Redundant code

In computer programming, redundant code is source code or compiled code that is unnecessary. Code that can be removed without affecting its desired behavior is redundant.

Categories

Noteble categoreis of redundant code include:

Recomputing

Recomputing a value that has previously been calculated ^[1] and is still available.

Dead code

Code that is executed but has no external effect; e.g., does not change the output produced by a program.

Unreachable code

Code that is never executed. Also, called dead code.

NOP padding

A NOP instruction might be considered redundant if it's for padding. But if the NOP is required for proper functionality then it's not redundant.

Unused identifier

Declared, but never referenced is a redundant declaration.

Examples

In the following C code, the second x * 2 expression is redundant code. Line 2 can be removed, or alternatively, line 3 can be changed to return y;.

intfoo(intx){inty=x*2;returnx*2;}

A more subtle example involves the C preprocessor that inserts code before compilation. Consider:

#define min(A,B) ((A)<(B)?(A):(B))intshorter_magnitude(inta,intb,intc,intd){returnsqrt(min(a*a+b*b,c*c+d*d));}

After preprocessing, the code expands to code that evaluates both a*a + b*b and c*c + d*d twice. To eliminate the duplicate code, the macro min could ge converted to a function.

intshorter_magnitude(inta,intb,intc,intd){returnsqrt(((a*a+b*b)<(c*c+d*d)?(a*a+b*b):(c*c+d*d)));}

See also

• Code bloat  – Production of unnecessarily long, slow or wasteful program code
• Code reuse  – Using existing code in new software
• Common subexpression elimination  – Compiler optimization
• Don't repeat yourself  – Principle of software development
• Duplicate code  – Repeated fragment of computer source code
• Redundancy (information theory)  – Message encoded with more bits than needed
• Code refactoring  – Restructuring existing computer code without changing its external behavior
• Code smell  – Computer programming characteristic

References

1. Debray, S. K., Evans, W., Muth, R., and De Sutter, B. 2000. Compiler techniques for code compaction. ACM Trans. Program. Lang. Syst. 22, 2 (Mar. 2000), 378–415.