faster pruning in chart decoding

moses/ChartCellLabel.h

@@ -22,6 +22,7 @@
 #include "HypoList.h"
 #include "Word.h"
 #include "WordsRange.h"
+#include "ChartParserCallback.h"
 
 namespace search
 {
@@ -52,7 +53,8 @@ public:
                  Stack stack=Stack())
     : m_coverage(coverage)
     , m_label(label)
-    , m_stack(stack) {
+    , m_stack(stack)
+    , m_bestScore(0) {
   }
 
   const WordsRange &GetCoverage() const {
@@ -68,6 +70,14 @@ public:
     return m_stack;
   }
 
+  //caching of best score on stack
+  float GetBestScore(const ChartParserCallback *outColl) const {
+    if (m_bestScore == 0) {
+      m_bestScore = outColl->GetBestScore(this);
+    }
+    return m_bestScore;
+  }
+
   bool operator<(const ChartCellLabel &other) const {
     // m_coverage and m_label uniquely identify a ChartCellLabel, so don't
     // need to compare m_stack.
@@ -81,6 +91,7 @@ private:
   const WordsRange &m_coverage;
   const Word &m_label;
   Stack m_stack;
+  mutable float m_bestScore;
 };
 
 }

moses/ChartParserCallback.h

@@ -12,6 +12,7 @@ class WordsRange;
 class TargetPhrase;
 class InputPath;
 class InputType;
+class ChartCellLabel;
 
 class ChartParserCallback
 {
@@ -26,7 +27,7 @@ public:
 
   virtual void Evaluate(const InputType &input, const InputPath &inputPath) = 0;
 
-  virtual float CalcEstimateOfBestScore(const TargetPhraseCollection &, const StackVec &) const = 0;
+  virtual float GetBestScore(const ChartCellLabel *chartCell) const = 0;
 
 };
 

moses/ChartTranslationOptionList.cpp

@@ -75,7 +75,11 @@ void ChartTranslationOptionList::Add(const TargetPhraseCollection &tpc,
     }
   }
 
-  float score = ChartTranslationOptions::CalcEstimateOfBestScore(tpc, stackVec);
+  const TargetPhrase &targetPhrase = **(tpc.begin());
+  float score = targetPhrase.GetFutureScore();
+  for (StackVec::const_iterator p = stackVec.begin(); p != stackVec.end(); ++p) {
+    score += (*p)->GetBestScore(this);
+  }
 
   // If the rule limit has already been reached then don't add the option
   // unless it is better than at least one existing option.
@@ -155,6 +159,15 @@ void ChartTranslationOptionList::ApplyThreshold()
   m_size = std::distance(m_collection.begin(), bound);
 }
 
+float ChartTranslationOptionList::GetBestScore(const ChartCellLabel *chartCell) const
+{
+    const HypoList *stack = chartCell->GetStack().cube;
+    assert(stack);
+    assert(!stack->empty());
+    const ChartHypothesis &bestHypo = **(stack->begin());
+    return bestHypo.GetTotalScore();
+}
+
 void ChartTranslationOptionList::Evaluate(const InputType &input, const InputPath &inputPath)
 {
   // NEVER iterate over ALL of the collection. Just over the first m_size

moses/ChartTranslationOptionList.h

@@ -32,6 +32,7 @@ class TargetPhraseCollection;
 class WordsRange;
 class InputType;
 class InputPath;
+class ChartCellLabel;
 
 //! a vector of translations options for a specific range, in a specific sentence
 class ChartTranslationOptionList : public ChartParserCallback
@@ -60,9 +61,7 @@ public:
     return m_size == 0;
   }
 
-  float CalcEstimateOfBestScore(const TargetPhraseCollection & tpc, const StackVec & stackVec) const {
-    return ChartTranslationOptions::CalcEstimateOfBestScore(tpc, stackVec);
-  }
+  float GetBestScore(const ChartCellLabel *chartCell) const;
 
   void Clear();
   void ApplyThreshold();

moses/ChartTranslationOptions.cpp

@@ -51,23 +51,6 @@ ChartTranslationOptions::~ChartTranslationOptions()
 
