Dead code elimination removes unneeded instructions from the program.
Dead code is a section in the source code of a program, which is executed but whose result is never used in any other computation.
Dead code execution prevents from wastes of computation time and memory.
z = x*y; a = x; // dead code w = x*y+6;
After dead code elimination above program become,
z = x*y; w = x*y+6;