Comments on: Generated Code for Variable Size Signals

By: Ashish Sadanandan

Ashish Sadanandan — Sun, 08 Nov 2009 15:16:17 +0000

@wei, I was talking about the case where the compiler would perform the ‘model_Xdim-1′ operation each time through the loop before checking the exit condition.

By: wei

wei — Sat, 07 Nov 2009 14:51:48 +0000

@Ashish, I agree with your observation on compiler optimization but fail to see why Han’s code would be less efficient than the original. Would you explain?

By: Ashish Sadanandan

Ashish Sadanandan — Fri, 06 Nov 2009 18:24:13 +0000

Han,
Sorry for butting in with a reply, but the modification to the for-loop you’ve suggested is really not an optimization IMHO. Even a moderately competent C compiler will generate identical code for the 2 versions since ‘model_Xdim’ is not being modified within the for-loop. However, if you have a really non-optimizing compiler, the code generated by your version would be very inefficient. So I feel its better to leave the implementation of that for-loop as it is.

Ashish.

By: Han Geerligs

Han Geerligs — Fri, 06 Nov 2009 12:38:56 +0000

Hi Aarti,

thanks for providing the example!

I was just wondering why the lines
model_YDim = model_XDim;
loop_ub = model_XDim – 1;
for (tmp = 0; tmp <= loop_ub; tmp++) {
Y[tmp] = 2.0 * X[tmp];
}

aren’t converted into
for (tmp = 0; tmp <= model_Xdim-1; tmp++) {
Y[tmp] = 2.0 * X[tmp];
}

This would be a special case of expression folding.

I was wondering if this optimisation was considered at design/is planned for implementation?

Han