Installing JBurg

Generating a BURM with JBurg

Integrating the generated BURM into your compiler

Required data structures

• int getOperator()
  Returns: a numeric designation of the node's operator type (e.g., PLUS). The generated BURM can implement multiple interfaces that contain symbolic names for these operators.

• INode class leftChild()
  Returns: This INode's left child, or null if the node has no left child.

• INode class rightChild()
  Returns: This INode's right child, or null if the node has no right child.

Setting properties in the generated BURM

Use the BURMProperty JBurg specification directive to include a property in your generated BURM. For example, to include a BCEL ClassGen object as the property classGen:

JBurg will include a field of the specified type and get/set methods.

Debugging your generated BURM

Unable to find a rule to process x(22){-1}

The BURM throws this exception if it cannot find any rule to match a particular node. The elements of the diagnostic line are:

• >Unable to find a rule to process x(22){-1}
  This is the INode's string representation of itself, from the INode's toString() method.
• >Unable to find a rule to process x(22){-1}
  This is the INode's operator, from the INode's getOperator() method.
• >Unable to find a rule to process x(22){-1}
  This is the goal state the BURM was attempting to satisfy. Goal state -1 tells the BURM to "use any available goal."

The most common causes of this exception are:

• "Type conversion" problems.

  For example, suppose the BURM is trying to reduce a + 1 and it has the following rules:

  
  	int_value = PLUS(int_value, int_value): 1 { ... }
  	int_value = INTEGER_LITERAL(void): 1 { ... }
  	obj_value = IDENTIFIER(void) : 5 { ... }
  	

  In this case, the BURM will not be able to match the PLUS pattern, because there is no rule that allows PLUS to accept an object and an int.

  The solution is to add a rule that allows the BURM to transform an object into an int:

  
  	int_value = obj_value: 5
  	{
  		//  Call Integer.parseInt(obj.toString)), or something similar.
  	}
  	

• Omitting a rule to handle a particular node type.

BURM debug option output

Your BURM will emit XML-formatted debugging information if you generate it with the JBurg -g command-line switch.

Debugging output is written to the current working directory, into a file named reducerName_jburg.xml.

For example, if your reducer is named MyReducer, debugging output will be written to MyReducer_jburg.xml

Recent versions of InternetExplorer and Netscape render XML files in a convenient tree display.

Debug Information

The debugging information has two main parts: the labelling pass dumps all the nodes' possible states, and the reducer emits a trace as it works.

Notes on modifying JBurg

Rebuilding JBurg

JBurg's build is ant-based. The ant targets are:

• buildall Builds or rebuilds JBurg, TL/2, mjava, and runs quick tests.
• jarfile compiles JBurg's Java files and builds jburg.jar
• parser rebuilds the parser. This target is rarely used.

The files that make up JBurg are:

• The ANTLR grammar, which also contains JBurg's main() method, in grammars/jburg.g.

  Java files generated by ANTLR are:

  • JBurgANTLRLexer.java
  • JBurgParser.java
  • JBurgTokenTypes.java

• JBurgGenerator.java

  JBurgGenerator.java contains the code that creates the actual BURM.
  TODO:Move the static inner classes into separate Java files.