MIPS: Use a special EnumLength field to indicate number of valid enum cache values.

Port r12400 (03ae62de)

Original commit message:
This is preparatory work for sharing Enum Caches.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10914025
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12417 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/full-codegen-mips.cc

@@ -1141,25 +1141,32 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   // modification check. Otherwise, we got a fixed array, and we have
   // to do a slow check.
   Label fixed_array;
-  __ mov(a2, v0);
-  __ lw(a1, FieldMemOperand(a2, HeapObject::kMapOffset));
+  __ lw(a2, FieldMemOperand(v0, HeapObject::kMapOffset));
   __ LoadRoot(at, Heap::kMetaMapRootIndex);
-  __ Branch(&fixed_array, ne, a1, Operand(at));
+  __ Branch(&fixed_array, ne, a2, Operand(at));
 
   // We got a map in register v0. Get the enumeration cache from it.
+  Label no_descriptors;
   __ bind(&use_cache);
-  __ LoadInstanceDescriptors(v0, a1, a2);
-  __ lw(a1, FieldMemOperand(a1, DescriptorArray::kEnumCacheOffset));
-  __ lw(a2, FieldMemOperand(a1, DescriptorArray::kEnumCacheBridgeCacheOffset));
+
+  __ EnumLength(a1, v0);
+  __ Branch(&no_descriptors, eq, a1, Operand(Smi::FromInt(0)));
+
+  __ LoadInstanceDescriptors(v0, a2, t0);
+  __ lw(a2, FieldMemOperand(a2, DescriptorArray::kEnumCacheOffset));
+  __ lw(a2, FieldMemOperand(a2, DescriptorArray::kEnumCacheBridgeCacheOffset));
 
   // Set up the four remaining stack slots.
   __ push(v0);  // Map.
-  __ lw(a1, FieldMemOperand(a2, FixedArray::kLengthOffset));
   __ li(a0, Operand(Smi::FromInt(0)));
   // Push enumeration cache, enumeration cache length (as smi) and zero.
   __ Push(a2, a1, a0);
   __ jmp(&loop);
 
+  __ bind(&no_descriptors);
+  __ Drop(1);
+  __ jmp(&exit);
+
   // We got a fixed array in register v0. Iterate through that.
   Label non_proxy;
   __ bind(&fixed_array);

src/mips/lithium-codegen-mips.cc

@@ -1224,6 +1224,13 @@ void LCodeGen::DoFixedArrayBaseLength(LFixedArrayBaseLength* instr) {
 }
 
 
+void LCodeGen::DoMapEnumLength(LMapEnumLength* instr) {
+  Register result = ToRegister(instr->result());
+  Register map = ToRegister(instr->InputAt(0));
+  __ EnumLength(result, map);
+}
+
+
 void LCodeGen::DoElementsKind(LElementsKind* instr) {
   Register result = ToRegister(instr->result());
   Register input = ToRegister(instr->InputAt(0));
@@ -5304,12 +5311,21 @@ void LCodeGen::DoForInCacheArray(LForInCacheArray* instr) {
   Register map = ToRegister(instr->map());
   Register result = ToRegister(instr->result());
   Register scratch = ToRegister(instr->scratch());
+  Label load_cache, done;
+  __ EnumLength(result, map);
+  __ Branch(&load_cache, ne, result, Operand(Smi::FromInt(0)));
+  __ li(result, Operand(isolate()->factory()->empty_fixed_array()));
+  __ jmp(&done);
+
+  __ bind(&load_cache);
   __ LoadInstanceDescriptors(map, result, scratch);
   __ lw(result,
         FieldMemOperand(result, DescriptorArray::kEnumCacheOffset));
   __ lw(result,
         FieldMemOperand(result, FixedArray::SizeFor(instr->idx())));
   DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
+
+  __ bind(&done);
 }
 
 

src/mips/lithium-mips.cc

@@ -1473,6 +1473,12 @@ LInstruction* LChunkBuilder::DoFixedArrayBaseLength(
 }
 
 
+LInstruction* LChunkBuilder::DoMapEnumLength(HMapEnumLength* instr) {
+  LOperand* map = UseRegisterAtStart(instr->value());
+  return DefineAsRegister(new(zone()) LMapEnumLength(map));
+}
+
+
 LInstruction* LChunkBuilder::DoElementsKind(HElementsKind* instr) {
   LOperand* object = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new(zone()) LElementsKind(object));

src/mips/lithium-mips.h

@@ -131,6 +131,7 @@ class LCodeGen;
   V(LoadNamedField)                             \
   V(LoadNamedFieldPolymorphic)                  \
   V(LoadNamedGeneric)                           \
+  V(MapEnumLength)                              \
   V(MathMinMax)                                 \
   V(ModI)                                       \
   V(MulI)                                       \
@@ -984,6 +985,16 @@ class LFixedArrayBaseLength: public LTemplateInstruction<1, 1, 0> {
 };
 
