More elimination of new space allocation, fix bugs in Symbols::FromConcatAll

runtime/vm/symbols.cc

Index: runtime/vm/symbols.cc
diff --git a/runtime/vm/symbols.cc b/runtime/vm/symbols.cc
index be081818ba689bfeff188d4dc054f38f1e4668c5..d8683fe7ab967f99998d6d50db5beeadb3725482 100644
--- a/runtime/vm/symbols.cc
+++ b/runtime/vm/symbols.cc
@@ -397,27 +397,59 @@ RawString* Symbols::FromConcat(const String& str1, const String& str2) {
 // up symbol from pieces instead of concatenating them first into a big string.
 RawString* Symbols::FromConcatAll(
     const GrowableHandlePtrArray<const String>& strs) {
-  GrowableArray<const char*> cchars(strs.length());
-  GrowableArray<intptr_t> lengths(strs.length());
+  const intptr_t strs_length = strs.length();
+  GrowableArray<intptr_t> lengths(strs_length);
+
   intptr_t len_sum = 0;
-  for (intptr_t i = 0; i < strs.length(); i++) {
-    const char* to_cstr = strs[i].ToCString();
-    intptr_t len = strlen(to_cstr);
-    cchars.Add(to_cstr);
-    lengths.Add(len);
-    len_sum += len;
+  bool is_one_byte_string = true;
+  for (intptr_t i = 0; i < strs_length; i++) {
+    const String& str = strs[i];
+    const intptr_t str_len = str.Length();
+    if ((String::kMaxElements - len_sum) < str_len) {
+      Exceptions::ThrowOOM();
+      UNREACHABLE();
+    }
+    len_sum += str_len;
+    lengths.Add(str_len);
+    if (!str.IsOneByteString()) {
+      is_one_byte_string = false;
+    }
   }
 
   Zone* zone = Thread::Current()->zone();
-  char* buffer = zone->Alloc<char>(len_sum);
-  const char* const orig_buffer = buffer;
-  for (intptr_t i = 0; i < cchars.length(); i++) {
-    intptr_t len = lengths[i];
-    strncpy(buffer, cchars[i], len);
-    buffer += len;
-  }
-  ASSERT(len_sum == buffer - orig_buffer);
-  return Symbols::New(orig_buffer, len_sum);
+
+  if (is_one_byte_string) {
+    uint8_t* buffer = zone->Alloc<uint8_t>(len_sum);
+    const uint8_t* const orig_buffer = buffer;
+    for (intptr_t i = 0; i < strs_length; i++) {
+      NoSafepointScope no_safepoint;
+      intptr_t str_len = lengths[i];
+      const String& str = strs[i];
+      memmove(buffer, OneByteString::CharAddr(str, 0), str_len);
+      buffer += str_len;
+    }
+    ASSERT(len_sum == buffer - orig_buffer);
+    return Symbols::FromLatin1(orig_buffer, len_sum);
+  } else {
+    uint16_t* buffer = zone->Alloc<uint16_t>(len_sum);
+    const uint16_t* const orig_buffer = buffer;
+    for (intptr_t i = 0; i < strs_length; i++) {
+      NoSafepointScope no_safepoint;
+      intptr_t str_len = lengths[i];
+      const String& str = strs[i];
+      if (str.IsTwoByteString()) {
+        memmove(buffer, TwoByteString::CharAddr(str, 0), str_len * 2);
+      } else {
+        uint8_t* src_p = OneByteString::CharAddr(str, 0);
+        for (int n = 0; n < str_len; n++) {
+          buffer[n] = src_p[n];
+        }
+      }
+      buffer += str_len;
+    }
+    ASSERT(len_sum == buffer - orig_buffer);
+    return Symbols::FromUTF16(orig_buffer, len_sum);
+  }
 }