Merge changes up to V8 version 2.1.3 into the partial snapshots

src/arm/codegen-arm.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 13 matching lines @@
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "v8.h"
 
 #include "bootstrapper.h"
 #include "codegen-inl.h"
 #include "compiler.h"
 #include "debug.h"
+#include "ic-inl.h"
 #include "parser.h"
 #include "register-allocator-inl.h"
 #include "runtime.h"
 #include "scopes.h"
-
+#include "virtual-frame-inl.h"
 
 namespace v8 {
 namespace internal {
 
 #define __ ACCESS_MASM(masm_)
 
 static void EmitIdenticalObjectComparison(MacroAssembler* masm,
                                           Label* slow,
                                           Condition cc,
                                           bool never_nan_nan);
@@ skipping 77 matching lines @@
       masm_(masm),
       info_(NULL),
       frame_(NULL),
       allocator_(NULL),
       cc_reg_(al),
       state_(NULL),
       function_return_is_shadowed_(false) {
 }
 
 
-Scope* CodeGenerator::scope() { return info_->function()->scope(); }
-
-
 // Calling conventions:
 // fp: caller's frame pointer
 // sp: stack pointer
 // r1: called JS function
 // cp: callee's context
 
 void CodeGenerator::Generate(CompilationInfo* info) {
   // Record the position for debugging purposes.
   CodeForFunctionPosition(info->function());
+  Comment cmnt(masm_, "[ function compiled by virtual frame code generator");
 
   // Initialize state.
   info_ = info;
   ASSERT(allocator_ == NULL);
   RegisterAllocator register_allocator(this);
   allocator_ = &register_allocator;
   ASSERT(frame_ == NULL);
   frame_ = new VirtualFrame();
   cc_reg_ = al;
   {
@@ skipping 3159 matching lines @@
 void CodeGenerator::GenerateIsNonNegativeSmi(ZoneList<Expression*>* args) {
   VirtualFrame::SpilledScope spilled_scope;
   ASSERT(args->length() == 1);
   LoadAndSpill(args->at(0));
   frame_->EmitPop(r0);
   __ tst(r0, Operand(kSmiTagMask | 0x80000000u));
   cc_reg_ = eq;
 }
 
 
+// Generates the Math.pow method - currently just calls runtime.
+void CodeGenerator::GenerateMathPow(ZoneList<Expression*>* args) {
+  ASSERT(args->length() == 2);
+  Load(args->at(0));
+  Load(args->at(1));
+  frame_->CallRuntime(Runtime::kMath_pow, 2);
+  frame_->EmitPush(r0);
+}
+
+
+// Generates the Math.sqrt method - currently just calls runtime.
+void CodeGenerator::GenerateMathSqrt(ZoneList<Expression*>* args) {
+  ASSERT(args->length() == 1);
+  Load(args->at(0));
+  frame_->CallRuntime(Runtime::kMath_sqrt, 1);
+  frame_->EmitPush(r0);
+}
+
+
 // This should generate code that performs a charCodeAt() call or returns
 // undefined in order to trigger the slow case, Runtime_StringCharCodeAt.
 // It is not yet implemented on ARM, so it always goes to the slow case.
 void CodeGenerator::GenerateFastCharCodeAt(ZoneList<Expression*>* args) {
   VirtualFrame::SpilledScope spilled_scope;
   ASSERT(args->length() == 2);
   Comment(masm_, "[ GenerateFastCharCodeAt");
 
   LoadAndSpill(args->at(0));
   LoadAndSpill(args->at(1));
@@ skipping 63 matching lines @@
   __ jmp(&try_again_with_new_string);
 
