Merge duplicate programs

lib/handlebars/compiler/compiler.js

@@ -38,6 +38,26 @@ Handlebars.JavaScriptCompiler = function() {};
 
       return out.join("\n");
     },
+    equals: function(other) {
+      var len = this.opcodes.length;
+      if (other.opcodes.length !== len) {
+        return false;
+      }
+
+      for (var i = 0; i < len; i++) {
+        var opcode = this.opcodes[i],
+            otherOpcode = other.opcodes[i];
+        if (opcode.opcode !== otherOpcode.opcode || opcode.args.length !== otherOpcode.args.length) {
+          return false;
+        }
+        for (var j = 0; j < opcode.args.length; j++) {
+          if (opcode.args[j] !== otherOpcode.args[j]) {
+            return false;
+          }
+        }
+      }
+      return true;
+    },
 
     guid: 0,
 
@@ -417,6 +437,7 @@ Handlebars.JavaScriptCompiler = function() {};
       this.isChild = !!context;
       this.context = context || {
         programs: [],
+        environments: [],
         aliases: { }
       };
 
@@ -452,7 +473,7 @@ Handlebars.JavaScriptCompiler = function() {};
       return opcodes[this.i + 1];
     },
 
-    eat: function(opcode) {
+    eat: function() {
       this.i = this.i + 1;
     },
 
@@ -905,11 +926,27 @@ Handlebars.JavaScriptCompiler = function() {};
         child = children[i];
         compiler = new this.compiler();
 
-        this.context.programs.push('');     // Placeholder to prevent name conflicts for nested children
-        var index = this.context.programs.length;
-        child.index = index;
-        child.name = 'program' + index;
-        this.context.programs[index] = compiler.compile(child, options, this.context);
+        var index = this.matchExistingProgram(child);
+
+        if (index == null) {
+          this.context.programs.push('');     // Placeholder to prevent name conflicts for nested children
+          index = this.context.programs.length;
+          child.index = index;
+          child.name = 'program' + index;
+          this.context.programs[index] = compiler.compile(child, options, this.context);
+          this.context.environments[index] = child;
+        } else {
+          child.index = index;
+          child.name = 'program' + index;
+        }
+      }
+    },
+    matchExistingProgram: function(child) {
+      for (var i = 0, len = this.context.environments.length; i < len; i++) {
+        var environment = this.context.environments[i];
+        if (environment && environment.equals(child)) {
+          return i;
+        }
       }
     },