rmuir commented on PR #12737:
URL: https://github.com/apache/lucene/pull/12737#issuecomment-1786433389
I tried naively writing the logic like this with a couple N (8, 16, 32,etc)
with FMA both off and on to see if I can baby this compiler to vectorize, nope,
nothing. I don't think autovectorization works except for BitSet :)
```
// loop one, where's my vectorization? no floating point excuses here. tried
with fma too.
float acc[] = new float[32];
int upperBound = a.length & ~(32 - 1);
for (; i < upperBound; i += 32) {
for (int j = 0; j < acc.length; j++) {
acc[j] = a[i+j] * b[i+j] + acc[j];
}
}
// second reduction loop
for (int j = 0; j < acc.length; j++) {
res += acc[j];
}
```
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