Optimization to evaluating tabulated functions

platforms/opencl/src/OpenCLExpressionUtilities.cpp

@@ -48,22 +48,27 @@ static string intToString(int value) {
 string OpenCLExpressionUtilities::createExpressions(const map<string, ParsedExpression>& expressions, const map<string, string>& variables,
         const vector<pair<string, string> >& functions, const string& prefix, const string& functionParams) {
     stringstream out;
+    vector<ParsedExpression> allExpressions;
+    for (map<string, ParsedExpression>::const_iterator iter = expressions.begin(); iter != expressions.end(); ++iter)
+        allExpressions.push_back(iter->second);
     vector<pair<ExpressionTreeNode, string> > temps;
     for (map<string, ParsedExpression>::const_iterator iter = expressions.begin(); iter != expressions.end(); ++iter) {
-        processExpression(out, iter->second.getRootNode(), temps, variables, functions, prefix, functionParams);
+        processExpression(out, iter->second.getRootNode(), temps, variables, functions, prefix, functionParams, allExpressions);
         out << iter->first << getTempName(iter->second.getRootNode(), temps) << ";\n";
     }
     return out.str();
 }
 
 void OpenCLExpressionUtilities::processExpression(stringstream& out, const ExpressionTreeNode& node, vector<pair<ExpressionTreeNode, string> >& temps,
-        const map<string, string>& variables, const vector<pair<string, string> >& functions, const string& prefix, const string& functionParams) {
+        const map<string, string>& variables, const vector<pair<string, string> >& functions, const string& prefix, const string& functionParams,
+        const vector<ParsedExpression>& allExpressions) {
     for (int i = 0; i < (int) temps.size(); i++)
         if (temps[i].first == node)
             return;
     for (int i = 0; i < (int) node.getChildren().size(); i++)
-        processExpression(out, node.getChildren()[i], temps, variables, functions, prefix, functionParams);
+        processExpression(out, node.getChildren()[i], temps, variables, functions, prefix, functionParams, allExpressions);
     string name = prefix+intToString(temps.size());
+    bool hasRecordedNode = false;
     
     out << "float " << name << " = ";
     switch (node.getOperation().getId()) {
@@ -85,7 +90,32 @@ void OpenCLExpressionUtilities::processExpression(stringstream& out, const Expre
                 ;
             if (i == functions.size())
                 throw OpenMMException("Unknown function in expression: "+node.getOperation().getName());
+            bool isDeriv = (dynamic_cast<const Operation::Custom*>(&node.getOperation())->getDerivOrder()[0] == 1);
             out << "0.0f;\n";
+            temps.push_back(make_pair(node, name));
+            hasRecordedNode = true;
+
+            // If both the value and derivative of the function are needed, it's faster to calculate them both
+            // at once, so check to see if both are needed.
+
+            const ExpressionTreeNode* valueNode = NULL;
+            const ExpressionTreeNode* derivNode = NULL;
+            for (int j = 0; j < (int) allExpressions.size(); j++)
+                findRelatedTabulatedFunctions(node, allExpressions[j].getRootNode(), valueNode, derivNode);
+            string valueName = name;
+            string derivName = name;
+            if (valueNode != NULL && derivNode != NULL) {
+                string name2 = prefix+intToString(temps.size());
+                out << "float " << name2 << " = 0.0f;\n";
+                if (isDeriv) {
+                    valueName = name2;
+                    temps.push_back(make_pair(*valueNode, name2));
+                }
+                else {
+                    derivName = name2;
+                    temps.push_back(make_pair(*derivNode, name2));
+                }
+            }
             out << "{\n";
             out << "float4 params = " << functionParams << "[" << i << "];\n";
             out << "float x = " << getTempName(node.getChildren()[0], temps) << ";\n";
@@ -93,10 +123,10 @@ void OpenCLExpressionUtilities::processExpression(stringstream& out, const Expre
             out << "int index = (int) (floor((x-params.x)*params.z));\n";
             out << "float4 coeff = " << functions[i].second << "[index];\n";
             out << "x = (x-params.x)*params.z-index;\n";
-            if (dynamic_cast<const Operation::Custom*>(&node.getOperation())->getDerivOrder()[0] == 0)
-                out << name << " = coeff.x+x*(coeff.y+x*(coeff.z+x*coeff.w));\n";
-            else
-                out << name << " = (coeff.y+x*(2.0f*coeff.z+x*3.0f*coeff.w))*params.z;\n";
+            if (valueNode != NULL)
+                out << valueName << " = coeff.x+x*(coeff.y+x*(coeff.z+x*coeff.w));\n";
+            if (derivNode != NULL)
+                out << derivName << " = (coeff.y+x*(2.0f*coeff.z+x*3.0f*coeff.w))*params.z;\n";
             out << "}\n";
             out << "}";
             break;
@@ -218,6 +248,7 @@ void OpenCLExpressionUtilities::processExpression(stringstream& out, const Expre
             throw OpenMMException("Internal error: Unknown operation in user-defined expression: "+node.getOperation().getName());
     }
     out << ";\n";
+    if (!hasRecordedNode)
         temps.push_back(make_pair(node, name));
 }
 
