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...hat the vectors can hold 256/32 == 8 single-precision values even though the real maximum is 4 values. How should we handle this? The loop vectorizer uses TTI to find the size of the vector register. It uses this number to calculate the maximum vectorization factor. The formula is MaxVF = (RegSize/LargestElementTypeSize). Next it checks for the costs of all of the possible vectorization factors from 1 (scalar) to MaxVF. I think that the best approach would be to improve the cost model because on blue gene <8 x float> ops would be more expensive than <4 x float>. > > 1. Do nothing and let t...

Nadav, et al., On the BG/Q, the vectors hold 4 double-precision values. For vectorizing single-precision code, there are single-precision-rounded instructions, and special load/store instructions, which allow the double-precision numbers to be treated as single-precision numbers. The problem is that the current vectorization code (in the BBVectorizer and, as far as I can tell, also in the

...; > single-precision values even though the real maximum is 4 values. > > How should we handle this? > > The loop vectorizer uses TTI to find the size of the vector register. > It uses this number to calculate the maximum vectorization factor. > The formula is MaxVF = (RegSize/LargestElementTypeSize). Next it > checks for the costs of all of the possible vectorization factors > from 1 (scalar) to MaxVF. > > I think that the best approach would be to improve the cost model > because on blue gene <8 x float> ops would be more expensive than <4 > x float>. I agree...