Critical Loops

If your program contains a short, heavily referenced for loop, consider expanding the code to a straight sequence of statements. For example:

array[0] = b[k+1]*c[m+1];
array[1] = b[k+2]*c[m+2];
array[2] = b[k+3]*c[m+3];
array[3] = b[k+4]*c[m+4];
array[4] = b[k+5]*c[m+5];

would run faster than:

for (i = 0; i < 5; i++)
   array[i] = b[k+i]*c[m+i];

The compiler will perform automatic unrolling of inner loops when the -O3 option is specified. In this case, the compiler will unroll the loop once.

Writing Optimized Code...
    Overview
    Variables
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    Functions
    Function Arguments
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    Conversions
    Arithmetic Conversions
    Inlined Components