@@ -229,3 +260,16 @@ string OpenCLExpressionUtilities::getTempName(const ExpressionTreeNode& node, co
     out << "Internal error: No temporary variable for expression node: " << node;
     throw OpenMMException(out.str());
 }
+
+void OpenCLExpressionUtilities::findRelatedTabulatedFunctions(const ExpressionTreeNode& node, const ExpressionTreeNode& searchNode,
+            const ExpressionTreeNode*& valueNode, const ExpressionTreeNode*& derivNode) {
+    if (searchNode.getOperation().getId() == Operation::CUSTOM && node.getChildren()[0] == searchNode.getChildren()[0]) {
+        if (dynamic_cast<const Operation::Custom*>(&searchNode.getOperation())->getDerivOrder()[0] == 0)
+            valueNode = &searchNode;
+        else
+            derivNode = &searchNode;
+    }
+    else
+        for (int i = 0; i < (int) searchNode.getChildren().size(); i++)
+            findRelatedTabulatedFunctions(node, searchNode.getChildren()[i], valueNode, derivNode);
+}

platforms/opencl/src/OpenCLExpressionUtilities.h

@@ -43,13 +43,25 @@ namespace OpenMM {
 
 class OpenCLExpressionUtilities {
 public:
+    /**
+     * Generate the source code for calculating a set of expressions.
+     *
+     * @param expressions    the expressions to generate code for (keys are the variables to store the output values in)
+     * @param variables      defines the source code to generate for each variable that may appear in the expressions
+     * @param functions      defines the variable name for each tabulated function that may appear in the expressions
+     * @param prefix         a prefix to put in front of temporary variables
+     * @param functionParams the variable name containing the parameters for each tabulated function
+     */
     static std::string createExpressions(const std::map<std::string, Lepton::ParsedExpression>& expressions, const std::map<std::string, std::string>& variables,
             const std::vector<std::pair<std::string, std::string> >& functions, const std::string& prefix, const std::string& functionParams);
 private:
     static void processExpression(std::stringstream& out, const Lepton::ExpressionTreeNode& node,
             std::vector<std::pair<Lepton::ExpressionTreeNode, std::string> >& temps, const std::map<std::string, std::string>& variables,
-            const std::vector<std::pair<std::string, std::string> >& functions, const std::string& prefix, const std::string& functionParams);
+            const std::vector<std::pair<std::string, std::string> >& functions, const std::string& prefix, const std::string& functionParams,
+            const std::vector<Lepton::ParsedExpression>& allExpressions);
     static std::string getTempName(const Lepton::ExpressionTreeNode& node, const std::vector<std::pair<Lepton::ExpressionTreeNode, std::string> >& temps);
+    static void findRelatedTabulatedFunctions(const Lepton::ExpressionTreeNode& node, const Lepton::ExpressionTreeNode& searchNode,
+            const Lepton::ExpressionTreeNode*& valueNode, const Lepton::ExpressionTreeNode*& derivNode);
 };
 
 } // namespace OpenMM