Fixing dead code in empty array init.

src/arm/builtins-arm.cc

Index: src/arm/builtins-arm.cc
diff --git a/src/arm/builtins-arm.cc b/src/arm/builtins-arm.cc
index 29bf19028cb7770963c8e1e76a530ffae05baf08..0422a8a070ea98c002b566d7094c3390d575eb05 100644
--- a/src/arm/builtins-arm.cc
+++ b/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
@@ -148,7 +156,6 @@ static void AllocateEmptyJSArray(MacroAssembler* masm,
   __ 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);

[Kevin Millikin (Chromium), 2011/10/27 10:35:54]

This can be a static assert.

   __ LoadRoot(scratch3, Heap::kTheHoleValueRootIndex);
   static const int kLoopUnfoldLimit = 4;