Re-landing of "replace TrySync with Metadata".

runtime/vm/code_descriptors.h

Index: runtime/vm/code_descriptors.h
diff --git a/runtime/vm/code_descriptors.h b/runtime/vm/code_descriptors.h
index 5a1528e174c0317a8659752016f9827bb46d4181..2dbe90332384c0e595cc99df4a36b05cdc11fed9 100644
--- a/runtime/vm/code_descriptors.h
+++ b/runtime/vm/code_descriptors.h
@@ -7,6 +7,7 @@
 
 #include "vm/ast.h"
 #include "vm/code_generator.h"
+#include "vm/datastream.h"
 #include "vm/globals.h"
 #include "vm/growable_array.h"
 #include "vm/object.h"
@@ -148,6 +149,59 @@ class ExceptionHandlerList : public ZoneAllocated {
 };
 
 
+// An encoded move from stack/constant to stack performed
+struct CatchEntryStatePair {
+  enum { kCatchEntryStateIsMove = 1, kCatchEntryStateDestShift = 1 };
+
+  intptr_t src, dest;
+
+  static CatchEntryStatePair FromConstant(intptr_t pool_id,
+                                          intptr_t dest_slot) {
+    CatchEntryStatePair pair;
+    pair.src = pool_id;
+    pair.dest = (dest_slot << kCatchEntryStateDestShift);
+    return pair;
+  }
+
+  static CatchEntryStatePair FromMove(intptr_t src_slot, intptr_t dest_slot) {
+    CatchEntryStatePair pair;
+    pair.src = src_slot;
+    pair.dest =
+        (dest_slot << kCatchEntryStateDestShift) | kCatchEntryStateIsMove;
+    return pair;
+  }
+
+  bool operator==(const CatchEntryStatePair& rhs) {
+    return src == rhs.src && dest == rhs.dest;
+  }
+};
+
+
+// Used to construct CatchEntryState metadata for AoT mode of compilation.
+class CatchEntryStateMapBuilder : public ZoneAllocated {
+ public:
+  CatchEntryStateMapBuilder();
+
+  void NewMapping(intptr_t pc_offset);
+  void AppendMove(intptr_t src_slot, intptr_t dest_slot);
+  void AppendConstant(intptr_t pool_id, intptr_t dest_slot);
+  void EndMapping();
+  RawTypedData* FinalizeCatchEntryStateMap();
+
+ private:
+  class TrieNode;
+
+  Zone* zone_;
+  TrieNode* root_;
+  intptr_t current_pc_offset_;
+  GrowableArray<CatchEntryStatePair> moves_;
+  uint8_t* buffer_;
+  WriteStream stream_;
+
+  DISALLOW_COPY_AND_ASSIGN(CatchEntryStateMapBuilder);
+};
+
+
 // A CodeSourceMap maps from pc offsets to a stack of inlined functions and
 // their positions. This is encoded as a little bytecode that pushes and pops
 // functions and changes the top function's position as the PC advances.