[heap] refactor inline allocation step code

src/heap/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/atomic-utils.h"
 #include "src/base/atomicops.h"
@@ skipping 2719 matching lines @@
   // when all allocation is performed from inlined generated code.
   intptr_t inline_allocation_limit_step_;
 
   Address top_on_previous_step_;
 
   HistogramInfo* allocated_histogram_;
   HistogramInfo* promoted_histogram_;
 
   bool EnsureAllocation(int size_in_bytes, AllocationAlignment alignment);
 
+  // If we are doing inline allocation in steps, this method performs the 'step'
+  // operation. Right now incremental mark is the only consumer of inline
+  // allocation steps. `top` the address just past the last byte allocated, i.e.

[Hannes Payer (out of office), 2015/09/21 07:48:10]

top is the memory address of the bump pointer at the last inline allocation
step.

[ofrobots, 2015/09/21 20:32:58]

Did you mean: "top is the memory address of the bump pointer at the last inline
allocation"? Having "step" at the end doesn't make sense to me. This was
probably a typo, but I want to make sure we are on the same .... page (heh).

+  // determines the numbers of bytes actually allocated since the last step.
+  // `new_top` is the address where that the next byte is going be allocated

[Hannes Payer (out of office), 2015/09/21 07:48:10]

address of the bump pointer

[Hannes Payer (out of office), 2015/09/21 07:48:10]

remove "that"

+  // from. `top` and `new_top` may be different when we cross a page boundary or
+  // reset the space.
+  void InlineAllocationStep(Address top, Address new_top);
+
   friend class SemiSpaceIterator;
 };
 
 // -----------------------------------------------------------------------------
 // Compaction space that is used temporarily during compaction.
 
 class CompactionSpace : public PagedSpace {
  public:
   CompactionSpace(Heap* heap, AllocationSpace id, Executability executable)
       : PagedSpace(heap, id, executable) {}
@@ skipping 231 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_SPACES_H_