 
+class LMapEnumLength: public LTemplateInstruction<1, 1, 0> {
+ public:
+  explicit LMapEnumLength(LOperand* value) {
+    inputs_[0] = value;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(MapEnumLength, "map-enum-length")
+};
+
+
 class LElementsKind: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LElementsKind(LOperand* value) {

src/mips/macro-assembler-mips.cc

@@ -5313,51 +5313,44 @@ void MacroAssembler::LoadInstanceDescriptors(Register map,
 }
 
 
+void MacroAssembler::EnumLength(Register dst, Register map) {
+  STATIC_ASSERT(Map::EnumLengthBits::kShift == 0);
+  lw(dst, FieldMemOperand(map, Map::kBitField3Offset));
+  And(dst, dst, Operand(Smi::FromInt(Map::EnumLengthBits::kMask)));
+}
+
+
 void MacroAssembler::CheckEnumCache(Register null_value, Label* call_runtime) {
-  Label next;
-  // Preload a couple of values used in the loop.
   Register  empty_fixed_array_value = t2;
   LoadRoot(empty_fixed_array_value, Heap::kEmptyFixedArrayRootIndex);
-  mov(a1, a0);
-  bind(&next);
+  Label next, start;
+  mov(a2, a0);
 
-  // Check that there are no elements.  Register a1 contains the
-  // current JS object we've reached through the prototype chain.
-  lw(a2, FieldMemOperand(a1, JSObject::kElementsOffset));
-  Branch(call_runtime, ne, a2, Operand(empty_fixed_array_value));
-
-  // Check that instance descriptors are not empty so that we can
-  // check for an enum cache.  Leave the map in a2 for the subsequent
-  // prototype load.
-  lw(a2, FieldMemOperand(a1, HeapObject::kMapOffset));
-  lw(a3, FieldMemOperand(a2, Map::kTransitionsOrBackPointerOffset));
+  // Check if the enum length field is properly initialized, indicating that
+  // there is an enum cache.
+  lw(a1, FieldMemOperand(a2, HeapObject::kMapOffset));
 
-  CheckMap(a3,
-           t3,
-           isolate()->factory()->fixed_array_map(),
-           call_runtime,
-           DONT_DO_SMI_CHECK);
+  EnumLength(a3, a1);
+  Branch(call_runtime, eq, a3, Operand(Smi::FromInt(Map::kInvalidEnumCache)));
 
-  LoadRoot(t3, Heap::kEmptyDescriptorArrayRootIndex);
-  lw(a3, FieldMemOperand(a3, TransitionArray::kDescriptorsOffset));
-  Branch(call_runtime, eq, a3, Operand(t3));
+  jmp(&start);
 
-  // Check that there is an enum cache in the non-empty instance
-  // descriptors (a3).  This is the case if the next enumeration
-  // index field does not contain a smi.
-  lw(a3, FieldMemOperand(a3, DescriptorArray::kEnumCacheOffset));
-  JumpIfSmi(a3, call_runtime);
+  bind(&next);
+  lw(a1, FieldMemOperand(a2, HeapObject::kMapOffset));
 
   // For all objects but the receiver, check that the cache is empty.
-  Label check_prototype;
-  Branch(&check_prototype, eq, a1, Operand(a0));
-  lw(a3, FieldMemOperand(a3, DescriptorArray::kEnumCacheBridgeCacheOffset));
-  Branch(call_runtime, ne, a3, Operand(empty_fixed_array_value));
-
-  // Load the prototype from the map and loop if non-null.
-  bind(&check_prototype);
-  lw(a1, FieldMemOperand(a2, Map::kPrototypeOffset));
-  Branch(&next, ne, a1, Operand(null_value));
+  EnumLength(a3, a1);
+  Branch(call_runtime, ne, a3, Operand(Smi::FromInt(0)));
+
+  bind(&start);
+
+  // Check that there are no elements. Register r2 contains the current JS
+  // object we've reached through the prototype chain.
+  lw(a2, FieldMemOperand(a2, JSObject::kElementsOffset));
+  Branch(call_runtime, ne, a2, Operand(empty_fixed_array_value));
+
+  lw(a2, FieldMemOperand(a1, Map::kPrototypeOffset));
+  Branch(&next, ne, a2, Operand(null_value));
 }
 
 

src/mips/macro-assembler-mips.h

@@ -1399,6 +1399,7 @@ class MacroAssembler: public Assembler {
   void LoadInstanceDescriptors(Register map,
                                Register descriptors,
                                Register scratch);
+  void EnumLength(Register dst, Register map);
 
 
   // Activation support.