table even in embedded handler configs

In an embedded handler build, it's not guaranteed that every handler
is embedded (and thus immovable). The GC must still iterate the
dispatch table to update pointers to moved code objects.

TBR=rmcilroy@chromium.org

Bug: v8:8068
Change-Id: I8b37f1758fdc670081e0c4f58795aea271811994
Reviewed-on: https://chromium-review.googlesource.com/1238236Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56148}

src/heap/heap.cc

@@ -3875,10 +3875,8 @@ void Heap::IterateStrongRoots(RootVisitor* v, VisitMode mode) {
   if (!isMinorGC) {
     IterateBuiltins(v);
     v->Synchronize(VisitorSynchronization::kBuiltins);
-#ifndef V8_EMBEDDED_BYTECODE_HANDLERS
     isolate_->interpreter()->IterateDispatchTable(v);
     v->Synchronize(VisitorSynchronization::kDispatchTable);
-#endif  // V8_EMBEDDED_BYTECODE_HANDLERS
   }
 
   // Iterate over global handles.

src/interpreter/interpreter.cc

@@ -112,10 +112,13 @@ size_t Interpreter::GetDispatchTableIndex(Bytecode bytecode,
                      kEntriesPerOperandScale;
 }
 
-#ifndef V8_EMBEDDED_BYTECODE_HANDLERS
 void Interpreter::IterateDispatchTable(RootVisitor* v) {
   for (int i = 0; i < kDispatchTableSize; i++) {
     Address code_entry = dispatch_table_[i];
+
+    // If the handler is embedded, it is immovable.
+    if (InstructionStream::PcIsOffHeap(isolate_, code_entry)) continue;
+
     Object* code = code_entry == kNullAddress
                        ? nullptr
                        : Code::GetCodeFromTargetAddress(code_entry);
@@ -126,7 +129,6 @@ void Interpreter::IterateDispatchTable(RootVisitor* v) {
     }
   }
 }
-#endif  // V8_EMBEDDED_BYTECODE_HANDLERS
 
 int Interpreter::InterruptBudget() {
   return FLAG_interrupt_budget;

src/interpreter/interpreter.h

@@ -58,10 +58,8 @@ class Interpreter {
   void SetBytecodeHandler(Bytecode bytecode, OperandScale operand_scale,
                           Code* handler);
 
-#ifndef V8_EMBEDDED_BYTECODE_HANDLERS
   // GC support.
   void IterateDispatchTable(RootVisitor* v);
-#endif  // V8_EMBEDDED_BYTECODE_HANDLERS
 
   // Disassembler support (only useful with ENABLE_DISASSEMBLER defined).
   const char* LookupNameOfBytecodeHandler(const Code* code);