[csa] Add GetCodeEntry function

Mirroring Code::entry and CodeDataContainer::code_entry_point.
Unused for now; will be used very soon.

Change-Id: I93b86f0c601a044bb4e6afea642d5d3f721ef73a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3205893Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77249}

src/codegen/code-stub-assembler.cc

@@ -14440,6 +14440,19 @@ TNode<Code> CodeStubAssembler::GetSharedFunctionInfoCode(
   return sfi_code.value();
 }
 
+TNode<RawPtrT> CodeStubAssembler::GetCodeEntry(TNode<CodeT> code) {
+#ifdef V8_EXTERNAL_CODE_SPACE
+  TNode<CodeDataContainer> cdc = CodeDataContainerFromCodeT(code);
+  return LoadExternalPointerFromObject(
+      cdc, IntPtrConstant(CodeDataContainer::kCodeEntryPointOffset),
+      kCodeEntryPointTag);
+#else
+  TNode<IntPtrT> object = BitcastTaggedToWord(code);
+  return ReinterpretCast<RawPtrT>(
+      IntPtrAdd(object, IntPtrConstant(Code::kHeaderSize - kHeapObjectTag)));
+#endif
+}
+
 TNode<JSFunction> CodeStubAssembler::AllocateFunctionWithMapAndContext(
     TNode<Map> map, TNode<SharedFunctionInfo> shared_info,
     TNode<Context> context) {

src/codegen/code-stub-assembler.h

@@ -837,6 +837,8 @@ class V8_EXPORT_PRIVATE CodeStubAssembler
 #endif
   }
 
+  TNode<RawPtrT> GetCodeEntry(TNode<CodeT> code);
+
   // The following Call wrappers call an object according to the semantics that
   // one finds in the EcmaScript spec, operating on an Callable (e.g. a
   // JSFunction or proxy) rather than a Code object.