Fixing dead code in empty array init.

TEST=set JSArray::kPreallocatedArrayElements to larger than 4.

Review URL: http://codereview.chromium.org/8381014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9816 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/builtins-arm.cc

@@ -104,7 +104,10 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
 
   // Allocate the JSArray object together with space for a fixed array with the
   // requested elements.
-  int size = JSArray::kSize + FixedArray::SizeFor(initial_capacity);
+  int size = JSArray::kSize;
+  if (initial_capacity > 0) {
+    size += FixedArray::SizeFor(initial_capacity);
+  }
   __ AllocateInNewSpace(size,
                         result,
                         scratch2,
@@ -124,6 +127,11 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
   __ mov(scratch3,  Operand(0, RelocInfo::NONE));
   __ str(scratch3, FieldMemOperand(result, JSArray::kLengthOffset));
 
+  if (initial_capacity == 0) {
+    __ str(scratch1, FieldMemOperand(result, JSArray::kElementsOffset));
+    return;
+  }
+
   // Calculate the location of the elements array and set elements array member
   // of the JSArray.
   // result: JSObject
@@ -132,7 +140,6 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
   __ str(scratch1, FieldMemOperand(result, JSArray::kElementsOffset));
 
   // Clear the heap tag on the elements array.
-  STATIC_ASSERT(kSmiTag == 0);
   __ sub(scratch1, scratch1, Operand(kHeapObjectTag));
 
   // Initialize the FixedArray and fill it with holes. FixedArray length is
@@ -141,15 +148,14 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
   // scratch1: elements array (untagged)
   // scratch2: start of next object
   __ LoadRoot(scratch3, Heap::kFixedArrayMapRootIndex);
-  ASSERT_EQ(0 * kPointerSize, FixedArray::kMapOffset);
+  STATIC_ASSERT(0 * kPointerSize == FixedArray::kMapOffset);
   __ str(scratch3, MemOperand(scratch1, kPointerSize, PostIndex));
   __ mov(scratch3,  Operand(Smi::FromInt(initial_capacity)));
-  ASSERT_EQ(1 * kPointerSize, FixedArray::kLengthOffset);
+  STATIC_ASSERT(1 * kPointerSize == FixedArray::kLengthOffset);
   __ str(scratch3, MemOperand(scratch1, kPointerSize, PostIndex));
 
   // Fill the FixedArray with the hole value. Inline the code if short.
-  if (initial_capacity == 0) return;
-  ASSERT_EQ(2 * kPointerSize, FixedArray::kHeaderSize);
+  STATIC_ASSERT(2 * kPointerSize == FixedArray::kHeaderSize);
   __ LoadRoot(scratch3, Heap::kTheHoleValueRootIndex);
   static const int kLoopUnfoldLimit = 4;
   if (initial_capacity <= kLoopUnfoldLimit) {

src/ia32/builtins-ia32.cc

@@ -996,13 +996,17 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
     }
   } else {
     Label loop, entry;
+    __ mov(scratch2, Immediate(initial_capacity));
     __ jmp(&entry);
     __ bind(&loop);
-    __ mov(Operand(scratch1, 0), factory->the_hole_value());
-    __ add(scratch1, Immediate(kPointerSize));
+    __ mov(FieldOperand(scratch1,
+                        scratch2,
+                        times_pointer_size,
+                        FixedArray::kHeaderSize),
+           factory->the_hole_value());
     __ bind(&entry);
-    __ cmp(scratch1, scratch2);
-    __ j(below, &loop);
+    __ dec(scratch2);
+    __ j(not_sign, &loop);
   }
 }
 

src/mips/builtins-mips.cc

@@ -106,7 +106,10 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
 
   // Allocate the JSArray object together with space for a fixed array with the
   // requested elements.
-  int size = JSArray::kSize + FixedArray::SizeFor(initial_capacity);
+  int size = JSArray::kSize;
+  if (initial_capacity > 0) {
+    size += FixedArray::SizeFor(initial_capacity);
+  }
   __ AllocateInNewSpace(size,
                         result,
                         scratch2,
@@ -125,6 +128,11 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
   __ mov(scratch3,  zero_reg);
   __ sw(scratch3, FieldMemOperand(result, JSArray::kLengthOffset));
 
+  if (initial_capacity == 0) {
+    __ sw(scratch1, FieldMemOperand(result, JSArray::kElementsOffset));
+    return;
+  }
+
   // Calculate the location of the elements array and set elements array member
   // of the JSArray.
   // result: JSObject
@@ -141,17 +149,16 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
   // scratch1: elements array (untagged)
   // scratch2: start of next object
   __ LoadRoot(scratch3, Heap::kFixedArrayMapRootIndex);
-  ASSERT_EQ(0 * kPointerSize, FixedArray::kMapOffset);
+  STATIC_ASSERT(0 * kPointerSize == FixedArray::kMapOffset);
   __ sw(scratch3, MemOperand(scratch1));
   __ Addu(scratch1, scratch1, kPointerSize);
   __ li(scratch3,  Operand(Smi::FromInt(initial_capacity)));
-  ASSERT_EQ(1 * kPointerSize, FixedArray::kLengthOffset);
+  STATIC_ASSERT(1 * kPointerSize == FixedArray::kLengthOffset);
   __ sw(scratch3, MemOperand(scratch1));
   __ Addu(scratch1, scratch1, kPointerSize);
 
   // Fill the FixedArray with the hole value. Inline the code if short.
-  if (initial_capacity == 0) return;
-  ASSERT_EQ(2 * kPointerSize, FixedArray::kHeaderSize);
+  STATIC_ASSERT(2 * kPointerSize == FixedArray::kHeaderSize);
   __ LoadRoot(scratch3, Heap::kTheHoleValueRootIndex);
   static const int kLoopUnfoldLimit = 4;
   if (initial_capacity <= kLoopUnfoldLimit) {

src/x64/builtins-x64.cc

@@ -1075,13 +1075,17 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
     }
   } else {
     Label loop, entry;
+    __ movq(scratch2, Immediate(initial_capacity));
     __ jmp(&entry);
     __ bind(&loop);
-    __ movq(Operand(scratch1, 0), scratch3);
-    __ addq(scratch1, Immediate(kPointerSize));
+    __ movq(FieldOperand(scratch1,
+                         scratch2,
+                         times_pointer_size,
+                         FixedArray::kHeaderSize),
+            scratch3);
     __ bind(&entry);
-    __ cmpq(scratch1, scratch2);
-    __ j(below, &loop);
+    __ decq(scratch2);
+    __ j(not_sign, &loop);
   }
 }