Removing Redundant Declarations Using TXL

TXL solution to TIL Chairmarks #4.1: Removing redundant declarations.

-- JamesCordy - 04 Jul 2006

File "TILredundant.Txl"

% TXL transformation to remove unused declarations in a TIL program
% Jim Cordy, July 2006

% Based on the TIL base grammar
include "TIL.Grm"

% Preserve comments, we're probably going to maintain the result
include "TILCommentOverrides.Grm"

% Transformation rule to remove all redundant variable declarations from a program.
% If a declared variable is not mentioned by the following statements, it is not used.

rule main
    % Find each variable declaration
    replace [statement*]
        'var Id [id] ';
        FollowingStatements [statement*]

    % Check to see if the declared identifier does not appear in the following statements
    deconstruct not * [id] FollowingStatements
        Id

    % If not, the declaration is redundant so we remove it
    by
        FollowingStatements
end rule

Example run:

<linux> cat redundantvareg.til
// Meaningless example TIL program with some redundant declarations
// (the ones with names like rr, rx, ry, rm)
var d;
var y;
d := 17;
read y;
var rr;
while y != 0 do
    var rx;
    var a;
    a := 3;
    var j;
    j := 1;
    while j != 100 do
        a := a * 2;
        var ry;
        j := j + 1;
    end
    var c;
    c := a + j;
    var n;
    n := c * y;
    write n;
    y := y - 1;
    var rm;
end
<linux> txl redundantvareg.til TILredundant.Txl 
TXL v10.4c (15.3.06) (c)1988-2006 Queen's University at Kingston
Compiling TILredundant.Txl ... 
Parsing redundantvareg.til ...
Transforming ...
// Meaningless example TIL program with some redundant declarations 
// (the ones with names like rr, rx, ry, rm)
var d;
var y;
d := 17;
read y;
while y != 0 do
    var a;
    a := 3;
    var j;
    j := 1;
    while j != 100 do
        a := a * 2;
        j := j + 1;
    end
    var c;
    c := a + j;
    var n;
    n := c * y;
    write n;
    y := y - 1;
end
<linux>