- Add a size field to the header.

vm/intrinsifier_ia32.cc

Index: vm/intrinsifier_ia32.cc
===================================================================
--- vm/intrinsifier_ia32.cc	(revision 2918)
+++ vm/intrinsifier_ia32.cc	(working copy)
@@ -98,7 +98,7 @@
   __ movl(EDI, Address(ESP, kArrayLengthOffset));  // Array Length.
   // Assert that length is a Smi.
   __ testl(EDI, Immediate(kSmiTagSize));
-  __ j(NOT_ZERO, &fall_through, Assembler::kNearJump);
+  __ j(NOT_ZERO, &fall_through);
   intptr_t fixed_size = sizeof(RawArray) + kObjectAlignment - 1;
   __ leal(EDI, Address(EDI, TIMES_2, fixed_size));  // EDI is a Smi.
   ASSERT(kSmiTagShift == 1);
@@ -114,7 +114,7 @@
   // EAX: potential new object start.
   // EBX: potential next object start.
   __ cmpl(EBX, Address::Absolute(heap->EndAddress()));
-  __ j(ABOVE_EQUAL, &fall_through, Assembler::kNearJump);
+  __ j(ABOVE_EQUAL, &fall_through);
 
   // Successfully allocated the object(s), now update top to point to
   // next object start and initialize the object.
@@ -130,8 +130,26 @@
   __ StoreIntoObject(EAX, FieldAddress(EAX, Array::class_offset()), EDI);
 
   // Initialize the tags.
-  __ movl(FieldAddress(EAX, Array::tags_offset()), Immediate(0));
+  // EAX: new object start as a tagged pointer.
+  // EBX: new object end address.
+  {
+    Label size_tag_overflow, done;
+    __ movl(EDI, Address(ESP, kArrayLengthOffset));  // Array length.
+    __ leal(EDI, Address(EDI, TIMES_2, fixed_size));  // EDX is Smi.

[siva, 2012/01/04 01:56:03]

EDI is Smi?

Also if you moved this block of code to initialize tags above the section that
stores the class value, EDI would not have been clobbered and you could save on
these two instructions which are setting up EDI again. 

[Ivan Posva, 2012/01/04 07:59:42]

Rearranged setting of class and tags to avoid recalculating allocation size.

+    ASSERT(kSmiTagShift == 1);
+    __ andl(EDI, Immediate(-kObjectAlignment));
+    __ cmpl(EDI,
+            Immediate(RawObject::SizeTag::kMaxSizeTag));

[siva, 2012/01/04 01:56:03]

Can this fit in one line?

[Ivan Posva, 2012/01/04 07:59:42]

Done.

+    __ j(ABOVE, &size_tag_overflow, Assembler::kNearJump);
+    __ shll(EDI, Immediate(RawObject::kSizeTagBit - kObjectAlignmentLog2));
+    __ movl(FieldAddress(EAX, Array::tags_offset()), EDI);  // Tags.
+    __ jmp(&done);
 
+    __ Bind(&size_tag_overflow);
+    __ movl(FieldAddress(EAX, Array::tags_offset()), Immediate(0));
+    __ Bind(&done);
+  }
+
   // Store the type argument field.
   __ movl(EDI, Address(ESP, kTypeArgumentsOffset));  // type argument.
   __ StoreIntoObject(EAX,