 }
 
-float ChartTranslationOptions::CalcEstimateOfBestScore(
-  const TargetPhraseCollection &tpc,
-  const StackVec &stackVec)
-{
-  const TargetPhrase &targetPhrase = **(tpc.begin());
-  float estimateOfBestScore = targetPhrase.GetFutureScore();
-  for (StackVec::const_iterator p = stackVec.begin(); p != stackVec.end();
-       ++p) {
-    const HypoList *stack = (*p)->GetStack().cube;
-    assert(stack);
-    assert(!stack->empty());
-    const ChartHypothesis &bestHypo = **(stack->begin());
-    estimateOfBestScore += bestHypo.GetTotalScore();
-  }
-  return estimateOfBestScore;
-}
-
 void ChartTranslationOptions::Evaluate(const InputType &input, const InputPath &inputPath)
 {
   SetInputPath(&inputPath);

moses/Incremental.cpp

@@ -83,7 +83,7 @@ public:
 
   void AddPhraseOOV(TargetPhrase &phrase, std::list<TargetPhraseCollection*> &waste_memory, const WordsRange &range);
 
-  float CalcEstimateOfBestScore(const TargetPhraseCollection & tpc, const StackVec & stackVec) const;
+  float GetBestScore(const ChartCellLabel *chartCell) const;
 
   bool Empty() const {
     return edges_.Empty();
@@ -124,8 +124,7 @@ template <class Model> void Fill<Model>::Add(const TargetPhraseCollection &targe
   float below_score = 0.0;
   for (StackVec::const_iterator i(nts.begin()); i != nts.end(); ++i) {
     vertices.push_back((*i)->GetStack().incr->RootAlternate());
-    if (vertices.back().Empty()) return;
-    below_score += vertices.back().Bound();
+    below_score += (*i)->GetBestScore(this);
   }
 
   std::vector<lm::WordIndex> words;
@@ -178,15 +177,12 @@ template <class Model> void Fill<Model>::AddPhraseOOV(TargetPhrase &phrase, std:
   edges_.AddEdge(edge);
 }
 
-// for early pruning
-template <class Model> float Fill<Model>::CalcEstimateOfBestScore(const TargetPhraseCollection &targets, const StackVec &nts) const
+// for pruning
+template <class Model> float Fill<Model>::GetBestScore(const ChartCellLabel *chartCell) const
 {
-  float below_score = 0.0;
-  for (StackVec::const_iterator i = nts.begin(); i != nts.end(); ++i) {
-    below_score += (*i)->GetStack().incr->RootAlternate().Bound();
-  }
-  const TargetPhrase &targetPhrase = **(targets.begin());
-  return targetPhrase.GetFutureScore() + below_score;
+    search::PartialVertex vertex = chartCell->GetStack().incr->RootAlternate();
+    UTIL_THROW_IF2(vertex.Empty(), "hypothesis with empty stack");
+    return vertex.Bound();
 }
 
 // TODO: factors (but chart doesn't seem to support factors anyway).

moses/TranslationModel/CYKPlusParser/CompletedRuleCollection.cpp

@@ -41,7 +41,12 @@ void CompletedRuleCollection::Add(const TargetPhraseCollection &tpc,
       return;
     }
 
-    const float score = outColl.CalcEstimateOfBestScore(tpc, stackVec);
+    const TargetPhrase &targetPhrase = **(tpc.begin());
+    float score = targetPhrase.GetFutureScore();
+    for (StackVec::const_iterator p = stackVec.begin(); p != stackVec.end(); ++p) {
+        float stackScore = (*p)->GetBestScore(&outColl);
+        score += stackScore;
+    }
 
     // If the rule limit has already been reached then don't add the option
     // unless it is better than at least one existing option.