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# Class gnu.jel.Optimizer

    java.lang.Object
       |
       +----gnu.jel.Optimizer

public class Optimizer
extends Object

This class handles storage of the expressions automatic widening type conversions and optimizations.

Currently the only supported type of optimization is evaluation of constant subexpressions. Unlike other compilers JEL not only evaluates arithmetic operators on constants but also attempts to call some (those which marked stateless) functions if all their arguments are constants. For example, expression "sin(1)" will be completely evaluated at compile time.

The gnu.jel.Library class handles details on which functions can be evaluated at compile time and which can not, see it's documentation for details.

Author:
  Konstantin L. Metlov (metlov@fzu.cz)
See Also:
  Library

##

code
  Double linked list of operations in this expression.

##

Optimizer(Library)
  Constructs the new "empty" optimizer with the library specified.

##

binaryOP(int, boolean)
  Generates a binary operation.
binaryOP_param()
  Specifies that the parameter for the binary operation is now in stack.
compile()
  Compiles the expression.
compileBits()
  Compiles the expression into an ExpressionBits object.
conditional_end()
  Finishes generation of conditional ?: .
conditional_false()
  Continues generation of conditional ?: .
conditional_true()
  Starts generation of conditional ?: .
convert(Class)
  Generates an explicit type conversion operation.
convert(Class, boolean)
  Generates an explicit type conversion operation.
finish()
  Finishes the function.
function_call(String)
  Generates the function call.
function_param()
  Specifies that the parameter for the function is now in stack.
function_start()
  Denotes the start of the function call.
load(boolean)
  Generates a "load boolean constant" operation.
load(byte)
  Generates a "load byte constant" operation.
load(char)
  Generates a "load char constant" operation.
load(double)
  Generates a "load double constant" operation.
load(float)
  Generates a "load float constant" operation.
load(int)
  Generates a "load int constant" operation.
load(long)
  Generates a "load long constant" operation.
load(short)
  Generates a "load short constant" operation.
load(String)
  Generates a "load String constant" operation.
logical_not()
  Inverts result of group of logical operators.
logical_not_start()
  Denotes start of group of logical operators whose result should be inverted.
main(String[])
  Performs unitary test of the interpreter.
optimize(int)
  Optimizes the function.
optimizeIteration(OPlist)
  Performs one optimization pass on the given list of operations.
test(Tester)
  Performs unitary test of the interpreter.
toString()
  Represents the expression, contained in this optimizer as `String`.
unary(int)
  Generates an unary operation.

##

code

     protected OPlist code

  Double linked list of operations in this expression.

##

Optimizer

     public Optimizer(Library lib)

  Constructs the new "empty" optimizer with the library specified.

  Parameters:
    lib - is the library, used for function names resolution.

##

load

     public void load(boolean c)

  Generates a "load boolean constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(byte c)

  Generates a "load byte constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(char c)

  Generates a "load char constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(short c)

  Generates a "load short constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(int c)

  Generates a "load int constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(long c)

  Generates a "load long constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(float c)

  Generates a "load float constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(double c)

  Generates a "load double constant" operation.

  Parameters:
    c - is the constant to load.

load

     public void load(String s)

  Generates a "load String constant" operation.

  Parameters:
    s - is the String constant to load.

convert

     public void convert(Class to,
                         boolean widening) throws IllegalStateException

  Generates an explicit type conversion operation.

  It has the sense to call this function only for narrowing conversions (see §5.1.3 and §5.1.5 of the Java Language Specification (JLS) ). Widening ( §5.1.2, §5.1.4 of JLS) type conversions are performed by this compiler automatically.

  Parameters:
    to - is the class to convert to.
    widening - if true prohibits doing narrowing conversions.
  Throws: IllegalStateException
    if requested conversion is not supported.

convert

     public void convert(Class to) throws IllegalStateException

  Generates an explicit type conversion operation.

  This function is equivalent to `convert(to,false)`. Widening ( §5.1.2, §5.1.4 of JLS) type conversions are performed by this compiler automatically.

  Parameters:
    to - is the class to convert to.
  Throws: IllegalStateException
    if requested conversion is not supported.

unary

     public void unary(int o)

  Generates an unary operation.

  The only unary operation for now is the negation (invert sign) operation.

  Parameters:
    is - the operation code, for now it can be only `ExpressionImage.UN_NE`.
  Throws: IllegalStateException
    if operation is not supported for types in stack.

logical_not_start

     public void logical_not_start()

  Denotes start of group of logical operators whose result should be inverted.

  See Also:
    logical_not

logical_not

     public void logical_not() throws IllegalStateException

  Inverts result of group of logical operators.