   __ bind(&slow);
   __ LoadRoot(r0, Heap::kUndefinedValueRootIndex);
 
   __ bind(&end);
   frame_->EmitPush(r0);
 }
 
 
+void CodeGenerator::GenerateCharFromCode(ZoneList<Expression*>* args) {
+  Comment(masm_, "[ GenerateCharFromCode");
+  ASSERT(args->length() == 1);
+
+  LoadAndSpill(args->at(0));
+  frame_->EmitPop(r0);
+
+  JumpTarget slow_case;
+  JumpTarget exit;
+
+  // Fast case of Heap::LookupSingleCharacterStringFromCode.
+  ASSERT(kSmiTag == 0);
+  ASSERT(kSmiShiftSize == 0);
+  ASSERT(IsPowerOf2(String::kMaxAsciiCharCode + 1));
+  __ tst(r0, Operand(kSmiTagMask |
+                     ((~String::kMaxAsciiCharCode) << kSmiTagSize)));
+  slow_case.Branch(nz);
+
+  ASSERT(kSmiTag == 0);
+  __ mov(r1, Operand(Factory::single_character_string_cache()));
+  __ add(r1, r1, Operand(r0, LSL, kPointerSizeLog2 - kSmiTagSize));
+  __ ldr(r1, MemOperand(r1, FixedArray::kHeaderSize - kHeapObjectTag));
+  __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
+  __ cmp(r1, ip);
+  slow_case.Branch(eq);
+
+  frame_->EmitPush(r1);
+  exit.Jump();
+
+  slow_case.Bind();
+  frame_->EmitPush(r0);
+  frame_->CallRuntime(Runtime::kCharFromCode, 1);
+  frame_->EmitPush(r0);
+
+  exit.Bind();
+}
+
+
 void CodeGenerator::GenerateIsArray(ZoneList<Expression*>* args) {
   VirtualFrame::SpilledScope spilled_scope;
   ASSERT(args->length() == 1);
   LoadAndSpill(args->at(0));
   JumpTarget answer;
   // We need the CC bits to come out as not_equal in the case where the
   // object is a smi.  This can't be done with the usual test opcode so
   // we use XOR to get the right CC bits.
   frame_->EmitPop(r0);
   __ and_(r1, r0, Operand(kSmiTagMask));
@@ skipping 1083 matching lines @@
     }
   }
 
   // Return result. The argument boilerplate has been popped already.
   __ Ret();
 
   // Create a new closure through the slower runtime call.
   __ bind(&gc);
   __ push(cp);
   __ push(r3);
-  __ TailCallRuntime(ExternalReference(Runtime::kNewClosure), 2, 1);
+  __ TailCallRuntime(Runtime::kNewClosure, 2, 1);
 }
 
 
 void FastNewContextStub::Generate(MacroAssembler* masm) {
   // Try to allocate the context in new space.
   Label gc;
   int length = slots_ + Context::MIN_CONTEXT_SLOTS;
 
   // Attempt to allocate the context in new space.
   __ AllocateInNewSpace(length + (FixedArray::kHeaderSize / kPointerSize),
@@ skipping 29 matching lines @@
     __ str(r1, MemOperand(r0, Context::SlotOffset(i)));
   }
 
   // Remove the on-stack argument and return.
   __ mov(cp, r0);
   __ pop();
   __ Ret();
 
   // Need to collect. Call into runtime system.
   __ bind(&gc);
-  __ TailCallRuntime(ExternalReference(Runtime::kNewContext), 1, 1);
+  __ TailCallRuntime(Runtime::kNewContext, 1, 1);
 }
 
 
 void FastCloneShallowArrayStub::Generate(MacroAssembler* masm) {
   // Stack layout on entry:
   //
   // [sp]: constant elements.
   // [sp + kPointerSize]: literal index.
   // [sp + (2 * kPointerSize)]: literals array.
 
@@ skipping 41 matching lines @@
       __ ldr(r1, FieldMemOperand(r3, i));
       __ str(r1, FieldMemOperand(r2, i));
     }
   }
 
   // Return and remove the on-stack parameters.
   __ add(sp, sp, Operand(3 * kPointerSize));
   __ Ret();
 
   __ bind(&slow_case);
-  ExternalReference runtime(Runtime::kCreateArrayLiteralShallow);
-  __ TailCallRuntime(runtime, 3, 1);
+  __ TailCallRuntime(Runtime::kCreateArrayLiteralShallow, 3, 1);
 }
 
 
 // Count leading zeros in a 32 bit word.  On ARM5 and later it uses the clz
 // instruction.  On pre-ARM5 hardware this routine gives the wrong answer for 0
 // (31 instead of 32).
 static void CountLeadingZeros(
     MacroAssembler* masm,
     Register source,
     Register scratch,
@@ skipping 1547 matching lines @@
       break;
     }
 
     default: UNREACHABLE();
   }
   // This code should be unreachable.
   __ stop("Unreachable");
 }
 
