Improve performance of String.fromCharCodes by implementing it in Dart. Add tow internal natives to…

runtime/vm/intrinsifier_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intrinsifier.h"
 
 #include "vm/assembler.h"
@@ skipping 1470 matching lines @@
   __ incq(RAX);
   __ Bind(&set_hash_code);
   __ SmiTag(RAX);
   __ movq(FieldAddress(RBX, String::hash_offset()), RAX);
   __ ret();
   return true;
 }
 
 
 // Allocates one-byte string of length 'end - start'. The content is not
-// initialized.
+// initialized. 'length-reg' contains tagged length.
+// Returns new string as tagged pointer in EAX.
 static void TryAllocateOnebyteString(Assembler* assembler,
+                                     Label* ok,
                                      Label* failure,
-                                     intptr_t start_index_offset,
-                                     intptr_t end_index_offset) {
-  __ movq(RDI, Address(RSP, + end_index_offset));
-  __ subq(RDI, Address(RSP, + start_index_offset));
+                                     Register length_reg) {
+  if (length_reg != RDI) {
+    __ movq(RDI, length_reg);
+  }
+  Label pop_and_fail;
+  __ pushq(RDI);  // Preserve length.
+  __ SmiUntag(RDI);
   const intptr_t fixed_size = sizeof(RawString) + kObjectAlignment - 1;
-  __ SmiUntag(RDI);
   __ leaq(RDI, Address(RDI, TIMES_1, fixed_size));  // RDI is a Smi.
   __ andq(RDI, Immediate(-kObjectAlignment));
 
   Isolate* isolate = Isolate::Current();
   Heap* heap = isolate->heap();
 
   __ movq(RAX, Immediate(heap->TopAddress()));
   __ movq(RAX, Address(RAX, 0));
 
   // RDI: allocation size.
   __ movq(RCX, RAX);
   __ addq(RCX, RDI);
-  __ j(CARRY, failure);
+  __ j(CARRY,  &pop_and_fail);
 
   // Check if the allocation fits into the remaining space.
   // RAX: potential new object start.
   // RCX: potential next object start.
   // RDI: allocation size.
   __ movq(R13, Immediate(heap->EndAddress()));
   __ cmpq(RCX, Address(R13, 0));
-  __ j(ABOVE_EQUAL, failure);
+  __ j(ABOVE_EQUAL, &pop_and_fail);
 
   // Successfully allocated the object(s), now update top to point to
   // next object start and initialize the object.
   __ movq(R13, Immediate(heap->TopAddress()));
   __ movq(Address(R13, 0), RCX);
   __ addq(RAX, Immediate(kHeapObjectTag));
 
   // Initialize the tags.
   // RAX: new object start as a tagged pointer.
   // RDI: allocation size.
   {
     Label size_tag_overflow, done;
     __ cmpq(RDI, Immediate(RawObject::SizeTag::kMaxSizeTag));
     __ j(ABOVE, &size_tag_overflow, Assembler::kNearJump);
     __ shlq(RDI, Immediate(RawObject::kSizeTagBit - kObjectAlignmentLog2));
     __ jmp(&done, Assembler::kNearJump);
 
     __ Bind(&size_tag_overflow);
     __ xorq(RDI, RDI);
     __ Bind(&done);
 
     // Get the class index and insert it into the tags.
     const Class& cls =
         Class::Handle(isolate->object_store()->one_byte_string_class());
     __ orq(RDI, Immediate(RawObject::ClassIdTag::encode(cls.id())));
     __ movq(FieldAddress(RAX, String::tags_offset()), RDI);  // Tags.
   }
 
   // Set the length field.
-  __ movq(RDI, Address(RSP, + end_index_offset));
-  __ subq(RDI, Address(RSP, + start_index_offset));  // Length.
+  __ popq(RDI);
   __ StoreIntoObjectNoBarrier(RAX,
                               FieldAddress(RAX, String::length_offset()),
                               RDI);
   // Clear hash.
   __ movq(FieldAddress(RAX, String::hash_offset()), Immediate(0));
+  __ jmp(ok, Assembler::kNearJump);
+
+  __ Bind(&pop_and_fail);
+  __ popq(RDI);
+  __ jmp(failure);
 }
 
 
 // Arg0: Onebyte String
 // Arg1: Start index as Smi.
 // Arg2: End index as Smi.
 // The indexes must be valid.
 bool Intrinsifier::OneByteString_substringUnchecked(Assembler* assembler) {
   const intptr_t kStringOffset = 3 * kWordSize;
   const intptr_t kStartIndexOffset = 2 * kWordSize;
   const intptr_t kEndIndexOffset = 1 * kWordSize;
-  Label fall_through;
-  TryAllocateOnebyteString(
-      assembler, &fall_through, kStartIndexOffset, kEndIndexOffset);
+  Label fall_through, ok;
+  __ movq(RDI, Address(RSP, + kEndIndexOffset));
+  __ subq(RDI, Address(RSP, + kStartIndexOffset));
+  TryAllocateOnebyteString(assembler, &ok, &fall_through, RDI);
+  __ Bind(&ok);
   // RAX: new string as tagged pointer.
   // Copy string.
   __ movq(RSI, Address(RSP, + kStringOffset));
   __ movq(RBX, Address(RSP, + kStartIndexOffset));
   __ SmiUntag(RBX);
   __ leaq(RSI, FieldAddress(RSI, RBX, TIMES_1, OneByteString::data_offset()));
   // RSI: Start address to copy from (untagged).
   // RBX: Untagged start index.
   __ movq(RCX, Address(RSP, + kEndIndexOffset));
   __ SmiUntag(RCX);
@@ skipping 12 matching lines @@
   __ incq(RDX);
   __ Bind(&check);
   __ cmpq(RDX, RCX);
   __ j(LESS, &loop, Assembler::kNearJump);
   __ ret();
   __ Bind(&fall_through);
   return false;
 }
 
 
+bool Intrinsifier::OneByteString_setAt(Assembler* assembler) {
+  __ movq(RCX, Address(RSP, + 1 * kWordSize));  // Value.
+  __ movq(RBX, Address(RSP, + 2 * kWordSize));  // Index.
+  __ movq(RAX, Address(RSP, + 3 * kWordSize));  // OneByteString.
+  __ SmiUntag(RBX);
+  __ SmiUntag(RCX);
+  __ movb(FieldAddress(RAX, RBX, TIMES_1, OneByteString::data_offset()), RCX);
+  __ ret();
+  return true;
+}
+
+
+bool Intrinsifier::OneByteString_allocate(Assembler* assembler) {
+  __ movq(RDI, Address(RSP, + 1 * kWordSize));  // Length.v=
+  Label fall_through, ok;
+  TryAllocateOnebyteString(assembler, &ok, &fall_through, RDI);
+  // EDI: Start address to copy from (untagged).
+
+  __ Bind(&ok);
+  __ ret();
+
+  __ Bind(&fall_through);
+  return false;
+}
+
+
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64