  To generate logical not operation it is needed :

       1. logical_not_start
       2. calculate value to be inverted
       3. logical_not

  See Also:
    logical_not

function_start

     public void function_start()

  Denotes the start of the function call.

  Example of the sequence of method calls to perform (compile) the function invocation is given in the description of gnu.jel.Optimizer.function_call(...) method.

  See Also:
    function_call

binaryOP_param

     public void binaryOP_param()

  Specifies that the parameter for the binary operation is now in stack.

  Example of the sequence of method calls to perform (compile) the binary operation is given in the description of gnu.jel.Optimizer.binaryOP() method.

  See Also:
    binaryOP

function_param

     public boolean function_param()

  Specifies that the parameter for the function is now in stack.

  Example of the sequence of method calls to perform (compile) the function is given in the description of gnu.jel.Optimizer.function_call(...) method.

  See Also:
    function_call

function_call

     public void function_call(String name) throws IllegalStateException

  Generates the function call. Example : "how to call the function"

       optimizer.function_start();
       optimizer.load(2L);
       optimizer.function_param();
       optimizer.load(2.0);
       optimizer.function_param();
       optimizer.function_call("name_in_the_library");

  The function name is searched in the library. If there are several applicable functions in the library with the same name (not necessary in the same object originally) the most specific one is called ( See § 15.11.2.2 in the Java Language Specification). Types conversion takes place automatically.

  Parameters:
    name - is the name of the function to call.
  Throws: IllegalStateException
    if no function with the given name and parameter types in stack can be found in the library.

binaryOP

     public void binaryOP(int o,
                          boolean logical) throws IllegalStateException

  Generates a binary operation.

  The binary operation codes are defined in `gnu.jel.ExpressionImage` as constants BI_XX .

  Example : "how to sum up two numbers with this optimizer"

       optimizer.load(2L);
       optimizer.binaryOP_param();
       optimizer.load(2.0);
       optimizer.binaryOP(ExpressionImage.BI_PL);

  Note different types of operands, conversion ( to double) will be performed automatically. Note also binaryOP_param() usage, its use is obligatory to denote that the parameter for subsequent binary operation is now ion stack.

  Parameters:
    is - the operation code, see above.
  Throws: IllegalStateException
    if this binary op is not supported for the types in stack.
  See Also:
    ExpressionImage

conditional_true

     public void conditional_true() throws IllegalStateException

  Starts generation of conditional ?: .

  The stack should contain boolean value.

  To generate complete conditional it is needed :

       1. calculate condition (boolean)
       2. conditional_true()
       3. add instructions to executed if condition is "true"
       4. conditional_false()
       5. add instructions to executed if condition is "false"
       6. conditional_end()

conditional_false

     public void conditional_false()

  Continues generation of conditional ?: .

  See Also:
    conditional_true

conditional_end

     public void conditional_end() throws IllegalStateException

  Finishes generation of conditional ?: .

  See Also:
    conditional_true

finish

     public void finish()

  Finishes the function.

  This method should be called exactly once before the attempt to instantiate expression (or obtain its image) is made. proper state to be finished (some extra items are in stack).

optimize

     public void optimize(int of)

  Optimizes the function.

  Currently only evaluation of constant subexpressions is performed.

  Parameters:
    of - is the maximum number of optimization iterations to perform.

optimizeIteration

     protected static boolean optimizeIteration(OPlist code)

  Performs one optimization pass on the given list of operations.

  Currently only evaluation of constant subexpressions is performed.

  Parameters:
    code - is a linked list of operations to optimize.
  Returns:
    true if additional optimization pass may simplify code further.

compile

     public CompiledExpression compile()

  Compiles the expression.

  Returns:
    The instance of the `gnu.jel.CompiledExpression` subclass, with the function, represented by this optimizer compiled in.

compileBits

     public ExpressionBits compileBits()

  Compiles the expression into an ExpressionBits object.

  ExpressionBits is a wrapper allowing to store expression in any `java.io.OutputStream` using Java serialization mechanism.

  Returns:
    instance of the `gnu.jel.ExpressionBits` object.
  See Also:
    ExpressionBits

toString

     public String toString()

  Represents the expression, contained in this optimizer as `String`.

  Returns:
    String representation of the expression.
  Overrides:
    toString in class Object

main

     public static void main(String args[])

  Performs unitary test of the interpreter.

  This function works only if the Debugging is turned "ON".

  Parameters:
    args - ignored.
  See Also:
    enabled

test

     public static void test(Tester t)

  Performs unitary test of the interpreter.

  This function works only if the Debugging is turned "ON". Used if all package is being tested and not just this class alone.

  Parameters:
    t - Tester to report test results.
  See Also:
    enabled

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