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

runtime/vm/intrinsifier_x64.cc

Index: runtime/vm/intrinsifier_x64.cc
===================================================================
--- runtime/vm/intrinsifier_x64.cc	(revision 22398)
+++ runtime/vm/intrinsifier_x64.cc	(working copy)
@@ -1488,15 +1488,19 @@
 
 
 // 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));
 
@@ -1509,7 +1513,7 @@
   // 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.
@@ -1517,7 +1521,7 @@
   // 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.
@@ -1547,13 +1551,17 @@
   }
 
   // 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);
 }
 
 
@@ -1565,9 +1573,11 @@
   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));
@@ -1600,6 +1610,32 @@
 }
 
 
+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