MATLAB Compiler

Loop Simplification

(optimize_integer_for_loops) This optimization detects when a loop starts and increments with integers and replaces the loop with a much simpler loop that uses C integer variables instead of array valued variables. The performance improvements with this optimization can be dramatic.

Note    This optimization causes the variable names in the resulting C program to differ from those in the M-file. Therefore, it is recommended that you do not use this option when debugging.

For example,

function test(x)
for i = 1:length(x)-1
    x(i) = x(i) + x(i+1)
end

If you compile this with the -O none option, you get

...
{
    mclForLoopIterator viter__;
    for (mclForStart(
           &viter__,
           mlfScalar(1),
           mclMinus(mclVe(mlfLength(mclVa(x, "x"))),
           mlfScalar(1)), NULL);
         mclForNext(&viter__, &i);
         ) {
         ...
    }
    mclDestroyForLoopIterator(viter__);
}
...

Compiling with -O none -O optimize_integer_for_loops:on gives

...
{
    int v_ = mclForIntStart(1);
    int e_ = mclForIntEnd(mlfScalar(mclLengthInt(mclVa(x, "x"))
             - 1));
    if (v_ > e_) {
        mlfAssign(&i, _mxarray0_);
    } else {
...
        for (; ; ) {
          ...
            if (v_ == e_) {
                break;
            }
            ++v_;
        }
        mlfAssign(&i, mlfScalar(v_));
    }
...

Optimizing Loops

Optimizing Conditionals