package jburg.test.tl1.reducer;

Rules Section

Each rule produces a goal. A goal is similar to a reduction in a parser generator, in reverse: a successful goal replaces the input AST with an output object. In the case of a code generator, the output is usually a code fragment, e.g., a BCEL InstructionList or an ABC InstructionList.

Each rule is also associated with a cost. In most cases, a cost is a simple integer; it can also be computed via a function, with the AST as a parameter.

• Pattern-Matching Rules

  EBNF	IDENTIFIER EQUALS operator_specification cost_specification { Java code }
  Usage	This rule reduces an AST node of a particular kind (NODE_KIND), with either no, one, or two subgoals. The subgoals are similar to non-terminals in a parse generator.
  Example 1	int = PLUS(int i1, int i2): 1 { /* code to add two int values */ } This pattern-matching rule produces an int, given a PLUS node with two children that can both satisfy the "int" goal.

• Terminal Rules

  EBNF	IDENTIFIER EQUALS IDENTIFER LPAREN VOID RPAREN { Java code }
  Usage	These are trivial pattern rules, where the pattern consists solely of the leaf.
  Example	int = INTEGER_LITERAL(void) { code to implement integer literal }

• Simple Transformation Rules

  EBNF	IDENTIFIER EQUALS IDENTIFIER SEMI
  Usage	Transformation rules allow the code generator to use one goal to satisfy another goal.
  Example	numeric_value = int;
  	This transformation tells the BURM that the "int" goal can satisfy the "numeric_value" goal. Since this is a simple transformation, the cost will be carried over from the int goal.

• Complex Transformation Rules

  EBNF	IDENTIFIER EQUALS IDENTIFIER cost_specification { Java code }
  Usage	This transformation rule also allows the code generator to use one goal to satisfy another, but specifies some additional processing that accomplishes the transformation. The cost spec should only consider the cost of the transformation code; the code generator will add in the cost of the original node.
  Example	int = numeric_value : 1 { code to convert an arbitrary number to an int}

/**
 *  @return "true" if the given node's int value is within
 *      the range representable in a byte.
 */
canBIPUSH()
{
    return (p.intValue() < 256)? 1: 1000000;
}