One more iteration of PcDescriptor iterator improvement: do not copy record but access individual …

runtime/vm/object.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include <limits>
 #include "include/dart_api.h"
 #include "platform/assert.h"
@@ skipping 3029 matching lines @@
 
   void PrintToJSONObject(JSONObject* jsobj) const;
 
   // We would have a VisitPointers function here to traverse the
   // pc descriptors table to visit objects if any in the table.
   // Note: never return a reference to a RawPcDescriptors::PcDescriptorRec
   // as the object can move.
   class Iterator : ValueObject {
    public:
     Iterator(const PcDescriptors& descriptors, intptr_t kind_mask)
-        : descriptors_(descriptors), kind_mask_(kind_mask), current_ix_(0) {
+        : descriptors_(descriptors),
+          kind_mask_(kind_mask),
+          next_ix_(0),
+          current_ix_(-1) {
       MoveToMatching();
     }
 
-    bool HasNext() const { return current_ix_ < descriptors_.Length(); }
+    bool HasNext() const { return next_ix_ < descriptors_.Length(); }
 
     intptr_t NextDeoptId() {

[hausner, 2014/07/17 23:22:56]

I find it a bit awkward that you have two accessors for each value, say
current_deopt_id() and NextDeoptId(), the latter having a side effect of moving
the iterator.

How about this iterator interface:
HasNext() // true if there is another entry
MoveNext() // moves the iterator
DeoptId() // get deopt id of current descriptor
TokenPos() // get token position of current descriptor 
etc...

Iterating over a pc descriptor array would then be:

PcDescriptors::Iterator i(desc, mask);
while (i.HasNext()) {
  i.MoveNext();
  // access all fields that you need
}

[srdjan, 2014/07/18 18:16:45]

Good suggestion, changed to:

while (i.MoveNext()) {
   // access all fields that you need
}

       ASSERT(HasNext());
-      const intptr_t res = descriptors_.recAt(current_ix_++)->deopt_id();
+      const intptr_t res = descriptors_.recAt(next_ix_)->deopt_id();
+      current_ix_ = next_ix_++;
       MoveToMatching();
       return res;
     }
 
     uword NextPc() {
       ASSERT(HasNext());
-      const uword res = descriptors_.recAt(current_ix_++)->pc();
+      const uword res = descriptors_.recAt(next_ix_)->pc();
+      current_ix_ = next_ix_++;
       MoveToMatching();
       return res;
     }
 
-    void NextRec(RawPcDescriptors::PcDescriptorRec* result) {
+    intptr_t NextTokenPos() {
       ASSERT(HasNext());
-      const RawPcDescriptors::PcDescriptorRec* r =
-          descriptors_.recAt(current_ix_++);
-      r->CopyTo(result);
+      const intptr_t res = descriptors_.recAt(next_ix_)->token_pos();
+      current_ix_ = next_ix_++;
       MoveToMatching();
+      return res;
+    }
+
+    uword current_pc() const { return descriptors_.recAt(current_ix_)->pc(); }
+    intptr_t current_deopt_id() const {
+      return descriptors_.recAt(current_ix_)->deopt_id();
+    }
+    intptr_t current_token_pos() const {
+      return descriptors_.recAt(current_ix_)->token_pos();
+    }
+    intptr_t current_try_index() const {
+      return descriptors_.recAt(current_ix_)->try_index();
+    }
+    RawPcDescriptors::Kind current_kind() const {
+      return descriptors_.recAt(current_ix_)->kind();
     }
 
    private:
     friend class PcDescriptors;
 
     // For nested iterations, starting at element after.
     explicit Iterator(const Iterator& iter)
         : ValueObject(),
           descriptors_(iter.descriptors_),
           kind_mask_(iter.kind_mask_),
+          next_ix_(iter.next_ix_),
           current_ix_(iter.current_ix_) {}
 
     // Moves to record that matches kind_mask_.
     void MoveToMatching() {
-      while (current_ix_ < descriptors_.Length()) {
+      while (next_ix_ < descriptors_.Length()) {
         const RawPcDescriptors::PcDescriptorRec& rec =
-            *descriptors_.recAt(current_ix_);
+            *descriptors_.recAt(next_ix_);
         if ((rec.kind() & kind_mask_) != 0) {
           return;  // Current is valid.
         } else {
-          ++current_ix_;
+          ++next_ix_;
         }
       }
     }
 
     const PcDescriptors& descriptors_;
     const intptr_t kind_mask_;
+    intptr_t next_ix_;
     intptr_t current_ix_;
   };
 
  private:
   static const char* KindAsStr(RawPcDescriptors::Kind kind);
 
   intptr_t Length() const;
   void SetLength(intptr_t value) const;
 
   void SetRecordSizeInBytes(intptr_t value) const;
   intptr_t RecordSizeInBytes() const;
 
   RawPcDescriptors::PcDescriptorRec* recAt(intptr_t ix) const {
-    ASSERT(ix < Length());
+    ASSERT((0 <= ix) && (ix < Length()));
     uint8_t* d = raw_ptr()->data() + (ix * RecordSizeInBytes());
     return reinterpret_cast<RawPcDescriptors::PcDescriptorRec*>(d);
   }
 
   FINAL_HEAP_OBJECT_IMPLEMENTATION(PcDescriptors, Object);
   friend class Class;
   friend class Object;
 };
 
 
@@ skipping 4113 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_