MATLAB Compiler

Loop Simplification

(optimize_integer_for_loops) This optimization detects when a loop starts and increments with integers. It 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, we recommend 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(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_ = 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