MIPS: Sharing of descriptor arrays.

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 bfa24252b9046e2e15e275c2c613ef6b18b5ee25..69b4e9a30238f182b5a85c1c93c67d442d049231 100644
--- a/src/mips/full-codegen-mips.cc
+++ b/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);