 
+Handle<Code> GetBinaryOpStub(int key, BinaryOpIC::TypeInfo type_info) {
+  return Handle<Code>::null();
+}
+
+
 void StackCheckStub::Generate(MacroAssembler* masm) {
   // Do tail-call to runtime routine.  Runtime routines expect at least one
   // argument, so give it a Smi.
   __ mov(r0, Operand(Smi::FromInt(0)));
   __ push(r0);
-  __ TailCallRuntime(ExternalReference(Runtime::kStackGuard), 1, 1);
+  __ TailCallRuntime(Runtime::kStackGuard, 1, 1);
 
   __ StubReturn(1);
 }
 
 
 void GenericUnaryOpStub::Generate(MacroAssembler* masm) {
   Label slow, done;
 
   if (op_ == Token::SUB) {
     // Check whether the value is a smi.
@@ skipping 588 matching lines @@
   // Read the argument from the adaptor frame and return it.
   __ sub(r3, r0, r1);
   __ add(r3, r2, Operand(r3, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(r0, MemOperand(r3, kDisplacement));
   __ Jump(lr);
 
   // Slow-case: Handle non-smi or out-of-bounds access to arguments
   // by calling the runtime system.
   __ bind(&slow);
   __ push(r1);
-  __ TailCallRuntime(ExternalReference(Runtime::kGetArgumentsProperty), 1, 1);
+  __ TailCallRuntime(Runtime::kGetArgumentsProperty, 1, 1);
 }
 
 
 void ArgumentsAccessStub::GenerateNewObject(MacroAssembler* masm) {
   // sp[0] : number of parameters
   // sp[4] : receiver displacement
   // sp[8] : function
 
   // Check if the calling frame is an arguments adaptor frame.
   Label adaptor_frame, try_allocate, runtime;
@@ skipping 82 matching lines @@
   __ cmp(r1, Operand(0));
   __ b(ne, &loop);
 
   // Return and remove the on-stack parameters.
   __ bind(&done);
   __ add(sp, sp, Operand(3 * kPointerSize));
   __ Ret();
 
   // Do the runtime call to allocate the arguments object.
   __ bind(&runtime);
-  __ TailCallRuntime(ExternalReference(Runtime::kNewArgumentsFast), 3, 1);
+  __ TailCallRuntime(Runtime::kNewArgumentsFast, 3, 1);
 }
 
 
 void CallFunctionStub::Generate(MacroAssembler* masm) {
   Label slow;
 
   // If the receiver might be a value (string, number or boolean) check for this
   // and box it if it is.
   if (ReceiverMightBeValue()) {
     // Get the receiver from the stack.
@@ skipping 270 matching lines @@
   __ cmp(dest, Operand(limit));
   __ ldrb(scratch1, MemOperand(src, 1, PostIndex), lt);
   __ b(ge, &done);
   __ strb(scratch1, MemOperand(dest, 1, PostIndex));
   __ b(&byte_loop);
 
