Manual loop unrolling VS. using #pragma unroll

Hello,

I noticed something strange with the offline compiler.

In the two codes below, the same operations are performed (since the# pragma directive unrolls the loops), except in the second version the accumulations are "packed" in a single operation (from a syntactic point of view).

I found that the second version is more efficient in terms of estimated throughput and logic blocks, according to aoc. In the context of my kernel, I get +5% on the throughput and -2% of logic blocks used ; it's a complex kernel, I'm guessing the difference could be more significant on smaller kernels.

I would have thought the compiler was able to unroll the MACs in the most efficient way... Am I missing something ?

Thanks

#pragma unroll 7
for(int j=-3; j<4; j++) {
    # pragma unroll 7
     for(int i=-3; i<4; i++) {
          temp += L * coeffs;
    }
}

temp  = L * coeffs    + L * coeffs     + L * coeffs
      + L * coeffs    + L * coeffs     + L * coeffs
      + L * coeffs    + L * coeffs     + L * coeffs
      + L * coeffs    + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs   + L * coeffs    + L * coeffs
      + L * coeffs;

btw, badOmen if you read this : I can't reply to your PM about my other topic because I need 10 posts. Getting close to that :)