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

src/mips/full-codegen-mips.cc

Index: src/mips/full-codegen-mips.cc
diff --git a/src/mips/full-codegen-mips.cc b/src/mips/full-codegen-mips.cc
index d691a1230894e074a140a53f53d8d58453160a78..6a697bc4f5e1250e77b1f8f1755303c4d584a61e 100644
--- a/src/mips/full-codegen-mips.cc
+++ b/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);