   __ bind(&done);
 }
 
 
+void StringStubBase::GenerateTwoCharacterSymbolTableProbe(MacroAssembler* masm,
+                                                          Register c1,
+                                                          Register c2,
+                                                          Register scratch1,
+                                                          Register scratch2,
+                                                          Register scratch3,
+                                                          Register scratch4,
+                                                          Register scratch5,
+                                                          Label* not_found) {
+  // Register scratch3 is the general scratch register in this function.
+  Register scratch = scratch3;
+
+  // Make sure that both characters are not digits as such strings has a
+  // different hash algorithm. Don't try to look for these in the symbol table.
+  Label not_array_index;
+  __ sub(scratch, c1, Operand(static_cast<int>('0')));
+  __ cmp(scratch, Operand(static_cast<int>('9' - '0')));
+  __ b(hi, &not_array_index);
+  __ sub(scratch, c2, Operand(static_cast<int>('0')));
+  __ cmp(scratch, Operand(static_cast<int>('9' - '0')));
+
+  // If check failed combine both characters into single halfword.
+  // This is required by the contract of the method: code at the
+  // not_found branch expects this combination in c1 register
+  __ orr(c1, c1, Operand(c2, LSL, kBitsPerByte), LeaveCC, ls);
+  __ b(ls, not_found);
+
+  __ bind(&not_array_index);
+  // Calculate the two character string hash.
+  Register hash = scratch1;
+  GenerateHashInit(masm, hash, c1);
+  GenerateHashAddCharacter(masm, hash, c2);
+  GenerateHashGetHash(masm, hash);
+
+  // Collect the two characters in a register.
+  Register chars = c1;
+  __ orr(chars, chars, Operand(c2, LSL, kBitsPerByte));
+
+  // chars: two character string, char 1 in byte 0 and char 2 in byte 1.
+  // hash:  hash of two character string.
+
+  // Load symbol table
+  // Load address of first element of the symbol table.
+  Register symbol_table = c2;
+  __ LoadRoot(symbol_table, Heap::kSymbolTableRootIndex);
+
+  // Load undefined value
+  Register undefined = scratch4;
+  __ LoadRoot(undefined, Heap::kUndefinedValueRootIndex);
+
+  // Calculate capacity mask from the symbol table capacity.
+  Register mask = scratch2;
+  __ ldr(mask, FieldMemOperand(symbol_table, SymbolTable::kCapacityOffset));
+  __ mov(mask, Operand(mask, ASR, 1));
+  __ sub(mask, mask, Operand(1));
+
+  // Calculate untagged address of the first element of the symbol table.
+  Register first_symbol_table_element = symbol_table;
+  __ add(first_symbol_table_element, symbol_table,
+         Operand(SymbolTable::kElementsStartOffset - kHeapObjectTag));
+
+  // Registers
+  // chars: two character string, char 1 in byte 0 and char 2 in byte 1.
+  // hash:  hash of two character string
+  // mask:  capacity mask
+  // first_symbol_table_element: address of the first element of
+  //                             the symbol table
+  // scratch: -
+
+  // Perform a number of probes in the symbol table.
+  static const int kProbes = 4;
+  Label found_in_symbol_table;
+  Label next_probe[kProbes];
+  for (int i = 0; i < kProbes; i++) {
+    Register candidate = scratch5;  // Scratch register contains candidate.
+
+    // Calculate entry in symbol table.
+    if (i > 0) {
+      __ add(candidate, hash, Operand(SymbolTable::GetProbeOffset(i)));
+    } else {
+      __ mov(candidate, hash);
+    }
+
+    __ and_(candidate, candidate, Operand(mask));
+
+    // Load the entry from the symble table.
+    ASSERT_EQ(1, SymbolTable::kEntrySize);
+    __ ldr(candidate,
+           MemOperand(first_symbol_table_element,
+                      candidate,
+                      LSL,
+                      kPointerSizeLog2));
+
+    // If entry is undefined no string with this hash can be found.
+    __ cmp(candidate, undefined);
+    __ b(eq, not_found);
+
+    // If length is not 2 the string is not a candidate.
+    __ ldr(scratch, FieldMemOperand(candidate, String::kLengthOffset));
+    __ cmp(scratch, Operand(2));
+    __ b(ne, &next_probe[i]);
+
+    // Check that the candidate is a non-external ascii string.
+    __ ldr(scratch, FieldMemOperand(candidate, HeapObject::kMapOffset));
+    __ ldrb(scratch, FieldMemOperand(scratch, Map::kInstanceTypeOffset));
+    __ JumpIfInstanceTypeIsNotSequentialAscii(scratch, scratch,
+                                              &next_probe[i]);
+
+    // Check if the two characters match.
+    // Assumes that word load is little endian.
+    __ ldrh(scratch, FieldMemOperand(candidate, SeqAsciiString::kHeaderSize));
+    __ cmp(chars, scratch);
+    __ b(eq, &found_in_symbol_table);
+    __ bind(&next_probe[i]);
+  }
+
+  // No matching 2 character string found by probing.
+  __ jmp(not_found);
+
+  // Scratch register contains result when we fall through to here.
+  Register result = scratch;
+  __ bind(&found_in_symbol_table);
+  if (!result.is(r0)) {
+    __ mov(r0, result);
+  }
+}
+
+
+void StringStubBase::GenerateHashInit(MacroAssembler* masm,
+                                      Register hash,
+                                      Register character) {
+  // hash = character + (character << 10);
+  __ add(hash, character, Operand(character, LSL, 10));
+  // hash ^= hash >> 6;
+  __ eor(hash, hash, Operand(hash, ASR, 6));
+}
+
+
+void StringStubBase::GenerateHashAddCharacter(MacroAssembler* masm,
+                                              Register hash,
+                                              Register character) {
+  // hash += character;
+  __ add(hash, hash, Operand(character));
+  // hash += hash << 10;
+  __ add(hash, hash, Operand(hash, LSL, 10));
+  // hash ^= hash >> 6;
+  __ eor(hash, hash, Operand(hash, ASR, 6));
+}
+
+
+void StringStubBase::GenerateHashGetHash(MacroAssembler* masm,
+                                         Register hash) {
+  // hash += hash << 3;
+  __ add(hash, hash, Operand(hash, LSL, 3));
+  // hash ^= hash >> 11;
+  __ eor(hash, hash, Operand(hash, ASR, 11));
+  // hash += hash << 15;
+  __ add(hash, hash, Operand(hash, LSL, 15), SetCC);
+
+  // if (hash == 0) hash = 27;
+  __ mov(hash, Operand(27), LeaveCC, nz);
+}
+
+
 void SubStringStub::Generate(MacroAssembler* masm) {
   Label runtime;
 
