Improve positions tracking inside the HGraphBuilder.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 186c8668b6ddbfcc6e0b81f8c4b57b339d61630a..7eaa30a4f43b5d55442c99193a60daf26004a48c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4938,7 +4938,8 @@ class DeoptimizationInputData: public FixedArray {
   static const int kLiteralArrayIndex = 2;
   static const int kOsrAstIdIndex = 3;
   static const int kOsrPcOffsetIndex = 4;
-  static const int kFirstDeoptEntryIndex = 5;
+  static const int kOptimizationIdIndex = 5;

[Vyacheslav Egorov (Chromium), 2014/01/29 16:41:36]

Rest of the change introduces no overhead unless FLAG_track_hydrogen_positions
is passed. This part however grows DeoptimizationInputData by one word to store
ID of the optimization.

In general DeoptimizationInputData is big and is also accompanied by a multiword
optimized code object so this overhead should not be noticable. 

However if we want to save space we can change encoding of this structure to be
more flexible. If we decide to pursue this as additional benefit of such action
we can remove OsrAstId and OsrPcOffset for many object (my guess they are not
used for many objects) and save 2 words.

+  static const int kFirstDeoptEntryIndex = 6;
 
   // Offsets of deopt entry elements relative to the start of the entry.
   static const int kAstIdRawOffset = 0;
@@ -4961,6 +4962,7 @@ class DeoptimizationInputData: public FixedArray {
   DEFINE_ELEMENT_ACCESSORS(LiteralArray, FixedArray)
   DEFINE_ELEMENT_ACCESSORS(OsrAstId, Smi)
   DEFINE_ELEMENT_ACCESSORS(OsrPcOffset, Smi)
+  DEFINE_ELEMENT_ACCESSORS(OptimizationId, Smi)
 
 #undef DEFINE_ELEMENT_ACCESSORS