[print] Don't allocate when printing JSRegExp

Fixed: v8:12889
Change-Id: Ia11cfc0fb1dfd2952b43b732256d8ed3a144d1cb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3702333
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81100}

src/diagnostics/objects-printer.cc

@@ -712,11 +712,11 @@ void JSPromise::JSPromisePrint(std::ostream& os) {
 }
 
 void JSRegExp::JSRegExpPrint(std::ostream& os) {
-  Isolate* isolate = GetIsolate();
   JSObjectPrintHeader(os, *this, "JSRegExp");
   os << "\n - data: " << Brief(data());
   os << "\n - source: " << Brief(source());
-  os << "\n - flags: " << Brief(*JSRegExp::StringFromFlags(isolate, flags()));
+  FlagsBuffer buffer;
+  os << "\n - flags: " << JSRegExp::FlagsToString(flags(), &buffer);
   JSObjectPrintBody(os, *this);
 }
 

src/objects/js-regexp-inl.h

@@ -65,6 +65,18 @@ JSRegExp::Flags JSRegExp::flags() const {
   return Flags(smi.value());
 }
 
+// static
+const char* JSRegExp::FlagsToString(Flags flags, FlagsBuffer* out_buffer) {
+  int cursor = 0;
+  FlagsBuffer& buffer = *out_buffer;
+#define V(Lower, Camel, LowerCamel, Char, Bit) \
+  if (flags & JSRegExp::k##Camel) buffer[cursor++] = Char;
+  REGEXP_FLAG_LIST(V)
+#undef V
+  buffer[cursor++] = '\0';
+  return buffer.begin();
+}
+
 String JSRegExp::EscapedPattern() {
   DCHECK(this->source().IsString());
   return String::cast(source());

src/objects/js-regexp.cc

@@ -135,16 +135,9 @@ base::Optional<JSRegExp::Flags> JSRegExp::FlagsFromString(
 // static
 Handle<String> JSRegExp::StringFromFlags(Isolate* isolate,
                                          JSRegExp::Flags flags) {
-  static constexpr int kStringTerminator = 1;
-  int cursor = 0;
-  char buffer[kFlagCount + kStringTerminator];
-#define V(Lower, Camel, LowerCamel, Char, Bit) \
-  if (flags & JSRegExp::k##Camel) buffer[cursor++] = Char;
-  REGEXP_FLAG_LIST(V)
-#undef V
-  buffer[cursor++] = '\0';
-  DCHECK_LE(cursor, kFlagCount + kStringTerminator);
-  return isolate->factory()->NewStringFromAsciiChecked(buffer);
+  FlagsBuffer buffer;
+  return isolate->factory()->NewStringFromAsciiChecked(
+      FlagsToString(flags, &buffer));
 }
 
 // static

src/objects/js-regexp.h

@@ -244,6 +244,9 @@ class JSRegExp : public TorqueGeneratedJSRegExp<JSRegExp, JSObject> {
   static constexpr int kMaxCaptures = 1 << 16;
 
  private:
+  using FlagsBuffer = base::EmbeddedVector<char, kFlagCount + 1>;
+  inline static const char* FlagsToString(Flags flags, FlagsBuffer* out_buffer);
+
   inline Object DataAt(int index) const;
   inline void SetDataAt(int index, Object value);