Introduce --zap-cpp-pointers (off by default)

src/regexp/regexp-macro-assembler.cc

Index: src/regexp/regexp-macro-assembler.cc
diff --git a/src/regexp/regexp-macro-assembler.cc b/src/regexp/regexp-macro-assembler.cc
index 681acc13255fb42ffa735471b126ab2fb8d34c1a..63de1726fe5573d5fa1b29f2d3a505bfbb432952 100644
--- a/src/regexp/regexp-macro-assembler.cc
+++ b/src/regexp/regexp-macro-assembler.cc
@@ -165,9 +165,12 @@ int NativeRegExpMacroAssembler::CheckStackGuardState(
   int return_value = 0;
   // Prepare for possible GC.
   HandleScope handles(isolate);
+  intptr_t return_address_offset =
+      *return_address - re_code->instruction_start();
   Handle<Code> code_handle(re_code);
   Handle<String> subject_handle(*subject);
   bool is_one_byte = subject_handle->IsOneByteRepresentationUnderneath();
+  intptr_t byte_length = *input_end - *input_start;
 
   StackLimitCheck check(isolate);
   bool js_has_overflowed = check.JsHasOverflowed();
@@ -189,11 +192,8 @@ int NativeRegExpMacroAssembler::CheckStackGuardState(
 
   DisallowHeapAllocation no_gc;
 
-  if (*code_handle != re_code) {  // Return address no longer valid
-    intptr_t delta = code_handle->address() - re_code->address();
-    // Overwrite the return address on the stack.
-    *return_address += delta;
-  }
+  // Fix up the return address (it might be no longer valid after GC).
+  *return_address = code_handle->instruction_start() + return_address_offset;
 
   // If we continue, we need to update the subject string addresses.
   if (return_value == 0) {
@@ -205,7 +205,6 @@ int NativeRegExpMacroAssembler::CheckStackGuardState(
       return_value = RETRY;
     } else {
       *subject = *subject_handle;
-      intptr_t byte_length = *input_end - *input_start;
       *input_start = StringCharacterPosition(*subject, start_index);
       *input_end = *input_start + byte_length;
     }