   // Stack frame on entry.
   //  lr: return address
   //  sp[0]: to
   //  sp[4]: from
   //  sp[8]: string
 
   // This stub is called from the native-call %_SubString(...), so
@@ skipping 15 matching lines @@
   ASSERT_EQ(1, kSmiTagSize + kSmiShiftSize);
   // I.e., arithmetic shift right by one un-smi-tags.
   __ mov(r2, Operand(r7, ASR, 1), SetCC);
   __ mov(r3, Operand(r6, ASR, 1), SetCC, cc);
   // If either r2 or r6 had the smi tag bit set, then carry is set now.
   __ b(cs, &runtime);  // Either "from" or "to" is not a smi.
   __ b(mi, &runtime);  // From is negative.
 
   __ sub(r2, r2, Operand(r3), SetCC);
   __ b(mi, &runtime);  // Fail if from > to.
-  // Handle sub-strings of length 2 and less in the runtime system.
+  // Special handling of sub-strings of length 1 and 2. One character strings
+  // are handled in the runtime system (looked up in the single character
+  // cache). Two character strings are looked for in the symbol cache.
   __ cmp(r2, Operand(2));
-  __ b(le, &runtime);
+  __ b(lt, &runtime);
 
   // r2: length
+  // r3: from index (untaged smi)
   // r6: from (smi)
   // r7: to (smi)
 
   // Make sure first argument is a sequential (or flat) string.
   __ ldr(r5, MemOperand(sp, kStringOffset));
   ASSERT_EQ(0, kSmiTag);
   __ tst(r5, Operand(kSmiTagMask));
   __ b(eq, &runtime);
   Condition is_string = masm->IsObjectStringType(r5, r1);
   __ b(NegateCondition(is_string), &runtime);
 
   // r1: instance type
   // r2: length
+  // r3: from index (untaged smi)
   // r5: string
   // r6: from (smi)
   // r7: to (smi)
   Label seq_string;
   __ and_(r4, r1, Operand(kStringRepresentationMask));
   ASSERT(kSeqStringTag < kConsStringTag);
   ASSERT(kExternalStringTag > kConsStringTag);
   __ cmp(r4, Operand(kConsStringTag));
   __ b(gt, &runtime);  // External strings go to runtime.
   __ b(lt, &seq_string);  // Sequential strings are handled directly.
 
   // Cons string. Try to recurse (once) on the first substring.
   // (This adds a little more generality than necessary to handle flattened
   // cons strings, but not much).
   __ ldr(r5, FieldMemOperand(r5, ConsString::kFirstOffset));
   __ ldr(r4, FieldMemOperand(r5, HeapObject::kMapOffset));
   __ ldrb(r1, FieldMemOperand(r4, Map::kInstanceTypeOffset));
   __ tst(r1, Operand(kStringRepresentationMask));
   ASSERT_EQ(0, kSeqStringTag);
   __ b(ne, &runtime);  // Cons and External strings go to runtime.
 
   // Definitly a sequential string.
   __ bind(&seq_string);
 
   // r1: instance type.
   // r2: length
+  // r3: from index (untaged smi)
   // r5: string
   // r6: from (smi)
   // r7: to (smi)
   __ ldr(r4, FieldMemOperand(r5, String::kLengthOffset));
   __ cmp(r4, Operand(r7, ASR, 1));
   __ b(lt, &runtime);  // Fail if to > length.
 
