[TTI] Reduction costs only need to include a single extract element cost
We were adding the entire scalarization extraction cost for reductions, which returns the total cost of extracting every element of a vector type.
For reductions we don't need to do this - we just need to extract the 0'th element after the reduction pattern has completed.
Fixes PR37731
Differential Revision: https://reviews.llvm.org/D54585
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346970 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed