讲解jack_opimiser_r留学生、辅导C/C++语言编程、讲解C/C++留学生、辅导C/C++程序

Assignment 3 jack_opimiser_r()

jack_opimiser_r()

Descripion

You must complete the implementation of the jopt-r program in the file optimiser-r.cpp.

The program reads an XML representation of an abstract syntax tree of a Jack class from standard input,

using jn_parse_xml() and writes an optimised version to standard output, using jn_print_as_xml(). The

jack_optimiser_r() function uses the functions described in j-ast.h to traverse the abstract syntax tree

and construct an optimised copy that does not include any redundant code

Compiling and Running jopt-r

When the Makefile attempts to compile the program jopt-r, it will use the file optimiser-r.cpp, any other

.cpp files it can find whose names start optimiser-r- and any .cpp files it can find whose names start

with shared-. For example, if we have our own class abc that we want to use when implementing joptr

and our own class xyz that we want to use with all of our programs, we would name the extra files,

optimiser-r-abc.cpp and shared-xyz.cpp respectively with matching optimiser-r-abc.h and sharedxyz.h

include files.

The program can be compiled using the command:

% make jopt-r

The suite of provided tests can be run using the command:

% make test-jopt-r

The test scripts do not show the program outputs, just passed or failed, but they do show you the

commands being used to run each test. You can copy-paste these commands if you want to run a

particular test yourself and see all of the output.

Note: Do not modify the provided Makefile or the sub-directories bin, includes or lib. These will be

replaced during testing by the web submission system.

jack_op!miser_r()

One advantage of having a parser produce an abstract syntax tree is that optimisations can be applied to

the abstract syntax tree before code generation. The purpose of the jack_optimiser_r() function is to

make a copy of an abstract syntax tree and where possible eliminate redundant code. That is, if part of

the abstract syntax tree represents code that can never be executed, it is eliminated.

The following cases of redundant code must be eliminated by the optimiser while performing a depth first

The following cases of redundant code must be eliminated by the optimiser while performing a depth first

copy of the original abstract syntax tree.

If Statements

An ifStatement node consists of three parts, an expression node for the condition, a statements node

for the then part and a statements node for the else part. There will not be a second statements node if

there is no else part.

If the expression node contains a single term node containing a keywordConstant node that has

value true, the statement node containing the ifStatement node is replaced by the all of

the statement nodes that are children of the statements node for the then part.

If the expression node contains a single term node containing a keywordConstant node that has

value false, the statement node containing the ifStatement node is replaced by all of

the statement nodes that are children of the statements node for the else part. If there is no else part

the statement node containing the ifStatement node is not copied.

While Statements

A whileStatement node consists of two parts, an expression node for the condition, and a statements

node for the loop body. If the expression node contains a single term node containing

a keywordConstant node that has value false, the statement node containing the whileStatement

node is not copied.

Return Statements

When a return statement is executed the current function terminates and the following code in the

enclosing block of statements will never be executed. Therefore, when a returnStatement node is

found whilst copying a statements node, no more of children of that statements node are copied.

If an ifStatement node has a statements node for the then part and the else, an both statements nodes

contain a returnStatement node, the parent of the ifStatement node is considered to be

a returnStatement node by its parent statements node.

If a whileStatement's expression node contains a single term node containing a keywordConstant

node that has value true, and while copying the statements node a returnStatement node is found, the

parent of the whileStatement node is considered to be a returnStatement node by its

parent statements node.

Notes:

All output must be written using the functions in iobuffer.h, remember to call print_output().

If an error occurs the program must immediately call exit(0) and have not produced any output.

During testing you may output error messages and other log messages using the functions in

iobuffer.h.