   // r1: instance type.
   // r2: result string length.
+  // r3: from index (untaged smi)
   // r5: string.
   // r6: from offset (smi)
   // Check for flat ascii string.
   Label non_ascii_flat;
   __ tst(r1, Operand(kStringEncodingMask));
   ASSERT_EQ(0, kTwoByteStringTag);
   __ b(eq, &non_ascii_flat);
 
+  Label result_longer_than_two;
+  __ cmp(r2, Operand(2));
+  __ b(gt, &result_longer_than_two);
+
+  // Sub string of length 2 requested.
+  // Get the two characters forming the sub string.
+  __ add(r5, r5, Operand(r3));
+  __ ldrb(r3, FieldMemOperand(r5, SeqAsciiString::kHeaderSize));
+  __ ldrb(r4, FieldMemOperand(r5, SeqAsciiString::kHeaderSize + 1));
+
+  // Try to lookup two character string in symbol table.
+  Label make_two_character_string;
+  GenerateTwoCharacterSymbolTableProbe(masm, r3, r4, r1, r5, r6, r7, r9,
+                                       &make_two_character_string);
+  __ IncrementCounter(&Counters::sub_string_native, 1, r3, r4);
+  __ add(sp, sp, Operand(3 * kPointerSize));
+  __ Ret();
+
+  // r2: result string length.
+  // r3: two characters combined into halfword in little endian byte order.
+  __ bind(&make_two_character_string);
+  __ AllocateAsciiString(r0, r2, r4, r5, r9, &runtime);
+  __ strh(r3, FieldMemOperand(r0, SeqAsciiString::kHeaderSize));
+  __ IncrementCounter(&Counters::sub_string_native, 1, r3, r4);
+  __ add(sp, sp, Operand(3 * kPointerSize));
+  __ Ret();
+
+  __ bind(&result_longer_than_two);
+
   // Allocate the result.
   __ AllocateAsciiString(r0, r2, r3, r4, r1, &runtime);
 
   // r0: result string.
   // r2: result string length.
   // r5: string.
   // r6: from offset (smi)
   // Locate first character of result.
   __ add(r1, r0, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
   // Locate 'from' character of string.
@@ skipping 37 matching lines @@
   // r5: first character of string to copy.
   ASSERT_EQ(0, SeqTwoByteString::kHeaderSize & kObjectAlignmentMask);
   GenerateCopyCharactersLong(masm, r1, r5, r2, r3, r4, r6, r7, r9,
                              DEST_ALWAYS_ALIGNED);
   __ IncrementCounter(&Counters::sub_string_native, 1, r3, r4);
   __ add(sp, sp, Operand(3 * kPointerSize));
   __ Ret();
 
   // Just jump to runtime to create the sub string.
   __ bind(&runtime);
-  __ TailCallRuntime(ExternalReference(Runtime::kSubString), 3, 1);
+  __ TailCallRuntime(Runtime::kSubString, 3, 1);
 }
 
 
 void StringCompareStub::GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                                         Register left,
                                                         Register right,
                                                         Register scratch1,
                                                         Register scratch2,
                                                         Register scratch3,
                                                         Register scratch4) {
@@ skipping 70 matching lines @@
   __ JumpIfNotBothSequentialAsciiStrings(r0, r1, r2, r3, &runtime);
 
   // Compare flat ascii strings natively. Remove arguments from stack first.
   __ IncrementCounter(&Counters::string_compare_native, 1, r2, r3);
   __ add(sp, sp, Operand(2 * kPointerSize));
   GenerateCompareFlatAsciiStrings(masm, r0, r1, r2, r3, r4, r5);
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
-  __ TailCallRuntime(ExternalReference(Runtime::kStringCompare), 2, 1);
+  __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 
 void StringAddStub::Generate(MacroAssembler* masm) {
   Label string_add_runtime;
   // Stack on entry:
   // sp[0]: second argument.
   // sp[4]: first argument.
 
