Reduce space used for stackmaps.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index a39ab30f6495388bce131c5af9d4595d42efa1f7..d71acd6670b74e6c1058a214f74c0b8d0afe18b9 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2340,19 +2340,20 @@ class Stackmap : public Object {
   // Return the index of the lowest stack slot that has an object.
   intptr_t MinimumBitIndex() const { return raw_ptr()->min_set_bit_index_; }
 
-  static const intptr_t kBytesPerElement = kWordSize;
-  static const intptr_t kMaxElements = kSmiMax / kBytesPerElement;
+  static const intptr_t kMaxLengthInBytes = kSmiMax;
 
   static intptr_t InstanceSize() {
     ASSERT(sizeof(RawStackmap) == OFFSET_OF(RawStackmap, data_));
     return 0;
   }
-  static intptr_t InstanceSize(intptr_t len) {

[Kevin Millikin (Google), 2012/08/14 13:02:32]

This was already a length in bytes, no need to multiply by kBytesPerElement.

(Bytes per element is really 1/8 because the elements are bits.  Better to get
rid of the concept of element in stackmaps.)

-    ASSERT(0 <= len && len <= kMaxElements);
-    return RoundedAllocationSize(
-        sizeof(RawStackmap) + (len * kBytesPerElement));
+  static intptr_t InstanceSize(intptr_t length_in_bytes) {

[Vyacheslav Egorov (Google), 2012/08/15 14:17:37]

I wonder if we can pass a real length here to align with e.g.
Array::InstanceSize.

[Kevin Millikin (Google), 2012/08/15 14:41:31]

Yes.  Will do with the next change.

+    ASSERT(length_in_bytes >= 0);
+    ASSERT(length_in_bytes <= kMaxLengthInBytes);
+    return RoundedAllocationSize(sizeof(RawStackmap) + length_in_bytes);
   }
-  static RawStackmap* New(uword pc, BitmapBuilder* bmap);
+  static RawStackmap* New(intptr_t pc_offset,
+                          intptr_t length_in_bits,
+                          BitmapBuilder* bmap);
 
  private:
   inline intptr_t SizeInBits() const;