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

Notable categories of redundant code include:

Recomputing

Calculating again a value that has previously been calculated and is still available.

Dead code

Code that is executed but has no external effect (i.e., 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 is for padding. But if the NOP is required for proper functionality, then it is not redundant.

Unused identifier

Something 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;.

int foo(int x) {
    int y = x * 2;
    return x * 2;
}

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

#define min(A,B) ((A)<(B)?(A):(B))
int shorter_magnitude(int a, int b, int c, int d) {
    return sqrt(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 be converted to a function.

int shorter_magnitude(int a, int b, int c, int d) {
    return sqrt(((a*a + b*b)<(c*c + d*d)?(a*a + b*b):(c*c + d*d)));
}

See also

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