   // Load the two arguments.
@@ skipping 39 matching lines @@
   }
 
   // Both strings are non-empty.
   // r0: first string
   // r1: second string
   // r2: length of first string
   // r3: length of second string
   // r4: first string instance type (if string_check_)
   // r5: second string instance type (if string_check_)
   // Look at the length of the result of adding the two strings.
-  Label string_add_flat_result;
+  Label string_add_flat_result, longer_than_two;
   // Adding two lengths can't overflow.
   ASSERT(String::kMaxLength * 2 > String::kMaxLength);
   __ add(r6, r2, Operand(r3));
   // Use the runtime system when adding two one character strings, as it
   // contains optimizations for this specific case using the symbol table.
   __ cmp(r6, Operand(2));
-  __ b(eq, &string_add_runtime);
+  __ b(ne, &longer_than_two);
+
+  // Check that both strings are non-external ascii strings.
+  if (!string_check_) {
+    __ ldr(r4, FieldMemOperand(r0, HeapObject::kMapOffset));
+    __ ldr(r5, FieldMemOperand(r1, HeapObject::kMapOffset));
+    __ ldrb(r4, FieldMemOperand(r4, Map::kInstanceTypeOffset));
+    __ ldrb(r5, FieldMemOperand(r5, Map::kInstanceTypeOffset));
+  }
+  __ JumpIfBothInstanceTypesAreNotSequentialAscii(r4, r5, r6, r7,
+                                                  &string_add_runtime);
+
+  // Get the two characters forming the sub string.
+  __ ldrb(r2, FieldMemOperand(r0, SeqAsciiString::kHeaderSize));
+  __ ldrb(r3, FieldMemOperand(r1, SeqAsciiString::kHeaderSize));
+
+  // Try to lookup two character string in symbol table. If it is not found
+  // just allocate a new one.
+  Label make_two_character_string;
+  GenerateTwoCharacterSymbolTableProbe(masm, r2, r3, r6, r7, r4, r5, r9,
+                                       &make_two_character_string);
+  __ IncrementCounter(&Counters::string_add_native, 1, r2, r3);
+  __ add(sp, sp, Operand(2 * kPointerSize));
+  __ Ret();
+
+  __ bind(&make_two_character_string);
+  // Resulting string has length 2 and first chars of two strings
+  // are combined into single halfword in r2 register.
+  // So we can fill resulting string without two loops by a single
+  // halfword store instruction (which assumes that processor is
+  // in a little endian mode)
+  __ mov(r6, Operand(2));
+  __ AllocateAsciiString(r0, r6, r4, r5, r9, &string_add_runtime);
+  __ strh(r2, FieldMemOperand(r0, SeqAsciiString::kHeaderSize));
+  __ IncrementCounter(&Counters::string_add_native, 1, r2, r3);
+  __ add(sp, sp, Operand(2 * kPointerSize));
+  __ Ret();
+
+  __ bind(&longer_than_two);
   // Check if resulting string will be flat.
   __ cmp(r6, Operand(String::kMinNonFlatLength));
   __ b(lt, &string_add_flat_result);
   // Handle exceptionally long strings in the runtime system.
   ASSERT((String::kMaxLength & 0x80000000) == 0);
   ASSERT(IsPowerOf2(String::kMaxLength + 1));
   // kMaxLength + 1 is representable as shifted literal, kMaxLength is not.
   __ cmp(r6, Operand(String::kMaxLength + 1));
   __ b(hs, &string_add_runtime);
 
@@ skipping 58 matching lines @@
   ASSERT(IsPowerOf2(kStringEncodingMask));  // Just one bit to test.
   __ eor(r7, r4, Operand(r5));
   __ tst(r7, Operand(kStringEncodingMask));
   __ b(ne, &string_add_runtime);
   // And see if it's ASCII or two-byte.
   __ tst(r4, Operand(kStringEncodingMask));
   __ b(eq, &non_ascii_string_add_flat_result);
 
   // Both strings are sequential ASCII strings. We also know that they are
   // short (since the sum of the lengths is less than kMinNonFlatLength).
+  // r6: length of resulting flat string
   __ AllocateAsciiString(r7, r6, r4, r5, r9, &string_add_runtime);
   // Locate first character of result.
   __ add(r6, r7, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
   // Locate first character of first argument.
   __ add(r0, r0, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
   // r0: first character of first string.
   // r1: second string.
   // r2: length of first string.
   // r3: length of second string.
   // r6: first character of result.
@@ skipping 48 matching lines @@
   // r7: result string.
   GenerateCopyCharacters(masm, r6, r1, r3, r4, false);
 
   __ mov(r0, Operand(r7));
   __ IncrementCounter(&Counters::string_add_native, 1, r2, r3);
   __ add(sp, sp, Operand(2 * kPointerSize));
   __ Ret();
 
   // Just jump to runtime to add the two strings.
   __ bind(&string_add_runtime);
-  __ TailCallRuntime(ExternalReference(Runtime::kStringAdd), 2, 1);
+  __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal