MIPS: Do not go to slow mode and back to fast in initializer blocks.

Port r12534 (4acfb92e)

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10905313
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12539 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/full-codegen-mips.cc

@@ -2759,27 +2759,31 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   __ Branch(if_false, eq, a2, Operand(t0));
 
   // Look for valueOf symbol in the descriptor array, and indicate false if
-  // found. The type is not checked, so if it is a transition it is a false
-  // negative.
-  __ LoadInstanceDescriptors(a1, t0, a3);
-  __ lw(a3, FieldMemOperand(t0, FixedArray::kLengthOffset));
-  // t0: descriptor array
-  // a3: length of descriptor array
-  // Calculate the end of the descriptor array.
+  // found. Since we omit an enumeration index check, if it is added via a
+  // transition that shares its descriptor array, this is a false positive.
+  Label entry, loop, done;
+
+  // Skip loop if no descriptors are valid.
+  __ NumberOfOwnDescriptors(a3, a1);
+  __ Branch(&done, eq, a3, Operand(zero_reg));
+
+  __ LoadInstanceDescriptors(a1, t0, a2);
+  // t0: descriptor array.
+  // a3: valid entries in the descriptor array.
   STATIC_ASSERT(kSmiTag == 0);
   STATIC_ASSERT(kSmiTagSize == 1);
   STATIC_ASSERT(kPointerSize == 4);
-  __ Addu(a2, t0, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
+  __ li(at, Operand(DescriptorArray::kDescriptorSize));
+  __ Mult(a3, at);
+  // Calculate location of the first key name.
+  __ Addu(t0, t0, Operand(DescriptorArray::kFirstOffset - kHeapObjectTag));
+  // Calculate the end of the descriptor array.
+  __ mov(a2, t0);
   __ sll(t1, a3, kPointerSizeLog2 - kSmiTagSize);
   __ Addu(a2, a2, t1);
 
-  // Calculate location of the first key name.
-  __ Addu(t0,
-          t0,
-          Operand(DescriptorArray::kFirstOffset - kHeapObjectTag));
   // Loop through all the keys in the descriptor array. If one of these is the
   // symbol valueOf the result is false.
-  Label entry, loop;
   // The use of t2 to store the valueOf symbol asumes that it is not otherwise
   // used in the loop below.
   __ LoadRoot(t2, Heap::kvalue_of_symbolRootIndex);
@@ -2791,7 +2795,8 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   __ bind(&entry);
   __ Branch(&loop, ne, t0, Operand(a2));
 
-  // If a valueOf property is not found on the object check that it's
+  __ bind(&done);
+  // If a valueOf property is not found on the object check that its
   // prototype is the un-modified String prototype. If not result is false.
   __ lw(a2, FieldMemOperand(a1, Map::kPrototypeOffset));
   __ JumpIfSmi(a2, if_false);

src/mips/macro-assembler-mips.cc

@@ -5299,20 +5299,37 @@ void MacroAssembler::LoadInstanceDescriptors(Register map,
   Register temp = descriptors;
   lw(temp, FieldMemOperand(map, Map::kTransitionsOrBackPointerOffset));
 
-  Label ok, fail;
+  Label ok, fail, load_from_back_pointer;
   CheckMap(temp,
            scratch,
            isolate()->factory()->fixed_array_map(),
            &fail,
            DONT_DO_SMI_CHECK);
-  lw(descriptors, FieldMemOperand(temp, TransitionArray::kDescriptorsOffset));
+  lw(temp, FieldMemOperand(temp, TransitionArray::kDescriptorsPointerOffset));
+  lw(descriptors, FieldMemOperand(temp, JSGlobalPropertyCell::kValueOffset));
   jmp(&ok);
+
   bind(&fail);
+  LoadRoot(scratch, Heap::kUndefinedValueRootIndex);
+  Branch(&load_from_back_pointer, ne, temp, Operand(scratch));
   LoadRoot(descriptors, Heap::kEmptyDescriptorArrayRootIndex);
+  jmp(&ok);
+
+  bind(&load_from_back_pointer);
+  lw(temp, FieldMemOperand(temp, Map::kTransitionsOrBackPointerOffset));
+  lw(temp, FieldMemOperand(temp, TransitionArray::kDescriptorsPointerOffset));
+  lw(descriptors, FieldMemOperand(temp, JSGlobalPropertyCell::kValueOffset));
+
   bind(&ok);
 }
 
 
+void MacroAssembler::NumberOfOwnDescriptors(Register dst, Register map) {
+  lbu(dst, FieldMemOperand(map, Map::kBitFieldOffset));
+  DecodeField<Map::NumberOfOwnDescriptorsBits>(dst);
+}
+
+
 void MacroAssembler::EnumLength(Register dst, Register map) {
   STATIC_ASSERT(Map::EnumLengthBits::kShift == 0);
   lw(dst, FieldMemOperand(map, Map::kBitField3Offset));

src/mips/macro-assembler-mips.h

@@ -1400,7 +1400,15 @@ class MacroAssembler: public Assembler {
                                Register descriptors,
                                Register scratch);
   void EnumLength(Register dst, Register map);
-
+  void NumberOfOwnDescriptors(Register dst, Register map);
+
+  template<typename Field>
+  void DecodeField(Register reg) {
+    static const int shift = Field::kShift;
+    static const int mask = (Field::kMask >> shift) << kSmiTagSize;
+    srl(reg, reg, shift);
+    And(reg, reg, Operand(mask));
+  }
 
   // Activation support.
   void EnterFrame(StackFrame::Type type);